# Patent

## Title
Genetic test for PSE-susceptible turkeys

## Abstract

This invention relates to methods and compounds for the improvement of turkey meat and turkey populations, but not limited to, a genetic screen to select for turkeys that produce a better quality of meat characterized by a higher postmortem pH and better water holding capacity.

## Background
This application for patent under 35 U.S.C. § 111(a) claims priority to Provisional Application Ser. No. 60/540,490 filed on Jan. 30, 2004 under 35 U.S.C. § 111(b).


FIELD OF THE INVENTION
This invention relates to methods and compounds for the improvement of turkey meat and turkey populations, but not limited to, a genetic screen to select for turkeys that produce a better quality of meat characterized by a higher postmortem pH and better water holding capacity.
BACKGROUND
The breeding of food animals for certain qualities desired by breeders, farmers and consumers can have the unintentional side effect of selecting for less desirable characteristics. For example, by breeding for animals that produce large amounts of meat quickly, breeders have also selected for animals that may have meat qualities that consumers find less than desirable. Both turkey and pork meat can have what is termed pale, soft and exudative (PSE) meat. PSE meat is characterized by an abnormally light color, a flaccid consistency and poor water holding capacity. These characteristics make the meat hard to process in packing facilities and consumers find meat with these characteristics less than desirable. It is estimated that the problem of PSE meat costs the poultry industry alone millions of dollars a year.
Presently, the poultry industry deals with the problem of PSE turkey meat in ineffective ways. For example, some people in the field have suggested alternative meat processing or transportation schemes to improve the qualities of PSE turkey meat (Alvarado, C. Z., A. R. Sams, “The Role of Carcass Chilling Rate in the Development of Pale, Exudative Turkey Pectoralis” Poultry Science 81:1365-1370, 2002; Owens, C. M. and A. R. Sams, “The Influence of Transportation on Turkey Meat Quality” Poultry Science 79:1204-1207, 2000). These suggestions have had only marginal impact on relieving the problem. At least one method of testing for turkeys prone to developing PSE meat has been proposed (Wheeler, et al., “A Halothane Test to Detect Turkeys Prone to Developing Pale, Soft and Exudative Meat” Poultry Science 78:1634-1638, 1999). However, the test did not identify PSE turkeys consistently. Others have proposed treating PSE meat after slaughter to make it more appealing to the consumer (U.S. Pat. No. 5,928,689 to Mikowski, et al.; U.S. Pat. No. 6,020,012 to Kauffman, et al.) However, even when these methods are successful, the quality of the treated PSE meat is still substandard as compared to non-PSE meat.
What is needed is an effective method by which turkeys that produce a better quality of meat can be identified and selected before farmers undergo the expense of raising the turkeys to maturity or using them used for breeding purposes.
SUMMARY OF THE INVENTION
This invention relates to methods and compounds for the improvement of turkey meat and turkey populations including, but not limited to, a genetic screen to select for turkeys that produce a better quality of meat characterized by a higher postmortem pH and a better water holding capacity. In one embodiment, selective breeding is contemplated for turkeys having a genotype that is associated with better meat quality.
In one embodiment, the present invention contemplates a method for the identification of turkeys that produce a better quality of meat when compared to PSE meat.
In one embodiment of the present invention, turkeys that are homozygous for αRYR-II have superior meat quality as compared to turkeys that are homozygous for αRYR-I or turkeys that are heterozygous for αRYR-II and αRYR-I. In this regard, in another embodiment, the present invention contemplates genetic screens for turkeys to identify turkeys that are homozygous for αRYR-II and αRYR-I or heterozygous.
One embodiment of the present invention comprises three novel variants of the αRYR alleles. The variants are referred to as W, AS-81 and AS-193. Additionally, an embodiment of the present invention comprises two αRYR alleles found by investigating turkey αRYR genomic DNA in the region corresponding to the transcript variants. In another embodiment, each of these alleles may be expressed as any of the three variants. Yet another embodiment of the present invention comprises characterization of the heterogeneity of turkey αRYR transcript variants, the two αRYR alleles, and the relationship of the expression pattern of the transcript variants to the two alleles. Still yet another embodiment of the present invention comprises a correlation of meat quality and traits with the turkey genotypes.
In one embodiment, the present invention contemplates a method of genotyping turkeys, comprising: a) providing nucleic acid samples from a plurality of turkeys; and b) genotyping said samples under conditions such that turkeys homozygous for TαRYRII are identified. In another embodiment, the present invention contemplates the method, wherein said genotyping comprises nucleic acid amplification. In yet another embodiment, the present invention contemplates the method, wherein said amplification comprises PCR utilizing a forward primer and a reverse primer. In still yet another embodiment, the present invention contemplates the method, wherein the sequence of said forward primer is set forth in SEQ ID NO:13. In still yet another embodiment, the present invention contemplates the method, wherein the sequence of said reverse primer is set forth in SEQ ID NO:14. In still yet another embodiment, the present invention contemplates the method, wherein said nucleic acid samples are obtained from muscle tissue. In still yet another embodiment, the present invention contemplates the method, wherein said muscle tissue is turkey breast muscle. In still yet another embodiment, the present invention contemplates the method, wherein said samples are taken from slaughtered turkeys. In still yet another embodiment, the present invention contemplates the method, wherein said samples are taken from live turkeys. In still yet another embodiment, the present invention contemplates the method, wherein said live turkeys identified as homozygous for TαRYRII are used for breeding. In still yet another embodiment, the present invention contemplates the method, wherein said live turkeys are young turkeys. In still yet another embodiment, the present invention contemplates the method, wherein said live young turkeys identified as homozygous for TαRYRII are subsequently grown to maturity. In still yet another embodiment, the present invention contemplates the method, wherein said live turkeys are mature turkeys. In still yet another embodiment, the present invention contemplates the method, wherein said live mature turkeys identified as homozygous for TαRYRII are slaughtered for commercial meat production.
In one embodiment, the present invention contemplates a method of selecting turkeys for meat production based on genotyping, comprising: a) providing nucleic acid samples from a plurality of live turkeys; b) genotyping said samples under conditions such that turkeys are identified that are i) homozygous for TαRYRII, ii) homozygous for TαRYRI, iii) heterozygous for TαRYRII, and iv) heterozygous for TαRYRI; and c) selecting said live turkeys identified as homozygous for TαRYRII for meat production. In another embodiment, the present invention contemplates the method of claim 15, wherein said genotyping comprises nucleic acid amplification. In yet another embodiment, the present invention contemplates the method, wherein said amplification comprises PCR utilizing a forward primer and a reverse primer. In still yet another embodiment, the present invention contemplates the method, wherein the sequence of said forward primer is set forth in SEQ ID NO:13. In still yet another embodiment, the present invention contemplates the method, wherein the sequence of said reverse primer is set forth in SEQ ID NO:14. In still yet another embodiment, the present invention contemplates the method, wherein said nucleic acid samples are obtained from muscle tissue. In still yet another embodiment, the present invention contemplates the method, wherein said muscle tissue is turkey breast muscle. In still yet another embodiment, the present invention contemplates the method, wherein said selecting for meat production comprises slaughtering said selected turkeys. In still yet another embodiment, the present invention contemplates the method, wherein said selecting for meat production comprises utilizing said turkeys identified as homozygous for TαRYRII for breeding. In still yet another embodiment, the present invention contemplates the method, wherein said live turkeys are young turkeys. In still yet another embodiment, the present invention contemplates the method, wherein said selecting for meat production comprises growing said turkeys identified as homozygous for TαRYRII to maturity. In still yet another embodiment, the present invention contemplates the method, wherein said turkeys identified as homozygous for TαRYRI are not used for meat production. In still yet another embodiment, the present invention contemplates the method, wherein said genotyping is performed with an assay selected from a group consisting of Southern blotting, Northern blotting, and nucleic acid sequencing.
In one embodiment, the present invention contemplates a method of identifying turkeys expressing protein encoded by TαRYRII, comprising: a) providing samples from a plurality of turkeys; and b) testing said samples under conditions such that turkeys expressing protein encoded by TαRYRII are identified. In another embodiment, the present invention contemplates the method, wherein said testing is performed with an assay selected from a group consisting of Western blotting, immunohistochemistry, and amino acid sequencing.
In one embodiment, the present invention contemplates a kit for genotyping turkeys, comprising primers capable of amplifying nucleic acid such that turkeys homozygous for TαRYRII can be identified. In another embodiment, the present invention contemplates the kit, wherein said kit comprises a forward PCR primer and a reverse PCR primer. In yet another embodiment, the present invention contemplates the kit, wherein the sequence of said forward primer is set forth in SEQ ID NO:13. In still yet another embodiment, the present invention contemplates the kit, wherein the sequence of said reverse primer is set forth in SEQ ID NO:14.
The present invention further provides a method for screening compounds for the ability to alter turkey RYR activity, comprising: providing: a first polypeptide sequence comprising at least a portion of turkey RYR; ii) a second polypeptide sequence comprising at least a portion of a protein known to interact with turkey RYR; and iii) one or more test compounds; combining in any order, the first polypeptide sequence comprising at least a portion of turkey RYR, the second polypeptide sequence comprising at least a portion of a protein known to interact with turkey RYR, and one or more test compounds under conditions such that the first polypeptide sequence, the second polypeptide sequence, and the test compound interact; and detecting the presence or absence of an interaction between the polypeptide sequence comprising at least a portion of turkey RYR and the polypeptide sequence comprising at least a portion of a protein known to interact with turkey RYR. In some embodiments, the first polypeptide sequence is selected from the group consisting of SEQ ID NOS: 5, 6 and 7. In some embodiments, the second polypeptide comprises DHPR.
The present invention also provides a method of identifying turkeys showing fewer symptoms of PSE meat production comprising: providing nucleic acid from an animal, wherein the nucleic acid comprises a turkey RYR allele and detecting a mutation in the nucleic acid, wherein the mutation results in a reduction in PSE meat symptoms. In some embodiments, the mutation is in the turkey RYR allele. In some embodiments, the mutation is a nucleotide residue insertion or deletion. In some embodiments, the detecting step is accomplished by hybridization analysis (e.g., Southern blotting and Northern blotting).
In yet other embodiments, the present invention provides a kit for determining if a subject is homozygous for the αRYR-II allele comprising: at least one reagent that specifically detects if a turkey is homozygous for the αRYR-II allele; and instructions for determining that the subject is homozygous for the αRYR-II allele.
The present invention also provides a purified polypeptide (or portion thereof) selected from the group consisting of SEQ ID NOS: 5, 6 and 7.
In one embodiment, the present invention contemplates a method of screening for turkeys homozygous for TαRYRII, comprising: a) providing, i) a sample from a subject and, ii) an assay for the detection of TαRYRI; b) testing said sample for the presence of TαRYRI. In another embodiment, the present invention contemplates that the method additionally comprises: a) an assay for the detection of TαRYRII and; b) testing for said sample for the presence of TαRYRII. In yet another embodiment, the present invention contemplates non-limiting examples of the assay that used for the detection of presence of TαRYRI and TαRYRII. For example, the assay can be selected from Western blotting, Southern blotting, Northern blotting, immunoassays, PCR, nucleotide sequencing, amino acid sequencing and yeast two-hybrid screening. In yet another embodiment, the present invention contemplates that the sample used in the assay comprises a nucleotide sequence encoding at least a portion of the TαRYRI protein and said nucleotide sequence is amplified before said assay.
In one embodiment, the present invention contemplates a method for detection of a polynucleotide encoding protein in a biological sample comprising the steps of: a) providing: i) a sample comprising a first polynucleotide from a subject and, ii) a second polynucleotide sequence selected from the group consisting of polynucleotide sequences encoding at least a portion of SEQ ID NO: 5, 6 or 7; b) combining said first and second nucleotides to form a hybridization complex; and c) detecting said hybridization complex. In another embodiment, the present invention contemplates that the assay is selected from a group consisting of Southern blotting, Northern blotting, PCR and nucleotide sequencing.
In one embodiment, the present invention contemplates a method for screening compounds for the ability to alter TαRYRI activity, comprising: a) providing: i) a first polypeptide sequence comprising at least a portion of TαRYRI; ii) a second polypeptide sequence comprising at least a portion of a protein known to interact with TαRYRI; and iii) one or more test compounds; b) combining in any order, said first polypeptide sequence comprising at least a portion of TαRYRI, said second polypeptide sequence comprising at least a portion of a protein known to interact with TαRYRI, and said one or more test compounds under conditions such that said first polypeptide sequence, said second polypeptide sequence, and said test compound interact; and c) detecting the presence or absence of an interaction between said polypeptide sequence comprising at least a portion of TαRYRI and said polypeptide sequence comprising at least a portion of a protein known to interact with TαRYRI. In another embodiment, the present invention contemplates that first polypeptide sequence is selected from the group consisting of SEQ ID NOS: 5, 6 and 7, in yet another embodiment, the present invention contemplates that the second polypeptide comprises DHPR.
In one embodiment, the present invention contemplates a compound comprising a purified polypeptide or portion thereof selected from the group consisting of SEQ ID NOs: 5, 6 and 7. In another embodiment, the present invention contemplates that the purified polypeptide encoded by SEQ ID NOS 5, 6 and 7 encodes allele αRYRI or αRYRII.
DEFINITIONS
The terms “protein,” “peptide” and “polypeptide” refer to compounds comprising amino acids joined via peptide bonds and are used interchangeably. A “protein,” “peptide” or “polypeptide” encoded by a gene is not limited to the amino acid sequence encoded by the gene, but includes post-translational modifications of the protein.
Where the term “amino acid sequence” is recited herein to refer to an amino acid sequence of a protein molecule, “amino acid sequence” and like terms, such as “polypeptide,” “peptide” or “protein” are not meant to limit the amino acid sequence to the complete, native amino acid sequence associated with the recited protein molecule. Furthermore, an “amino acid sequence” can be deduced from the nucleic acid sequence encoding the protein. Detecting amino acids sequences encoded by the turkey RYR gene or portions thereof is contemplated by one embodiment of the present invention.
The term “portion” when used in reference to a protein (as in “a portion of a given protein”) refers to fragments of that protein. The fragments may range in size from four amino acid residues to the entire amino sequence minus one amino acid. The term “potion” when used in reference to a nucleic acid (as in “a portion of a given nucleic acid”) refers to fragments of that nucleic acid. The fragments may range in size from ten bases to the entire nucleic acid sequence minus one base.
The term “chimera” when used in reference to a polypeptide refers to the expression product of two or more coding sequences obtained from different genes, that have been cloned together and that, after translation, act as a single polypeptide sequence. Chimeric polypeptides are also referred to as “hybrid” polypeptides. The coding sequences includes those obtained from the same or from different species of organisms.
In one embodiment of the present invention it is contemplated that exogenous genes expressing the protein encoded by the αRYRII allele will be used to produce transgenic animals. The expressed exogenous proteins may be part of a fusion protein. The term “fusion” when used in reference to a polypeptide refers to a chimeric protein containing a protein of interest joined to an exogenous protein fragment (the fusion partner). The fusion partner may serve various functions, including enhancement of solubility of the polypeptide of interest, as well as providing an “affinity tag” to allow purification of the recombinant fusion polypeptide from a host cell or from a supernatant or from both. If desired, the fusion partner may be removed from the protein of interest after or during purification.
The term “homolog” or “homologous” when used in reference to a polypeptide refers to a high degree of sequence identity between two polypeptides, or to a high degree of similarity between the three-dimensional structure or to a high degree of similarity between the active site and the mechanism of action. In a preferred embodiment, a homolog has a greater than 60% sequence identity, and more preferably greater than 75% sequence identity, and still more preferably greater than 90% sequence identity, with a reference sequence.
As applied to polypeptides, the term “substantial identity” means that two peptide sequences, when optimally aligned, such as by the programs GAP or BESTFIT using default gap weights, share at least 80% sequence identity, preferably at least 90% sequence identity, more preferably at least 95% sequence identity or more (e.g., 99% sequence identity). Preferably, residue positions which are not identical differ by conservative amino acid substitutions.
In one embodiment of the present invention it is contemplated that varients of the αRYR gene (i.e., w, as-81 and as-193) may be used for, e.g., transfections. The terms “variant” and “mutant” when used in reference to a polypeptide refer to an amino acid sequence that differs by one or more amino acids from another, usually related polypeptide. The variant may have “conservative” changes, wherein a substituted amino acid has similar structural or chemical properties. One type of conservative amino acid substitutions refers to the interchangeability of residues having similar side chains. For example, a group of amino acids having aliphatic side chains is glycine, alanine, valine, leucine, and isoleucine; a group of amino acids having aliphatic-hydroxyl side chains is serine and threonine; a group of amino acids having amide-containing side chains is asparagine and glutamine; a group of amino acids having aromatic side chains is phenylalanine, tyrosine, and tryptophan; a group of amino acids having basic side chains is lysine, arginine, and histidine; and a group of amino acids having sulfur-containing side chains is cysteine and methionine. Preferred conservative amino acids substitution groups are: valine-leucine-isoleucine, phenylalanine-tyrosine, lysine-arginine, alanine-valine, and asparagine-glutamine. More rarely, a variant may have “non-conservative” changes (e.g., replacement of a glycine with a tryptophan). Similar minor variations may also include amino acid deletions or insertions (i.e., additions), or both. Guidance in determining which and how many amino acid residues may be substituted, inserted or deleted without abolishing biological activity may be found using computer programs well known in the art, for example, DNAStar software. Variants can be tested in functional assays. Preferred variants have less than 10%, preferably less than 5% and still more preferably less than 2% changes (whether substitutions, deletions, and so on).
The term “domain” when used in reference to a polypeptide refers to a subsection of the polypeptide which possesses a unique structural and/or functional characteristic; typically, this characteristic is similar across diverse polypeptides. The subsection typically comprises contiguous amino acids, although it may also comprise amino acids which act in concert or which are in close proximity due to folding or other configurations.
In one embodiment of the present invention contemplates several genes (e.g., αRYR and βRYR). The term “gene” refers to a nucleic acid (e.g., DNA or RNA) sequence that comprises coding sequences necessary for the production of an RNA, or a polypeptide or its precursor (e.g., proinsulin). A functional polypeptide can be encoded by a full length coding sequence or by any portion of the coding sequence as long as the desired activity or functional properties (e.g., enzymatic activity, ligand binding, signal transduction, etc.) of the polypeptide are retained. The term “portion” when used in reference to a gene refers to fragments of that gene. The fragments may range in size from a few nucleotides to the entire gene sequence minus one nucleotide. Thus, “a nucleotide comprising at least a portion of a gene” may comprise fragments of the gene or the entire gene.
The term “gene” also encompasses the coding regions of a structural gene and includes sequences located adjacent to the coding region on both the 5′ and 3′ ends for a distance of about 1 kb on either end such that the gene corresponds to the length of the full-length mRNA. The sequences which are located 5′ of the coding region and which are present on the mRNA are referred to as 5′ non-translated sequences. The sequences which are located 3′ or downstream of the coding region and which are present on the mRNA are referred to as 3′ non-translated sequences. The term “gene” encompasses both cDNA and genomic forms of a gene.
In one embodiment of the present invention it is contemplated that the genes of the present invention comprise introns and exons. A genomic form or clone of a gene contains the coding region interrupted with non-coding sequences termed “introns” or “intervening regions” or “intervening sequences.” Introns are segments of a gene which are transcribed into heterogeneous nuclear RNA (hnRNA); introns may contain regulatory elements such as enhancers. Introns are removed or “spliced out” from the nuclear or primary transcript; introns therefore are absent in the messenger RNA (mRNA) transcript. The mRNA functions during translation to specify the sequence or order of amino acids in a nascent polypeptide.
In addition to containing introns, genomic forms of a gene may also include sequences located on both the 5′ and 3′ end of the sequences which are present on the RNA transcript. These sequences are referred to as “flanking” sequences or regions (these flanking sequences are located 5′ or 3′ to the non-translated sequences present on the mRNA transcript). The 5′ flanking region may contain regulatory sequences such as promoters and enhancers which control or influence the transcription of the gene. The 3′ flanking region may contain sequences which direct the termination of transcription, posttranscriptional cleavage and polyadenylation.
In particular, the term “TαRYR gene” refers to a full-length TαRYR nucleotide sequence (e.g., FIG. 6). However, it is also intended that the term encompass fragments of TαRYR, as well as other domains with the full-length nucleotide sequence. Furthermore, the terms “TαRYR nucleotide sequence” or “TαRYR polynucleotide sequence” encompass DNA, cDNA, and RNA (e.g., mRNA) sequences. Further still, the term TαRYR is synonymous with “Turkey αRYR” and refers to both TαRYRI and TαRYRII unless specified otherwise.
In one embodiment of the present invention, it is contemplated that the nucleic acids encoding the RYR peptides may be expressed in organisms or cells that are not derived from turkeys. The term “heterologous,” when used in reference to a gene, refers to a gene encoding a factor that is not in its natural environment (i.e., has been altered by the hand of man). For example, a heterologous gene includes a gene from one species introduced into another species. A heterologous gene also includes a gene native to an organism that has been altered in some way (e.g., mutated, added in multiple copies, linked to a non-native promoter or enhancer sequence, etc.). Heterologous genes may comprise, e.g., plant or animal gene sequences that comprise cDNA forms of a plant or animal gene; the cDNA sequences may be expressed in either a sense (to produce mRNA) or anti-sense orientation (to produce an anti-sense RNA transcript that is complementary to the mRNA transcript). Heterologous genes are distinguished from endogenous genes in that the heterologous gene sequences are typically joined to nucleotide sequences comprising regulatory elements such as promoters that are not found naturally associated with the gene for the protein encoded by the heterologous gene or with gene sequences in the chromosome, or are associated with portions of the chromosome not found in nature (e.g., genes expressed in loci where the gene is not normally expressed). In the present invention, it is contemplated that the nucleotide sequence that encodes TαRYR (FIG. 6) and portions thereof may comprise a heterologous gene. For example, the TαRYR sequence may be joined to promoter specific for muscle tissues. Examples of such promoters include, but are not limited to the ankyrin 1 muscle promoter, the desmin gene promoter, the actin promoter and the myosin promoter.
In one embodiment of the present invention, it is contemplated that a portion of the RYR nucleic acid sequence (i.e., a “nucleic acid sequence of interest”) may be used. The term “nucleotide sequence of interest” or “nucleic acid sequence of interest” refers to any nucleotide sequence (e.g., RNA or DNA), the manipulation of which may be deemed desirable for any reason (e.g., treat disease, confer improved qualities, etc.), by one of ordinary skill in the art. Such nucleotide sequences include, but are not limited to, coding sequences of structural genes (e.g., reporter genes, selection marker genes, oncogenes, drug resistance genes, growth factors, etc.), and non-coding regulatory sequences which do not encode an mRNA or protein product (e.g., promoter sequence, polyadenylation sequence, termination sequence, enhancer sequence, etc.).
The term “structural” when used in reference to a gene or to a nucleotide or nucleic acid sequence refers to a gene or a nucleotide or nucleic acid sequence whose ultimate expression product is a protein (such as an enzyme or a structural protein), an rRNA, an sRNA, a tRNA, etc.
The terms “oligonucleotide” or “polynucleotide” or “nucleotide” or “nucleic acid” refer to a molecule comprised of two or more deoxyribonucleotides or ribonucleotides, preferably more than three, and usually more than ten. The exact size will depend on many factors, which in turn depends on the ultimate function or use of the oligonucleotide. The oligonucleotide may be generated in any manner, including chemical synthesis, DNA replication, reverse transcription, or a combination thereof. The terms “an oligonucleotide having a nucleotide sequence encoding a gene” or “a nucleic acid sequence encoding” a specified polypeptide refer to a nucleic acid sequence comprising the coding region of a gene or in other words the nucleic acid sequence which encodes a gene product. The coding region may be present in either a cDNA, genomic DNA or RNA form. When present in a DNA form, the oligonucleotide may be single-stranded (i.e., the sense strand) or double-stranded. Suitable control elements such as enhancers/promoters, splice junctions, polyadenylation signals, etc. may be placed in close proximity to the coding region of the gene if needed to permit proper initiation of transcription and/or correct processing of the primary RNA transcript. Alternatively, the coding region utilized in the expression vectors of the present invention may contain endogenous enhancers/promoters, splice junctions, intervening sequences, polyadenylation signals, etc. or a combination of both endogenous and exogenous control elements.
In one embodiment of the present invention, it is contmeplated that recombinant techniques are used with the nucleic acid sequences of the present invention. The term “recombinant” when made in reference to a nucleic acid molecule refers to a nucleic acid molecule which is comprised of segments of nucleic acid joined together by means of molecular biological techniques. The term “recombinant” when made in reference to a protein or a polypeptide refers to a protein molecule which is expressed using a recombinant nucleic acid molecule.
The terms “complementary” and “complementarity” refer to polynucleotides (i.e., a sequence of nucleotides) related by the base-pairing rules. For example, for the sequence “A-G-T,” is complementary to the sequence “T-C-A.” Complementarity may be “partial,” in which only some of the nucleic acids′ bases are matched according to the base pairing rules. Or, there may be “complete” or “total” complementarity between the nucleic acids. The degree of complementarity between nucleic acid strands has significant effects on the efficiency and strength of hybridization between nucleic acid strands. This is of particular importance in amplification reactions, as well as detection methods which depend upon binding between nucleic acids.
The term “homology” when used in relation to nucleic acids refers to a degree of complementarity. There may be partial homology or complete homology (i.e., identity). “Sequence identity” refers to a measure of relatedness between two or more nucleic acids or proteins, and is given as a percentage with reference to the total comparison length. The identity calculation takes into account those nucleotide or amino acid residues that are identical and in the same relative positions in their respective larger sequences. Calculations of identity may be performed by algorithms contained within computer programs such as “GAP” (Genetics Computer Group, Madison, Wis.) and “ALIGN” (DNAStar, Madison, Wis.). A partially complementary sequence is one that at least partially inhibits (or competes with) a completely complementary sequence from hybridizing to a target nucleic acid is referred to using the functional term “substantially homologous.” The inhibition of hybridization of the completely complementary sequence to the target sequence may be examined using a hybridization assay (Southern or Northern blot, solution hybridization and the like) under conditions of low stringency. A substantially homologous sequence or probe will compete for and inhibit the binding (i.e., the hybridization) of a sequence which is completely homologous to a target under conditions of low stringency. This is not to say that conditions of low stringency are such that non-specific binding is permitted; low stringency conditions require that the binding of two sequences to one another be a specific (i.e., selective) interaction. The absence of non-specific binding may be tested by the use of a second target which lacks even a partial degree of complementarity (e.g., less than about 30% identity); in the absence of non-specific binding the probe will not hybridize to the second non-complementary target.
The following terms are used to describe the sequence relationships between two or more polynucleotides: “reference sequence,” “sequence identity,” “percentage of sequence identity” and “substantial identity.” A “reference sequence” is a defined sequence used as a basis for a sequence comparison; a reference sequence may be a subset of a larger sequence, for example, as a segment of a full-length cDNA sequence given in a sequence listing or may comprise a complete gene sequence. Generally, a reference sequence is at least 20 nucleotides in length, frequently at least 25 nucleotides in length, and often at least 50 nucleotides in length. Since two polynucleotides may each (1) comprise a sequence (i.e., a portion of the complete polynucleotide sequence) that is similar between the two polynucleotides, and (2) may further comprise a sequence that is divergent between the two polynucleotides, sequence comparisons between two (or more) polynucleotides are typically performed by comparing sequences of the two polynucleotides over a “comparison window” to identify and compare local regions of sequence similarity. A “comparison window,” as used herein, refers to a conceptual segment of at least 20 contiguous nucleotide positions wherein a polynucleotide sequence may be compared to a reference sequence of at least 20 contiguous nucleotides and wherein the portion of the polynucleotide sequence in the comparison window may comprise additions or deletions (i.e., gaps) of 20% or less as compared to the reference sequence (which does not comprise additions or deletions) for optimal alignment of the two sequences. Optimal alignment of sequences for aligning a comparison window may be conducted by the local homology algorithm of Smith and Waterman [Smith and Waterman, Adv. Appl. Math. 2: 482 (1981)] by the homology alignment algorithm of Needleman and Wunsch [Needleman and Wunsch, J. Mol. Biol. 48:443 (1970)], by the search for similarity method of Pearson and Lipman [Pearson and Lipman, Proc. Natl. Acad. Sci. (U.S.A.) 85:2444 (1988)], by computerized implementations of these algorithms (GAP, BESTFIT, FASTA, and TFASTA in the Wisconsin Genetics Software Package Release 7.0, Genetics Computer Group, 575 Science Dr., Madison, Wis.), or by inspection, and the best alignment (i.e., resulting in the highest percentage of homology over the comparison window) generated by the various methods is selected. The term “sequence identity” means that two polynucleotide sequences are identical (i.e., on a nucleotide-by-nucleotide basis) over the window of comparison. The term “percentage of sequence identity” is calculated by comparing two optimally aligned sequences over the window of comparison, determining the number of positions at which the identical nucleic acid base (e.g., A, T, C, G, U, or I) occurs in both sequences to yield the number of matched positions, dividing the number of matched positions by the total number of positions in the window of comparison (i.e., the window size), and multiplying the result by 100 to yield the percentage of sequence identity. The terms “substantial identity” as used herein denotes a characteristic of a polynucleotide sequence, wherein the polynucleotide comprises a sequence that has at least 85 percent sequence identity, preferably at least 90 to 95% sequence identity, more usually at least 99 percent sequence identity as compared to a reference sequence over a comparison window of at least 20 nucleotide positions, frequently over a window of at least 25-50 nucleotides, wherein the percentage of sequence identity is calculated by comparing the reference sequence to the polynucleotide sequence which may include deletions or additions which total 20 percent or less of the reference sequence over the window of comparison. The reference sequence may be a subset of a larger sequence, for example, as a segment of the full-length sequences of the compositions claimed in the present invention.
The term “substantially homologous” when used in reference to a double-stranded nucleic acid sequence such as a cDNA or genomic clone refers to any probe that can hybridize to either or both strands of the double-stranded nucleic acid sequence under conditions of low to high stringency as described above.
The term “substantially homologous” when used in reference to a single-stranded nucleic acid sequence refers to any probe that can hybridize (i.e., it is the complement of) the single-stranded nucleic acid sequence under conditions of low to high stringency as described above.
The term “hybridization” refers to the pairing of complementary nucleic acids. Hybridization and the strength of hybridization (i.e., the strength of the association between the nucleic acids) is impacted by such factors as the degree of complementary between the nucleic acids, stringency of the conditions involved, the Tm of the formed hybrid, and the G:C ratio within the nucleic acids. A single molecule that contains pairing of complementary nucleic acids within its structure is said to be “self-hybridized.”
The term “Tm” refers to the “melting temperature” of a nucleic acid. The melting temperature is the temperature at which a population of double-stranded nucleic acid molecules becomes half dissociated into single strands. The equation for calculating the Tm of nucleic acids is well known in the art. As indicated by standard references, a simple estimate of the Tm value may be calculated by the equation: Tm=81.5+0.41(% G+C), when a nucleic acid is in aqueous solution at 1 M NaCl (See e.g., Anderson and Young, Quantitative Filter Hybridization, in Nucleic Acid Hybridization [1985]). Other references include more sophisticated computations that take structural as well as sequence characteristics into account for the calculation of Tm.
In one embodiment of the present invention, it is contemplated that assays will be used for genotyping with, for example, labeled probes. In this regard, complementary sequences will hybridize to each other. Hybridization may occur at different stringencies. The term “stringency” refers to the conditions of temperature, ionic strength, and the presence of other compounds such as organic solvents, under which nucleic acid hybridizations are conducted. With “high stringency” conditions, nucleic acid base pairing will occur only between nucleic acid fragments that have a high frequency of complementary base sequences. Thus, conditions of “low” stringency are often required with nucleic acids that are derived from organisms that are genetically diverse, as the frequency of complementary sequences is usually less.
“Low stringency conditions” when used in reference to nucleic acid hybridization comprise conditions equivalent to binding or hybridization at 42° C. in a solution consisting of 5×SSPE (43.8 g/l NaCl, 6.9 g/l NaH2PO4(H2O and 1.85 g/l EDTA, pH adjusted to 7.4 with NaOH), 0.1% SDS, 5× Denhardt's reagent [50× Denhardt's contains per 500 ml: 5 g Ficoll (Type 400, Pharmacia), 5 g BSA (Fraction V; Sigma)] and 100 μg/ml denatured salmon sperm DNA followed by washing in a solution comprising 5×SSPE, 0.1% SDS at 42° C. when a probe of about 500 nucleotides in length is employed.
“Medium stringency conditions” when used in reference to nucleic acid hybridization comprise conditions equivalent to binding or hybridization at 42° C. in a solution consisting of 5×SSPE (43.8 g/l NaCl, 6.9 g/l NaH2PO4(H2O and 1.85 g/l EDTA, pH adjusted to 7.4 with NaOH), 0.5% SDS, 5× Denhardt's reagent and 100 μg/ml denatured salmon sperm DNA followed by washing in a solution comprising 1.0×SSPE, 1.0% SDS at 42° C. when a probe of about 500 nucleotides in length is employed.
“High stringency conditions” when used in reference to nucleic acid hybridization comprise conditions equivalent to binding or hybridization at 42° C. in a solution consisting of 5×SSPE (43.8 g/l NaCl, 6.9 g/l NaH2PO4(H2O and 1.85 g/l EDTA, pH adjusted to 7.4 with NaOH), 0.5% SDS, 5× Denhardt's reagent and 100 μg/ml denatured salmon sperm DNA followed by washing in a solution comprising 0.1×SSPE, 1.0% SDS at 42° C. when a probe of about 500 nucleotides in length is employed.
It is well known that numerous equivalent conditions may be employed to comprise low stringency conditions; factors such as the length and nature (DNA, RNA, base composition) of the probe and nature of the target (DNA, RNA, base composition, present in solution or immobilized, etc.) and the concentration of the salts and other components (e.g., the presence or absence of formamide, dextran sulfate, polyethylene glycol) are considered and the hybridization solution may be varied to generate conditions of low stringency hybridization different from, but equivalent to, the above listed conditions. In addition, the art knows conditions that promote hybridization under conditions of high stringency (e.g., increasing the temperature of the hybridization and/or wash steps, the use of formamide in the hybridization solution, etc.).
