Patent Publication Number: US-2005118681-A1

Title: Novel regulatory molecule and genetic sequences encoding same

Description:
FIELD OF THE INVENTION  
      The present invention relates generally to a regulatory molecule and to genetic sequences encoding same. More particularly, the present invention provides a molecule involved in, associated with or which otherwise facilitates myogenesis. In a particularly preferred embodiment, the regulatory molecule is a transcription factor involved in the expression of genes resulting in the determination of skeletal muscle. The identification of the regulatory molecule of the present invention permits the development of agents capable of modulating myogenesis including therapeutic agents capable of ameliorating aberrations in myogenesis such as but not limited to myogenic cancers.  
     BACKGROUND OF THE INVENTION  
      Bibliographic details of the publications numerically referred to in this specification are collected at the end of the description.  
      The exploitation of recombinant DNA technology in the treatment and prophylaxis of disease conditions requires a level of understanding of regulatory mechanisms involved in gene expression commensurate with the complexity of the genetic disorder to be treated. This is particularly the case for the myriad of regulatory molecules involved in cell fate determination and tissue differentiation during developmental processes.  
      One important class of regulatory molecules are members of the basic helix-loop-helix (bHLH) family of transcription factor proteins which are involved in cellular proliferation and differentiation during developmental processes including haemopoiesis, myogenesis and neurogenesis (1, 2). These proteins share a common sequence motif consisting of a basic (b) region and an adjacent helix-loop-helix (HLH) structure. The b region is important for DNA binding while the HLH domain mediates dimerization (3, 4).  
      Myogenic-specific bHLH proteins are involved in the activation of genes required for proper vertebrate development. bHLH proteins MyoD, Myf-5, Myf-4 and myogenin interact with class I HLH proteins.  
      bHLH proteins are also involved in antigen dependent B-cell differentiation. ABF-1 is a bHLH protein capable of binding with the product of the E2A gene to the E2 box elements of the b region of ABF-1.  
      In work leading up to the present invention, the inventors sought to identify other bHLH genes. The inventors have identified a gene having nucleotide sequence similarity to ABF-1 but which is involved in myogenesis.  
     SUMMARY OF THE INVENTION  
      Throughout this specification, unless the context requires otherwise, the word “comprise”, or variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated element or integer or group of elements or integers but not the exclusion of any other element or integer or group of elements or integers.  
      The subject specification contains nucleotide and amino acid sequence information prepared using the programme PatentIn Version 2.0, presented herein after the bibliography. Each nucleotide or amino acid sequence is identified in the sequence listing by the numeric indicator &lt;210&gt; followed by the sequence identifier (e.g. &lt;210&gt;1, &lt;210&gt;2, etc). The length, type of sequence (DNA, protein (PRT), etc) and source organism for each nucleotide or amino acid sequence are indicated by information provided in the numeric indicator fields &lt;211&gt;, &lt;212&gt; and &lt;213&gt;, respectively. Nucleotide and amino acid sequences referred to in the specification are defined by the information provided in numeric indicator field &lt;400&gt; followed by the sequence identifier (eg. &lt;400&gt;1, &lt;400&gt;2, etc).  
      One aspect of the present invention provides an isolated nucleic acid molecule encoding a regulatory protein involved in, associated with or which otherwise facilitates the activation of genes involved in myogenesis, said regulatory protein lacking the alanine-threonine myogenic recognition motif.  
      Another aspect of the present invention contemplates an isolated nucleic acid molecule comprising a sequence of nucleotides encoding or a complementary sequence of nucleotides encoding the amino acid sequence substantially as set forth in &lt;400&gt;2 or an amino acid sequence having at least 60% identity thereto, wherein said nucleic acid molecule encodes a protein involved in, associated with or which otherwise facilitates the activation of genes involved in myogenesis but which lacks the alanine-threonine myogenic recognition motif.  
      Still another aspect of the present invention is directed to an isolated nucleic acid molecule comprising a sequence of nucleotides or a complementary sequence of nucleotides substantially as set forth in &lt;400&gt;1 or a sequence having at least 60% identity thereto or which is capable of hybridizing to &lt;400&gt;1 under low stringency conditions at 42° C., wherein said nucleic acid molecule encodes a protein involved in, associated with or which otherwise facilitates the activation of genes involved in myogenesis but which lacks the alanine-threonine myogenic recognition motif.  
      Yet another aspect of the present invention contemplates an isolated protein or a functional derivative thereof comprising a sequence of amino acids substantially as set forth in &lt;400&gt;2 or an amino acid sequence having at least about 60% similarity to &lt;400&gt;2 wherein said protein is involved in, associated with or which otherwise facilitates activation of genes involved with myogenesis and lacks the alanine-threonine myogenic recognition motif found in the myogenic regulatory factors myoD, mrf-4, mrf-5 and myogenin (25).  
      The nucleic acid of the present invention is referred to herein as “musculin”. The product of the musculin gene is “musculin”.  
    
    
     BRIEF DESCRIPTION OF THE FIGURES  
       FIG. 1  is a representation of (A) nucleotide sequence (&lt;400&gt;1) and deduced amino acid sequence (&lt;400&gt;2) of murine musculin. (B) Comparison of the predicted musculin bHLH amino acid sequence with selected bHLH factors. Amino acid identities are shown as white on black. The myogenic (AT) recognition motif is shaded. References for the protein sequences are as follows: [6, 7, 12-18]. (C)RNase protection analysis of adult murine tissues with a musculin riboprobe (nt 306-524). Probe, full length probe; t-RNA, probe after RNase digestion; ES cells, embryonic stem cells.  
