bluuebunny/crossref_metadata_2025 huggingface dataset:
Intranuclear regulation of cell proliferation
Authors: Rueda J. , Espino F. J. , Ruiz M. L. , Vázquez A. M.
Published: April 2011

After colchicine treatment of root meristems of Crepis capillaris, a multinucleate cell population was induced with micro-nuclei being formed from decondensed chromatids. When these cells entered mitosis, both condensed chromosomes and interphase micronuclei were observed. Thus, it was possible to ascertain the capacity of each mitosis-entering chromosome by analysing the metaphases that contained micronuclei. Most of the micronuclei with at least one chromosome II entered mitosis, while those containing chromosomes I or III remained in interphase. These data suggest that one particular chromosome could be essential to cell proliferation. Therefore, we postulate that intranuclear factors encoded by this chromosome are necessary for nuclei to progress through interphase to enter mitosis.Key words: multinucleate cell system, intranuclear factors, cell proliferation, Crpis capillaris.
Cold hardiness expression in interspecific hybrids and amphiploids of the Triticeae
Authors: Limin A. E. , Fowler D. B.
Published: April 2011

Gene expression for cold hardiness was investigated in a number of interspecific or intergeneric hybrids and amphiploids of wheat (Triticum aestivum L. em. Thell. or T. turgidum L.) and other members of the tribe Triticeae to assess the potential of alien species as donors of cold-hardiness genes for the improvement of wheat. Thinopyrum ponticum (Agropyron elongatum) hybrids with nonhardy T. aestivum had cold-hardiness levels similar to that of the more hardy Thinopyrum parent. Hybrids of Triticum cylindricum and both hardy and nonhardy T. aestivum were intermediate in cold hardiness with a tendency toward greater hardiness than the parental mean. Cold hardiness of hybrids between T. aestivum and Thinopyrum intermedium (Agropyron intermedium) was also close to the parental midpoint. Cold hardiness of T. aestivum – Secale cereale hybrids was greater than the less hardy parent. In contrast, cold-hardiness genes were not expressed beyond the level of the wheat parent in amphiploids combining wheat and the very hardy diploid species Agropyron cristatum and Secale cereale. The cold-hardiness level was also poor in an amphiploid produced from two relatively hardy tetraploid species (T. turgidum and T. cylindricum). These observations indicate that changes in ploidy level, relative to the parents, may influence the cold-hardiness potential of an interspecific combination by affecting gene dosage and possibly cell size. Poor expression of cold-hardiness genes from very hardy diploid genomes also indicated some degree of suppression, or homoeoallelic dominance of wheat cold-hardiness genes in amphiploids. Therefore, the performance of an interspecific hybrid or amphiploid of wheat may not give an accurate indication of the potential of alien species as gene donors for the improvement of wheat cold hardiness.Key words: gene expression, Triticum sp., triticale, Thinopyrum sp., Agropyron sp., Secale cereale.
Inheritance of novel high-molecular-weight glutenin subunits in the Tunisian bread wheat 'BT-2288'
Authors: Gupta R. B. , Shepherd K. W.
Published: April 2011

Using sodium dodecyl sulphate-polyacrylamide gel electrophoresis, three new high-molecular-weight glutenin subunit/subunit combinations were detected in a Tunisian wheat cultivar (BT-2288) and these were designated bands 26, 7 + 11, and 5 + 9. Analysis of 112 testcross seeds revealed that the genes controlling them were additional alleles at Glu-A1, Glu-B1, and Glu-D1 loci, respectively. These alleles enhance the genetic variability available for cultivar identification and possibly for improving the bread-making quality of hexaploid wheat.Key words: Triticum aestivum, Glu-1 loci, high-molecular-weight glutenin subunits.
DNA fragments isolated from the left end of chromosome III in yeast are repaired to generate functional telomeres
Authors: Button Linda L. , Astell Caroline R.
Published: April 2011