The term “wild-type” when made in reference to a gene refers to a gene that has the characteristics of a gene isolated from a naturally occurring source. The term “wild-type” when made in reference to a gene product refers to a gene product that has the characteristics of a gene product isolated from a naturally occurring source. The term “naturally-occurring” as applied to an object refers to that an object can be found in nature. For example, a polypeptide or polynucleotide sequence that is present in an organism (including viruses) that can be isolated from a source in nature and which has not been intentionally modified by man in the laboratory is naturally-occurring. A wild-type gene is often the gene which is most frequently observed in a population and is thus arbitrarily designated the “normal” or “wild-type” form of the gene. In contrast, the term “modified” or “mutant” when made in reference to a gene or to a gene product refers, respectively, to a gene or to a gene product which displays modifications in sequence and/or functional properties (i.e., altered characteristics) when compared to the wild-type gene or gene product. It is noted that naturally-occurring mutants can be isolated; these are identifiable since they have altered characteristics when compared to the wild-type gene or gene product. In the present invention, FIG. 6 comprises one allele of the wild-type gene.
Thus, the terms “variant” and “mutant” when used in reference to a nucleotide sequence refer to an nucleic acid sequence that differs by one or more nucleotides from another, usually related nucleotide acid sequence. A “variation” is a difference between two different nucleotide sequences; typically, one sequence is a reference sequence. In the present invention, W, AS-81 and AS-193 are example of variants of the RYR gene.
The term “polymorphic locus” refers to a genetic locus present in a population that shows variation between members of the population (i.e., the most common allele has a frequency of less than 0.95). Thus, “polymorphism” refers to the existence of a character in two or more variant forms in a population. A “single nucleotide polymorphism” (or SNP) refers a genetic locus of a single base which may be occupied by one of at least two different nucleotides. In contrast, a “monomorphic locus” refers to a genetic locus at which little or no variations are seen between members of the population (generally taken to be a locus at which the most common allele exceeds a frequency of 0.95 in the gene pool of the population).
A “frameshift mutation” refers to a mutation in a nucleotide sequence, usually resulting from insertion or deletion of a single nucleotide (or two or four nucleotides) which results in a change in the correct reading frame of a structural DNA sequence encoding a protein. The altered reading frame usually results in the translated amino-acid sequence being changed or truncated. The AS-193 variant of the present invention is believed to have a frameshift mutation that produces a premature stop codon after amino acid 416.
A “splice mutation” refers to any mutation that affects gene expression by affecting correct RNA splicing. Splicing mutation may be due to mutations at intron-exon boundaries which alter splice sites. The W, AS-81 and AS-193 variants of the present invention are believed to be the result of splice mutations.
The term “detection assay” refers to an assay for detecting the presence or absence of a sequence or a variant nucleic acid sequence (e.g., mutation or polymorphism in a given allele of a particular gene, as e.g., TαRYR gene [FIG. 6]), or for detecting the presence or absence of a particular protein (e.g., TβRYR [SEQ ID NO: 5]) or the structure or activity or effect of a particular protein (e.g., a binding assay or activity assay) or for detecting the presence or absence of a variant of a particular protein.
The term “antisense” refers to a deoxyribonucleotide sequence whose sequence of deoxyribonucleotide residues is in reverse 5′ to 3′ orientation in relation to the sequence of deoxyribonucleotide residues in a sense strand of a DNA duplex. A “sense strand” of a DNA duplex refers to a strand in a DNA duplex which is transcribed by a cell in its natural state into a “sense mRNA.” Thus an “antisense” sequence is a sequence having the same sequence as the non-coding strand in a DNA duplex. The term “antisense RNA” refers to a RNA transcript that is complementary to all or part of a target primary transcript or mRNA and that blocks the expression of a target gene by interfering with the processing, transport and/or translation of its primary transcript or mRNA. The complementarity of an antisense RNA may be with any part of the specific gene transcript, i.e., at the 5′ non-coding sequence, 3′ non-coding sequence, introns, or the coding sequence. In addition, as used herein, antisense RNA may contain regions of ribozyme sequences that increase the efficacy of antisense RNA to block gene expression. “Ribozyme” refers to a catalytic RNA and includes sequence-specific endoribonucleases. “Antisense inhibition” refers to the production of antisense RNA transcripts capable of preventing the expression of the target protein.
In one embodiment of the present invention, it is contemplated that the nucleotide sequences of the present invention may be “amplified”. “Amplification” is a special case of nucleic acid replication involving template specificity. It is to be contrasted with non-specific template replication (i.e., replication that is template-dependent but not dependent on a specific template). Template specificity is here distinguished from fidelity of replication (i.e., synthesis of the proper polynucleotide sequence) and nucleotide (ribo- or deoxyribo-) specificity. Template specificity is frequently described in terms of “target” specificity. Target sequences are “targets” in the sense that they are sought to be sorted out from other nucleic acid. Amplification techniques have been designed primarily for this sorting out. Examples of amplification include, but are not limited to, PCR and the INVADER® assay (Third Wave Technologies, Madison Wis.).
Template specificity is achieved in most amplification techniques by the choice of enzyme. Amplification enzymes are enzymes that, under conditions they are used, will process only specific sequences of nucleic acid in a heterogeneous mixture of nucleic acid. For example, in the case of Qβ replicase, MDV-1 RNA is the specific template for the replicase (Kacian, et al., Proc. Natl. Acad. Sci. USA, 69:3038 [1972]). Other nucleic acid will not be replicated by this amplification enzyme. Similarly, in the case of T7 RNA polymerase, this amplification enzyme has a stringent specificity for its own promoters (Chamberlain, et al., Nature, 228:227 [1970]). In the case of T4 DNA ligase, the enzyme will not ligate the two oligonucleotides or polynucleotides, where there is a mismatch between the oligonucleotide or polynucleotide substrate and the template at the ligation junction (Wu and Wallace, Genomics, 4:560 [1989]). Finally, Taq and Pfu polymerases, by virtue of their ability to function at high temperature, are found to display high specificity for the sequences bounded and thus defined by the primers; the high temperature results in thermodynamic conditions that favor primer hybridization with the target sequences and not hybridization with non-target sequences (H. A. Erlich (ed.), PCR Technology, Stockton Press [1989]).
The term “amplifiable nucleic acid” refers to nucleic acids that may be amplified by any amplification method. It is contemplated that “amplifiable nucleic acid” will usually comprise “sample template.” Examples of amplification include, but are not limited to, PCR and the INVADER® assay (Third Wave Technologies, Madison Wis.).
Allele specific nucleic acid sequences may also be identified by hybridizaiton with crosslinkable oligonucleotide probes as disclosed in U.S. Pat. No. 5,652,096 to G. D. Cimino, which is herein incorporated by reference.
The term “sample template” refers to nucleic acid originating from a sample that is analyzed for the presence of “target” (defined below). In contrast, “background template” is used in reference to nucleic acid other than sample template that may or may not be present in a sample. Background template is most often inadvertent. It may be the result of carryover, or it may be due to the presence of nucleic acid contaminants sought to be purified away from the sample. For example, nucleic acids from organisms other than those to be detected may be present as background in a test sample.
In one embodiment of the present invention, it is contemplated that primers will be used for the amplification of nucleic acid sequences. Examples of such primers are SEQ ID NOS: 13, 14, 15 an 16. The term “primer” refers to an oligonucleotide, whether occurring naturally as in a purified restriction digest or produced synthetically, which is capable of acting as a point of initiation of synthesis when placed under conditions in which synthesis of a primer extension product which is complementary to a nucleic acid strand is induced, (i.e., in the presence of nucleotides and an inducing agent such as DNA polymerase and at a suitable temperature and pH). The primer is preferably single stranded for maximum efficiency in amplification, but may alternatively be double stranded. If double stranded, the primer is first treated to separate its strands before being used to prepare extension products. Preferably, the primer is an oligodeoxyribonucleotide. The primer must be sufficiently long to prime the synthesis of extension products in the presence of the inducing agent. The exact lengths of the primers will depend on many factors, including temperature, source of primer and the use of the method.
The term “probe” refers to an oligonucleotide (i.e., a sequence of nucleotides), whether occurring naturally as in a purified restriction digest or produced synthetically, recombinantly or by PCR amplification, that is capable of hybridizing to another oligonucleotide of interest. A probe may be single-stranded or double-stranded. Probes are useful in the detection, identification and isolation of particular gene sequences. It is contemplated that any probe used in the present invention will be labeled with any “reporter molecule,” so that is detectable in any detection system, including, but not limited to enzyme (e.g., ELISA, as well as enzyme-based histochemical assays), fluorescent, radioactive, and luminescent systems. It is not intended that the present invention be limited to any particular detection system or label.
The term “target,” when used in reference to the polymerase chain reaction, refers to the region of nucleic acid bounded by the primers used for polymerase chain reaction. Thus, the “target” is sought to be sorted out from other nucleic acid sequences. A “segment” is defined as a region of nucleic acid within the target sequence.
In one embodiment of the present invention, it is contemplated that turkeys will be identified for being homozygous for the αRYRII allele via PCR amplification. The term “polymerase chain reaction” (“PCR”) refers to the method of K. B. Mullis U.S. Pat. Nos. 4,683,195, 4,683,202, and 4,965,188, that describe a method for increasing the concentration of a segment of a target sequence in a mixture of genomic DNA without cloning or purification. This process for amplifying the target sequence consists of introducing a large excess of two oligonucleotide primers to the DNA mixture containing the desired target sequence, followed by a precise sequence of thermal cycling in the presence of a DNA polymerase. The two primers are complementary to their respective strands of the double stranded target sequence. To effect amplification, the mixture is denatured and the primers then annealed to their complementary sequences within the target molecule. Following annealing, the primers are extended with a polymerase so as to form a new pair of complementary strands. The steps of denaturation, primer annealing, and polymerase extension can be repeated many times (i.e., denaturation, annealing and extension constitute one “cycle”; there can be numerous “cycles”) to obtain a high concentration of an amplified segment of the desired target sequence. The length of the amplified segment of the desired target sequence is determined by the relative positions of the primers with respect to each other, and therefore, this length is a controllable parameter. By virtue of the repeating aspect of the process, the method is referred to as the “polymerase chain reaction” (hereinafter “PCR”). Because the desired amplified segments of the target sequence become the predominant sequences (in terms of concentration) in the mixture, they are said to be “PCR amplified.”
With PCR, it is possible to amplify a single copy of a specific target sequence in genomic DNA to a level detectable by several different methodologies (e.g., hybridization with a labeled probe; incorporation of biotinylated primers followed by avidin-enzyme conjugate detection; incorporation of 32P-labeled deoxynucleotide triphosphates, such as dCTP or dATP, into the amplified segment). In addition to genomic DNA, any oligonucleotide or polynucleotide sequence can be amplified with the appropriate set of primer molecules. In particular, the amplified segments created by the PCR process itself are, themselves, efficient templates for subsequent PCR amplifications.
The terms “PCR product,” “PCR fragment,” and “amplification product” refer to the resultant mixture of compounds after two or more cycles of the PCR steps of denaturation, annealing and extension are complete. These terms encompass the case where there has been amplification of one or more segments of one or more target sequences.
The term “amplification reagents” refers to those reagents (deoxyribonucleotide triphosphates, buffer, etc.), needed for amplification except for primers, nucleic acid template, and the amplification enzyme. Typically, amplification reagents along with other reaction components are placed and contained in a reaction vessel (test tube, microwell, etc.).
One embodiment of the present invention contemplates reverse-transcription of turkey RYR mRNA. The term “reverse-transcriptase” or “RT-PCR” refers to a type of PCR where the starting material is mRNA. The starting mRNA is enzymatically converted to complementary DNA or “cDNA” using a reverse transcriptase enzyme. The cDNA is then used as a “template” for a “PCR” reaction.
The term “gene expression” refers to the process of converting genetic information encoded in a gene into RNA (e.g., mRNA, rRNA, tRNA, or snRNA) through “transcription” of the gene (i.e., via the enzymatic action of an RNA polymerase), and into protein, through “translation” of mRNA. Gene expression can be regulated at many stages in the process. “Up-regulation” or “activation” refers to regulation that increases the production of gene expression products (i.e., RNA or protein), while “down-regulation” or “repression” refers to regulation that decrease production. Molecules (e.g., transcription factors) that are involved in up-regulation or down-regulation are often called “activators” and “repressors,” respectively.
The terms “in operable combination,” “in operable order” and “operably linked” refer to the linkage of nucleic acid sequences in such a manner that a nucleic acid molecule capable of directing the transcription of a given gene and/or the synthesis of a desired protein molecule is produced. The term also refers to the linkage of amino acid sequences in such a manner so that a functional protein is produced.
The term “regulatory element” refers to a genetic element which controls some aspect of the expression of nucleic acid sequences. For example, a promoter is a regulatory element which facilitates the initiation of transcription of an operably linked coding region. Other regulatory elements are splicing signals, polyadenylation signals, termination signals, etc.
In one embodiment of the present invention, it is contemplated that the genes and alleles of the present invention may comprise promoters regulator elements and enhancer elements. Transcriptional control signals in eukaryotes comprise “promoter” and “enhancer” elements. Promoters and enhancers consist of short arrays of DNA sequences that interact specifically with cellular proteins involved in transcription (Maniatis, et al., Science 236:1237, 1987). Promoter and enhancer elements have been isolated from a variety of eukaryotic sources including genes in yeast, insect, mammalian and plant cells. Promoter and enhancer elements have also been isolated from viruses and analogous control elements, such as promoters, are also found in prokaryotes. The selection of a particular promoter and enhancer depends on the cell type used to express the protein of interest. Some eukaryotic promoters and enhancers have a broad host range while others are functional in a limited subset of cell types (for review, see Voss, et al., Trends Biochem. Sci., 11:287, 1986; and Maniatis, et al., supra 1987). In the present invention, it is contemplated that, for example, the TαRYR gene may be joined to promoter specific for muscle tissues of skeletal tissues. Examples of such promoters include, but are not limited to the ankyrin 1 muscle promoter, the desmin gene promoter, the actin promoter and the myosin promoter. Additionally, it is contemplated that the TαRYR gene may be joined to a constitutive promoter or an inducible promoter (both defined below) or to a promoter specific for other cell or tissue types (defined below) (e.g., promoters specific for muscle or skin).
The terms “promoter element,” “promoter,” or “promoter sequence” refer to a DNA sequence that is located at the 5′ end (i.e. precedes) of the coding region of a DNA polymer. The location of most promoters known in nature precedes the transcribed region. The promoter functions as a switch, activating the expression of a gene. If the gene is activated, it is said to be transcribed, or participating in transcription. Transcription involves the synthesis of mRNA from the gene. The promoter, therefore, serves as a transcriptional regulatory element and also provides a site for initiation of transcription of the gene into mRNA.
The term “regulatory region” refers to a gene's 5′ transcribed but untranslated regions, located immediately downstream from the promoter and ending just prior to the translational start of the gene.
The term “promoter region” refers to the region immediately upstream of the coding region of a DNA polymer, and is typically between about 500 bp and 4 kb in length, and is preferably about 1 to 1.5 kb in length.
Promoters may be tissue specific or cell specific. Examples of promoters specific for muscle tissues are given above. The term “tissue specific” as it applies to a promoter refers to a promoter that is capable of directing selective expression of a nucleotide sequence of interest to a specific type of tissue (e.g., muscle) in the relative absence of expression of the same nucleotide sequence of interest in a different type of tissue (e.g., bone). Tissue specificity of a promoter may be evaluated by, for example, operably linking a reporter gene to the promoter sequence to generate a reporter construct, introducing the reporter construct into the genome of an organism such that the reporter construct is integrated into every tissue of the resulting transgenic organism, and detecting the expression of the reporter gene (e.g., detecting mRNA, protein, or the activity of a protein encoded by the reporter gene) in different tissues of the transgenic organism. The detection of a greater level of expression of the reporter gene in one or more tissues relative to the level of expression of the reporter gene in other tissues shows that the promoter is specific for the tissues in which greater levels of expression are detected. The term “cell type specific” as applied to a promoter refers to a promoter which is capable of directing selective expression of a nucleotide sequence of interest in a specific type of cell in the relative absence of expression of the same nucleotide sequence of interest in a different type of cell within the same tissue. The term “cell type specific” when applied to a promoter also means a promoter capable of promoting selective expression of a nucleotide sequence of interest in a region within a single tissue. Cell type specificity of a promoter may be assessed using methods well known in the art, e.g., immunohistochemical staining. Briefly, tissue sections are embedded in paraffin, and paraffin sections are reacted with a primary antibody which is specific for the polypeptide product encoded by the nucleotide sequence of interest whose expression is controlled by the promoter. A labeled (e.g., peroxidase conjugated) secondary antibody which is specific for the primary antibody is allowed to bind to the sectioned tissue and specific binding detected (e.g., with avidin/biotin) by microscopy.
Promoters may be constitutive or inducible. The term “constitutive” when made in reference to a promoter means that the promoter is capable of directing transcription of an operably linked nucleic acid sequence in the absence of a stimulus (e.g., heat shock, chemicals, light, etc.). Typically, constitutive promoters are capable of directing expression of a transgene in substantially any cell and any tissue.
In contrast, an “inducible” promoter is one which is capable of directing a level of transcription of an operably linked nucleic acid sequence in the presence of a stimulus (e.g., heat shock, chemicals, light, etc.) which is different from the level of transcription of the operably linked nucleic acid sequence in the absence of the stimulus.
The term “regulatory element” refers to a genetic element that controls some aspect of the expression of nucleic acid sequence(s). For example, a promoter is a regulatory element that facilitates the initiation of transcription of an operably linked coding region. Other regulatory elements are splicing signals, polyadenylation signals, termination signals, etc.
The enhancer and/or promoter may be “endogenous” or “exogenous” or “heterologous.” An “endogenous” enhancer or promoter is one that is naturally linked with a given gene in the genome. An “exogenous” or “heterologous” enhancer or promoter is one that is placed in juxtaposition to a gene by means of genetic manipulation (i.e., molecular biological techniques) such that transcription of the gene is directed by the linked enhancer or promoter. For example, an endogenous promoter in operable combination with a first gene can be isolated, removed, and placed in operable combination with a second gene, thereby making it a “heterologous promoter” in operable combination with the second gene. A variety of such combinations are contemplated (e.g., the first and second genes can be from the same species, or from different species).
The term “naturally linked” or “naturally located” when used in reference to the relative positions of nucleic acid sequences means that the nucleic acid sequences exist in nature in the relative positions.
The presence of “splicing signals” on an expression vector often results in higher levels of expression of the recombinant transcript in eukaryotic host cells. Splicing signals mediate the removal of introns from the primary RNA transcript and consist of a splice donor and acceptor site (Sambrook, et al., Molecular Cloning: A Laboratory Manual, 2nd ed., Cold Spring Harbor Laboratory Press, New York [1989] pp. 16.7-16.8). An example of a commonly used splice donor and acceptor site is the splice junction from the 16S RNA of SV40.
Efficient expression of recombinant DNA sequences in eukaryotic cells requires expression of signals directing the efficient termination and polyadenylation of the resulting transcript. Transcription termination signals are generally found downstream of the polyadenylation signal and are a few hundred nucleotides in length. The term “poly(A) site” or “poly(A) sequence” as used herein denotes a DNA sequence which directs both the termination and polyadenylation of the nascent RNA transcript. Efficient polyadenylation of the recombinant transcript is desirable, as transcripts lacking a poly(A) tail are unstable and are rapidly degraded. The poly(A) signal utilized in an expression vector may be “heterologous” or “endogenous.” An endogenous poly(A) signal is one that is found naturally at the 3′ end of the coding region of a given gene in the genome. A heterologous poly(A) signal is one which has been isolated from one gene and positioned 3′ to another gene. A commonly used heterologous poly(A) signal is the SV40 poly(A) signal. The SV40 poly(A) signal is contained on a 237 bp BamHI/BclI restriction fragment and directs both termination and polyadenylation (Sambrook, supra, at 16.6-16.7).
The term “vector” refers to nucleic acid molecules that transfer DNA segment(s) from one cell to another. The term “vehicle” is sometimes used interchangeably with “vector.” In one embodiment, vectors comprising the sequences and portions of sequences of the present invention are contemplated.
The terms “expression vector” or “expression cassette” refer to a recombinant DNA molecule containing a desired coding sequence and appropriate nucleic acid sequences necessary for the expression of the operably linked coding sequence in a particular host organism. Nucleic acid sequences necessary for expression in prokaryotes usually include a promoter, an operator (optional), and a ribosome binding site, often along with other sequences. Eukaryotic cells are known to utilize promoters, enhancers, and termination and polyadenylation signals.
In one embodiment of the present invention, it is contemplated that the sequences of the present invention (and portions thereof) may be used in in transfection protocols. The term “transfection” refers to the introduction of foreign DNA into cells. Transfection may be accomplished by a variety of means known to the art including calcium phosphate-DNA co-precipitation, DEAE-dextran-mediated transfection, polybrene-mediated transfection, glass beads, electroporation, microinjection, liposome fusion, lipofection, protoplast fusion, viral infection, biolistics (i.e., particle bombardment) and the like.
The term “stable transfection” or “stably transfected” refers to the introduction and integration of foreign DNA into the genome of the transfected cell. The term “stable transfectant” refers to a cell that has stably integrated foreign DNA into the genomic DNA.
The term “transient transfection” or “transiently transfected” refers to the introduction of foreign DNA into a cell where the foreign DNA fails to integrate into the genome of the transfected cell. The foreign DNA persists in the nucleus of the transfected cell for several days. During this time the foreign DNA is subject to the regulatory controls that govern the expression of endogenous genes in the chromosomes. The term “transient transfectant” refers to cells that have taken up foreign DNA but have failed to integrate this DNA.
The term “calcium phosphate co-precipitation” refers to a technique for the introduction of nucleic acids into a cell. The uptake of nucleic acids by cells is enhanced when the nucleic acid is presented as a calcium phosphate-nucleic acid co-precipitate. The original technique of Graham and van der Eb (Graham and van der Eb, Virol., 52:456 [1973]), has been modified by several groups to optimize conditions for particular types of cells. The art is well aware of these numerous modifications.
The terms “infecting” and “infection” when used with a bacterium refer to co-incubation of a target biological sample, (e.g., cell, tissue, etc.) with the bacterium under conditions such that nucleic acid sequences contained within the bacterium are introduced into one or more cells of the target biological sample.
The terms “bombarding, “bombardment,” and “biolistic bombardment” refer to the process of accelerating particles towards a target biological sample (e.g., cell, tissue, etc.) to effect wounding of the cell membrane of a cell in the target biological sample and/or entry of the particles into the target biological sample. Methods for biolistic bombardment are known in the art (e.g., U.S. Pat. No. 5,584,807, the contents of which are incorporated herein by reference), and are commercially available (e.g., the helium gas-driven microprojectile accelerator (PDS-1000/He, BioRad).
The term “transgene” refers to a foreign gene (e.g., αRYR and βRYR) that is placed into an organism by the process of transfection. The term “foreign gene” refers to any nucleic acid (e.g., gene sequence) that is introduced into the genome of an organism by experimental manipulations and may include gene sequences found in that organism so long as the introduced gene does not reside in the same location as does the naturally-occurring gene.
The term “transgenic” when used in reference to a host cell or an organism refers to a host cell or an organism that contains at least one heterologous or foreign gene in the host cell or in one or more of cells of the organism.
The term “host cell” refers to any cell capable of replicating and/or transcribing and/or translating a heterologous gene. Thus, a “host cell” refers to any eukaryotic or prokaryotic cell (e.g., bacterial cells such as E. coli, yeast cells, mammalian cells, avian cells, amphibian cells, plant cells, fish cells, and insect cells), whether located in vitro or in vivo. For example, host cells may be located in a transgenic animal. In the present invention, it is contemplated that host cells are, for example, myoblasts, and myocytes.
The terms “transformants” or “transformed cells” include the primary transformed cell and cultures derived from that cell without regard to the number of transfers. All progeny may not be precisely identical in DNA content, due to deliberate or inadvertent mutations. Mutant progeny that have the same functionality as screened for in the originally transformed cell are included in the definition of transformants.
The term “selectable marker” refers to a gene which encodes an enzyme having an activity that confers resistance to an antibiotic or drug upon the cell in which the selectable marker is expressed, or which confers expression of a trait which can be detected (e.g., luminescence or fluorescence). Selectable markers may be “positive” or “negative.” Examples of positive selectable markers include the neomycin phosphotrasferase (NPTII) gene which confers resistance to G418 and to kanamycin, and the bacterial hygromycin phosphotransferase gene (hyg), which confers resistance to the antibiotic hygromycin. Negative selectable markers encode an enzymatic activity whose expression is cytotoxic to the cell when grown in an appropriate selective medium. For example, the HSV-tk gene is commonly used as a negative selectable marker. Expression of the HSV-tk gene in cells grown in the presence of gancyclovir or acyclovir is cytotoxic; thus, growth of cells in selective medium containing gancyclovir or acyclovir selects against cells capable of expressing a functional HSV TK enzyme.
The term “reporter gene” refers to a gene encoding a protein that may be assayed. Examples of reporter genes include, but are not limited to, luciferase (See, e.g., deWet et al., Mol. Cell. Biol. 7:725 [1987] and U.S. Pat. Nos. 6,074,859; 5,976,796; 5,674,713; and 5,618,682; all of which are incorporated herein by reference), green fluorescent protein (e.g., GenBank Accession Number U43284; a number of GFP variants are commercially available from CLONTECH Laboratories, Palo Alto, Calif.), chloramphenicol acetyltransferase, β-galactosidase, alkaline phosphatase, and horse radish peroxidase.
In one embodiment, the present invention contemplates the overexpressionog the turkey RYR genes. The term “overexpression” refers to the production of a gene product in transgenic organisms that exceeds levels of production in normal or non-transformed organisms. The term “cosuppression” refers to the expression of a foreign gene which has substantial homology to an endogenous gene resulting in the suppression of expression of both the foreign and the endogenous gene. As used herein, the term “altered levels” refers to the production of gene product(s) in transgenic organisms in amounts or proportions that differ from that of normal or non-transformed organisms.
In one embodiment, the present invention contemplates a method of geneotyping turkeys comprising: a) providing nucleic acid samples from a plurality of turkeys; and b) genotyping said samples under conditions such that turkeys homozygous for TaRYRII are identified by, for example, Southern blotting, Northern blotting and nucleic acid sequencing. The terms “Southern blot analysis” and “Southern blot” and “Southern” refer to the analysis of DNA on agarose or acrylamide gels in which DNA is separated or fragmented according to size followed by transfer of the DNA from the gel to a solid support, such as nitrocellulose or a nylon membrane. The immobilized DNA is then exposed to a labeled probe to detect DNA species complementary to the probe used. The DNA may be cleaved with restriction enzymes prior to electrophoresis. Following electrophoresis, the DNA may be partially depurinated and denatured prior to or during transfer to the solid support. Southern blots are a standard tool of molecular biologists (J. Sambrook et al. [1989] Molecular Cloning: A Laboratory Manual, Cold Spring Harbor Press, NY, pp 9.31-9.58). Genotyping may be performed via Southern blotting. This may be performed by testing for the hybridization of a complementary test sequence (i.e., a probe for αRYRI or αRYRII) to the subject DNA.
The term “Northern blot analysis” and “Northern blot” and “northern” refer to the analysis of RNA by electrophoresis of RNA on agarose gels to fractionate the RNA according to size followed by transfer of the RNA from the gel to a solid support, such as nitrocellulose or a nylon membrane. The immobilized RNA is then probed with a labeled probe to detect RNA species complementary to the probe used. Northern blots are a standard tool of molecular biologists (J. Sambrook, et al. [1989] supra, pp 7.39-7.52). Genotyping may be performed via Northern blotting. This may be performed by testing for the hybridization of a complementary test sequence (i.e., a probe for αRYRI or αRYRII) to the subject RNA.
In one embodiment, the present invention contemplates a method of geneotyping turkeys comprising: a) providing nucleic acid samples from a plurality of turkeys; and b) genotyping said samples under conditions such that turkeys homozygous for TaRYRII are identified by, for example, Western blotting and peptide sequencing. The terms “Western blot analysis” and “Western blot” and “Western” refers to the analysis of protein(s) (or polypeptides) immobilized onto a support such as nitrocellulose or a membrane. A mixture comprising at least one protein is first separated on an acrylamide gel, and the separated proteins are then transferred from the gel to a solid support, such as nitrocellulose or a nylon membrane. The immobilized proteins are exposed to at least one antibody with reactivity against at least one antigen of interest. The bound antibodies may be detected by various methods, including the use of radiolabeled antibodies. Genotyping may be performed via Western blotting. This may be performed by testing for the recognition of a probe (i.e., an antibody for αRYRI or αRYRII) to the subject peptides.
The term “antigenic determinant” refers to that portion of an antigen that makes contact with a particular antibody (i.e., an epitope). When a protein or fragment of a protein is used to immunize a host animal, numerous regions of the protein may induce the production of antibodies that bind specifically to a given region or three-dimensional structure on the protein; these regions or structures are referred to as antigenic determinants. An antigenic determinant may compete with the intact antigen (i.e., the “immunogen” used to elicit the immune response) for binding to an antibody.
In one embodiment, the present invention contemplates isolated transcripts. The term “isolated” when used in relation to a nucleic acid, as in “an isolated oligonucleotide” refers to a nucleic acid sequence that is identified and separated from at least one contaminant nucleic acid with which it is ordinarily associated in its natural source. Isolated nucleic acid is present in a form or setting that is different from that in which it is found in nature. In contrast, non-isolated nucleic acids, such as DNA and RNA, are found in the state they exist in nature. Examples of non-isolated nucleic acids include: a given DNA sequence (e.g., a gene) found on the host cell chromosome in proximity to neighboring genes; RNA sequences, such as a specific mRNA sequence encoding a specific protein, found in the cell as a mixture with numerous other mRNAs which encode a multitude of proteins. However, isolated nucleic acid encoding a particular protein includes, by way of example, such nucleic acid in cells ordinarily expressing the protein, where the nucleic acid is in a chromosomal location different from that of natural cells, or is otherwise flanked by a different nucleic acid sequence than that found in nature. The isolated nucleic acid or oligonucleotide may be present in single-stranded or double-stranded form. When an isolated nucleic acid or oligonucleotide is to be utilized to express a protein, the oligonucleotide will contain at a minimum the sense or coding strand (i.e., the oligonucleotide may single-stranded), but may contain both the sense and anti-sense strands (i.e., the oligonucleotide may be double-stranded).
In one embodiment, the present invention contemplates purified nucleic acid and amino acid sequences. The term “purified” refers to molecules, either nucleic or amino acid sequences, that are removed from their natural environment, isolated or separated. An “isolated nucleic acid sequence” may therefore be a purified nucleic acid sequence. “Substantially purified” molecules are at least 60% free, preferably at least 75% free, and more preferably at least 90% free from other components with which they are naturally associated. As used herein, the term “purified” or “to purify” also refer to the removal of contaminants from a sample. The removal of contaminating proteins results in an increase in the percent of polypeptide of interest in the sample. In another example, recombinant polypeptides are expressed in plant, bacterial, yeast, or mammalian host cells and the polypeptides are purified by the removal of host cell proteins; the percent of recombinant polypeptides is thereby increased in the sample.
One embodiment of the present invention contemplates that nucleic acids, peptides, vectors, antibodies, etc, of the present invention may comprise part of a composition. The term “composition comprising” a given polynucleotide sequence or polypeptide refers broadly to any composition containing the given polynucleotide sequence or polypeptide. The composition may comprise an aqueous solution. Compositions comprising polynucleotide sequences encoding TαRYR (e.g., SEQ ID NOS:5, 6 and 7) or fragments thereof may be employed as hybridization probes. In this case, the TαRYR encoding polynucleotide sequences are typically employed in an aqueous solution containing salts (e.g., NaCl), detergents (e.g., SDS), and other components (e.g., Denhardt's solution, dry milk, salmon sperm DNA, etc.).
The term “test compound” refers to any chemical entity, pharmaceutical, drug, and the like that can be used to treat or prevent a disease, illness, sickness, or disorder of bodily function, or otherwise alter the physiological or cellular status of a sample. Test compounds comprise both known and potential therapeutic compounds. A test compound can be determined to be therapeutic by screening using the screening methods of the present invention. A “known therapeutic compound” refers to a therapeutic compound that has been shown (e.g., through animal trials or prior experience with administration to humans) to be effective in such treatment or prevention.
As used herein, the term “response,” when used in reference to an assay, refers to the generation of a detectable signal (e.g., accumulation of reporter protein, increase in ion concentration, accumulation of a detectable chemical product).
The term “sample” is used in its broadest sense. In one sense it can refer to a cell or tissue. In another sense, it is meant to include a specimen or culture obtained from any source and encompass fluids, solids and tissues. Environmental samples include environmental material such as surface matter, soil, water, and industrial samples. These examples are not to be construed as limiting the sample types applicable to the present invention.
One embodiment of the present invention contemplates the genotyping of turkeys. “Genotyping” shall be defined as determining the genetic constitution of an organism or cell, as distinct from its expressed features or phenotype. Genotyping need not include the determination of all genetic constituents of a cell or organism. Indeed, only one genetic marker need be determined (e.g., αRYR) to identify the genotype of a cell or organism as an embodiment of the present invention.
“Slaughter” and “slaughtered” shall be defined as the killing of animals for food or research purposes or for the practice of certain health control measures.
“Used for breeding” shall be defined as the controlled mating of animals (e.g., turkeys) for the purpose of, for example, acquiring offspring of a certain genotype or phenotype. For example, the selected turkeys identified as homozygous for αRYRII are bred with other turkeys selected as homozygous for αRYRII. “Young turkeys” shall be defined as turkeys that are not fully grown or matured. The National Turkey Federation defines a young turkey as a hen under about 15 pounds and less than about 14 weeks of age. A young Tom turkey is defined as being under about 32 pounds and less than 18 weeks of age. A “mature” turkey is a turkey at about or over these weights and ages.
“Commercial meat production” shall be defined as the growing of turkeys for slaughter for food and encompasses the growing of young turkeys (of a particular genotype) to maturity before slaughter as well as the slaughtering of young turkeys.
“Selecting turkeys” shall be defined as, for example, the identification of a turkey or group of turkeys that share, e.g., a similar or identical genotype for at least one gene. The turkeys may be (but need not be) separated from other turkeys not sharing the genotype selected for. Turkeys may also be selected based on phenotype or an(other) characteristic(s).
“Immunohistochemistry” shall be defined as, for example, the histochemical localization of immunoreactive substances using labelled antibodies as reagents