       FIG. 2  is a photographic representation of expression of musculin in the developing murine embryo. (A-C) expression of musculin in (A) 9.5 days post coitus (dpc), (B) 10.5 dpc (C) 11.5 dpc embryos, detected by in situ hybridization with digoxigenin-labelled musculin riboprobes. Arrow: musculin expression in mesoderm adjacent to foregut and midgut endoderm. Arrow heads: musculin expression in the branchial arches. (D) traverse section of 9.5 dpc embryo after in situ hybridization with a musculin riboprobe. Arrow: region of mesoderm indicated in (A); mg, midgut; nt, neural tube, pc, peritoneal cavity. (E) Transverse section of myotome of 11.5 dpc embryo after in situ hybridization with a musculin riboprobe. Expression is seen in the epaxial dermomyotomal lip, drg, dorsal root ganglion; m, myotome; nt, neural tube. (F, G) Sagittal section of a 14.5 dpc embryo, hybridized with sense control (F) and antisense (G) { 32 P}-radiolabelled musculin riboprobes. fl, fetal liver. (H) Lateral sagittal section of 18.5 dpc embryo, probed with an antisense musculin riboprobe. The signal in dermis was also seen in sections hybridized with a sense probe and is an artefact. (I) Section of latissimus dorsi muscle in a 14.5 dpc embryo showing localization of musculin expression in a subset of muscle fibres. 
    
    
     DETAIL DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      The present invention is predicated in part on the identification of a regulatory gene termed “musculin” involved in myogenesis.  
      Reference herein to “musculin” includes reference to all mammalian functional homologues as well as all derivatives thereof.  
      Accordingly, one aspect of the present invention provides an isolated nucleic acid molecule encoding a regulatory protein involved in, associated with or which otherwise facilitates the activation of genes involved in myogenesis, said regulatory protein lacking the alanine-threonine myogenic recognition motif.  
      The term “protein” includes a polypeptide or peptide.  
      Preferably, the nucleic acid molecule, musculin, encodes the amino acid sequence set forth in &lt;400&gt;2.  
      Accordingly, another aspect of the present invention is directed to an isolated nucleic acid molecule comprising a sequence of nucleotides encoding or a complementary sequence of nucleotides encoding the amino acid sequence substantially as set forth in &lt;400&gt;2 or an amino acid sequence having at least 60% identity thereto, wherein said nucleic acid molecule encodes a protein involved in, associated with or which otherwise facilitates the activation of genes involved in myogenesis but which lacks the alanine-threonine myogenic recognition motif.  
      More particularly, the present invention contemplates an isolated nucleic acid molecule comprising a sequence of nucleotides or a complementary sequence of nucleotides substantially as set forth in &lt;400&gt;1 or a sequence having at least 60% identity thereto or which is capable of hybridizing to &lt;400&gt;1 under low stringency conditions at 42° C., wherein said nucleic acid molecule encodes a protein involved in, associated with or which otherwise facilitates the activation of genes involved in myogenesis but which lacks the alanine-threonine myogenic recognition motif.  
      The musculin may be in DNA (e.g. cDNA or genomic DNA), RNA (e.g. mRNA) or hybrid DNA:RNA form. The nucleic acid molecule of the present invention does not correspond to ABF-1 and is not a functional homologue of ABF-1 notwithstanding their structural homology.  
      In a particularly preferred embodiment, the present invention provides an isolated protein or a functional derivative thereof comprising a sequence of amino acids substantially as set forth in &lt;400&gt;2 or an amino acid sequence having at least about 60% similarity to &lt;400&gt;2 wherein said protein is involved in, associated with or which otherwise facilitates activation of genes involved with myogenesis and lacks the alanine-threonine myogenic recognition motif.  
      The term “identity” is used in its broadest sense to include the number of exact nucleotide or amino acid matches having regard to an appropriate alignment using a standard algorithm, such as but not limited to the Geneworks program (Intelligenetics).  
      The nucleotide sequence of &lt;400&gt; 1  corresponds to musculin. The amino acid sequence of &lt;400&gt;2 corresponds to musculin.  
      Reference herein to a low stringency at 42° C. includes and encompasses from at least about 1% v/v to at least about 15% v/v formamide and from at least about 1M to at least about 2M salt for hybridisation, and at least about 1M to at least about 2M salt for washing conditions. Alternative stringency conditions may be applied where necessary, such as medium stringency, which includes and encompasses from at least about 16% v/v to at least about 30% v/v formamide and from at least about 0.5M to at least about 0.9M salt for hybridisation, and at least about 0.5M to at least about 0.9M salt for washing conditions, or high stringency, which includes and encompasses from at least about 31% v/v to at least about 50% v/v formamide and from at least about 0.01M to at least about 0.15M salt for hybridisation, and at least about 0.01M to at least about 0.15M salt for washing conditions. In general, washing is carried out at T m =69.3+0.41 (G+C) % [19]=−12° C. However, the T m  of a duplex DNA decreases by 1° C. with every increase of 1% in the number of mismatched based pairs (20).  
      Although the musculin of the present invention is exemplified in relation to the gene in murine species, the present invention extends to functional homologues in human and other non-human animals such as in primates, laboratory test animals (e.g. rates, rabbits, guinea pigs, hamsters), companion animals (e.g. dogs, cats), livestock animals (e.g. sheep, pigs, horses, donkeys, cows) and captive wild animals (e.g. deer, fox).  
      The present invention further extends to single or multiple nucleotide substitutions, deletions and/or additions to the nucleotide sequence set forth in &lt;400&gt;1. Such substitutions, deletions and/or additions of nucleotides defining musculin are encompassed by the term “derivatives” which covers mutants, fragments, parts and segments of the musculin nucleotide sequence.  
      A derivative of the musculin of the present invention also includes nucleic acid molecules capable of hybridizing to the nucleotide sequence set forth in &lt;400&gt;1 under low stringency conditions at 42° C. The present invention extends to alternative levels of stringency such as medium and high.  
      The derivatives of the nucleic acid molecule of the present invention include oligonucleotides, PCR primers, antisense molecules, molecules suitable for use in co-suppression and fusion nucleic acid molecules. Ribozymes are also contemplated by the present invention directed to musculin.  
      The nucleic acid molecules of the present invention may be ligated to an expression vector capable of expression in a prokaryotic cell (e.g.  E coli ) or a eukaryotic cell (e.g. yeast cells, fungal cells, insect cells, mammalian cells or plant cells).  
      In accordance with the present invention, it is proposed that mutations in musculin cause, facilitate or contribute to aberrations in muscle development. The cloning of this gene now provides a means for genetic screening for myogenic disease conditions. Myogenic disease conditions include but are not limited to myopathics and muscular dystrophies such as hereditary, inflammatory, endocrine, metabolic and toxic disorders. Myogenic disease conditions also extend to neuromuscular and skeletomuscular disorders.  