DNA fragments isolated from the left end of chromosome III in the yeast Saccharomyces cerevisiae are recognized as telomeres in yeast, since plasmids constructed with such fragments are replicated as linear molecules in yeast. The fragments have a 1.18-kb region homologous with the type X regions at yeast telomeres that contain ARS elements that allow the autonomous replication of plasmids in yeast. The X region contains a functional ARS element including the ARS consensus sequence and a distal 200-bp region that enhances ARS function. Distal to the type X region, the fragments have a region of tandemly repeated DNA sequence defined by the formula 5′-C1–3A-3′, and designated as the T region at yeast telomeres. Although the terminus of the chromosome was removed in the procedure used to molecularly isolate the left end of chromosome III, the fragments containing the X and T region are recognized as chromosome ends in yeast. Plasmids with inverted repeats of the chromosome III end fragments are resolved in yeast to produce linear plasmids with telomeres that are similar in length and heterogeneity with the natural left end on chromosome III. Fragments with progressive deletions from the distal end of chromosome III were prepared and used to study the X – T region requirements for distinguishing the fragments as telomeres in yeast.Key words: yeast, S. cerevisiae, functional telomere, linear plasmids.
Coenocytism, ameiosis, and chromosome diminution in intergeneric hybrids in the perennial Triticeae
Authors: Wang Richard R.-C.
Published: April 2011

Three different pathways of ameiotic microsporogenesis were observed in some intergeneric hybrids of the perennial Triticeae grasses. In one of the hybrids between Pseudoroegneria spicata ssp. inermis and Psathyrostachys juncea, pollen mother cells remained as premeiotic interphase cells when the pollen grain wall started to form. The microspores in such an ameiotic plant are presumably unreduced. Coenocyte formation coupled with ameiosis occurred in two hybrid plants of Psathyrostachys huashanica × Secale montanum. Less than 10% of the pollen mother cells had one nucleus. An average of 4.44 nuclei, ranging from 1 to 25 per pollen mother cell, was observed. The nuclei in coenocytes remained unfused when the pollen grain wall was formed. Nucleus splitting followed by cytoplasmic budding or cleavage, possibly a process of chromosome diminution or elimination, replaced meiotic divisions in most of the pollen mother cells in one plant of Leymus angustus × Hordeum bulbosum and two plants of Thinopyrum elongatum × Psathyrostachys juncea. It is evident that these meiotic abnormalities are under genetic control. Probable locations for these genes controlling these phenomena are suggested.Key words: coenocyte, ameiosis, chromosome diminution, chromosome elimination, microsporogenesis, unreduced gamete, polyploidy, intergeneric hybrid.
Geographic pattern of variation among Asian native rice cultivars (Oryza sativa L.) based on fifteen isozyme loci
Authors: Glaszmann J. C.
Published: April 2011

The geographic pattern of isozyme variation among rice varieties (Oryza sativa L.) in Asia is described based on an electrophoretic survey of 1688 accessions for 15 loci. The distribution patterns are strongly determined by the existence of several varietal groups that are characterized by contrasting multilocus types with dissimilar environmental and macrogeographic distributions. The two main groups correspond to the indica and japonica subspecies. Other types are frequently found in the Indian subcontinent, especially along the Himalayan foothills. These types are predominant in the Indus River basin. They are differentiated into four groups in the eastern part of the Himalayan foothills. There is variation within the groups. Non-random allele distributions are observed, such as regional clines and narrow localization of alleles. Diversity among indica rice is evenly distributed in whole tropical Asia. Variation among japonica rice shows the hilly part of continental Southeast Asia to be the region of highest genetic diversity and its probable area of origin. All this information provides a guide for further analysis aimed at elucidating the history of cultivated rice in Asia and, subsequently, in other continents.Key words: Asian rice, genetic diversity, isozymes, geographic distributions.
Different genetic systems in rye affecting homoeologous pairing in wheat – rye combinations
Authors: Cuadrado M. C. , Romero C.
Published: April 2011

The present study analyzed meiotic pairing in wheat – rye hybrids obtained by crossing of Triticum aestivum cv. Chinese Spring with allogamous ryes, two cultivars of Secale cereale ('Don Enrique' and 'Selectión') and Secale cereale ssp. segetale. The results indicate that each rye type has different behaviour on hybrid meiotic pairing because they contain distinct genetic systems affecting meiotic pairing. In the case of 'Don Enrique' and 'Selección,' a polygenic system could be present, but not identical in both cultivars. On the other hand, Secale cereale ssp. segetale contained genes that strongly affect the genetic system controlling homoeologous pairing in wheat.Key words: homoeologous pairing, wheat – rye hybrids, polygenic system, major genes.
Mitochondrial gene expression in a nuclear mutant of Neurospora deficient in large subunits of mitochondrial ribosomes
Authors: Videira A. , Grilo M. L. Teles , Werner S. , Bertrand H.
Published: April 2011