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows the alignment of turkey αRYR amino acid sequence with published skeletal muscle RYR isoforms. Amino acid residues of turkey αRYR (SEQ ID NO:5) (TαRYR; see, FIG. 6) from 376-615 were compared to human RYR1 (HRYR1; accession no. AAA60294), pig RYR1 (PRYR1; accession no. I46646), bullfrog αRYR (BFr-αRYR; accession no. BAA04646) and fish αRYR (FαRYR; accession no. AAB58117). TαRYR-AS81 (SEQ ID NO:6) shows the 27 amino acid residue deletion of turkey αRYR caused by an 81-bp deletion in the cDNA sequence. TαRYR-AS193 (SEQ ID NO:7) show the amino acid sequence translated from αRYR cDNA sequence with the 193-bp deletion. Deletions in the amino acid sequence are indicated by dots and the dash is added to adjust the alignment. The underlined amino acid residues are the point mutation found in human MH (Jurkat-Rott, et al., 2000). The asterisk indicates a stop codon.
FIG. 2 shows partial restriction endonuclease maps of turkey αRYR alleles derived from restriction digests with Bam HI (A) and PstI (B). 1) the digested fragments of αRYR-I (lane 1) and αRYR-II (lane 2) were analyzed by electrophoresis on a 0.9% agarose gel. II) The digested fragments were transferred to nylon membrane and probed either with E12 (lanes 3 and 4) or E14 probes (lanes 5 and 6) in the Southern Hybrid analysis. Probe E12 carried the last 92 bp of exon 12 and probe E14 carried the last 111 bp of exon 14. III) Partial restriction endonuclease maps of fragments of each allele. M: 1 kb DNA ladder.
FIG. 3 shows Expression pattern of turkey αRYR transcript variants. αRYR cDNA samples corresponding to nucleotides 1231-1760 from individual birds were analyzed by RT-PCR and electrophoresis on a 1.5% agarose gel. The identification number of each bird is shown on the top of each lane in the gel. Three patterns of expression aer observed. Bird 31-23 shows expression of all three transcript variants; bird 31-32 shows expression of only W; bird 31-2 shoes expression of W and AS-193 and bird 29-15 shows expression of AS-81 and AS-193. M: 100 bp DNA ladder.
FIG. 4 shows locations and sequences of the alternative splice junctions. The nucleotide and amino acid sequence of turkey αRYR around the splice junctions are shown. The exon sequences are shown in the boxes and the intron sequences are in italics. Tilted lines represent alternative splicing found in this study. The three conserved sequence elements for the splicing acceptor site in exon 13, including the special “a” residue, the polypyrimidine tract (tcct) and the terminal cag at the 3′ end of the splicing site are shown in bold.
FIG. 5 shows turkey genotypes based on αRYR-I and αRYR-II alleles. Screening of genotypes was performed by PCR. PCR products were analyzed by electrophoresis on a 0.9% agarose gel. The results showed that turkeys could be grouped into three different genotypes: homozygous αRYR-II (lane 1), homozygous αRYR-I (lane 2) and heterozygous αRYR-I and αRYR-II (lane 3). M: 1 kb DNA ladder.
FIG. 6 shows the nucleic acid (SEQ ID NOS:8 and 21) and amino acid (SEQ ID NOS:22 and 21) sequences of turkey αRYR.
FIG. 7 shows the nucleic acid (SEQ ID NO:17) and amino acid (SEQ ID NO:24) sequences of turkey βRYR.
FIG. 8 shows the nucleic acid and amino acid sequences of the W (SEQ ID NOS: 18 and 25), AS-81 (SEQ ID NOS: 19 and 26) and AS-193 (SEQ ID NOS: 20 and 27) variants.