      Genetic screening may be conducted by determining full expression or full-length transcript production by Northern blot, cloning and sequencing of the musculin or identifying mutations by oligonucleotide hybridisation or by direct sequencing of PCR products of the musculin. In addition, the present invention extends to nucleic acid molecules having translation-terminating mutations leading to truncation mutants. The detection of truncation mutants may be important for genetic analysis of people with myogenic disease conditions or with a propensity to develop myogenic disease conditions, determined on, for example, hereditary grounds. Truncated 110 musculin translation products may also be useful in developing therapeutic agents such as antagonists or for developing antibodies. Truncational mutants may be readily detected by a direct protein truncation test. See for example Van der Luut et al (11). In essence, DNA fragments including PCR products or corresponding mRNA molecules are subjected to in vitro translation and optionally also transcription and the translation products assayed by, for example, SDS-PAGE or by differential antibody binding assays. This assay may also be employed to screen for agents capable of inducing truncation mutations or for acting as antagonists for truncation mutant-inducing agents.  
      Alternatively, the expression product of musculin (i.e. musculin), may be assayed by, for example, antibody screening such as in an ELISA.  
      Accordingly, another aspect of the present invention provides a proteinaceous molecule having an amino acid sequence substantially as set forth in &lt;400&gt;2 or having at least about 60% identity thereto. The amino acid sequence of &lt;400&gt;2 corresponds to musculin. The present invention also encompasses derivatives of musculin such as amino acid substitutions, deletions and/or additions to the musculin amino acid sequence. Particularly important derivatives include antigenic fragments and analogues useful in immunoassays and as therapeutic agents as well as other fragments carrying B cell and/or T cell linear or conformational epitopes. “Additions” to the amino acid sequence include fusion with peptides, polypeptides and proteins.  
      Analogues of musculin contemplated herein include, but are not limited to, modification to side chains, incorporating of unnatural amino acids and/or their derivatives during peptide, polypeptide or protein synthesis and the use of crosslinkers and other methods which impose conformational constraints on the proteinaceous molecule or their analogues. Such chemical analogues may be useful in providing stable means for diagnostic purposes or for producing agonists or antagonists or for producing stable molecules for use in natural product screening.  
      Examples of side chain modifications contemplated by the present invention include modifications of amino groups such as by reductive alkylation by reaction with an aldehyde followed by reduction with NaBH 4 ; amidination with methylacetimidate; acylation with acetic anhydride; carbamoylation of amino groups with cyanate; trinitrobenzylation of amino groups with 2, 4, 6-trinitrobenzene sulphonic acid (TNBS); acylation of amino groups with succinic anhydride and tetrahydrophthalic anhydride; and pyridoxylation of lysine with pyridoxal-5-phosphate followed by reduction with NaBH 4 .  
      The guanidine group of arginine residues may be modified by the formation of heterocyclic condensation products with reagents such as 2,3-butanedione, phenylglyoxal and glyoxal.  
      The carboxyl group may be modified by carbodiimide activation via O-acylisourea formation followed by subsequent derivitisation, for example, to a corresponding amide.  
      Sulphydryl groups may be modified by methods such as carboxymethylation with iodoacetic acid or iodoacetamide; performic acid oxidation to cysteic acid; formation of a mixed disulphides with other thiol compounds; reaction with maleimide, maleic anhydride or other substituted maleimide; formation of mercurial derivatives using 4-chloromercuribenzoate, 4-chloromercuriphenylsulphonic acid, phenylmercury chloride, 2-chloromercuri-4-nitrophenyl and other mercurials; carbamoylation with cyanate at alkaline pH.  
      Tryptophan residues may be modified by, for example, oxidation with N-bromosuccinimide or alkylation of the indole ring with 2-hydroxy-5-nitrobenzyl bromide or sulphenyl halides. Tyrosine residues on the other hand, may be altered by nitration with tetranitromethane to form a 3-nitrotyrosine derivative.  
      Modification of the imidazole ring of a histidine residue may be accomplished by alkylation with iodoacetic acid derivatives or N-carbethoxylation with diethylpyrocarbonate.  
      Examples of incorporating unnatural amino acids and derivatives during peptide synthesis include, but are not limited to, use of norleucine, 4-amino butyric acid, 4-amino-3-hydroxy-5 phenylpentanoic acid, 6-aminohexanoic acid, t-butylglycine, norvaline, phenylglycine, omithine, sarcosine, 4-amino-3-hydroxy-6-methylheptanoic acid, 2-thienyl alanine and/or D-isomers of amino acids. A list of unnatural amino acids, contemplated herein is shown in Table  
                           TABLE 1                                   Non-conventional               amino acid   Code                          α-aminobutyric acid   Abu           α-amino-α-methylbutyrate   Mgabu           aminocyclopropane-   Cpro           carboxylate           aminoisobutyric acid   Aib           aminonorbornyl-   Norb           carboxylate           cyclohexylalanine           cyclopentylalanine   Cpen           D-alanine   Dal           D-arginine   Darg           D-aspartic acid   Dasp           D-cysteine   Dcys           D-glutamine   Dgln           D-glutamic acid   Dglu           D-histidine   Dhis           D-isoleucine   Dile           D-leucine   Dleu           D-lysine   Dlys           D-methionine   Dmet           D-ornithine   Dorn           D-phenylalanine   Dphe           D-proline   Dpro           D-serine   Dser           D-threonine   Dthr           D-tryptophan   Dtrp           D-tyrosine   Dtyr           D-valine   Dval           D-α-methylalanine   Dmala           D-α-methylarginine   Dmarg           D-α-methylasparagine   Dmasn           D-α-methylaspartate   Dmasp           D-α-methylcysteine   