A new cytochrome a and b deficient nuclear mutant of Neurospora crassa, cyt-U-28, is defective in the assembly of large subunits of mitochondrial ribosomes. Nonetheless, this mutant overproduces apparently normal small subunits of mitochondrial ribosomes, even though it should be deficient for the S5 ribosomal protein required for assembly of the particles beyond the CAP30S stage. The mitochondria of cyt-U-28 indeed synthesize only small amounts of most mitochondrial polypeptides, including cytochrome oxidase subunits I, II, and III, contain very low amounts of the normal seven-polypeptide cytochrome oxidase complex, and, unlike the organelles from other cytochrome a deficient mutants, do not accumulate the nuclear-encoded cytochrome oxidase subunits 5 and 6. Nonetheless, the mutant markedly oversynthesizes a mitochondrial protein that comigrates with subunit 9 of the mitochondrial ATPase on S DS–polyacrylamide electrophoresis gels. The overproduction of this protein and the accumulation of mature small subunits of mitochondrial ribosomes indicate that the cyt-U-28 mutant preferentially expresses two mitochondrial genes, one coding for ATPase subunit 9, the other for the S5 ribosomal protein.Key words: Neurospora, mitochondria, ribosomes, protein synthesis.
Clustering of genotypes for selection for heterosis in yield and response to environmental variations in mung bean (Vigna radiata (L.) Wilczek): a proposed method
Authors: Singh S. P.
Published: April 2011

Forty genotypes of mung bean (Vigna radiata (L.) Wilczek) were grown in four environments and analysed for standardized distances [Formula: see text]for mean grain yield (g) per plot. All the genotypes were included in nine clusters. The criterion of grouping was that two populations belonging to the same cluster should at least on the average show smaller [Formula: see text] than those belonging to different clusters. A maximum number of 21 genotypes were included in cluster I followed by cluster III (8 genotypes) and cluster II (5 genotypes). The remaining clusters had one genotype each. Genotypes in the same cluster were similar in response to environmental changes; however, these were divergent for yield. In cluster I, genotypes showed maximum divergence for yield ranging from 150.0 g (LM 305) to 212.2 g (K 851). Therefore, it is to be concluded that yield and response are the two independent attributes and are governed by separate sets of genes. For obtaining the high-yield hybrid that shows heterosis effects due to sets of genes responsible for yield and not for response, crossing among the divergent varieties within the cluster is recommended.Key words: cluster analysis, heterosis, mung bean.
The ribosomal DNA of Luzula pilosa (L.) Willd, a plant with holocentric chromosomes
Authors: Bowen B. A. , Lee D. , Creissen G. P. , Marks G. E. , Cullis C. A.
Published: April 2011

The ribosomal DNA (rDNA) of Luzula pilosa (L.) Willd, a plant with holocentric chromosomes, has been cloned and characterized by restriction mapping. The major variant is present in about 730 tandemly arranged copies per haploid genome which occupy nearly an entire chromosome. We propose that much of the rDNA is flanked or interspersed by kinetochores, so that reciprocal interchromatid exchanges in this region would lead to chromosome breakage. Homogenization and amplification of rDNA spacer length variants may occur largely by intrachromatid exchanges and gene conversion. By trying to isolate rDNA junction fragments which might be closely linked to centromeric DNA, we have isolated three minor rDNA variants whose spacer regions do not cross-hybridize with one another or with the major variant. The possibility that these minor variants may be rRNA pseudogenes is discussed.Key words: centromere, holocentric, Luzula, rDNA, recombination.
Elimination of multivalents during meiotic prophase in Scilla autumnalis. I. Diploid and triploid
Authors: White J. , Jenkins G. , Parker J. S.
Published: April 2011

The ultrastructure and pairing behaviour of the chromosomes of two diploid cytotypes and a triploid of Scilla autumnalis were investigated using the techniques of three-dimensional reconstruction from serial electron micrographs and whole-mount surface spreading of synaptonemal complexes. The diploids, designated AA and B7B7, have karyotypes that are virtually identical in appearance at mitotic metaphase but differ in length by 47% and in DNA content by 66%. All the chromosomes were identified during meiotic prophase in both diploids, enabling construction of accurate karyotypes, which were the same as those derived from root tip metaphases. Chromosome pairing was largely regular with very few structural chromosome rearrangements. These two observations permitted confident interpretations of multivalent configurations observed in polyploids containing multiples of the A and B7 genomes. In the triploid (AB7B7) during meiotic prophase lateral components are associated in groups of three, either as trivalents with several exchanges of pairing partners, or as bivalents and univalents in close alignment. The overall difference in length between A and B7 chromosomes is close to expected, but varies to some degree depending on the extent of pairing between the two chromosome types. Most of the synaptonemal complexes between A and B7 homoeologues are ineffective in terms of chiasma formation, as revealed by the low frequency of multivalents and heteromorphic bivalents at metaphase I. In other words, there is an elimination of multivalents during meiotic prophase in the triploid.Key words: Scilla autumnalis, synaptonemal complex, multivalents, elimination.
Recombination of bacteriophage λ in recD mutants of Escherichia coli
Authors: Thaler David S. , Sampson Elizabeth , Siddiqi Imran , Rosenberg Susan M. , Thomason Lynn C. , Stahl Franklin W. , Stahl Mary M.
Published: April 2011