GENERAL DESCRIPTION OF THE INVENTION
The skeletal muscle ryanodine receptor (RYRI), a homotetrameric Ca2+ channel protein with a subunit molecular mass of 565 kDa, is localized to the terminal cisternae of the sarcoplasmic reticulum (SR) (Lai, et al., 1988). The large N-terminal domains of each RYR subunit combine to form the “foot” structure which protrudes from the SR and binds to the dihydropyridine receptor (DHPR) embedded in the T-tubule membrane. During skeletal muscle excitation-contraction coupling, depolarization of the sarcolemma/T-tubule membrane system leads to a conformational change in the DHPR which is transmitted to RYR1, causing the channel to open and release Ca2+ from the SR (Catterall, 1991).
Malignant hyperthermia (MH) is an inherited autosomal dominant disorder of skeletal muscle Ca2+ regulation characterized by hypermetablism and accelerated glycogenolysis resulting in excess heat and lactate production. More that twenty missense mutations and one amino acid deletion in RYRI have been associated with human MH (Jurket-Rott, et al., 2000; Sambuughin, et al., 2001). MH-associated mutations in RYR1 mainly cluster in two regions: mutation hot spot 1 (amino acid residues 35-615) and hot spot 2 (residues 2162-2458). One mutation in human MH, Arg614Cys, is homologous with the porcine MH mutation (Fujii, et al., 1991). The major concerns with porcine MH are death from stress and inferior meat quality known as pale, soft, exudative (PSE) meat. PSE meat is characterized by an abnormally light color, a flaccid consistency and poor water holding capacity.
The incidence of MH and PSE meat in the pork industry may have increased as an inadvertent result of genetic selection for muscularity and leanness (Fujii, et al., 1991). Turkey processing industry has reported an increased incidence of PSE turkey meat. The concern has been raised in the growth-selected commercial turkey line (Toelle, et al., 1991). The contemporary turkey breeding industry has, likewise, intensively selected birds for rapid growth and muscularity leading to an increased incidence of meat quality problems including PSE meat. The postmortem biochemical changes which lead to development of PSE turkey are very similar to those observed in PSE pork. These include increased rates of postmortem pH decline, ATP depletion and glycolysis (Pietrzak, et al., 1997). These similarities prompted us to hypothesize that one or more mutations exist in the turkey RYR which alter the rate of postmortem glycolysis and thus account for the observed increase in product quality defects.
In contrast to mammalian skeletal muscle, avian skeletal muscle comprises two RYR isoforms: αRYR (homologous to mammalian RYR1) and βRYR (homologous to mammalian RYR3), which are expressed in approximately equal abundance (Airey, et al., 1993; Ottini, et al., 1996). The presence of numerous mutations in the N-terminal region of human RYR1, together with the existence of the porcine MH mutation in the region prompted us to screen for mutations in the corresponding region of turkey αRYR. Upon cloning and sequencing turkey αRYR cDNA homologous to human RYR1 amino acid residues 376 to 615, we found three different αRYR cDNA transcript variants. One embodiment of the present invention comprises these three novel variants. Additionally, an embodiment of the resent invention comprises two αRYR alleles found by investigating turkey αRYR genomic DNA in the region corresponding to the transcript variants. Yet another embodiment of the present invention comprises characterization of the heterogeneity of turkey αRYR transcript variants, the two αRYR alleles, and the relationship of the expression pattern of the transcript variants to the two alleles. Still yet another embodiment of the present invention comprises a correlation of meat quality and traits with the turkey genotypes.
DETAILED DESCRIPTION OF THE INVENTION
In certain embodiments, the present invention relates to methods to screen for turkeys homozygous for the αRYR-II allele and, therefore, show a higher postmortem muscle pH and better water holding capacity. Embodiments of the present invention also relate to the screening of compounds and methods that, for example, may alter or reduce the occurrence of turkeys displaying symptoms of PSE meat. One such example of a method would be selective breeding of turkeys homozygous for the αRYR-II allele.
I. Turkey RYR Polynucleotides
As described above, variants of the turkey TαRYR peptide have been discovered. Accordingly, the present invention provides nucleic acids encoding these variant turkey TαRYR genes and homologs (e.g., mutations and polymorphisms (e.g., SEQ ID NOs: 6 and 7). In some embodiments, the present invention provide polynucleotide sequences that are capable of hybridizing to nucleotide sequences that encode the peptides SEQ ID NOs: 5, 6 and 7 under conditions of low to high stringency as long as the polynucleotide sequence capable of hybridizing encodes a protein that retains a biological activity of the naturally occurring TαRYR. In some embodiments, the protein that retains a biological activity of naturally occurring TαRYR is 70% homologous to wild-type TαRYR (i.e. SEQ ID NO:5), preferably 80% homologous to wild-type TαRYR, more preferably 90% homologous to wild-type TαRYR, and most preferably 95% homologous to wild-type TαRYR. In preferred embodiments, hybridization conditions are based on the melting temperature (Tm) of the nucleic acid binding complex and confer a defined “stringency” as explained above (See e.g., Wahl, et al., Meth. Enzymol., 152:399-407 [1987], incorporated herein by reference).
In other embodiments of the present invention, alleles of TαRYR are provided. In preferred embodiments, alleles result from a polymorphism or mutation, (i.e., a change in the nucleic acid sequence) and generally produce altered mRNAs or polypeptides whose structure or function may or may not be altered. Any given gene may have none, one or many allelic forms. Common mutational changes which give rise to alleles are generally ascribed to deletions, additions or substitutions of nucleic acids. Each of these types of changes may occur alone, or in combination with the others, and at the rate of one or more times in a given sequence. Examples of the alleles of the present invention include TαRYRI and TαRYRII.
In still other embodiments of the present invention, the nucleotide sequences of the present invention may be engineered in order to alter an TαRYR coding sequence for a variety of reasons, including but not limited to, alterations which modify the cloning, processing and/or expression of the gene product. For example, mutations may be introduced using techniques that are well known in the art (e.g., site-directed mutagenesis to insert new restriction sites, to alter glycosylation patterns, to change codon preference, etc.).
In some embodiments of the present invention, the polynucleotide sequence of TαRYR may be extended utilizing the nucleotide sequences by various methods known in the art to detect upstream sequences such as promoters and regulatory elements. For example, it is contemplated that restriction-site polymerase chain reaction (PCR) will find use in the present invention. This is a direct method which uses universal primers to retrieve unknown sequence adjacent to a known locus (Gobinda et al., PCR Methods Applic., 2:318-22 [1993]). First, genomic DNA is amplified in the presence of primer to a linker sequence and a primer specific to the known region. The amplified sequences are then subjected to a second round of PCR with the same linker primer and another specific primer internal to the first one. Products of each round of PCR are transcribed with an appropriate RNA polymerase and sequenced using reverse transcriptase.
In another embodiment, inverse PCR can be used to amplify or extend sequences using divergent primers based on a known region (Triglia et al., Nucleic Acids Res., 16:8186 [1988]). The primers may be designed using Oligo 4.0 (National Biosciences Inc, Plymouth Minn.), or another appropriate program, to be 22-30 nucleotides in length, to have a GC content of 50% or more, and to anneal to the target sequence at temperatures about 68-72° C. The method uses several restriction enzymes to generate a suitable fragment in the known region of a gene. The fragment is then circularized by intramolecular ligation and used as a PCR template. In still other embodiments, walking PCR is utilized. Walking PCR is a method for targeted gene walking that permits retrieval of unknown sequence (Parker et al., Nucleic Acids Res., 19:3055-60 [1991]). The PROMOTERFINDER® kit (Clontech) uses PCR, nested primers and special libraries to “walk in” genomic DNA. This process avoids the need to screen libraries and is useful in finding intron/exon junctions.
Preferred libraries for screening for full length cDNAs include mammalian libraries that have been size-selected to include larger cDNAs. Also, random primed libraries are preferred, in that they will contain more sequences which contain the 5′ and upstream gene regions. A randomly primed library may be particularly useful in case where an oligo d(T) library does not yield full-length cDNA. Genomic mammalian libraries are useful for obtaining introns and extending 5′ sequence.
In other embodiments of the present invention, variants of the disclosed TαRYR sequences are provided. In preferred embodiments, variants result from polymorphisms or mutations, (i.e., a change in the nucleic acid sequence) and generally produce altered mRNAs or polypeptides whose structure or function may or may not be altered. Any given gene may have none, one, or many variant forms. Common mutational changes that give rise to variants are generally ascribed to deletions, additions or substitutions of nucleic acids. Each of these types of changes may occur alone, or in combination with the others, and at the rate of one or more times in a given sequence.
It is contemplated that it is possible to modify the structure of a peptide having a function (e.g., TαRYR function) for such purposes as, for example, increasing binding affinity of the TαRYR for it's substrate. Such modified peptides are considered functional equivalents of peptides having an activity of TαRYR as defined herein. A modified peptide can be produced in which the nucleotide sequence encoding the polypeptide has been altered, such as by substitution, deletion, or addition. In particularly preferred embodiments, these modifications do not significantly reduce the synthetic activity of the modified TαRYR. In other words, construct “X” can be evaluated in order to determine whether it is a member of the genus of modified or variant TαRYR's of the present invention as defined functionally, rather than structurally.
Moreover, as described above, variant forms of TαRYR are also contemplated as being equivalent to those peptides and DNA molecules that are set forth in more detail herein. For example, it is contemplated that isolated replacement of a leucine with an isoleucine or valine, an aspartate with a glutamate, a threonine with a serine, or a similar replacement of an amino acid with a structurally related amino acid (i.e., conservative mutations) will not have a major effect on the biological activity of the resulting molecule. Accordingly, some embodiments of the present invention provide variants of TαRYR disclosed herein containing conservative replacements.
Conservative replacements are those that take place within a family of amino acids that are related in their side chains. Genetically encoded amino acids can be divided into four families: (1) acidic (aspartate, glutamate); (2) basic (lysine, arginine, histidine); (3) nonpolar (alanine, valine, leucine, isoleucine, proline, phenylalanine, methionine, tryptophan); and (4) uncharged polar (glycine, asparagine, glutamine, cysteine, serine, threonine, tyrosine). Phenylalanine, tryptophan, and tyrosine are sometimes classified jointly as aromatic amino acids. In similar fashion, the amino acid repertoire can be grouped as (1) acidic (aspartate, glutamate); (2) basic (lysine, arginine, histidine), (3) aliphatic (glycine, alanine, valine, leucine, isoleucine, serine, threonine), with serine and threonine optionally be grouped separately as aliphatic-hydroxyl; (4) aromatic (phenylalanine, tyrosine, tryptophan); (5) amide (asparagine, glutamine); and (6) sulfur-containing (cysteine and methionine) (e.g., Stryer ed., Biochemistry, pg. 17-21, 2nd ed, WH Freeman and Co., 1981). Whether a change in the amino acid sequence of a peptide results in a functional homolog can be readily determined by assessing the ability of the variant peptide to function in a fashion similar to the wild-type protein. Peptides having more than one replacement can readily be tested in the same manner.
More rarely, a variant includes “nonconservative” changes (e.g., replacement of a glycine with a tryptophan). Analogous minor variations can also include amino acid deletions or insertions, or both. Guidance in determining which amino acid residues can be substituted, inserted, or deleted without abolishing biological activity can be found using computer programs (e.g., LASERGENE software, DNASTAR Inc., Madison, Wis.).
As described in more detail below, variants may be produced by methods such as directed evolution or other techniques for producing combinatorial libraries of variants, described in more detail below. In still other embodiments of the present invention, the nucleotide sequences of the present invention may be engineered in order to alter a TαRYR coding sequence including, but not limited to, alterations that modify the cloning, processing, localization, secretion, and/or expression of the gene product. For example, mutations may be introduced using techniques that are well known in the art (e.g., site-directed mutagenesis to insert new restriction sites, alter glycosylation patterns, or change codon preference, etc.).
II. Turkey RYR Polypeptides
In other embodiments, the present invention provides Turkey αRYR (TαRYR) polynucleotide sequences that encode TαRYR polypeptide sequences. TαRYR (e.g., SEQ ID NOs: 5, 6 and 7) are described in FIG. 1. Other embodiments of the present invention provide fragments, fusion proteins or functional equivalents of these TαRYR proteins. In still other embodiments of the present invention, nucleic acid sequences corresponding to TαRYR variants, homologs, and mutants may be used to generate recombinant DNA molecules that direct the expression of the TαRYR variants, homologs and mutants in appropriate host cells. In some embodiments of the present invention, the polypeptide may be a naturally purified product, in other embodiments it may be a product of chemical synthetic procedures, and in still other embodiments it may be produced by recombinant techniques using a prokaryotic or eukaryotic host (e.g., by bacterial, yeast, higher plant, insect and mammalian cells in culture). In some embodiments, depending upon the host employed in a recombinant production procedure, the polypeptide of the present invention may be glycosylated or may be non-glycosylated. In other embodiments, the polypeptides of the invention may also include an initial methionine amino acid residue.
In one embodiment of the present invention, due to the inherent degeneracy of the genetic code, DNA sequences other than the polynucleotide sequences that encode SEQ ID NOS: 5, 6 and 7 which encode substantially the same or a functionally equivalent amino acid sequence, may be used to clone and express TαRYR. In general, such polynucleotide sequences hybridize to the sequences that encode SEQ ID NOS: 5, 6 and 7 under conditions of high to medium stringency as described above. As will be understood by those of skill in the art, it may be advantageous to produce TαRYR-encoding nucleotide sequences possessing non-naturally occurring codons. Therefore, in some preferred embodiments, codons preferred by a particular prokaryotic or eukaryotic host (Murray, et al., Nucl. Acids Res., 17 [1989]) are selected, for example, to increase the rate of Turkey RYR expression or to produce recombinant RNA transcripts having desirable properties, such as a longer half-life, than transcripts produced from naturally occurring sequence.
1. Vectors for Production of Turkey αRYR
The polynucleotides of the present invention may be employed for producing polypeptides by recombinant techniques. Thus, for example, the polynucleotide may be included in any one of a variety of expression vectors for expressing a polypeptide. In some embodiments of the present invention, vectors include, but are not limited to, chromosomal, nonchromosomal and synthetic DNA sequences (e.g., derivatives of SV40, bacterial plasmids, phage DNA; baculovirus, yeast plasmids, vectors derived from combinations of plasmids and phage DNA, and viral DNA such as vaccinia, adenovirus, fowl pox virus, and pseudorabies). It is contemplated that any vector may be used as long as it is replicable and viable in the host.
In particular, some embodiments of the present invention provide recombinant constructs comprising one or more of the sequences as broadly described above (e.g., nucleotide sequences that encode SEQ ID NOS: 5, 6 and 7). In some embodiments of the present invention, the constructs comprise a vector, such as a plasmid or viral vector, into which a sequence of the invention has been inserted, in a forward or reverse orientation. In still other embodiments, the heterologous structural sequence (e.g., nucleotide sequences that encode SEQ ID NOS: 5, 6 and 7) is assembled in appropriate phase with translation initiation and termination sequences. In preferred embodiments of the present invention, the appropriate DNA sequence is inserted into the vector using any of a variety of procedures. In general, the DNA sequence is inserted into an appropriate restriction endonuclease site(s) by procedures known in the art.
Large numbers of suitable vectors are known to those of skill in the art, and are commercially available. Such vectors include, but are not limited to, the following vectors: 1) Bacterial—pQE70, pQE60, pQE-9 (Qiagen), pBS, pD10, phagescript, psiX174, pbluescript SK, pBSKS, pNH8A, pNH16a, pNH18A, pNH46A (Stratagene); ptrc99a, pKK223-3, pKK233-3, pDR540, pRIT5 (Pharmacia); and 2) Eukaryotic—pWLNEO, pSV2CAT, pOG44, PXT1, pSG (Stratagene) pSVK3, pBPV, pMSG, pSVL (Pharmacia). Any other plasmid or vector may be used as long as they are replicable and viable in the host. In some preferred embodiments of the present invention, mammalian expression vectors comprise an origin of replication, a suitable promoter and enhancer, and also any necessary ribosome binding sites, polyadenylation sites, splice donor and acceptor sites, transcriptional termination sequences, and 5′ flanking non-transcribed sequences. In other embodiments, DNA sequences derived from the SV40 splice, and polyadenylation sites may be used to provide the required non-transcribed genetic elements.
In certain embodiments of the present invention, the DNA sequence in the expression vector is operatively linked to an appropriate expression control sequence(s) (promoter) to direct mRNA synthesis. Promoters useful in the present invention include, but are not limited to, the LTR or SV40 promoter, the E. coli lac or trp, the phage lambda PL and PR, T3 and T7 promoters, and the cytomegalovirus (CMV) immediate early, herpes simplex virus (HSV) thymidine kinase, and mouse metallothionein-I promoters and other promoters known to control expression of gene in prokaryotic or eukaryotic cells or their viruses. In other embodiments of the present invention, recombinant expression vectors include origins of replication and selectable markers permitting transformation of the host cell (e.g., dihydrofolate reductase or neomycin resistance for eukaryotic cell culture, or tetracycline or ampicillin resistance in E. coli).
In some embodiments of the present invention, transcription of the DNA encoding the polypeptides of the present invention by higher eukaryotes is increased by inserting an enhancer sequence into the vector. Enhancers are cis-acting elements of DNA, usually about from 10 to 300 bp that act on a promoter to increase its transcription. Enhancers useful in the present invention include, but are not limited to, the SV40 enhancer on the late side of the replication origin bp 100 to 270, a cytomegalovirus early promoter enhancer, the polyoma enhancer on the late side of the replication origin, and adenovirus enhancers.
In other embodiments, the expression vector also contains a ribosome binding site for translation initiation and a transcription terminator. In still other embodiments of the present invention, the vector may also include appropriate sequences for amplifying expression.
2. Host Cells for Production of Turkey αRYR
In a further embodiment, the present invention provides host cells containing the above-described constructs. In some embodiments of the present invention, the host cell is a higher eukaryotic cell (e.g., a mammalian or insect cell). In other embodiments of the present invention, the host cell is a lower eukaryotic cell (e.g., a yeast cell). In still other embodiments of the present invention, the host cell can be a prokaryotic cell (e.g., a bacterial cell). Specific examples of host cells include, but are not limited to, Escherichia coli, Salmonella typhimurium, Bacillus subtilis, and various species within the genera Pseudomonas, Streptomyces, and Staphylococcus, as well as Saccharomycees cerivisiae, Schizosaccharomycees pombe, Drosophila S2 cells, Spodoptera Sf9 cells, Chinese hamster ovary (CHO) cells, COS-7 lines of monkey kidney fibroblasts, (Gluzman, Cell 23:175 [1981]), C127, 3T3, 293, 293T, HeLa and BHK cell lines.
The constructs in host cells can be used in a conventional manner to produce the gene product encoded by the recombinant sequence. In some embodiments, introduction of the construct into the host cell can be accomplished by calcium phosphate transfection, DEAE-Dextran mediated transfection, or electroporation (See e.g., Davis et al., Basic Methods in Molecular Biology, [1986]). Alternatively, in some embodiments of the present invention, the polypeptides of the invention can be synthetically produced by conventional peptide synthesizers.
Proteins can be expressed in mammalian cells, yeast, bacteria, or other cells under the control of appropriate promoters. Cell-free translation systems can also be employed to produce such proteins using RNAs derived from the DNA constructs of the present invention. Appropriate cloning and expression vectors for use with prokaryotic and eukaryotic hosts are described by Sambrook, et al., Molecular Cloning: A Laboratory Manual, Second Edition, Cold Spring Harbor, N.Y., (1989).
In some embodiments of the present invention, following transformation of a suitable host strain and growth of the host strain to an appropriate cell density, the selected promoter is induced by appropriate means (e.g., temperature shift or chemical induction) and cells are cultured for an additional period. In other embodiments of the present invention, cells are typically harvested by centrifugation, disrupted by physical or chemical means, and the resulting crude extract retained for further purification. In still other embodiments of the present invention, microbial cells employed in expression of proteins can be disrupted by any convenient method, including freeze-thaw cycling, sonication, mechanical disruption, or use of cell lysing agents.
3. Purification of Turkey αRYR
The present invention also provides methods for recovering and purifying Turkey RYR from recombinant cell cultures including, but not limited to, ammonium sulfate or ethanol precipitation, acid extraction, anion or cation exchange chromatography, phosphocellulose chromatography, hydrophobic interaction chromatography, affinity chromatography, hydroxylapatite chromatography and lectin chromatography. In other embodiments of the present invention, protein refolding steps can be used as necessary, in completing configuration of the mature protein. In still other embodiments of the present invention, high performance liquid chromatography (HPLC) can be employed for final purification steps.
The present invention further provides polynucleotides having the coding sequence (e.g., polynucleotides encoding the peptide sequences SEQ ID NOs: 5, 6 and 7) fused in frame to a marker sequence which allows for purification of the polypeptide of the present invention. A non-limiting example of a marker sequence is a hexahistidine tag which may be supplied by a vector, preferably a pQE-9 vector, which provides for purification of the polypeptide fused to the marker in the case of a bacterial host, or, for example, the marker sequence may be a hemagglutinin (HA) tag when a mammalian host (e.g., COS-7 cells) is used. The HA tag corresponds to an epitope derived from the influenza hemagglutinin protein (Wilson et al., Cell, 37:767 [1984]).
4. Truncation Mutants of Turkey αRYR
In addition, the present invention provides fragments of TαRYR (i.e., truncation mutants, e.g., SEQ ID NOS: 6 and 7). In some embodiments of the present invention, when expression of a portion of the Turkey RYR protein is desired, it may be necessary to add a start codon (ATG) to the oligonucleotide fragment containing the desired sequence to be expressed. It is well known in the art that a methionine at the N-terminal position can be enzymatically cleaved by the use of the enzyme methionine aminopeptidase (MAP). MAP has been cloned from E. coli (Ben-Bassat, et al., J. Bacteriol., 169:751-757 [1987]) and Salmonella typhimurium and its in vitro activity has been demonstrated on recombinant proteins (Miller et al., Proc. Natl. Acad. Sci. USA 84:2718-1722 [1990]). Therefore, removal of an N-terminal methionine, if desired, can be achieved either in vivo by expressing such recombinant polypeptides in a host which produces MAP (e.g., E. coli or CM89 or S. cerevisiae), or in vitro by use of purified MAP.
5. Fusion Proteins Containing Turkey αRYR
The present invention also provides fusion proteins incorporating all or part of TαRYR. Accordingly, in some embodiments of the present invention, the coding sequences for the polypeptide can be incorporated as a part of a fusion gene including a nucleotide sequence encoding a different polypeptide. It is contemplated that this type of expression system will find use under conditions where it is desirable to produce an immunogenic fragment of a TαRYR protein. In some embodiments of the present invention, the VP6 capsid protein of rotavirus is used as an immunologic carrier protein for portions of the TαRYR polypeptide, either in the monomeric form or in the form of a viral particle. In other embodiments of the present invention, the nucleic acid sequences corresponding to the portion of TαRYR against which antibodies are to be raised can be incorporated into a fusion gene construct which includes coding sequences for a late vaccinia virus structural protein to produce a set of recombinant viruses expressing fusion proteins comprising a portion of TαRYR as part of the virion. It has been demonstrated with the use of immunogenic fusion proteins utilizing the hepatitis B surface antigen fusion proteins that recombinant hepatitis B virions can be utilized in this role as well. Similarly, in other embodiments of the present invention, chimeric constructs coding for fusion proteins containing a portion of TαRYR and the poliovirus capsid protein are created to enhance immunogenicity of the set of polypeptide antigens (See e.g., EP Publication No. 025949; and Evans, et al., Nature 339:385 [1989]; Huang, et al., J. Virol., 62:3855 [1988]; and Schlienger, et al., J. Virol., 66:2 [1992]).
In still other embodiments of the present invention, the multiple antigen peptide system for peptide-based immunization can be utilized. In this system, a desired portion of TαRYR is obtained directly from organo-chemical synthesis of the peptide onto an oligomeric branching lysine core (see e.g., Posnett, et al., J. Biol. Chem., 263:1719 [1988]; and Nardelli, et al., J. Immunol., 148:914 [1992]). In other embodiments of the present invention, antigenic determinants of the TαRYR proteins can also be expressed and presented by bacterial cells.
In addition to utilizing fusion proteins to enhance immunogenicity, it is widely appreciated that fusion proteins can also facilitate the expression of proteins, such as the TαRYR proteins of the present invention (e.g., SEQ ID NOS: 5, 6 and 7). Accordingly, in some embodiments of the present invention, TαRYR can be generated as a glutathione-S-transferase (i.e., GST fusion protein). It is contemplated that such GST fusion proteins will enable easy purification of TαRYR, such as by the use of glutathione-derivatized matrices (See, e.g, Ausabel et al. (eds.), Current Protocols in Molecular Biology, John Wiley & Sons, NY [1991]). In another embodiment of the present invention, a fusion gene coding for a purification leader sequence, such as a poly-(His)/enterokinase cleavage site sequence at the N-terminus of the desired portion of Turkey RYR, can allow purification of the expressed Turkey RYR fusion protein by affinity chromatography using a Ni2+ metal resin. In still another embodiment of the present invention, the purification leader sequence can then be subsequently removed by treatment with enterokinase (See e.g., Hochuli, et al., J. Chromatogr., 411:177 [1987]; and Janknecht, et al., Proc. Natl. Acad. Sci. USA 88:8972).
Techniques for making fusion genes are well known. Essentially, the joining of various DNA fragments coding for different polypeptide sequences is performed in accordance with conventional techniques, employing blunt-ended or stagger-ended termini for ligation, restriction enzyme digestion to provide for appropriate termini, filling-in of cohesive ends as appropriate, alkaline phosphatase treatment to avoid undesirable joining, and enzymatic ligation. In another embodiment of the present invention, the fusion gene can be synthesized by conventional techniques including automated DNA synthesizers. Alternatively, in other embodiments of the present invention, PCR amplification of gene fragments can be carried out using anchor primers which give rise to complementary overhangs between two consecutive gene fragments which can subsequently be annealed to generate a chimeric gene sequence (See e.g., Current Protocols in Molecular Biology, supra).
6. Variants of Turkey αRYR
Still other embodiments of the present invention provide mutant or variant forms of TαRYR (i.e., muteins). It is possible to modify the structure of a peptide having an activity of TαRYR for such purposes as enhancing therapeutic or prophylactic efficacy, or stability (e.g., ex vivo shelf life, and/or resistance to proteolytic degradation in vivo). Such modified peptides are considered functional equivalents of peptides having an activity of the subject TαRYR proteins as defined herein. A modified peptide can be produced in which the amino acid sequence has been altered, such as by amino acid substitution, deletion, or addition.
Moreover, as described above, variant forms (e.g., mutants or polymorphic sequences) of the subject TαRYR proteins are also contemplated as being equivalent to those peptides and DNA molecules that are set forth in more detail. For example, as described above, the present invention encompasses mutant and variant proteins that contain conservative or non-conservative amino acid substitutions.
This invention further contemplates a method of generating sets of combinatorial mutants of the present TαRYR proteins, as well as truncation mutants, and is especially useful for identifying potential variant sequences (i.e., mutants or polymorphic sequences). The purpose of screening such combinatorial libraries is to generate, for example, novel TαRYR variants which can act as either agonists or antagonists, or alternatively, possess novel activities all together.