Dmcys           D-α-methylglutamine   Dmgln           D-α-methylhistidine   Dmhis           D-α-methylisoleucine   Dmile           D-α-methylleucine   Dmleu           D-α-methyllysine   Dmlys           D-α-methylmethionine   Dmmet           D-α-methylornithine   Dmorn           D-α-methylphenylalanine   Dmphe           D-α-methylproline   Dmpro           D-α-methylserine   Dmser           D-α-methylthreonine   Dmthr           D-α-methyltryptophan   Dmtrp           D-α-methyltyrosine   Dmty           D-α-methylvaline   Dmval           D-N-methylalanine   Dnmala           D-N-methylarginine   Dnmarg           D-N-methylasparagine   Dnmasn           D-N-methylaspartate   Dnmasp           D-N-methylcysteine   Dnmcys           D-N-methylglutamine   Dnmgln           D-N-methylglutamate   Dnmglu           D-N-methylhistidine   Dnmhis           D-N-methylisoleucine   Dnmile           D-N-methylleucine   Dnmleu           D-N-methyllysine   Dnmlys           N-methylcyclohexylalanine   Nmchexa           D-N-methylornithine   Dnmorn           N-methylglycine   Nala           N-methylaminoisobutyrate   Nmaib           N-(1-methylpropyl)glycine   Nile           N-(2-methylpropyl)glycine   Nleu           D-N-methyltryptophan   Dnmtrp           D-N-methyltyrosine   Dnmtyr           D-N-methylvaline   Dnmval           γ-aminobutyric acid   Gabu           L-t-butylglycine   Tbug           L-ethylglycine   Etg           L-homophenylalanine   Hphe           L-α-methylarginine   Marg           L-α-methylaspartate   Masp           L-α-methylcysteine   Mcys           L-α-methylglutamine   Mgln           L-α-methylhistidine   Mhis           L-α-methylisoleucine   Mile           L-α-methylleucine   Mleu           L-α-methylmethionine   Mmet           L-α-methylnorvaline   Mnva           L-α-methylphenylalanine   Mphe           L-α-methylserine   Mser           L-α-methyltryptophan   Mtrp           L-α-methylvaline   Mval           N-(N-(2,2-diphenylethyl)   Nnbhm           carbamylmethyl)glycine           1-carboxy-1-(2,2-diphenyl-   Nmbc           ethylamino)cyclopropane           L-N-methylalanine   Nmala           L-N-methylarginine   Nmarg           L-N-methylasparagine   Nmasn           L-N-methylaspartic acid   Nmasp           L-N-methylcysteine   Nmcys           L-N-methylglutamine   Nmgln           L-N-methylglutamic acid   Nmglu           Chexa L-N-methylhistidine   Nmhis           L-N-methylisolleucine   Nmile           L-N-methylleucine   Nmleu           L-N-methyllysine   Nmlys           L-N-methylmethionine   Nmmet           L-N-methylnorleucine   Nmnle           L-N-methylnorvaline   Nmnva           L-N-methylornithine   Nmorn           L-N-methylphenylalanine   Nmphe           L-N-methylproline   Nmpro           L-N-methylserine   Nmser           L-N-methylthreonine   Nmthr           L-N-methyltryptophan   Nmtrp           L-N-methyltyrosine   Nmtyr           L-N-methylvaline   Nmval           L-N-methylethylglycine   Nmetg           L-N-methyl-t-butylglycine   Nmtbug           L-norleucine   Nle           L-norvaline   Nva           α-methyl-aminoisobutyrate   Maib           α-methyl-γ-aminobutyrate   Mgabu           α-methylcyclohexylalanine   Mchexa           α-methylcylcopentylalanine   Mcpen           α-methyl-α-napthylalanine   Manap           α-methylpenicillamine   Mpen           N-(4-aminobutyl)glycine   Nglu           N-(2-aminoethyl)glycine   Naeg           N-(3-aminopropyl)glycine   Norn           N-amino-α-methylbutyrate   Nmaabu           α-napthylalanine   Anap           N-benzylglycine   Nphe           N-(2-carbamylethyl)glycine   Ngln           N-(carbamylmethyl)glycine   Nasn           N-(2-carboxyethyl)glycine   Nglu           N-(carboxymethyl)glycine   Nasp           N-cyclobutylglycine   Ncbut           N-cycloheptylglycine   Nchep           N-cyclohexylglycine   Nchex           N-cyclodecylglycine   Ncdec           N-cylcododecylglycine   Ncdod           N-cyclooctylglycine   Ncoct           N-cyclopropylglycine   Ncpro           N-cycloundecylglycine   Ncund           N-(2,2-diphenylethyl)glycine   Nbhm           N-(3,3-diphenylpropyl)glycine   Nbhe           N-(3-guanidinopropyl)glycine   Narg           N-(1-hydroxyethyl)glycine   Nthr           N-(hydroxyethyl))glycine   Nser           N-(imidazolylethyl))glycine   Nhis           N-(3-indolylyethyl)glycine   Nhtrp           N-methyl-γ-aminobutyrate   Nmgabu           D-N-methylmethionine   Dnmmet           N-methylcyclopentylalanine   Nmcpen           D-N-methylphenylalanine   Dnmphe           D-N-methylproline   Dnmpro           D-N-methylserine   Dnmser           D-N-methylthreonine   Dnmthr           N-(1-methylethyl)glycine   Nval           N-methyla-napthylalanine   Nmanap           N-methylpenicillamine   Nmpen           N-(p-hydroxyphenyl)glycine   Nhtyr           N-(thiomethyl)glycine   Ncys           penicillamine   Pen           L-α-methylalanine   Mala           L-α-methylasparagine   Masn           L-α-methyl-t-butylglycine   Mtbug           L-methylethylglycine   Metg           L-α-methylglutamate   Mglu           L-α-methylhomophenylalanine   Mhphe           N-(2-methylthioethyl)glycine   Nmet           L-α-methyllysine   Mlys           L-α-methylnorleucine   Mnle           L-α-methylornithine   Morn           L-α-methylproline   Mpro           L-α-methylthreonine   Mthr           L-α-methyltyrosine   Mtyr           L-N-methylhomophenylalanine   Nmhphe           N-(N-(3,3-diphenylpropyl)   Nnbhe           carbamylmethyl)glycine                      
 
      Crosslinkers can be used, for example, to stabilise 3D conformations, using homo-bifunctional crosslinkers such as the bifunctional imido esters having (CH 2 ) n  spacer groups with n=1 to n=6, glutaraldehyde, N-hydroxysuccinimide esters and hetero-bifunctional reagents which usually contain an amino-reactive moiety such as N-hydroxysuccinimide and another group specific-reactive moiety such as maleimido or dithio moiety (SH) or carbodiimide (COOH). In addition, peptides can be conformationally constrained by, for example, incorporation of C α  and N α -methylamino acids, introduction of double bonds between  α C and  β C atoms of amino acids and the formation of cyclic peptides or analogues by introducing covalent bonds such as forming an amide bond between the N and C termini, between two side chains or between a side chain and the N or C terminus.  