RecBCD enzyme is centrally important in homologous recombination in Escherichia coli and is the source of ExoV activity. Null alleles of either the recB or the recC genes, which encode the B and C subunits, respectively, manifest no recombination and none of the nuclease functions characteristic of the holoenzyme. Loss of the D subunit, by a recD mutation, likewise results in loss of ExoV activity. However, mutants lacking the D subunit are competent for homologous recombination. We report that the distribution of exchanges along the chromosome of Red−Gam−phage λ is strikingly altered by recD null mutations in the host. When λ DNA replication is blocked, recombination in recD mutant strains is high near λ's right end. In contrast, recombination in isogenic recD+ strains is approximately uniform along λ unless the λ chromosome contains a χ sequence. Recombination in recD mutant strains is focused toward the site of action of a type II restriction enzyme acting in vivo on λ. The distribution of exchanges in isogenic recD+ strains is scarcely altered by the restriction enzyme (unless the phage contains an otherwise silent χ). The distribution of exchanges in recD mutants is strongly affected by λ DNA replication. The distribution of exchanges on λ growing in rec+ cells is not influenced by DNA replication. The exchange distribution along λ in recD mutant cells is independent of χ in a variety of conditions. Recombination in rec+ cells is χ influenced. Recombination in recD mutants depends on recC function, occurs in strains deleted for rac prophage, and is independent of recJ, which is known to be required for λ recombination via the RecF pathway. We entertain two models for recombination in recD mutants: (i) recombination in recD mutants may proceed via double-chain break–repair, as it does in λ's Red pathway and E. coli's RecE pathway; (ii) the RecBC enzyme, missing its D subunit, is equivalent to the wild-type, RecBCD, enzyme after that enzyme has been activated by a χ sequence.Key words: χ sequence, RecBCD pathway, Red pathway, RecBC‡ pathway.
Are there morphologically abnormal early recombination nodules in the Drosophila melanogaster meiotic mutant mei-218?
Authors: Carpenter Adelaide T. C.
Published: April 2011

Early recombination nodules have been suggested to perform a role in meiotic gene conversion recombination events. The meiotic recombination-defective mutant mei-218 greatly reduces the frequency of meiotic crossover (reciprocal) recombination events and reduces the number of late recombination nodules to the same extent. However, it does not reduce the frequency of simple gene conversion events, although they are abnormal in having shorter coconversion tracts than controls. The original cytological study yielded somewhat fewer early nodules in mei-218 than in controls, although very abnormal ones might have been missed. The present study failed to identify a mei-218 specific abnormal category. However, because recombination nodules are at present recognizable only by their morphology, a definitive answer to this question must await a specific probe for recombination nodules. Moreover, the possibility remains that early nodules in mei-218 are more ephemeral than are early nodules in wild type.Key words: synaptonemal complex, recombination nodules, meiotic mutants, Drosophila melanogaster.
Immunoglobulin molecular genetics: the prospects for mutational analysis of the chromosomal immunoglobulin genes
Authors: Shulman Marc J. , Bosnoyan Lucine , Collins Catherine , Pennell Nancy , Baker Mark D.
Published: April 2011

Homologous recombination between transferred and chromosomal DNA can be used to effect precise, predetermined modifications of the chromosomal genes. Ultimately this phenomenon should allow the assessment of genetic regulatory elements as they function in the normal chromosomal environment. We have previously described a system for isolating mutant hybridoma cells that are defective in immunoglobulin (Ig) production, with a view toward using these mutants to define cis-acting elements that influence Ig gene expression. Here we describe results that indicate that homologous recombination between transferred and chromosomal Ig genes can be used to map Ig mutations by marker rescue.Key words: homologous recombination, gene expression.
Sewall Wright and quantitative genetics
Authors: Hill William G.
Published: April 2011