Therefore, in some embodiments of the present invention, TαRYR variants are engineered by the present method to promote, for example, a higher pH in harvested turkey meat. In other embodiments of the present invention, combinatorially-derived homologs are generated which have a selective potency relative to a naturally occurring TαRYR. Such proteins, when expressed from recombinant DNA constructs, can be used, for example, in gene therapy protocols or in the generation of transgenic animals.
Still other embodiments of the present invention provide TαRYR variants which have intracellular half-lives dramatically different than the corresponding wild-type protein. For example, the altered protein can be rendered either more stable or less stable to proteolytic degradation or other cellular process which result in destruction of, or otherwise inactivate, TαRYR. Such variants, and the genes which encode them, can be utilized to alter the location of TαRYR expression by modulating the half-life of the protein. For instance, a short half-life can give rise to more transient TαRYR biological effects and, when part of an inducible expression system, can allow tighter control of TαRYR levels within the cell. As above, such proteins, and particularly their recombinant nucleic acid constructs, can be used in gene therapy protocols.
In still other embodiments of the present invention, TαRYR variants are generated by the combinatorial approach to act as antagonists, in that they are able to interfere with the ability of the corresponding wild-type protein to regulate cell function.
In some embodiments of the combinatorial mutagenesis approach of the present invention, the amino acid sequences for a population of TαRYR variants or other related proteins are aligned, preferably to promote the highest homology possible. Such a population of variants can include, for example, TαRYR homologs from one or more strain or TαRYR variants from the same strain but which differ due to mutation. Amino acids which appear at each position of the aligned sequences are selected to create a degenerate set of combinatorial sequences.
In a preferred embodiment of the present invention, the combinatorial TαRYR library is produced by way of a degenerate library of genes encoding a library of polypeptides which each include at least a portion of potential TαRYR protein sequences. For example, a mixture of synthetic oligonucleotides can be enzymatically ligated into gene sequences such that the degenerate set of potential TαRYR sequences are expressible as individual polypeptides, or alternatively, as a set of larger fusion proteins (e.g., for phage display) containing the set of TαRYR sequences therein.
There are many ways by which the library of potential TαRYR homologs and variants can be generated from a degenerate oligonucleotide sequence. In some embodiments, chemical synthesis of a degenerate gene sequence is carried out in an automatic DNA synthesizer, and the synthetic genes are ligated into an appropriate gene for expression. The purpose of a degenerate set of genes is to provide, in one mixture, all of the sequences encoding the desired set of potential TαRYR sequences. The synthesis of degenerate oligonucleotides is well known in the art (See e.g., Narang, Tetrahedron Lett., 39:3 9 [1983]; Itakura, et al., Recombinant DNA, in Walton (ed.), Proceedings of the 3rd Cleveland Symposium on Macromolecules, Elsevier, Amsterdam, pp 273-289 [1981]; Itakura, et al., Annu. Rev. Biochem., 53:323 [1984]; Itakura et al., Science 198:1056 [1984]; Ike, et al., Nucl. Acid Res., 11:477 [1983]). Such techniques have been employed in the directed evolution of other proteins (See e.g., Scott, et al., Science 249:386-390 [1980]; Roberts, et al., Proc. Natl. Acad. Sci. USA 89:2429-2433 [1992]; Devlin, et al., Science 249: 404-406 [1990]; Cwirla, et al., Proc. Natl. Acad. Sci. USA 87: 6378-6382 [1990]; as well as U.S. Pat. Nos. 5,223,409, 5,198,346, and 5,096,815, each of which is incorporated herein by reference).
It is contemplated that the TαRYR nucleic acids (e.g., FIG. 6 and fragments and variants thereof) can be utilized as starting nucleic acids for directed evolution. These techniques can be utilized to develop TαRYR variants having desirable properties such as, for example, promoting increased postmortem muscle pH. Such variants could then be used, e.g., for the generation of transgenic animals
In some embodiments, artificial evolution is performed by random mutagenesis (e.g., by utilizing error-prone PCR to introduce random mutations into a given coding sequence). This method requires that the frequency of mutation be finely tuned. As a general rule, beneficial mutations are rare, while deleterious mutations are common. This is because the combination of a deleterious mutation and a beneficial mutation often results in an inactive enzyme. The ideal number of base substitutions for targeted gene is usually between 1.5 and 5 (Moore and Arnold, Nat. Biotech., 14, 458-67 [1996]; Leung, et al., Technique, 1:11-15 [1989]; Eckert and Kunkel, PCR Methods Appl., 1:17-24 [1991]; Caldwell and Joyce, PCR Methods Appl., 2:28-33 (1992); and Zhao and Arnold, Nuc. Acids. Res., 25:1307-08 [1997]). After mutagenesis, the resulting clones are selected for desirable activity (e.g., screened for Turkey RYR activity). Successive rounds of mutagenesis and selection are often necessary to develop enzymes with desirable properties. It should be noted that only the useful mutations are carried over to the next round of mutagenesis.
In other embodiments of the present invention, the polynucleotides of the present invention are used in gene shuffling or sexual PCR procedures (e.g., Smith, Nature, 370:324-25 [1994]; U.S. Pat. Nos. 5,837,458; 5,830,721; 5,811,238; 5,733,731; all of which are herein incorporated by reference). Gene shuffling involves random fragmentation of several mutant DNAs followed by their reassembly by PCR into full length molecules. Examples of various gene shuffling procedures include, but are not limited to, assembly following DNase treatment, the staggered extension process (STEP), and random priming in vitro recombination. In the DNase mediated method, DNA segments isolated from a pool of positive mutants are cleaved into random fragments with DNaseI and subjected to multiple rounds of PCR with no added primer. The lengths of random fragments approach that of the uncleaved segment as the PCR cycles proceed, resulting in mutations in present in different clones becoming mixed and accumulating in some of the resulting sequences. Multiple cycles of selection and shuffling have led to the functional enhancement of several enzymes (Stemmer, Nature, 370:398-91 [1994]; Stemmer, Proc. Natl. Acad. Sci. USA, 91, 10747-51 [1994]; Crameri, et al., Nat. Biotech., 14:315-19 [1996]; Zhang, et al., Proc. Natl. Acad. Sci. USA, 94:4504-09 [1997]; and Crameri, et al., Nat. Biotech., 15:436-38 [1997]). Variants produced by directed evolution can be screened for TαRYR activity (in vitro) or for the affect on the production of PSE meat (in vivo).
A wide range of techniques are known in the art for screening gene products of combinatorial libraries made by point mutations, and for screening cDNA libraries for gene products having a certain property. Such techniques will be generally adaptable for rapid screening of the gene libraries generated by the combinatorial mutagenesis or recombination of TαRYR homologs. The most widely used techniques for screening large gene libraries typically comprises cloning the gene library into replicable expression vectors, transforming appropriate cells with the resulting library of vectors, and expressing the combinatorial genes under conditions in which detection of a desired activity facilitates relatively easy isolation of the vector encoding the gene whose product was detected.
7. Chemical Synthesis of TαRYR
In an alternate embodiment of the invention, the coding sequence of TαRYR is synthesized, whole or in part, using chemical methods well known in the art (See e.g., Caruthers, et al., Nucl. Acids Res. Symp. Ser., 7:215-233 [1980]; Crea and Horn, Nucl. Acids Res., 9:2331 [1980]; Matteucci and Caruthers, Tetrahedron Lett., 21:719 [1980]; and Chow and Kempe, Nucl. Acids Res., 9:2807-2817 [1981]). In other embodiments of the present invention, the protein itself is produced using chemical methods to synthesize either an entire TαRYR amino acid sequence or a portion thereof. For example, peptides can be synthesized by solid phase techniques, cleaved from the resin, and purified by preparative high performance liquid chromatography (See e.g., Creighton, Proteins Structures And Molecular Principles, W H Freeman and Co, New York N.Y. [1983]). In other embodiments of the present invention, the composition of the synthetic peptides is confirmed by amino acid analysis or sequencing (See e.g., Creighton, supra).
Direct peptide synthesis can be performed using various solid-phase techniques (Roberge, et al., Science 269:202-204 [1995]) and automated synthesis may be achieved, for example, using ABI 431A Peptide Synthesizer (Perkin Elmer) in accordance with the instructions provided by the manufacturer. Additionally, the amino acid sequence of TαRYR, or any part thereof, may be altered during direct synthesis and/or combined using chemical methods with other sequences to produce a variant polypeptide.
III. Detection of TαRYR Alleles
In some embodiments, the present invention includes alleles of TαRYR that, when expressed homozygously, descrease symptoms of PSE meat (e.g., including, but not limited to, nucleotide sequences that encode SEQ ID NOs: 5, 6 and 7). Analysis of naturally occurring turkey TαRYR alleles revealed that turkeys with decreased susceptibility for the production of meat having symptoms of PSE meat are homozygous for TαRYRII.
The present invention is not limited to a particular mechanism of action. Indeed, an understanding of the mechanism of action is not necessary to practice the present invention. Nevertheless, it is contemplated that turkeys homozygous for TαRYRII have altered transport of metabolites from the sarcoplasmic reticulum that alter, for example, postmortem muscle pH.
Accordingly, in one embodiment, the present invention provides methods for determining whether a turkey has decreased susceptablility for the production of meat having higher postmortem pH and better water holding capacity by determining whether the turkey is homozygous for the TαRYRII allele.
A number of methods are available for analysis of variant (e.g., mutant or polymorphic) nucleic acid sequences and presence of particular alleles of a gene. Assays for detections variants and alleles (e.g., polymorphisms or mutations) fall into several categories, including, but not limited to direct sequencing assays, fragment polymorphism assays, hybridization assays, and computer based data analysis. Protocols and commercially available kits or services for performing multiple variations of these assays are available. In some embodiments, assays are performed in combination or in hybrid (e.g., different reagents or technologies from several assays are combined to yield one assay). The following assays are useful in the present invention.
1. Direct Sequencing Assays
In some embodiments of the present invention, variant sequences are detected using a direct sequencing technique. In these assays, DNA samples are first isolated from a subject using any suitable method. In some embodiments, the region of interest is cloned into a suitable vector and amplified by growth in a host cell (e.g., a bacteria). In other embodiments, DNA in the region of interest is amplified using PCR.
Following amplification, DNA in the region of interest (e.g., the region containing the SNP or mutation of interest) is sequenced using any suitable method, including but not limited to manual sequencing using radioactive marker nucleotides, or automated sequencing. The results of the sequencing are displayed using any suitable method. The sequence is examined and the presence or absence of a given SNP or mutation is determined.
2. PCR Assay
In some embodiments of the present invention, variant sequences are detected using a PCR-based assay. In some embodiments, the PCR assay comprises the use of oligonucleotide primers that hybridize only to the variant or wild type allele of TαRYR (e.g., to the region of polymorphism or mutation). Both sets of primers are used to amplify a sample of DNA. If only the mutant primers result in a PCR product, then the patient has the mutant TαRYR allele or an allelic homolog. For example, if only the TαRYRII primers result in a PCR product, then the turkey is homozygous for the TαRYRII allele.
3. Fragment Length Polymorphism Assays
In some embodiments of the present invention, variant sequences and alleles are detected using a fragment length polymorphism assay. In a fragment length polymorphism assay, a unique DNA banding pattern based on cleaving the DNA at a series of positions is generated using an enzyme (e.g., a restriction enzyme or a CLEAVASE I [Third Wave Technologies, Madison, Wis.] enzyme). DNA fragments from a sample containing a SNP or a mutation will have a different banding pattern than wild type.
a. RFLP Assay
In some embodiments of the present invention, variant sequences or alleles are detected using a restriction fragment length polymorphism assay (RFLP). The region of interest is first isolated using PCR. The PCR products are then cleaved with restriction enzymes known to give a unique length fragment for a given polymorphism. The restriction-enzyme digested PCR products are separated by agarose gel electrophoresis and visualized by ethidium bromide staining. The length of the fragments is compared to molecular weight markers and fragments generated from wild-type and mutant controls.
b. CFLP Assay
In other embodiments, variant sequences are detected using a CLEAVASE fragment length polymorphism assay (CFLP; Third Wave Technologies, Madison, Wis.; See e.g., U.S. Pat. Nos. 5,843,654; 5,843,669; 5,719,208; and 5,888,780; each of which is herein incorporated by reference). This assay is based on the observation that when single strands of DNA fold on themselves, they assume higher order structures that are highly individual to the precise sequence of the DNA molecule. These secondary structures involve partially duplexed regions of DNA such that single stranded regions are juxtaposed with double stranded DNA hairpins. The CLEAVASE I enzyme, is a structure-specific, thermostable nuclease that recognizes and cleaves the junctions between these single-stranded and double-stranded regions.
The region of interest is first isolated, for example, using PCR. Then, DNA strands are separated by heating. Next, the reactions are cooled to allow intrastrand secondary structure to form. The PCR products are then treated with the CLEAVASE I enzyme to generate a series of fragments that are unique to a given SNP or mutation. The CLEAVASE enzyme treated PCR products are separated and detected (e.g., by agarose gel electrophoresis) and visualized (e.g., by ethidium bromide staining). The length of the fragments is compared to molecular weight markers and fragments generated from allelic controls.
4. Hybridization Assays
In preferred embodiments of the present invention, variant sequences are detected a hybridization assay. In a hybridization assay, the presence of absence of a given SNP or mutation is determined based on the ability of the DNA from the sample to hybridize to a complementary DNA molecule (e.g., a oligonucleotide probe). A variety of hybridization assays using a variety of technologies for hybridization and detection are available. A description of a selection of assays is provided below.
a. Direct Detection of Hybridization
In some embodiments, hybridization of a probe to the sequence of interest (e.g., a SNP or mutation) is detected directly by visualizing a bound probe (e.g., a Northern or Southern assay; See e.g., Ausabel et al. (eds.), Current Protocols in Molecular Biology, John Wiley & Sons, NY [1991]). In a these assays, genomic DNA (Southern) or RNA (Northern) is isolated from a subject. The DNA or RNA is then cleaved with a series of restriction enzymes that cleave infrequently in the genome and not near any of the markers being assayed. The DNA or RNA is then separated (e.g., on an agarose gel) and transferred to a membrane. A labelled (e.g., by incorporating a radionucleotide) probe or probes specific for the SNP or mutation being detected is allowed to contact the membrane under a condition or low, medium, or high stringency conditions. Unbound probe is removed and the presence of binding is detected by visualizing the labelled probe.
b. Detection of Hybridization Using “DNA Chip” Assays
In some embodiments of the present invention, variant sequences are detected using a DNA chip hybridization assay. In this assay, a series of oligonucleotide probes are affixed to a solid support. The oligonucleotide probes are designed to be unique to a given SNP or mutation. The DNA sample of interest is contacted with the DNA “chip” and hybridization is detected.
In some embodiments, the DNA chip assay is a GeneChip (Affymetrix, Santa Clara, Calif.; See e.g., U.S. Pat. Nos. 6,045,996; 5,925,525; and 5,858,659; each of which is herein incorporated by reference) assay. The GeneChip technology uses miniaturized, high-density arrays of oligonucleotide probes affixed to a “chip.” Probe arrays are manufactured by Affymetrix's light-directed chemical synthesis process, which combines solid-phase chemical synthesis with photolithographic fabrication techniques employed in the semiconductor industry. Using a series of photolithographic masks to define chip exposure sites, followed by specific chemical synthesis steps, the process constructs high-density arrays of oligonucleotides, with each probe in a predefined position in the array. Multiple probe arrays are synthesized simultaneously on a large glass wafer. The wafers are then diced, and individual probe arrays are packaged in injection-molded plastic cartridges, which protect them from the environment and serve as chambers for hybridization.
The nucleic acid to be analyzed is isolated, amplified by PCR, and labeled with a fluorescent reporter group. The labeled DNA is then incubated with the array using a fluidics station. The array is then inserted into the scanner, where patterns of hybridization are detected. The hybridization data are collected as light emitted from the fluorescent reporter groups already incorporated into the target, which is bound to the probe array. Probes that perfectly match the target generally produce stronger signals than those that have mismatches. Since the sequence and position of each probe on the array are known, by complementarity, the identity of the target nucleic acid applied to the probe array can be determined.
In other embodiments, a DNA microchip containing electronically captured probes (Nanogen, San Diego, Calif.) is utilized (See e.g., U.S. Pat. Nos. 6,017,696; 6,068,818; and 6,051,380; each of which are herein incorporated by reference). Through the use of microelectronics, Nanogen's technology enables the active movement and concentration of charged molecules to and from designated test sites on its semiconductor microchip. DNA capture probes unique to a given SNP or mutation are electronically placed at, or “addressed” to, specific sites on the microchip. Since DNA has a strong negative charge, it can be electronically moved to an area of positive charge.
First, a test site or a row of test sites on the microchip is electronically activated with a positive charge. Next, a solution containing the DNA probes is introduced onto the microchip. The negatively charged probes rapidly move to the positively charged sites, where they concentrate and are chemically bound to a site on the microchip. The microchip is then washed and another solution of distinct DNA probes is added until the array of specifically bound DNA probes is complete.
A test sample is then analyzed for the presence of target DNA molecules by determining which of the DNA capture probes hybridize, with complementary DNA in the test sample (e.g., a PCR amplified gene of interest). An electronic charge is also used to move and concentrate target molecules to one or more test sites on the microchip. The electronic concentration of sample DNA at each test site promotes rapid hybridization of sample DNA with complementary capture probes (hybridization may occur in minutes). To remove any unbound or nonspecifically bound DNA from each site, the polarity or charge of the site is reversed to negative, thereby forcing any unbound or nonspecifically bound DNA back into solution away from the capture probes. A laser-based fluorescence scanner is used to detect binding,
In still further embodiments, an array technology based upon the segregation of fluids on a flat surface (chip) by differences in surface tension (ProtoGene, Palo Alto, Calif.) is utilized (See e.g., U.S. Pat. Nos. 6,001,311; 5,985,551; and 5,474,796; each of which is herein incorporated by reference). Protogene's technology is based on the fact that fluids can be segregated on a flat surface by differences in surface tension that have been imparted by chemical coatings. Once so segregated, oligonucleotide probes are synthesized directly on the chip by ink-jet printing of reagents. The array with its reaction sites defined by surface tension is mounted on a X/Y translation stage under a set of four piezoelectric nozzles, one for each of the four standard DNA bases. The translation stage moves along each of the rows of the array and the appropriate reagent is delivered to each of the reaction site. For example, the A amidite is delivered only to the sites where amidite A is to be coupled during that synthesis step and so on. Common reagents and washes are delivered by flooding the entire surface and then removing them by spinning.
DNA probes unique for the SNP or mutation of interest are affixed to the chip using Protogene's technology. The chip is then contacted with the PCR-amplified genes of interest. Following hybridization, unbound DNA is removed and hybridization is detected using any suitable method (e.g., by fluorescence de-quenching of an incorporated fluorescent group).
In yet other embodiments, a “bead array” is used for the detection of polymorphisms (Illumina, San Diego, Calif.; See e.g., PCT Publications WO 99/67641 and WO 00/39587, each of which is herein incorporated by reference). Illumina uses a BEAD ARRAY technology that combines fiber optic bundles and beads that self-assemble into an array. Each fiber optic bundle contains thousands to millions of individual fibers depending on the diameter of the bundle. The beads are coated with an oligonucleotide specific for the detection of a given SNP or mutation. Batches of beads are combined to form a pool specific to the array. To perform an assay, the BEAD ARRAY is contacted with a prepared subject sample (e.g., DNA). Hybridization is detected using any suitable method.
c. Enzymatic Detection of Hybridization
In some embodiments of the present invention, genomic profiles are generated using a assay that detects hybridization by enzymatic cleavage of specific structures (INVADER assay, Third Wave Technologies; See e.g., U.S. Pat. Nos. 5,846,717; 6,090,543; 6,001,567; 5,985,557; and 5,994,069; each of which is herein incorporated by reference). The INVADER assay detects specific DNA and RNA sequences by using structure-specific enzymes to cleave a complex formed by the hybridization of overlapping oligonucleotide probes. Elevated temperature and an excess of one of the probes enable multiple probes to be cleaved for each target sequence present without temperature cycling. These cleaved probes then direct cleavage of a second labeled probe. The secondary probe oligonucleotide can be 5′-end labeled with fluorescein that is quenched by an internal dye. Upon cleavage, the de-quenched fluorescein labeled product may be detected using a standard fluorescence plate reader.
The INVADER assay detects specific mutations and SNPs in unamplified genomic DNA. The isolated DNA sample is contacted with the first probe specific either for a SNP/mutation or wild type sequence and allowed to hybridize. Then a secondary probe, specific to the first probe, and containing the fluorescein label, is hybridized and the enzyme is added. Binding is detected by using a fluorescent plate reader and comparing the signal of the test sample to known positive and negative controls.
In some embodiments, hybridization of a bound probe is detected using a TaqMan assay (PE Biosystems, Foster City, Calif; See e.g., U.S. Pat. Nos. 5,962,233 and 5,538,848, each of which is herein incorporated by reference). The assay is performed during a PCR reaction. The TaqMan assay exploits the 5′-3′ exonuclease activity of the AMPLITAQ GOLD DNA polymerase. A probe, specific for a given allele or mutation, is included in the PCR reaction. The probe consists of an oligonucleotide with a 5′-reporter dye (e.g., a fluorescent dye) and a 3′-quencher dye. During PCR, if the probe is bound to its target, the 5′-3′ nucleolytic activity of the AMPLITAQ GOLD polymerase cleaves the probe between the reporter and the quencher dye. The separation of the reporter dye from the quencher dye results in an increase of fluorescence. The signal accumulates with each cycle of PCR and can be monitored with a fluorimeter.
In still further embodiments, polymorphisms are detected using the SNP-IT primer extension assay (Orchid Biosciences, Princeton, N.J.; See e.g., U.S. Pat. Nos. 5,952,174 and 5,919,626, each of which is herein incorporated by reference). In this assay, SNPs are identified by using a specially synthesized DNA primer and a DNA polymerase to selectively extend the DNA chain by one base at the suspected SNP location. DNA in the region of interest is amplified and denatured. Polymerase reactions are then performed using miniaturized systems called microfluidics. Detection is accomplished by adding a label to the nucleotide suspected of being at the SNP or mutation location. Incorporation of the label into the DNA can be detected by any suitable method (e.g., if the nucleotide contains a biotin label, detection is via a fluorescently labelled antibody specific for biotin).
5. Mass Spectroscopy Assay
In some embodiments, a MassARRAY system (Sequenom, San Diego, Calif.) is used to detect variant sequences (See e.g., U.S. Pat. Nos. 6,043,031; 5,777,324; and 5,605,798; each of which is herein incorporated by reference). DNA is isolated from blood samples using standard procedures. Next, specific DNA regions containing the mutation or SNP of interest, about 200 base pairs in length, are amplified by PCR. The amplified fragments are then attached by one strand to a solid surface and the non-immobilized strands are removed by standard denaturation and washing. The remaining immobilized single strand then serves as a template for automated enzymatic reactions that produce genotype specific diagnostic products.
Very small quantities of the enzymatic products, typically five to ten nanoliters, are then transferred to a SpectroCHIP array for subsequent automated analysis with the SpectroREADER mass spectrometer. Each spot is preloaded with light absorbing crystals that form a matrix with the dispensed diagnostic product. The MassARRAY system uses MALDI-TOF (Matrix Assisted Laser Desorption Ionization—Time of Flight) mass spectrometry. In a process known as desorption, the matrix is hit with a pulse from a laser beam. Energy from the laser beam is transferred to the matrix and it is vaporized resulting in a small amount of the diagnostic product being expelled into a flight tube. As the diagnostic product is charged when an electrical field pulse is subsequently applied to the tube they are launched down the flight tube towards a detector. The time between application of the electrical field pulse and collision of the diagnostic product with the detector is referred to as the time of flight. This is a very precise measure of the product's molecular weight, as a molecule's mass correlates directly with time of flight with smaller molecules flying faster than larger molecules. The entire assay is completed in less than one thousandth of a second, enabling samples to be analyzed in a total of 3-5 second including repetitive data collection. The SpectroTYPER software then calculates, records, compares and reports the genotypes at the rate of three seconds per sample.
6. Variant Analysis by Differential Antibody Binding
In other embodiments of the present invention, antibodies (See below for antibody production) are used to determine if an individual contains an allele encoding a variant Turkey RYR gene. In preferred embodiments, antibodies are utilized that discriminate between mutant (i.e., truncated proteins; e.g., SEQ ID NOS: 6 and 7); and wild-type proteins (SEQ ID NO: 5). In some particularly preferred embodiments, the antibodies are directed to the C-terminus of TαRYR.
7. Kits for Analyzing Risk of PSE Meat
The present invention also provides kits for determining whether an individual animal contains a wild-type or variant (e.g., polymorphic or mutant) allele of Turkey RYR. In some embodiments, the kits are useful determining whether the subject is at risk of developing PSE meat. The diagnostic kits are produced in a variety of ways. In some embodiments, the kits contain at least one reagent for specifically detecting a mutant Turkey RYR allele or protein. In preferred embodiments, the kits contains reagents for detecting if the turkey is homozygous for the TαRYRII allele. In preferred embodiments, the reagent is a nucleic acid that hybridizes to nucleic acids containing the SNP and that does not bind to nucleic acids that do not contain the SNP. In other preferred embodiments, the reagents are primers for amplifying the region of DNA containing the SNP. In still other embodiments, the reagents are antibodies which preferentially bind either the wild-type or truncated TαRYR proteins. In some embodiments, the kit contains instructions for determining whether the subject is susceptible to producing PSE meat. In preferred embodiments, the instructions specify that risk for developing Crohn's disease is determined by detecting the presence of alleles homozygous for TαRYRII. In some embodiments, the kits include ancillary reagents such as buffering agents, nucleic acid stabilizing reagents, protein stabilizing reagents, and signal producing systems (e.g., florescence generating systems as Fret systems). The test kit may be packages in any suitable manner, typically with the elements in a single container or various containers as necessary along with a sheet of instructions for carrying out the test in some embodiments, the kits also preferably include a positive control sample.
IV. Generation of Turkey RYR Antibodies
Antibodies can be generated to allow for the detection of Turkey RYR protein. The antibodies may be prepared using various immunogens. In one embodiment, the immunogen is a TαRYR peptide to generate antibodies that recognize TαRYR. Such antibodies include, but are not limited to polyclonal, monoclonal, chimeric, single chain, Fab fragments, and Fab expression libraries.
Various procedures known in the art may be used for the production of polyclonal antibodies directed against TαRYR. For the production of antibody, various host animals can be immunized by injection with the peptide corresponding to the TαRYR epitope including but not limited to rabbits, mice, rats, sheep, goats, etc. In a preferred embodiment, the peptide is conjugated to an immunogenic carrier (e.g., diphtheria toxoid, bovine serum albumin (BSA), or keyhole limpet hemocyanin (KLH)). Various adjuvants may be used to increase the immunological response, depending on the host species, including but not limited to Freund's (complete and incomplete), mineral gels (e.g., aluminum hydroxide), surface active substances (e.g., lysolecithin, pluronic polyols, polyanions, peptides, oil emulsions, keyhole limpet hemocyanins, dinitrophenol, and potentially useful human adjuvants such as BCG (Bacille Calmette-Guerin) and Corynebacterium parvum).