      The present invention further contemplates chemical analogues of musculin capable of acting as antagonists or agonists of musculin or which can act as functional analogues of musculin. Chemical analogues may not necessarily be derived from musculin but may share certain conformational similarities. Alternatively, chemical analogues may be specifically designed to mimic certain physiochemical properties of musculin. Chemical analogues may be chemically synthesised or may be detected following, for example, natural product screening. Useful sources for screening for natural products include coral, reefs, sea beds, river beds, plants, microorganisms and aquatic and antarctic environments.  
      The identification of musculin permits the generation of a range of therapeutic molecules capable of modulating expression of musculin or modulating the activity of musculin. Modulators contemplated by the present invention includes agonists and antagonists of musculin expression. Antagonists of musculin expression include antisense molecules, ribozymes and co-suppression molecules. Agonists include molecules which increase promoter activity or interfere with negative regulatory mechanisms. Agonists of musculin include molecules which overcome any negative regulatory mechanism. Antagonists of musculin include antibodies and inhibitor peptide fragments.  
      In accordance with the present invention, it is proposed that musculin functions as a regulatory-type molecule in myogenesis. Hereditary myogenic cancers can arise with a mutation in the wild-type gene. The present invention extends to the use of modulating levels of expression of musculin or musculin in the context of regulating myogenesis.  
      Accordingly, another embodiment of the present invention contemplates a method for modulating expression of musculin in a human, said method comprising contacting musculin with an effective amount of a modulator of musculin expression for a time and under conditions sufficient to up-regulate or down-regulate or otherwise modulate expression of musculin. For example, a nucleic acid molecule encoding musculin or a derivative thereof may be introduced into a cell to enhance the ability of that cell to survive, conversely, musculin antisense sequences such as oligonucleotides may be introduced to decrease the survival capacity of any cell expressing an endogenous musculin.  
      Another aspect of the present invention contemplates a method of modulating activity of musculin in a human, said method comprising administering to said human a modulating effective amount of a molecule for a time and under conditions sufficient to increase or decrease the activity of musculin. The molecule may be a proteinaceous molecule or a chemical entity and may also be a derivative of musculin or a receptor thereof or a chemical analogue or truncation mutant of musculin or a receptor thereof. The present invention extends to these methods being applied in non-human mammals.  
      Both increased and decreased musculin expression or musculin activity may be important depending on the condition to be treated.  
      Accordingly, the present invention contemplates a pharmaceutical composition comprising musculin or a derivative thereof or a modulator of musculin expression or musculin activity and one or more pharmaceutically acceptable carriers and/or diluents. These components are referred to herein as the “active ingredients”.  
      The pharmaceutical forms suitable for injectable use include sterile aqueous solutions (where water soluble) and sterile powders for the extemporaneous preparation of sterile injectable solutions. It must be stable under the conditions of manufacture and storage and must be preserved against the contaminating action of microorganisms such as bacteria and fingi. The carrier can be a solvent or, for example, water, ethanol, polyol (for example, glycerol, propylene glycol and liquid polyethylene glycol, and the like) or suitable mixtures thereof as well as vegetable oils. The preventions of the action of microorganisms can be brought about by various antibacterial and antifungal agents, for example, parabens, chlorobutanol, phenyl, sorbic acid, thirmersal and the like. In many cases, it will be preferable to include isotonic agents, for example, sugars or sodium chloride. Prolonged absorption of the injectable compositions can be brought about by the use in the compositions of agents delaying absorption, for example, aluminum monostearate and gelatin.  
      Sterile injectable solutions are prepared by incorporating the active compounds in the required amount in the appropriate solvent with various of the other ingredients enumerated above, as required, followed by filtered sterilization. In the case of sterile powders for the preparation of sterile injectable solutions, the preferred methods of preparation are vacuum drying and the freeze-drying technique which yield a powder of the active ingredient plus any additional desired ingredient from previously sterile-filtered solution thereof.  
      When the active ingredients are suitably protected they may be orally administered, for example, with an inert diluent or with an assimilable edible carrier, or it may be enclosed in hard or soft shell gelatin capsule, or it may be compressed into tablets, or it may be incorporated directly with the food of the diet. For oral therapeutic administration, the active compound may be incorporated with excipients and used in the form of ingestible tablets, buccal tablets, troches, capsules, elixirs, suspensions, syrups, wafers, and the like. Such compositions and preparations should contain at least 1% by weight of active compound. The percentage of the compositions and preparations may, of course, be varied and may conveniently be between about 5 to about 80% of the weight of the unit. The amount of active compound in such therapeutically useful compositions in such that a suitable dosage will be obtained. Preferred compositions or preparations according to the present invention are prepared so that an oral dosage unit form contains between about 0.1 μg and 2000 mg of active ingredient.  
      The tablets, troches, pills, capsules and the like may also contain the components as listed hereafter: a binder such as gum, acacia, corn starch or gelatin; excipients such as dicalcium phosphate; a disintegrating agent such as corn starch, potato starch, alginic acid and the like; a lubricant such as magnesium stearate; and a sweetening agent such a sucrose, lactose or saccharin may be added or a flavouring agent such as peppermint, oil of wintergreen, or cherry flavouring. When the dosage unit form is a capsule, it may contain, in addition to materials of the above type, a liquid carrier. Various other materials may be present as coatings or to otherwise modify the physical form of the dosage unit. For instance, tablets, pills, or capsules may be coated with shellac, sugar or both. A syrup or elixir may contain the active compound, sucrose as a sweetening agent, methyl and propylparabens as preservatives, a dye and flavouring such as cherry or orange flavour. Of course, any material used in preparing any dosage unit form should be pharmaceutically pure and substantially non-toxic in the amounts employed. In addition, the active compound(s) may be incorporated into sustained-release preparations and formulations.  