For preparation of monoclonal antibodies directed toward TαRYR, it is contemplated that any technique that provides for the production of antibody molecules by continuous cell lines in culture will find use with the present invention (See e.g., Harlow and Lane, Antibodies: A Laboratory Manual, Cold Spring Harbor Laboratory Press, Cold Spring Harbor, N.Y.). These include but are not limited to the hybridoma technique originally developed by Köhler and Milstein (Köhler and Milstein, Nature 256:495-497 [1975]), as well as the trioma technique, the human B-cell hybridoma technique (See, e.g., Kozbor, et al., Immunol. Tod., 4:72 [1983]), and the EBV-hybridoma technique to produce human monoclonal antibodies (Cole, et al., in Monoclonal Antibodies and Cancer Therapy, Alan R. Liss, Inc., pp. 77-96 [1985]).
In an additional embodiment of the invention, monoclonal antibodies are produced in germ-free animals utilizing technology such as that described in PCT/US90/02545). Furthermore, it is contemplated that human antibodies will be generated by human hybridomas (Cote et al., Proc. Natl. Acad. Sci. USA 80:2026-2030 [1983]) or by transforming human B cells with EBV virus in vitro (Cole et al., in Monoclonal Antibodies and Cancer Therapy, Alan R. Liss, pp. 77-96 [1985]).
In addition, it is contemplated that techniques described for the production of single chain antibodies (U.S. Pat. No. 4,946,778; herein incorporated by reference) will find use in producing Turkey RYR specific single chain antibodies. An additional embodiment of the invention utilizes the techniques described for the construction of Fab expression libraries (Huse, et al., Science 246:1275-1281 [1989]) to allow rapid and easy identification of monoclonal Fab fragments with the desired specificity for TαRYR.
It is contemplated that any technique suitable for producing antibody fragments will find use in generating antibody fragments that contain the idiotype (antigen binding region) of the antibody molecule. For example, such fragments include but are not limited to: F(ab′)2 fragment that can be produced by pepsin digestion of the antibody molecule; Fab′ fragments that can be generated by reducing the disulfide bridges of the F(ab′)2 fragment, and Fab fragments that can be generated by treating the antibody molecule with papain and a reducing agent.
In the production of antibodies, it is contemplated that screening for the desired antibody will be accomplished by techniques known in the art (e.g., radioimmunoassay, ELISA (enzyme-linked immunosorbant assay), “sandwich” immunoassays, immunoradiometric assays, gel diffusion precipitation reactions, immunodiffusion assays, in situ immunoassays (e.g., using colloidal gold, enzyme or radioisotope labels, for example), Western blots, precipitation reactions, agglutination assays (e.g.,gel agglutination assays, hemagglutination assays, etc.), complement fixation assays, immunofluorescence assays, protein A assays, and immunoelectrophoresis assays, etc.
In one embodiment, antibody binding is detected by detecting a label on the primary antibody. In another embodiment, the primary antibody is detected by detecting binding of a secondary antibody or reagent to the primary antibody. In a further embodiment, the secondary antibody is labeled. Many means are known in the art for detecting binding in an immunoassay and are within the scope of the present invention. (As is well known in the art, the immunogenic peptide should be provided free of the carrier molecule used in any immunization protocol. For example, if the peptide was conjugated to KLH, it may be conjugated to BSA, or used directly, in a screening assay.)
The foregoing antibodies can be used in methods known in the art relating to the localization and structure of Turkey RYR (e.g., for Western blotting), measuring levels thereof in appropriate biological samples, etc. The antibodies can be used to detect TαRYR in a biological sample from an individual. The biological sample can be a biological fluid, such as, but not limited to, blood, serum, plasma, interstitial fluid, urine, cerebrospinal fluid, and the like, containing cells.
The biological samples can then be tested directly for the presence of TαRYR using an appropriate strategy (e.g., ELISA or radioimmunoassay) and format (e.g., microwells, dipstick (e.g., as described in International Patent Publication WO 93/03367), etc. Alternatively, proteins in the sample can be size separated (e.g., by polyacrylamide gel electrophoresis (PAGE), in the presence or not of sodium dodecyl sulfate (SDS), and the presence of TαRYR detected by immunoblotting (Western blotting). Immunoblotting techniques are generally more effective with antibodies generated against a peptide corresponding to an epitope of a protein, and hence, are particularly suited to the present invention.
Another method uses antibodies as agents to alter signal transduction. Specific antibodies that bind to the binding domains of TαRYR or other proteins involved in intracellular signalling can be used to inhibit the interaction between the various proteins and their interaction with other ligands. Antibodies that bind to the complex can also be used therapeutically to inhibit interactions of the protein complex in the signal transduction pathways leading to the various physiological and cellular effects of TαRYR ion transport. Such antibodies can also be used diagnostically to measure abnormal expression of TαRYR, or the aberrant formation of protein complexes, which may be indicative of a disease state.
V. Gene Therapy Using TαRYR
The present invention also provides methods and compositions suitable for gene therapy to alter TαRYR expression, production, or function. As described above, the present invention provides TαRYR genes and provides methods of obtaining RYR genes from other species. Thus, the methods described below are generally applicable across many species. In some embodiments, it is contemplated that the gene therapy is performed by providing a subject with a wild-type allele of TαRYRI (i.e., the allele associated with non-PSE meat). Subjects in need of such therapy are identified by the methods described above. As described above, TαRYR is (primarily) expressed in the muscle cells. Accordingly, subjects could be treated after birth or, in a preferred embodiment, subjects are the product of transgenic engineering wherein the desired gene is incorporated into the genome of the subject before fertilization of the oocyte (see, section VI, below).
Viral vectors commonly used for in vivo or ex vivo targeting and therapy procedures are DNA-based vectors and retroviral vectors. Methods for constructing and using viral vectors are known in the art (See, e.g., Miller and Rosman, BioTech., 7:980-990 [1992]). Preferably, the viral vectors are replication defective, that is, they are unable to replicate autonomously in the target cell. In general, the genome of the replication defective viral vectors that are used within the scope of the present invention lack at least one region that is necessary for the replication of the virus in the infected cell. These regions can either be eliminated (in whole or in part), or be rendered non-functional by any technique known to a person skilled in the art. These techniques include the total removal, substitution (by other sequences, in particular by the inserted nucleic acid), partial deletion or addition of one or more bases to an essential (for replication) region. Such techniques may be performed in vitro (i.e., on the isolated DNA) or in situ, using the techniques of genetic manipulation or by treatment with mutagenic agents.
Preferably, the replication defective virus retains the sequences of its genome that are necessary for encapsidating the viral particles. DNA viral vectors include an attenuated or defective DNA viruses, including, but not limited to, herpes simplex virus (HSV), papillomavirus, Epstein Barr virus (EBV), adenovirus, adeno-associated virus (AAV), and the like. Defective viruses, that entirely or almost entirely lack viral genes, are preferred, as defective virus is not infective after introduction into a cell. Use of defective viral vectors allows for administration to cells in a specific, localized area, without concern that the vector can infect other cells. Thus, a specific tissue can be specifically targeted. Examples of particular vectors include, but are not limited to, a defective herpes virus 1 (HSV1) vector (Kaplitt, et al., Mol. Cell. Neurosci., 2:320-330 [1991]), defective herpes virus vector lacking a glycoprotein L gene (See e.g., Patent Publication RD 371005 A), or other defective herpes virus vectors (See e.g., WO 94/21807; and WO 92/05263); an attenuated adenovirus vector, such as the vector described by Stratford-Perricaudet, et al. (J. Clin. Invest., 90:626-630 [1992]; See also, La Salle et al., Science 259:988-990 [1993]); and a defective adeno-associated virus vector (Samulski et al., J. Virol., 61:3096-3101 [1987]; Samulski, et al., J. Virol., 63:3822-3828 [1989]; and Lebkowski, et al., Mol. Cell. Biol., 8:3988-3996 [1988]).
Preferably, for in vivo administration, an appropriate immunosuppressive treatment is employed in conjunction with the viral vector (e.g., adenovirus vector), to avoid immuno-deactivation of the viral vector and transfected cells. For example, immunosuppressive cytokines, such as interleukin-12 (IL-12), interferon-gamma (IFN-β), or anti-CD4 antibody, can be administered to block humoral or cellular immune responses to the viral vectors. In addition, it is advantageous to employ a viral vector that is engineered to express a minimal number of antigens.
In a preferred embodiment, the vector is an adenovirus vector. Adenoviruses are eukaryotic DNA viruses that can be modified to efficiently deliver a nucleic acid of the invention to a variety of cell types. Various serotypes of adenovirus exist. Of these serotypes, preference is given, within the scope of the present invention, to type 2 or type 5 human adenoviruses (Ad 2 or Ad 5), or adenoviruses of animal origin (See e.g., WO94/26914). Those adenoviruses of animal origin that can be used within the scope of the present invention include adenoviruses of canine, bovine, murine (e.g., Mav1, Beard, et al., Virol., 75-81 [1990]), ovine, porcine, avian, and simian (e.g., SAV) origin. Preferably, the adenovirus of animal origin is a canine adenovirus, more preferably a CAV2 adenovirus (e.g., Manhattan or A26/61 strain (ATCC VR-800)).
Preferably, the replication defective adenoviral vectors of the invention comprise the ITRs, an encapsidation sequence and the nucleic acid of interest. Still more preferably, at least the E1 region of the adenoviral vector is non-functional. The deletion in the E1 region preferably extends from nucleotides 455 to 3329 in the sequence of the Ad5 adenovirus (PvuII-BglII fragment) or 382 to 3446 (HinfII-Sau3A fragment). Other regions may also be modified, in particular the E3 region (e.g., WO95/02697), the E2 region (e.g., WO94/28938), the E4 region (e.g., W094/28152, WO94/12649 and WO95/02697), or in any of the late genes L1-L5.
In a preferred embodiment, the adenoviral vector has a deletion in the E1 region (Ad 1.0). Examples of E1-deleted adenoviruses are disclosed in EP 185,573, the contents of which are incorporated herein by reference. In another preferred embodiment, the adenoviral vector has a deletion in the E1 and E4 regions (Ad 3.0). Examples of E1/E4-deleted adenoviruses are disclosed in WO95/02697 and W096/22378. In still another preferred embodiment, the adenoviral vector has a deletion in the E1 region into which the E4 region and the nucleic acid sequence are inserted.
The replication defective recombinant adenoviruses according to the invention can be prepared by any technique known to the person skilled in the art (See e.g., Levrero et al., Gene 101:195 [1991]; EP 185 573; and Graham, EMBO J., 3:2917 [1984]). In particular, they can be prepared by homologous recombination between an adenovirus and a plasmid which carries, inter alia, the DNA sequence of interest. The homologous recombination is accomplished following co-transfection of the adenovirus and plasmid into an appropriate cell line. The cell line that is employed should preferably (i) be transformable by the elements to be used, and (ii) contain the sequences that are able to complement the part of the genome of the replication defective adenovirus, preferably in integrated form in order to avoid the risks of recombination. Examples of cell lines that may be used are the human embryonic kidney cell line 293 (Graham et al., J. Gen. Virol., 36:59 [1977]), which contains the left-hand portion of the genome of an Ad5 adenovirus (12%) integrated into its genome, and cell lines that are able to complement the E1 and E4 functions, as described in applications WO94/26914 and WO95/02697. Recombinant adenoviruses are recovered and purified using standard molecular biological techniques, that are well known to one of ordinary skill in the art.
The adeno-associated viruses (AAV) are DNA viruses of relatively small size that can integrate, in a stable and site-specific manner, into the genome of the cells that they infect. They are able to infect a wide spectrum of cells without inducing any effects on cellular growth, morphology or differentiation, and they do not appear to be involved in human pathologies. The AAV genome has been cloned, sequenced and characterized. It encompasses approximately 4700 bases and contains an inverted terminal repeat (ITR) region of approximately 145 bases at each end, which serves as an origin of replication for the virus. The remainder of the genome is divided into two essential regions that carry the encapsidation functions: the left-hand part of the genome, that contains the rep gene involved in viral replication and expression of the viral genes; and the right-hand part of the genome, that contains the cap gene encoding the capsid proteins of the virus.
The use of vectors derived from the AAVs for transferring genes in vitro and in vivo has been described (See e.g., WO 91/18088; WO 93/09239; U.S. Pat. No. 4,797,368; U.S. Pat. No. 5,139,941; and EP 488 528, all of which are herein incorporated by reference). These publications describe various AAV-derived constructs in which the rep and/or cap genes are deleted and replaced by a gene of interest, and the use of these constructs for transferring the gene of interest in vitro (into cultured cells) or in vivo (directly into an organism). The replication defective recombinant AAVs according to the invention can be prepared by co-transfecting a plasmid containing the nucleic acid sequence of interest flanked by two AAV inverted terminal repeat (ITR) regions, and a plasmid carrying the AAV encapsidation genes (rep and cap genes), into a cell line that is infected with a human helper virus (for example an adenovirus). The AAV recombinants that are produced are then purified by standard techniques.
In another embodiment, the gene can be introduced in a retroviral vector (e.g., as described in U.S. Pat. Nos. 5,399,346, 4,650,764, 4,980,289 and 5,124,263; all of which are herein incorporated by reference; Mann et al., Cell 33:153 [1983]; Markowitz, et al., J. Virol., 62:1120 [1988]; PCT/US95/14575; EP 453242; EP178220; Bernstein, et al. Genet. Eng., 7:235 [1985]; McCormick, BioTechnol., 3:689 [1985]; WO 95/07358; and Kuo, et al., Blood 82:845 [1993]). The retroviruses are integrating viruses that infect dividing cells. The retrovirus genome includes two LTRs, an encapsidation sequence and three coding regions (gag, pol and env). In recombinant. retroviral vectors, the gag, pol and env genes are generally deleted, in whole or in part, and replaced with a heterologous nucleic acid sequence of interest. These vectors can be constructed from different types of retrovirus, such as, HIV, MoMuLV (“murine Moloney leukaemia virus” MSV (“murine Moloney sarcoma virus”), HaSV (“Harvey sarcoma virus”); SNV (“spleen necrosis virus”); RSV (“Rous sarcoma virus”) and Friend virus. Defective retroviral vectors are also disclosed in WO95/02697.
In general, in order to construct recombinant retroviruses containing a nucleic acid sequence, a plasmid is constructed that contains the LTRs, the encapsidation sequence and the coding sequence. This construct is used to transfect a packaging cell line, which cell line is able to supply in trans the retroviral functions that are deficient in the plasmid. In general, the packaging cell lines are thus able to express the gag, pol and env genes. Such packaging cell lines have been described in the prior art, in particular the cell line PA317 (U.S. Pat. No. 4,861,719, herein incorporated by reference), the PsiCRIP cell line (See, WO90/02806), and the GP+envAm-12 cell line (See, WO89/07150). In addition, the recombinant retroviral vectors can contain modifications within the LTRs for suppressing transcriptional activity as well as extensive encapsidation sequences that may include a part of the gag gene (Bender et al., J. Virol., 61:1639 [1987]). Recombinant retroviral vectors are purified by standard techniques known to those having ordinary skill in the art.
Alternatively, the vector can be introduced in vivo by lipofection. For the past decade, there has been increasing use of liposomes for encapsulation and transfection of nucleic acids in vitro. Synthetic cationic lipids designed to limit the difficulties and dangers encountered with liposome mediated transfection can be used to prepare liposomes for in vivo transfection of a gene encoding a marker (Feigner, et. al., Proc. Natl. Acad. Sci. USA 84:7413-7417 [1987]; See also, Mackey, et al., Proc. Natl. Acad. Sci. USA 85:8027-8031 [1988]; Ulmer, et al., Science 259:1745-1748 [1993]). The use of cationic lipids may promote encapsulation of negatively charged nucleic acids, and also promote fusion with negatively charged cell membranes (Feigner, and Ringold, Science 337:387-388 [1989]). Particularly useful lipid compounds and compositions for transfer of nucleic acids are described in WO95/18863 and WO96/17823, and in U.S. Pat. No. 5,459,127, herein incorporated by reference.
Other molecules are also useful for facilitating transfection of a nucleic acid in vivo, such as a cationic oligopeptide (e.g., WO95/21931), peptides derived from DNA binding proteins (e.g., WO96/25508), or a cationic polymer (e.g., WO95/21931).
It is also possible to introduce the vector in vivo as a naked DNA plasmid. Methods for formulating and administering naked DNA to mammalian muscle tissue are disclosed in U.S. Pat. Nos. 5,580,859 and 5,589,466, both of which are herein incorporated by reference.
DNA vectors for gene therapy can be introduced into the desired host cells by methods known in the art, including but not limited to transfection, electroporation, microinjection, transduction, cell fusion, DEAE dextran, calcium phosphate precipitation, use of a gene gun, or use of a DNA vector transporter (See e.g., Wu et al., J. Biol. Chem., 267:963-967 [1992]; Wu and Wu, J. Biol. Chem., 263:14621-14624 [1988]; and Williams et al., Proc. Natl. Acad. Sci. USA 88:2726-2730 [1991]). Receptor-mediated DNA delivery approaches can also be used (Curiel, et al., Hum. Gene Ther., 3:147-154 [1992]; and Wu and Wu, J. Biol. Chem., 262:4429-4432 [1987]).
VI. Transgenic Animals Expressing Exogenous TαRYR Genes and Alleles, Homologs, Mutants, and Variants Thereof
The present invention contemplates the generation of transgenic animals comprising an exogenous TαRYR gene or alleles, homologs, mutants, or variants thereof. In preferred embodiments, the transgenic animal displays an altered phenotype as compared to PSE susceptable animals (for example, meat having higher postmortem pH and better water holding capacity). In some embodiments, the altered phenotype is the overexpression of mRNA for a TαRYRI gene as compared to levels of TαRYRII expression. In other embodiments, the altered phenotype is the decreased expression of mRNA for an endogenous TαRYRII gene as compared to TαRYRI. Methods for analyzing the presence or absence of such phenotypes include Northern blotting, mRNA protection assays, and RT-PCR as well as examination of postmortem meat. In other embodiments, the transgenic animals have a knock out mutation of the TαRYRII allele.
The transgenic animals of the present invention find use in dietary and drug screens. In some embodiments, the transgenic animals (e.g., animals displaying PSE-meat phenotype) are treated with drugs or diets and the production of PSE-meat is evaluated. In other embodiments, test compounds (e.g., a drug that is suspected of being useful to decrease of eliminate the production of PSE-meat) and control compounds (e.g., a placebo) are administered to the transgenic animals and the control animals and the effects evaluated.
The transgenic animals can be generated via a variety of methods. In some embodiments, embryonal cells at various developmental stages are used to introduce transgenes for the production of transgenic animals. Different methods are used depending on the stage of development of the embryonal cell. The zygote is the best target for micro-injection. In the mouse, the male pronucleus reaches the size of approximately 20 micrometers in diameter which allows reproducible injection of 1-2 picoliters (pl) of DNA solution. The use of zygotes as a target for gene transfer has a major advantage in that in most cases the injected DNA will be incorporated into the host genome before the first cleavage (Brinster, et al., Proc. Natl. Acad. Sci. USA 82:4438-4442 [1985]). As a consequence, all cells of the transgenic non-human animal will carry the incorporated transgene. This will in general also be reflected in the efficient transmission of the transgene to offspring of the founder since 50% of the germ cells will harbor the transgene. U.S. Pat. No. 4,873,191 describes a method for the micro-injection of zygotes; the disclosure of this patent is incorporated herein in its entirety.
In other embodiments, retroviral infection is used to introduce transgenes into a non-human animal. In some embodiments, the retroviral vector is utilized to transfect oocytes by injecting the retroviral vector into the perivitelline space of the oocyte (U.S. Pat. No. 6,080,912, incorporated herein by reference). In other embodiments, the developing non-human embryo can be cultured in vitro to the blastocyst stage. During this time, the blastomeres can be targets for retroviral infection (Janenich, Proc. Natl. Acad. Sci. USA 73:1260-1264 [1976]). Efficient infection of the blastomeres is obtained by enzymatic treatment to remove the zona pellucida (Hogan et al., in Manipulating the Mouse Embryo, Cold Spring Harbor Laboratory Press, Cold Spring Harbor, N.Y. [1986]). The viral vector system used to introduce the transgene is typically a replication-defective retrovirus carrying the transgene (D. Jahner, et al., Proc. Natl. Acad Sci. USA 82:6927-693 [1985]). Transfection is easily and efficiently obtained by culturing the blastomeres on a monolayer of virus-producing cells (Van der Putten, supra; Stewart, et al., EMBO J., 6:383-388 [1987]). Alternatively, infection can be performed at a later stage. Virus or virus-producing cells can be injected into the blastocoele (D. Jahner, et al., Nature 298:623-628 [1982]). Most of the founders will be mosaic for the transgene since incorporation occurs only in a subset of cells which form the transgenic animal. Further, the founder may contain various retroviral insertions of the transgene at different positions in the genome which generally will segregate in the offspring. In addition, it is also possible to introduce transgenes into the germline, albeit with low efficiency, by intrauterine retroviral infection of the midgestation embryo (Jahner, et al., supra [1982]). Additional means of using retroviruses or retroviral vectors to create transgenic animals known to the art involves the micro-injection of retroviral particles or mitomycin C-treated cells producing retrovirus into the perivitelline space of fertilized eggs or early embryos (PCT International Application WO 90/08832 [1990], and Haskell and Bowen, Mol. Reprod. Dev., 40:386 [1995]).
In other embodiments, the transgene is introduced into embryonic stem cells and the transfected stem cells are utilized to form an embryo. ES cells are obtained by culturing pre-implantation embryos in vitro under appropriate conditions (Evans, et al., Nature 292:154-156 [1981]; Bradley, et al., Nature 309:255-258 [1984]; Gossler, et al., Proc. Acad. Sci. USA 83:9065-9069 [1986]; and Robertson, et al., Nature 322:445-448 [1986]). Transgenes can be efficiently introduced into the ES cells by DNA transfection by a variety of methods known to the art including calcium phosphate co-precipitation, protoplast or spheroplast fusion, lipofection and DEAE-dextran-mediated transfection. Transgenes may also be introduced into ES cells by retrovirus-mediated transduction or by micro-injection. Such transfected ES cells can thereafter colonize an embryo following their introduction into the blastocoel of a blastocyst-stage embryo and contribute to the germ line of the resulting chimeric animal (for review, See, Jaenisch, Science 240:1468-1474 [1988]). Prior to the introduction of transfected ES cells into the blastocoel, the transfected ES cells may be subjected to various selection protocols to enrich for ES cells which have integrated the transgene assuming that the transgene provides a means for such selection. Alternatively, the polymerase chain reaction may be used to screen for ES cells which have integrated the transgene. This technique obviates the need for growth of the transfected ES cells under appropriate selective conditions prior to transfer into the blastocoel.
In still other embodiments, homologous recombination is utilized knock-out gene function or create deletion mutants (e.g., mutants in which the LRRs of TαRYR are deleted). Methods for homologous recombination are described in U.S. Pat. No. 5,614,396, incorporated herein by reference.
VII. Drug Screening Using TαRYR
The present invention provides methods and compositions for using TαRYR as a target for screening drugs that can alter, for example, the pH of post-mortem muscle.
The present invention is not limited to any particular mechanism of action. Indeed, an understanding of the mechanism of action is not necessary to practice the present invention. Nevertheless, it is contemplated that the TαRYR protein is a homotetrameric Ca2+ channel protein localized to the sarcoplasmic reticulum (SR) (Lai, et al., 1988). The large N-terminal domains of each RYR subunit combine to form the “foot” structure which protrudes from the SR and binds to the DHPR embedded in the T-tubule membrane. During skeletal muscle excitation-contraction coupling, depolarization of the sarcolemma/T-tubule membrane system leads to a conformational change in the DHPR which is transmitted to RYR, causing the channel to open and release Ca2+ from the SR (Catterall, 1991).
In one screening method, the two-hybrid system is used to screen for compounds (e.g., drug) capable of altering (e.g., inhibiting) TαRYR function(s) (e.g., membrane channel function) in vitro or in vivo. In one embodiment, a GAL4 binding site, linked to a reporter gene such as lacZ, is contacted in the presence and absence of a candidate compound with a GAL4 binding domain linked to a TαRYR fragment and a GAL4 transactivation domain II linked to a dihydropyridine receptor (DHPR) fragment. Expression of the reporter gene is monitored and a decrease in the expression is an indication that the candidate compound inhibits the interaction of TαRYR with DHPR. Alternately, the effect of candidate compounds on the interaction of TαRYR with other proteins (e.g., proteins known to interact directly or indirectly with DHPR) can be tested in a similar manner.
In another screening method, candidate compounds are evaluated for their ability to alter TαRYR signalling by contacting TαRYR, DHPR, DHPR-associated proteins, or fragments thereof, with the candidate compound and determining binding of the candidate compound to the peptide. The protein or protein fragments is/are immobilized using methods known in the art such as binding a GST-TαRYR fusion protein to a polymeric bead containing glutathione. A chimeric gene encoding a GST fusion protein is constructed by fusing DNA encoding the polypeptide or polypeptide fragment of interest to the DNA encoding the carboxyl terminus of GST (See e.g., Smith et al., Gene 67:31 [1988]). The fusion construct is then transformed into a suitable expression system (e.g., E. coli XA90) in which the expression of the GST fusion protein can be induced with isopropyl-beta-D-thiogalactopyranoside (IPTG). Induction with IPTG should yield the fusion protein as a major constituent of soluble, cellular proteins. The fusion proteins can be purified by methods known to those skilled in the art, including purification by glutathione affinity chromatography. Binding of the candidate compound to the proteins or protein fragments is correlated with the ability of the compound to disrupt the signal transduction pathway and thus regulate TαRYR physiological effects (e.g., Ca2+ flux of the sarcoplasmic reticulum).
In another screening method, one of the components of the TαRYR/DHPR signalling system, such as TαRYR or a fragment of TαRYR, is immobilized. Polypeptides can be immobilized using methods known in the art, such as adsorption onto a plastic microtiter plate or specific binding of a GST-fusion protein to a polymeric bead containing glutathione. For example, GST-TαRYR is bound to glutathione-Sepharose beads. The immobilized peptide is then contacted with another peptide with which it is capable of binding in the presence and absence of a candidate compound. Unbound peptide is then removed and the complex solubilized and analyzed to determine the amount of bound labeled peptide. A decrease in binding is an indication that the candidate compound inhibits the interaction of TαRYR with the other peptide. A variation of this method allows for the screening of compounds that are capable of disrupting a previously-formed protein/protein complex. For example, in some embodiments a complex comprising TαRYR or a TαRYR fragment bound to another peptide is immobilized as described above and contacted with a candidate compound. The dissolution of the complex by the candidate compound correlates with the ability of the compound to disrupt or inhibit the interaction between TαRYR and the other peptide.
Another technique for drug screening provides high throughput screening for compounds having suitable binding affinity to TαRYR peptides and is described in detail in WO 84/03564, incorporated herein by reference. Briefly, large numbers of different small peptide test compounds are synthesized on a solid substrate, such as plastic pins or some other surface. The peptide test compounds are then reacted with TαRYR peptides and washed. Bound TαRYR peptides are then detected by methods well known in the art.
Another technique uses TαRYR antibodies, generated as discussed above. Such antibodies capable of specifically binding to TαRYR peptides compete with a test compound for binding to TαRYR. In this manner, the antibodies can be used to detect the presence of any peptide that shares one or more antigenic determinants of the TαRYR peptide.
In some embodiments of the present invention, compounds are screened for their ability to inhibit the binding of pathogen components (e.g., including, but not limited to, bacterial cell surface proteins; fungi proteins, parasite proteins, and virus proteins) to TαRYR. Any suitable screening assay may be utilized, including, but not limited to, those described herein.
The present invention contemplates many other means of screening compounds. The examples provided above are presented merely to illustrate a range of techniques available. One of ordinary skill in the art will appreciate that many other screening methods can be used.