      Pharmaceutically acceptable carriers and/or diluents include any and all solvents, dispersion media, coatings, antibacterial and antifungal agents, isotonic and absorption delaying agents and the like. The use of such media and agents for pharmaceutically active substances is well known in the art. Except insofar as any conventional media or agent is incompatible with the active ingredient, use thereof in the therapeutic compositions is contemplated. Supplementary active ingredients can also be incorporated into the compositions.  
      It is especially advantageous to formulate parenteral compositions in dosage unit form for ease of administration and uniformity of dosage. Dosage unit form as used herein refers to physically discrete units suited as unitary dosages for the mammalian subjects to be treated; each unit containing a predetermined quantity of active material calculated to produce the desired therapeutic effect in association with the required pharmaceutical carrier. The specification for the novel dosage unit forms of the invention are dictated by and directly dependent on (a) the unique characteristics of the active material and the particular therapeutic effect to be achieved, and (b) the limitations inherent in the art of compounding such an active material for the treatment of disease in living subjects having a diseased condition in which bodily health is impaired.  
      The principal active ingredient is compounded for convenient and effective administration in effective amounts with a suitable pharmaceutically acceptable carrier in dosage unit form as hereinbefore disclosed. A unit dosage form can, for example, contain the principal active compound in amounts ranging from 0.5 μg to about 2000 mg. Expressed in proportions, the active compound is generally present in from about 0.5 μg to about 2000 mg/ml of carrier. In the case of compositions containing supplementary active ingredients, the dosages are determined by reference to the usual dose and manner of administration of the said ingredients. It is also convenient to represent the effective amounts of active ingredients as an amount per kg body weight. For example, the present invention encompasses effective amounts from about 0.005 μg/kg body weight to about 200 mg/kg body weight or from about 0.01 μg/kg body weight to about 20 mg/kg body weight or about 0.1 μg/kg body weight about 15 mg/kg body weight.  
      The pharmaceutical composition may also comprise genetic molecules such as a vector capable of transfecting target cells where the vector carries a nucleic acid molecule capable of modulating musculin expression or musculin activity. The vector may, for example, be a viral vector.  
      Still another aspect of the present invention is directed to antibodies to musculin and its derivatives. Such antibodies may be monoclonal or polyclonal and may be selected from naturally occurring antibodies to musculin or may be specifically raised to musculin or derivatives thereof. In the case of the latter, musculin or its derivatives may first need to be associated with a carrier molecule. The antibodies to musculin or its derivatives of the present invention are particularly useful as therapeutic or diagnostic agents.  
      For example, musculin and its derivatives can be used to screen for naturally occurring antibodies to musculin. These may occur, for example in some autoimmune diseases. Alternatively, specific antibodies can be used to screen for musculin. Techniques for such assays are well known in the art and include, for example, sandwich assays and ELISA. Knowledge of musculin levels may be important for diagnosis of myogenic disorders or a predisposition to developing myogenic disorders or for monitoring certain therapeutic protocols.  
      Antibodies to the musculin of the present invention may be monoclonal or polyclonal. Alternatively, fragments of antibodies may be used such as Fab fragments. Furthermore, the present invention extends to recombinant and synthetic antibodies and to antibody hybrids. A “synthetic antibody” is considered herein to include fragments and hybrids of antibodies. The antibodies of this aspect of the present invention are particularly useful for immunotherapy and may also be used as a diagnostic tool for assessing cell apoptosis or monitoring the program of a therapeutic regimum.  
      For example, specific antibodies can be used to screen for the musculin gene translation product proteins. The latter would be important, for example, as a means for screening for levels of musculin in a cell extract or other biological fluid or purifying the musculin gene translation product made by recombinant means from culture supernatant fluid. Techniques for the assays contemplated herein are known in the art and include, for example, sandwich assays and ELISA.  
      It is within the scope of this invention to include any second antibodies (monoclonal, polyclonal or fragments of antibodies or synthetic antibodies) directed to the first mentioned antibodies discussed above. Both the first and second antibodies may be used in detection assays or a first antibody may be used with a commercially available anti-immunoglobulin antibody. An antibody as contemplated herein includes any antibody specific to any region of musculin.  
      Both polyclonal and monoclonal antibodies are obtainable by immunization with the enzyme or protein and either type is utilizable for immunoassays. The methods of obtaining both types of sera are well known in the art. Polyclonal sera are less preferred but are relatively easily prepared by injection of a suitable laboratory animal with an effective amount of the tumour suppression gene translation product, or antigenic parts thereof, collecting serum from the animal, and isolating specific sera by any of the known immunoadsorbent techniques. Although antibodies produced by this method are utilizable in virtually any type of immunoassay, they are generally less favoured because of the potential heterogeneity of the product.  
      The use of monoclonal antibodies in an immunoassay is particularly preferred because of the ability to produce them in large quantities and the homogeneity of the product. The preparation of hybridoma cell lines for monoclonal antibody production derived by fusing an immortal cell line and lymphocytes sensitized against the immunogenic preparation can be done by techniques which are well known to those who are skilled in the art (see, for example references 8, 9, 10).  
      Another aspect of the present invention contemplates a method for detecting musculin in a biological sample from a subject said method comprising contacting said biological sample with an antibody specific for musculin or its derivatives or homologues for a time and under conditions sufficient for an antibody-musculin complex to form, and then detecting said complex.  
      The presence of musculin may be accomplished in a number of ways such as by Western blotting and ELISA procedures. A wide range of immunoassay techniques are available as can be seen by reference to U.S. Pat. Nos. 4,016,043, 4, 424,279 and 4,018,653. These include both single-site and two-site or “sandwich”-assays of the non-competitive types, as well as in the traditional competitive binding assays. These assays also include direct binding of a labelled antibody to a target.  