In particular, the present invention contemplates the use of cell lines transfected with TαRYR and variants or mutants thereof for screening compounds for activity, and in particular to high throughput screening of compounds from combinatorial libraries (e.g., libraries containing greater than 104 compounds). The cell lines of the present invention can be used in a variety of screening methods. In some embodiments, the cells can be used in second messenger assays that monitor signal transduction following activation of cell-surface receptors. In other embodiments, the cells can be used in reporter gene assays that monitor cellular responses at the transcription/translation level. In still further embodiments, the cells can be used in cell proliferation assays to monitor the overall growth/no growth response of cells to external stimuli.
In second messenger assays, the host cells are preferably transfected as described above with vectors encoding TαRYR or variants or mutants thereof. The host cells are then treated with a compound or plurality of compounds (e.g., from a combinatorial library) and assayed for the presence or absence of a response. It is contemplated that at least some of the compounds in the combinatorial library can serve as agonists, antagonists, activators, or inhibitors of the protein or proteins encoded by the vectors. It is also contemplated that at least some of the compounds in the combinatorial library can serve as agonists, antagonists, activators, or inhibitors of protein acting upstream or downstream of the protein encoded by the vector in a signal transduction pathway.
In some embodiments, the second messenger assays measure fluorescent signals from reporter molecules that respond to intracellular changes (e.g., Ca2+ concentration, membrane potential, pH, IP3, cAMP, arachidonic acid release) due to stimulation of membrane receptors and ion channels (e.g., ligand gated ion channels; see Denyer, et al., Drug Discov. Today 3:323-32 [1998]; and Gonzales, et al., Drug. Discov. Today 4:431-39 [1999]). Examples of reporter molecules include, but are not limited to, FRET (florescence resonance energy transfer) systems (e.g., Cuo-lipids and oxonols, EDAN/DABCYL), calcium sensitive indicators (e.g., Fluo-3, FURA 2, INDO 1, and FLUO3/AM, BAPTA AM), chloride-sensitive indicators (e.g., SPQ, SPA), potassium-sensitive indicators (e.g., PBFI), sodium-sensitive indicators (e.g., SBFI), and pH sensitive indicators (e.g., BCECF).
In general, the host cells are loaded with the indicator prior to exposure to the compound. Responses of the host cells to treatment with the compounds can be detected by methods known in the art, including, but not limited to, fluorescence microscopy, confocal microscopy (e.g., FCS systems), flow cytometry, microfluidic devices, FLIPR systems (See, e.g., Schroeder and Neagle, J. Biomol. Screening 1:75-80 [1996]), and plate-reading systems. In some preferred embodiments, the response (e.g., increase in fluorescent intensity) caused by compound of unknown activity is compared to the response generated by a known agonist and expressed as a percentage of the maximal response of the known agonist. The maximum response caused by a known agonist is defined as a 100% response. Likewise, the maximal response recorded after addition of an agonist to a sample containing a known or test antagonist is detectably lower than the 100% response.
The cells are also useful in reporter gene assays. Reporter gene assays involve the use of host cells transfected with vectors encoding a nucleic acid comprising transcriptional control elements of a target gene (i.e., a gene that controls the biological expression and function of a disease target) spliced to a coding sequence for a reporter gene. Therefore, activation of the target gene results in activation of the reporter gene product. As described above, it is contemplated that TαRYR binds to DHRP, and this binding results in the conformational change in TαRYR. Therefore, in some embodiments, the reporter gene construct comprises the 5′ regulatory region (e.g., promoters and/or enhancers) of a protein whose expression is controlled by DHRP in operable association with a reporter gene (see, Inohara, et al., J. Biol. Chem. 275:27823-31 [2000] for a description of the luciferase reporter construct pBVIx-Luc). Examples of reporter genes finding use in the present invention include, but are not limited to, chloramphenicol transferase, alkaline phosphatase, firefly and bacterial luciferases, beta-galactosidase, beta-lactamase, and green fluorescent protein. The production of these proteins, with the exception of green fluorescent protein, is detected through the use of chemiluminescent, colorimetric, or bioluminescent products of specific substrates (e.g., X-gal and luciferin). Comparisons between compounds of known and unknown activities may be conducted as described above.
VIII. Pharmaceutical Compositions Containing TαRYR Nucleic Acid, Peptides, and Analogs
The present invention further provides pharmaceutical compositions which may comprise all or portions of TαRYR polynucleotide sequences, TαRYR polypeptides, inhibitors or antagonists of TαRYR bioactivity, including antibodies, alone or in combination with at least one other agent, such as a stabilizing compound, and may be administered in any sterile, biocompatible pharmaceutical carrier, including, but not limited to, saline, buffered saline, dextrose, and water.
Peptides can be administered to the subject intravenously in a pharmaceutically acceptable carrier such as physiological saline. Standard methods for intracellular delivery of peptides can be used (e.g., delivery via liposome). Such methods are well known to those of ordinary skill in the art. The formulations of this invention are useful for parenteral administration, such as intravenous, subcutaneous, intramuscular, and intraperitoneal. Therapeutic administration of a polypeptide intracellularly can also be accomplished using gene therapy as described above.
As is well known in the medical arts, dosages for any one subject depends upon many factors, including the subject's size, body surface area, age, the particular compound to be administered, sex, time and route of administration, general health, and interaction with other drugs being concurrently administered.
Accordingly, in some embodiments of the present invention, Turkey RYR nucleotide and Turkey RYR amino acid sequences can be administered to an animal alone, or in combination with other nucleotide sequences, drugs or hormones or in pharmaceutical compositions where it is mixed with excipient(s) or other pharmaceutically acceptable carriers. In one embodiment of the present invention, the pharmaceutically acceptable carrier is pharmaceutically inert. In another embodiment of the present invention, Turkey RYR polynucleotide sequences or Turkey RYR amino acid sequences may be administered alone to individuals subject to or suffering from a disease.
Depending on the condition being treated, these pharmaceutical compositions may be formulated and administered systemically or locally. Techniques for formulation and administration may be found in the latest edition of “Remington's Pharmaceutical Sciences” (Mack Publishing Co, Easton Pa.). Suitable routes may, for example, include oral or transmucosal administration; as well as parenteral delivery, including intramuscular, subcutaneous, intramedullary, intrathecal, intraventricular, intravenous, intraperitoneal, or intranasal administration.
For injection, the pharmaceutical compositions of the invention may be formulated in aqueous solutions, preferably in physiologically compatible buffers such as Hanks' solution, Ringer's solution, or physiologically buffered saline. For tissue or cellular administration, penetrants appropriate to the particular barrier to be permeated are used in the formulation. Such penetrants are generally known in the art.
In other embodiments, the pharmaceutical compositions of the present invention can be formulated using pharmaceutically acceptable carriers well known in the art in dosages suitable for oral administration. Such carriers enable the pharmaceutical compositions to be formulated as tablets, pills, capsules, liquids, gels, syrups, slurries, suspensions and the like, for oral or nasal ingestion by a subject to be treated.
Pharmaceutical compositions suitable for use in the present invention include compositions wherein the active ingredients are contained in an effective amount to achieve the intended purpose. For example, an effective amount of Turkey RYR may be that amount that suppresses the production of PSE meat. Determination of effective amounts is well within the capability of those skilled in the art, especially in light of the disclosure provided herein.
In addition to the active ingredients these pharmaceutical compositions may contain suitable pharmaceutically acceptable carriers comprising excipients and auxiliaries which facilitate processing of the active compounds into preparations which can be used pharmaceutically. The preparations formulated for oral administration may be in the form of tablets, dragees, capsules, or solutions.
The pharmaceutical compositions of the present invention may be manufactured in a manner that is itself known (e.g., by means of conventional mixing, dissolving, granulating, dragee-making, levigating, emulsifying, encapsulating, entrapping or lyophilizing processes).
Pharmaceutical formulations for parenteral administration include aqueous solutions of the active compounds in water-soluble form. Additionally, suspensions of the active compounds may be prepared as appropriate oily injection suspensions. Suitable lipophilic solvents or vehicles include fatty oils such as sesame oil, or synthetic fatty acid esters, such as ethyl oleate or triglycerides, or liposomes. Aqueous injection suspensions may contain substances which increase the viscosity of the suspension, such as sodium carboxymethyl cellulose, sorbitol, or dextran. Optionally, the suspension may also contain suitable stabilizers or agents which increase the solubility of the compounds to allow for the preparation of highly concentrated solutions.
Pharmaceutical preparations for oral use can be obtained by combining the active compounds with solid excipient, optionally grinding a resulting mixture, and processing the mixture of granules, after adding suitable auxiliaries, if desired, to obtain tablets or dragee cores. Suitable excipients are carbohydrate or protein fillers such as sugars, including lactose, sucrose, mannitol, or sorbitol; starch from corn, wheat, rice, potato, etc; cellulose such as methyl cellulose, hydroxypropylmethyl-cellulose, or sodium carboxymethylcellulose; and gums including arabic and tragacanth; and proteins such as gelatin and collagen. If desired, disintegrating or solubilizing agents may be added, such as the cross-linked polyvinyl pyrrolidone, agar, alginic acid or a salt thereof such as sodium alginate.
Dragee cores are provided with suitable coatings such as concentrated sugar solutions, which may also contain gum arabic, talc, polyvinylpyrrolidone, carbopol gel, polyethylene glycol, and/or titanium dioxide, lacquer solutions, and suitable organic solvents or solvent mixtures. Dyestuffs or pigments may be added to the tablets or dragee coatings for product identification or to characterize the quantity of active compound, (i.e., dosage).
Pharmaceutical preparations which can be used orally include push-fit capsules made of gelatin, as well as soft, sealed capsules made of gelatin and a coating such as glycerol or sorbitol. The push-fit capsules can contain the active ingredients mixed with a filler or binders such as lactose or starches, lubricants such as talc or magnesium stearate, and, optionally, stabilizers. In soft capsules, the active compounds may be dissolved or suspended in suitable liquids, such as fatty oils, liquid paraffin, or liquid polyethylene glycol with or without stabilizers.
Compositions comprising a compound of the invention formulated in a pharmaceutical acceptable carrier may be prepared, placed in an appropriate container, and labeled for treatment of an indicated condition. For polynucleotide or amino acid sequences of Turkey RYR, conditions indicated on the label may include treatment of condition related to the production of PSE meat.
The pharmaceutical composition may be provided as a salt and can be formed with many acids, including but not limited to hydrochloric, sulfuric, acetic, lactic, tartaric, malic, succinic, etc. Salts tend to be more soluble in aqueous or other protonic solvents that are the corresponding free base forms. In other cases, the preferred preparation may be a lyophilized powder in 1 mM-50 mM histidine, 0.1%-2% sucrose, 2%-7% mannitol at a pH range of 4.5 to 5.5 that is combined with buffer prior to use.
For any compound used in the method of the invention, the therapeutically effective dose can be estimated initially from cell culture assays. Then, preferably, dosage can be formulated in animal models (particularly murine models) to achieve a desirable circulating concentration range that adjusts lessens the production of PSE meat.
A therapeutically effective dose refers to that amount of Turkey RYR which ameliorates symptoms of the disease state (i.e., the production of PSE meat). Toxicity and therapeutic efficacy of such compounds can be determined by standard pharmaceutical procedures in cell cultures or experimental animals, e.g., for determining the LD50 (the dose lethal to 50% of the population) and the ED50 (the dose therapeutically effective in 50% of the population). The dose ratio between toxic and therapeutic effects is the therapeutic index, and it can be expressed as the ratio LD50/ED50. Compounds which exhibit large therapeutic indices are preferred. The data obtained from these cell culture assays and additional animal studies can be used in formulating a range of dosage for human use. The dosage of such compounds lies preferably within a range of circulating concentrations that include the ED50 with little or no toxicity. The dosage varies within this range depending upon the dosage form employed, sensitivity of the subject, and the route of administration.
The exact dosage is chosen by the individual physician in view of the subject to be treated. Dosage and administration are adjusted to provide sufficient levels of the active moiety or to maintain the desired effect. Additional factors which may be taken into account include the severity of the disease state; age, weight, and gender of the subject; diet, time and frequency of administration, drug combination(s), reaction sensitivities, and tolerance/response to therapy. Long acting pharmaceutical compositions might be administered every 3 to 4 days, every week, or once every two weeks depending on half-life and clearance rate of the particular formulation.
Normal dosage amounts may vary from 0.1 to 100,000 micrograms, up to a total dose of about 1 g, depending upon the route of administration. Guidance as to particular dosages and methods of delivery is provided in the literature (See, U.S. Pat. Nos. 4,657,760; 5,206,344; or 5,225,212, all of which are herein incorporated by reference). Those skilled in the art will employ different formulations for TαRYR than for the inhibitors of TαRYR. Administration to the bone marrow may necessitate delivery in a manner different from intravenous injections.
EXPERIMENTAL
The following examples serve to illustrate certain preferred embodiments and aspects of the present invention and are not to be construed as limiting the scope thereof.
In the disclosure which follows, the following abbreviations apply: ° C. (degrees Centigrade); vol (volume); w/v (weight to volume); v/v (volume to volume); μl (microliters); ml (milliliters); μg (micrograms); mg (milligrams); M (molar); mM (milliMolar); μM (microMolar); nm (nanometers); kdal (kilodaltons); SDS (sodium dodecyl sulfate); NaPO4 (sodium phosphate); Tris (tris(hydroxymethyl)-aminomethane); PMSF (phenylmethylsulfonylfluoride); TBE (Tris-Borate-EDTA, e.g., Tris buffer titrated with boric acid rather than HCl and containing EDTA); PBS (phosphate buffered saline); PAGE (polyacrylamide gel electrophoresis); Tween (polyoxyethylene-sorbitan); Hybrid, Inc. (Kitchener, ON); Invitrogen (Carlsbad, Calif.); Clontech (Palo Alto, Calif.); MRC (Cincinnati, Ohio); Roche (Indianapolis, Ind.); Promega (Madison, Wis.); Epicenter (Madison, Wis.); New England Biolabs (Beverly, Mass.); Scleicher & Schuell (Keene, N.H.); Sigma (Saint Louis, Mo.).
Materials and Methods
Turkey Breast Muscle Sampling and Breast Meat Quality Evaluation. Genetically unimproved random-bred control (RBC1) turkeys (McCartney, 1964) were obtained from Dr. K. Nestor (Ohio Agricultural Research and Development Center, Wooster, Ohio). The growth-selected turkeys were obtained from Hybrid, Inc. (Kitchener, ON). Both turkey lines were simultaneously raised from 1 day-old hatchlings to market weight (average weights were 22.8 lbs. for RBC1 turkey line and 30.4 lbs. for the growth-selected turkey line) at the MSU poultry farm. Turkeys were slaughtered according to industry practices. The pectoralis major muscle from one side was collected within 5 minutes of death and was immediately sectioned, snap frozen in liquid nitrogen and stored at −80° C. for total RNA and genomic DNA extraction. The pectoralis major muscle from the remaining side was used to evaluate meat quality indicators including the pH of the muscle at 15 minutes post mortem and the percentage of water loss from the meat at 24 h post mortem (Pietrzak, et al., 1998).
RNA Preparation and PCR Amplification of cDNA. Total RNA was extracted from turkey breast muscle using Trizol reagent (Invitrogen, Carlsbad, Calif.). First strand cDNA was synthesized using SuperScript II RNase H Reverse Transcriptase (Invitrogen) following the manufacturer's protocols. Primers used in the reverse transcription and PCR were designed by using the CODEHOP program (Rose, et al., 1998). The sequence for the forward primer was 5′-CTGCACCAGGAGGGCCACATGGACGA-3′ [SEQ ID NO: 13] and for the reverse primer was 5′-CGGTCCAGTTTGCACCAGCCAGTCCAGG-3′ [SEQ ID NO: 14]. The PCR amplification was conducted using Advantage cDNA polymerase (Clontech, Palo Alto, Calif.) and the first strand cDNA as template. The amplification consisted of an initial denaturation at 94° C. for 1 minute followed by 35 cycles of 94° C. for 20 sec, 63° C. for 20 sec and 68° C. for 1 min and a final extension at 68° C. for 5 minutes.
Isolation and PCR Amplification of Genomic DNA. Genomic DNA was isolated from turkey skeletal muscle using DNAzol (MRC, Cincinnati, Ohio) following the manufacturer's protocols. The standard PCR mix, in a final volume of 50 ul, consisted of 100-200 mg of template, 20 nM of primers, 500 uM dNTPs, 1× buffer 1 from the Expand Long Template PCR system (Roche, Indianapolis, Ind.) and 0.75 ul of enzyme mix provided as part of the system. The amplification consisted of an initial denaturation at 94° C. for 1 min followed by 35 cycles at 94° C. for 10 sec, 52° C. for 45 sec 68° C. for 3 min and a final extension at 68° C. for 7 min. Forward and reverse primers were designed based on the turkey aRYR cDNA sequence. The forward primer sequence was 5′-GACGCGTGTCGCTCAGCCGCTCGC-3′ [SEQ ID NO: 15] and the reverse primer sequence was 5′-CCAGCAGCTCATAGAGGAGGTTGACG-3′ [SEQ ID NO: 16].
Cloning and Sequencing of Turkey aRYR. All PCR products were cloned into either pGEM T-Easy (Promega, Madison, Wis.) or pCC1 (Epicenter, Madison, Wis.) vectors following the manufacturer's protocols. Clones were screened, isolated and sequenced on both strands. Some clones were further digested into smaller fragments and subcloned into the pNEB193 vector (New England Biolabs, Beverly, Mass.) to facilitate sequencing.
Restriction Digestion and Hybridization. The insert carrying each aRYR allele was released from the cloning vector through restriction digestion and the insert was further digested with Bam HI and Pst I. The digested fragments were analyzed by agarose gel electrophoresis and transferred to nylon membranes (Nytran, Scleicher & Schuell, Keene, N.H.) for hybridization analysis. Two probes, E12 and E14, used in hybridization were designed based on the turkey aRYR cDNA sequence. These probes correspond to human RYR1 cDNA nucleotides number 1231 to 1348 and numbers 1568 to 1678, respectively. Probes were labeled with digoxigenin-11-dUTP and were detected with an anti-DIG antibody conjugated with alkaline phosphatase (Roche). The color development was conducted by using pre-mixed BCIP/NBT solution (Sigma, Saint Louis, Mo.).
Statistical Analysis. Least squares means of meat quality traits by genotype were compared using the mixed model procedure of SAS with a protected least significant difference test (Freud and Wilson, 1997).
EXAMPLE 1 
Identification of aRYR Transcript Variants in Turkey. To test the hypothesis that mutations in turkey αRYR predispose turkeys to development of PSE meat, we began screening the region corresponding to the 3′ end of mutation hot spot 1 of human RYRI. We identified three transcript variants spanning nucleotides number 1231-1947, corresponding to the human RYR1 cDNA sequence (accession no. Jo5200). The longest transcript (W) shared 70% and 60% amino acid sequence identity with mammalian RYR1 and bullfrog αRYR (Oyamada, et al., 1994), respectively (FIG. 1). Compared to turkey βRYR (our unpublished data) and chicken βRYR (Ottini, et al., 1996), the amino acid sequence identity was 66% and 58%, respectively. The other two transcript variants were characterized by the deletion of either 81-bp (variant AS-81; nucleotides number 1350-1430) or 193-bp (variant AS-193; nucleotides number 1350-1542) from the W transcript. The 81-bp deletion is predicted to result in a 27-amino acid deletion corresponding to SER416-SER443 of human RYR1. These 27 amino acid residues are highly conserved compared with mammalian RYR1, but are less conserved compared with bullfrog, fish and turkey αRYRs. The removal of 193-bp is predicted to lead to a frame-shift which would introduce a premature stop codon after amino acid residue 416. Thus, this transcript variant would not encode a complete functional channel protein. During analysis of the turkey αRYR cDNA sequence between bases 1231-1947, we did not observe any of the point mutations reported for human or porcine MH (Jurkat-Rott, et al., 2000).
EXAMPLE 2 
Two aRYR Genomic DNA Alleles. We next addressed the question of whether the deletions in the aRYR cDNA sequence originate in the genome or were the result of alternative splicing. Upon analysis of the genomic DNA sequence in the region corresponding to W, AS-81 and AS-193, we identified two copies of αRYR from different birds using genomic DNA as template. These alleles differed in size by approximately 1 kb. We refer to these two copies of turkey αRYR genomic DNA as alleles αRYR-I and αRYR-II. Due to the size of the inserts and the abundance of tandem repeated sequences in the introns which made it difficult to design sequencing primers, each allele was digested to smaller fragments with restriction enzymes, subcloned and sequenced. This strategy allowed us to sequence approximately 90% of αRYR-I and 75% of αRYR-II including their complete exon sequences. The turkey αRYR genomic DNA sequence is still unknown; therefore, each intron and exon and exon/intron boundaries of both alleles were identified according to the corresponding intron and exon of the human RYR1 gene (Phillips, et al., 1996). The sequences of both turkey genomic DNA alleles analyzed in this study spanned from the last one-third of exon 12, intron 12, exon 13, intron 13 and to the end of exon 14. Splice junction boundaries agreed with the consensus sequences reported for splice donor sites (starting with GT) and splice acceptor sites (ending with TAG) (Shapiro and Senapathy, 1987).
Each allele was subjected to digestion by two different restriction enzymes, Bam HI and Pst I, and each allele showed a unique digestion pattern for both enzymes. In order to map the location of the restriction fragments, two different probes were used in Southern hybridization analysis. Based on the patterns of digestion and hybridization, we constructed a map for each allele (FIG. 2). According to the Pst I restriction digestion pattern, we estimated that the size of intron 12 in αRYR-II in approximately 1 kb longer than that in αRYR-I and that size of intron 13 in αRYR-I is approximately 100 bp longer than that in αRYR-II. However, sequence analysis showed that exons 12-14 in alleles αRYR-I and αRYR-II were identical.
Sequence comparison of turkey and human genomic DNA indicated that both turkey αRYR alleles were 3 nucleotides shorter than human RYRI in exon 13. The nucleotides numbers in exon 14 of both turkey alleles were the same as in human RYRI. However, the sizes of introns 12 and 13 in both turkey alleles were different from those observed in human RYRI.
EXAMPLE 3 
Expression of αRYR Transcript Variants. cDNA from turkeys (N=76) was screened by RT-PCR to study the expression patterns of the transcript variants. Most birds expressed all three transcript variants but there were birds that expressed W only, W with AS-193 but no AS-81 or AS-81 and AS-193 but no W (FIG. 3). These data were reproducible upon three screening experiments. We have not yet observed any birds expressing only AS-81 or AS-193 or W with AS-81. If birds expressed only AS-193, they probably could not survive because they would not have a functional α channel protein. The presence of a functional β channel does not rescue this deficiency (Airey, et al., 1993). Sequence analysis of both turkey αRYR alleles showed no evidence that the missing nucleotides in the cDNA sequence result from deletion of the analogous residues in the genomic DNA. Therefore, we concluded that the different transcript variants result form alternative splicing. Consistent with this conclusion was the identification in the 81-bp segment of three conserved sequence elements for the 3′ splice site (Black, 2003). These include a special “A” residue followed by a polypyrimidine tract (TCCT), followed by a terminal CAG at the end of 81 bp (FIG. 4). When analyzed using a splice site prediction program (SpliceProximalCheck, EBI, UK), the 3′ end of the 81-bp segment was recognized as a true acceptor site. Compared to the genomic DNA sequence, the three αRYR transcripts were characterized as: 1) the W transcript which carries a deletion of 81 bp located at the beginning of exon 13; 2) the AS-81 transcript which carries a deletion of 193 bp corresponding to the exon 13; 3) and the AS-193 transcript which carries a deletion of 193 bp corresponding to the exon 13. A schematic diagram of the locations of the alternative splicing sites in the turkey αRYR allele and the corresponding splice variants is shown in FIG. 4. The coexistence of W, AS-81 and AS-193 suggests that the use of splicing acceptor sites including the 3′ end of intron 12 and 3′ end of the 81 bp segment and the 3′ end of intron 13 is not mutually exclusive even though they shared the same splice donor site at the 5′ end of intron 12. In addition, to make AS-81 or AS-193, the splice acceptor site at the end of intron 12 is simply skipped and the splice acceptor site in exon 13 or at the end of intron 13 is used.
The physiological significance of the 27-amino acid deletion in the foot domain of turkey RYR is unknown. The deletion occurs within the cytoplasmic clamp domain which has been proposed to serve as part of the protein-protein contact site of RYR1 with the DHPR (Wu, et al., 1997); Baker, et al., 2002). Coupling of the DHPR and RYR in avian skeletal muscle controls the opening and closing of RYR during muscle contraction (O'Brien, et al., 1995). The deletion also occurs in a region which is highly sensitive to amino acid changes as indicated by the clustering of five mutations in this region in human MH (Jurkat-Rott, et al., 2000). Thus, the deletion in RYR may affect the interaction between the RYR and DHPR, which in turn could affect regulation of Ca-release.
It is not clear at this point whether AS-81 transcript variant of turkey RYR can only form homotetrameric channels or if formation of heterotetramers with the wild-type transcript is possible. A recent study showed that a RYR3 splice variant which had a 29-amino acid deletion of His4406-Lys4434 did not form a functional channel when expressed alone in HEK293 cells. However, when it was co-expressed with the wild type RYR3, it formed functional heterotetrameric channels with reduced caffeine sensitivity (Jiang, et al., 2003).
Several transcript variants have been reported in mammalian RYR1 and RYR3; this is the first report of avian RYR transcript variants. Most of the RYR1 or RYR3 transcript variants are characterized by the presence or absence of amino acid residues in either the modulatory or transmembrane domains in the C-terminal half of the protein (Zorzato, et al., 1994; Futatsugi, et al., 1995; Marziali, et al., 1996; Miyatake, et al., 1996; Tosso and Brenig, 1998; Jaing, et al., 2002). There are no previous reports of alternative spicing in the N-terminal domain of RYRI. The two splice regions of rabbit RYR3, located near the 5′-end and the middle, have been identified (Jiang, et al., 2003). Like the 193-bp deletion identified in the N-terminus of turkey αRYR in our study, the latter two splicing products were predicted to result in the synthesis of truncated RYR3 proteins.
EXAMPLE 4 
Distribution and Meat Quality Evaluation of Turkey αRYR Genotypes. Muscle samples from birds were randomly selected (N=35) from the RBC1 and Hybrid lines and screened by PCR to determine their genotypes. Based on the two αRYR alleles, turkeys could be grouped into three different genotypes: birds homozygous for αRYR-I, birds homozygous for αRYR-II and heterozygous birds carrying αRYR-I and αRYR-II alleles (FIG. 5). Based on the genotypes of turkey and the corresponding expression of the mRNA transcript variants, we concluded that birds expressing the transcripts with either 81-bp or 193-bp deletions were either homozygous for αRYR-I or αRYR-II or were heterozygous. This suggests that alternative splicing occurred in transcripts derived from both αRYR alleles. In addition, both homozygous genotypes were identified in random-bred and in growth-selected turkey populations. Homozygous αRYR-I was the most frequent genotype in our random-bred group (56%) whereas the frequencies of αRYR-I and αRYR-II in growth-selected group were approximately equal (47% vs. 41%). The heterozygous birds accounted for less than 12% in both populations. Each genotype was correlated with meat quality traits. PSE turkey meat is characterized by low early postmortem muscle pH and poor water holding capacity due to the denaturation of myosin (Pietrzak, et al., 1997). The 15-minute postmortem pH of muscle from the homozygous αRYR-II genotype (pH15+6.01±0.054, N=12) was significantly higher that the homozygous αRYR-I genotype (pH15=5.80±0.043, N=19; P<0.01). The percentage of exudate between the two homozygous genotypes was not significantly different. However, there appeared to be an association between the αRYR-II genotype and improved water-holding capacity (% exudate+0.53±0.1 for αRYR-II and 0.79±0.08 for αRYR-I genotypes respectively; P+0.056). Because only four heterozygous birds were identified, the statistical analysis was not performed for these birds.
There was no significant relationship between the presence of the alternative splice transcript variants and meat quality. However, we did not quantify the expression of transcript variant. It is possible that environmental factors such as heat stress could alter the ratio of splice variants. Our results suggest that turkeys homozygous for αRYR-I are more likely to develop PSE meat under standard growth and slaughter processes. Additionally, our results show that turkeys homozygous for the αRYR-II genotype exhibited a significantly higher postmortem muscle pH and a better water-holding capacity than the αRYR-I genotype. That is, they showed a significant reduction of PSE meat symptoms.
From the foregoing, it should be obvious that the present invention provides for methods for the selection of turkeys having reduced symptoms of PSE-meat production.

## Claims

1. A method of genotyping turkeys, comprising:
a) providing i) a forward primer and a reverse primer, wherein the sequence of said forward primer is SEQ ID NO:15 and wherein the sequence of said reverse primer is SEQ ID NO:16; and ii) genomic nucleic acid samples from a plurality of turkeys;
b) amplifying said genomic nucleic acid samples with said primers so as to generate amplified products; and
c) visualizing said amplified products on a gel to genotype said plurality of turkeys.

2. The method of claim 1, further comprising d) identifying amplified product consisting of a single band approximately 4 kilobases.

3. The method of claim 1, wherein said nucleic acid samples are obtained from muscle tissue.

4. The method of claim 3, wherein said muscle tissue is turkey breast muscle.

5. The method of claim 1, wherein said samples are taken from slaughtered turkeys.

6. The method of claim 1, wherein said samples are taken from live turkeys.

7. The method of claim 6, wherein said live turkeys identified as generating amplified product consisting of a single band of approximately 4 kilobases are used for breeding.

8. The method of claim 6, wherein said live turkeys are young turkeys.

9. The method of claim 8, wherein said live young turkeys identified as generating amplified product consisting of a single band of approximately 4 kilobases are subsequently grown to maturity.

10. The method of claim 6, wherein said live turkeys are mature turkeys.

11. The method of claim 10, wherein said live mature turkeys identified as generating amplified product consisting of a single band of approximately 4 kilobases are slaughtered for commercial meat production.

12. A method of selecting turkeys for meat production based on genotyping, comprising:
a) providing i) a forward primer and a reverse primer, wherein the sequence of said forward primer is set forth in SEQ ID NO:15 and wherein the sequence of said reverse primer is set forth in SEQ ID NO:16; and ii) genomic nucleic acid samples from a plurality of live turkeys;
b) amplifying said genomic nucleic acid samples with said primers to generate amplified products under conditions such that turkeys with an amplified product consisting of a single band approximately 4 kilobases are identified;
c) selecting said live turkeys identified as in step b) for meat production.

13. The method of claim 12, wherein said nucleic acid samples are obtained from muscle tissue.

14. The method of claim 13, wherein said muscle tissue is turkey breast muscle.

15. The method of claim 12, wherein said selecting for meat production comprises slaughtering said selected turkeys.

16. The method of claim 12, wherein said selecting for meat production comprises utilizing said turkeys identified as in step b) for breeding.

17. The method of claim 12, wherein said live turkeys are young turkeys.

18. The method of claim 17, wherein said selecting for meat production comprises growing said turkeys identified as in step b) to maturity.

19. The method of claim 12, wherein said turkeys not identified as in step b) are not used for meat production.