      Sandwich assays are among the most useful and commonly used assays and are favoured for use in the present invention. A number of variations of the sandwich assay technique exist and all are intended to be encompassed by the present invention. Briefly, in a typical forward assay, an unlabelled antibody is immobilized to a solid substrate and the sample to be tested brought into contact with the bound molecule. After a suitable period of incubation, for a period of time sufficient to allow formation of an antibody-antigen complex, a second antibody specific to the antigen, labelled with a reporter molecule capable of producing a detectable signal is then added and incubated, allowing time sufficient for the formation of another complex of antibody-antigen-labelled antibody. Any unreacted material is washed away and the presence of the antigen is determined by observation of a signal produced by the reporter molecule. The results may either be qualitative, by simple observation of the visible signal, or may be quantitated by comparing with a control sample containing known amounts of hapten. Variations on the forward assay include a simultaneous assay, in which both sample and labelled antibody are added simultaneously to the bound antibody. These techniques are well known to those skilled in the art, including any minor variations as will be readily apparent. In accordance with the present invention the sample is one which might contain musculin including cell extract, tissue biopsy or possibly serum, saliva, mucosal secretions, lymph, tissue fluid and gastrointestinal fluid. The sample is, therefore, generally a biological sample comprising biological fluid but also extends to fermentation fluid and supernatant fluid such as from a cell culture.  
      In the typical forward sandwich assay, a first antibody having specificity for musculin or antigenic parts thereof, is either covalently or passively bound to a solid surface. The solid surface is typically glass or a polymer, the most commonly used polymers being cellulose, polyacrylamide, nylon, polystyrene, polyvinyl chloride or polypropylene. The solid supports may be in the form of tubes, beads, discs of microplates, or any other surface suitable for conducting an immunoassay. The binding processes are well-known in the art and generally consist of cross-linking covalently binding or physically adsorbing, the polymer-antibody complex is washed in preparation for the test sample. An aliquot of the sample to be tested is then added to the solid phase complex and incubated for a period of time sufficient (e.g. 2-40 minutes or overnight if more convenient) and under suitable conditions (e.g. from room temperature to 37° C.) to allow binding of any subunit present in the antibody. Following the incubation period, the solid phase complex is washed and dried and incubated with a second antibody which is specific for a portion of the antigen (i.e. musculin). The second antibody is linked to a reporter molecule which is used to indicate the binding of the second antibody to musculin.  
      An alternative method involves immobilizing the target molecules in the biological sample and then exposing the immobilized target to specific antibody which may or may not be labelled with a reporter molecule. Depending on the amount of target and the strength of the reporter molecule signal, a bound target may be detectable by direct labelling with the antibody. Alternatively, a second labelled antibody, specific to the first antibody is exposed to the target-first antibody complex to form a target-first antibody-second antibody tertiary complex. The complex is detected by the signal emitted by the reporter molecule.  
      By “reporter molecule” as used in the present specification, is meant a molecule which, by its chemical nature, provides an analytically identifiable signal which allows the detection of antigen-bound antibody. Detection may be either qualitative or quantitative. The most commonly used reporter molecules in this type of assay are either enzymes, fluorophores or radionuclide containing molecules (i.e. radioisotopes) and chemiluminescent molecules.  
      In the case of an enzyme immunoassay, an enzyme is conjugated to the second antibody, such as via glutaraldehyde or periodate amongst other means. As will be readily recognized, however, a wide variety of different conjugation techniques exist, which are readily available to the skilled artisan. Commonly used enzymes include horseradish peroxidase, glucose oxidase, beta-galactosidase and alkaline phosphatase, amongst others. The substrates to be used with the specific enzymes are generally chosen for the production, upon hydrolysis by the corresponding enzyme, of a detectable colour change. It is also possible to employ fluorogenic substrates, which yield a fluorescent product rather than the chromogenic substrates noted above. In all cases, the enzyme-labelled antibody is added to the first antibody-antigen complex, allowed to bind, and then the excess reagent is washed away. A solution containing the appropriate substrate is then added to the complex of antibody-antigen-antibody. The substrate will react with the enzyme linked to the second antibody, giving a qualitative visual signal, which may be further quantitated, usually spectrophotometrically, to give an indication of the amount of antigen which was present in the sample. The term “reporter molecule” also extends to use of cell agglutination or inhibition of agglutination such as red blood cells on latex beads, and the like.  
      Alternately, fluorescent compounds, such as fluorescein and rhodamine, may be chemically coupled to antibodies without altering their binding capacity. When activated by illumination with light of a particular wavelength, the fluorochrome-labelled antibody adsorbs the light energy, inducing a state of excitability in the molecule, followed by emission of the light at a characteristic colour visually detectable with a light microscope. As in the EIA, the fluorescent labelled antibody is allowed to bind to the first antibody-hapten complex. After washing off the unbound reagent, the remaining tertiary complex is then exposed to light of the appropriate wavelength and the fluorescence observed indicates the presence of the antigen of interest. Immunofluorescene and EIA techniques are both very well established in the art. Other reporter molecules, such as radioisotope, chemiluminescent or bioluminescent molecules, may also be employed.  
      The present invention also contemplates genetic assays such as involving PCR analysis to detect musculin or its derivatives. Alternative methods or methods used in conjunction include direct nucleotide sequencing or mutation scanning such as single stranded conformation polymorphoms analysis (SSCP) as specific oligonucleotide hybridisation, as methods such as direct protein truncation tests (see, for example, Van der Luut et al, [11]). Although the present invention does not extend to ABF-1, genetic sequences from, complementary to or capable of hybridizing with the ABF-1 gene or its mRNA, may be useful as antagonists of musculin gene expression. A human gene corresponding to musculin was identified by the inventors and this is shown in &lt;400&gt;3 together with its corresponding amino acid sequence (&lt;400&gt;4). Nucleotide sequences from this gene may also be used as antisense molecules, sense molecules, probes or primers for murine musculin or musculin genes from other species.  
      The present invention is further described by the following non-limiting Examples.  
     EXAMPLE 1  
      The genetic sequence database of The National Center for Biotechnology Information (Genbank) was searched with a bHLH search motif using the TBLASTN programme (27). The search motif is NXXERXRX 7 F/L-X 8-30 -KXXI/V/TLXXAXXY wherein X is any amino acid. The EST YX52E05.R1 was used as a probe to screen a human placental cDNA library, with additional clones obtained from human bone marrow, peripheral blood and HL60 libraries. Murine musculin cDNA clones were obtained from a 11 dpc embryo cDNA library.  
     EXAMPLE 2  
      Northern blot analysis and RNase protection analysis of polyA+ RNA from murine tissues and cell lines were performed as described (21, 22). Activated B-cells were prepared by incubation of splenocytes at 5×10 5 /ml with 20 μg/ml  E. coli  LPS, (Difco) for three days followed by anti-Thyl T-cell depletion. Protocols for in situ hybridisation of embryos and paraffin-embedded sections were as described (23, 24), except that embryos and sections were treated with 20 μg/ml of proteinase K (Boehringer).  
     EXAMPLE 3  
      This example presents a novel bHLH gene called herein “musculin”, based on its expression in embryonic skeletal muscle.  
      Using the strategy described herein (Example 1), a human EST (YX52E05.R1) with the potential to encode a novel bHLH protein was identified and used to screen human cDNA libraries. A cDNA molecule similar in sequence to the human gene ABF-1 (5), was cloned and characterised (see nucleotide sequence in &lt;400&gt;3), then used to screen for murine cDNAs. The murine musculin cDNA encoded an amino acid sequence set forth in  FIG. 1A  and in &lt;400&gt;2 ( FIG. 1A ).  
      Northern analysis of polyA+ mRNA extracted from a range of adult murine tissues, including lymphoid organs and skeletal muscle, failed to detect musculin expression, although a single transcript of 1.8 kb was observed in RNA from 14.5 days post coitum (dpc) embryos. However, RNase protection analysis detected low expression in spleen and a range of other adult tissues ( FIG. 1C ). Analysis of polyA+ RNA from 42 cell lines representing numerous hemopoietic lineages, as well as activated murine splenic B-cells, failed to detect musculin expression. This pattern differs from that of human ABF-1, which is highly expressed in SAC-activated B-cells and adult lymphoid tissues (5).  
      Musculin expression in 7.5-11.5 dpc embryos was analysed by whole mount in situ hybridisation. Transcripts were first detected at 9.5 dpc in myoblasts located centrally within the first and second branchial arches ( FIG. 2A , B). At E10.5, expression was also observed in the myotomal compartment of rostral somites ( FIG. 2B ), and by 11.5 dpc in myotomes along the antero-posterior axis, as well as in developing muscles of forelimbs and hindlimbs ( FIG. 2C ). Within the myotome, expression was strongest in the epaxial dermamyotomal lip ( FIG. 2E ). The only non-myogenic site of musculin expression was located in a region of splanchnic mesoderm at 9.5 dpc located close to the foregut/midgut junction ( FIG. 2A , D). This was transient and no longer detected by 10 dpc.  
      In situ hybridisation to sections of 12.5, 14.5 and 18.5 dpc embryos using ( 33 P)-radiolabelled musculin riboprobes revealed expression was confined to the skeletal muscle lineage ( FIG. 2F-1 ). All skeletal muscles of the embryo expressed the gene, including those of the head, neck, trunk, limbs, and diaphragm ( FIG. 2F -H). Cardiac and smooth muscles were negative. RNase protection revealed peak expression in embryonic limbs around 15 dpc, although expression in neonatal limbs was still robust. Higher power examination of sections revealed that musculin expression was localised to only a subset of muscle fibres from at least as early as 12.5 dpc ( FIG. 21 ).  
      Although expressed almost exclusively in embryonic skeletal muscle, musculin does not contain the alanine/threonine dipeptide which is found in the basic region of myoD-related bHLH factors ( FIG. 1B ) and which plays a critical role in activation of skeletal myogenesis through a direct interaction with the MADS box factor Mef2 (25). The myotome, from which most skeletal muscles derive, is a complex structure what may be assembled from cell populations arising in different regions of the dermamyotome (26).  
      Those skilled in the art will appreciate that the invention described herein is susceptible to variations and modifications other than those specifically described. It is to be understood that the invention includes all such variations and modifications. The invention also includes all of the steps, features, compositions and compounds referred to or indicated in this specification, individually or collectively, and any and all combinations of any two or more of said steps or features.  
     BIBLIOGRAPHY  
     
         
          1. Jan and Jan  Cell  75: 827-830, 1993.  
          2. Murre et al.  biochim. Biophysica Acta  1218: 129-135, 1994.  
          3. Murre et al.  Cell  56: 777-783, 1989.  
          4. Voronova and Baltimore  Proc. Natl. Acad. Sci. USA  87: 47224726, 1990.  
          5. Massari et al.  Mol. Cell. Biol.  18: 3130-3139, 1998.  
          6. Akajawa et al.  J. Biol. Chem.  270: 8730-8736, 1995.  
          7. Begley et al.  Proc. Natl. Acad. Sci. USA  89: 3842, 1992.  
          8. Doullard and Hoffman “Basic facts about hybridomas” in  Compendium of Immunology  vol. II ed. by Schwartz (1981).  
          9. Kohler &amp; Milstein  Nature Nature  256: 495499, 1975.  
          10. Kohler &amp; Milstein  Euro. J. Immunol.  6: 511-519, 1996.  
          11. van de Luut et al.  Genomics  20: 14, 1994.  
          12. Burgess et al.  Dev. Biol.  168: 296-306, 1995.  
          13. Cserjesi et al.  Development  121:1099-1510, 1995.  
          14. Davis et al.  Cell  51: 957-1000, 1987.  
          15. Edmondson and Olson  Genes. Devel.  3: 628-640, 1989.  
          16. Georgias et al.  Mech. Dev.  69: 115-124, 1997.  
          17. Srivastava et al.  Science  270: 1995-1999, 1995.  
          18. Wolf et al.  Dev. Biol.  143: 363-373, 1991.  
          19. Marmur and Doty  J. Mol. Biol.  5: 109, 1962.  
          20. Bonner et al.  J. Mol. Biol.  81: 123, 1973.  
          21. Robb et al.  J. Biol. Chem.  271: 13754-13761, 1996.  
          22. Robb et al.  Nature Med.  4: 303-308, 1998.  
          23. Lyons et al.  Genes. Deve.  9: 1654-1666, 1995.  
          24. Wilkinson  Whole mount in situ hybridization of vertebrate embryos . In situ hybridisation. A practical approach. Wilkinson (ed.) Oxford University Press, Oxford, UK.  
          25. Molkentin et al.  Cell  83: 1125-1136, 1995.  
          26. Tajbakhsh and Sporle  Cell  92: 9-16, 1998.  
          27. Altschul et al.  J. Mol. Biol.  215: 403-410, 1990.