Some aspects of Wright's great contribution to quantitative genetics and animal breeding are reviewed in relation to current research and practice. Particular aspects discussed are as follows: the utility of his definition of inbreeding coefficient in terms of the correlation of uniting gametes; the maintenance of genetic variation in the optimum model; the inter-relations between past and present animal-breeding practice and the shifting-balance theory of evolution.Key words: quantitative genetics, inbreeding coefficient, genetic variation, evolution.
Fisherian and Wrightian theories of speciation
Authors: Lande Russell
Published: April 2011

Fisher's theory of sexual selection, Wright's shifting-balance theory, and recent models based on them are reviewed as mechanisms of animal speciation. The joint evolution of mating preferences and secondary sexual characters can cause rapid nonadaptive phenotypic divergence and premating isolation between geographically separated populations, or along a cline. Extensive comparative data on Drosophila species support the suggestion of R. A. Fisher and T. Dobzhansky that the evolution of mating preferences can reinforce partial postmating isolation between sympatric populations. The interaction of natural selection and random genetic drift in local populations with a small effective size can produce a rapid transition between relatively stable phenotypes separated by an adaptive valley, or between chromosomal rearrangements with a heterozygote disadvantage. Large demographic fluctuations, such as frequent random local extinction and colonization, are required for the rapid spread of new adaptations (or karyotypes) when intermediate phenotypes (or rearrangement heterozygotes) are selected against.Key words: reproductive isolation, hybridization, sexual selection, reinforcement, subdivided population, shifting balance, adaptive landscape, random genetic drift.
Nuclear power plants and natural populations of Mexican Drosophila
Authors: Levine L. , Olvera O. , Rockwell R. F. , de La Rosa M. E. , Guzmán J.
Published: April 2011

With the worldwide proliferation of nuclear power plants has come the need to study the biological effects of the operation of the reactors on surrounding populations. We have begun a long-term study of the sibling species Drosophila melanogaster and D. simulans in the area of Laguna Verde in the state of Veracruz in Mexico. Laguna Verde, on the Gulf of Mexico about 75 km north of the city of Veracruz, is the location of the country's first nuclear power plant. This plant has not yet gone "on-line." The species have been collected from two sites, one of which is south of the reactor and is in the path of the prevailing north to south wind flow. The other collecting site is west of the plant. The species are being studied for the following: species frequency, desiccation resistance, vagility, proportion of larvae pupating, pupation height, and egg to adult survival after irradiation. To date we have noted both spatial and seasonal differences in a number of these characteristics. The information being gathered will serve as base-line data for monitoring the future operation of the nuclear power plant.Key words: Drosophila melanogaster, Drosophila simulans, species frequencies, desiccation resistance, vagility, pupation, egg to adult survival.
Selection, adaptation, and bacterial operons
Authors: Hall Barry G.
Published: April 2011

Bacteria are especially useful as systems to study the molecular basis of adaptive evolution. Selection for novel metabolic capabilities has allowed us to study the evolutionary potential of organisms and has shown that there are three major "strategies" for the evolution of new metabolic functions. (i) Regulatory mutations may allow a gene to be expressed under unusual conditions. If the product ofthat gene is already active toward a novel resource, then a regulatory mutation alone may confer a new metabolic capability. (ii) Structural gene mutations may alter the catalytic properties of enzymes so that they can act on novel substrates. These structural gene mutations may dramatically improve catalytic capabilities, and in some cases they can confer entirely new capabilities upon enzymes. In most cases both regulatory and structural gene mutations are required for the effective evolution of new metabolic functions. (iii) Operons that are normally silent, or cryptic, may be activated by either point mutations or by the action of mobile genetic elements. When activated, these operons can provide entirely new pathways for the metabolism of novel resources. Selection can also play a role in modulating the probability that a particular adaptive mutation will occur. In this paper I present evidence that a specific adaptive mutation, reversion of the metB1 mutation, occurs 60 to 80 times more frequently during prolonged selection on plates under conditions where the members of the population are not growing than it does in growing cells under nonselective conditions. This selective condition, methionine starvation, does not increase the frequency of other mutations unrelated to methionine biosynthesis. Thus, contrary to our present notions, selection can act not only to reveal preexisting mutations but to modulate the frequency with which adaptive mutations occur.Key words: mutation rates, molecular evolution, adaptive mutations, cryptic genes.
Molecular basis of the early events in plant–fungus interaction
Authors: Kolattukudy P. E. , Podila G. K. , Mohan R.
Published: April 2011

Fungal spores that land on aerial surfaces of plants first come into contact with plant cuticle. The cuticle is composed of an insoluble polyester called cutin, which is composed of hydroxy and hydroxyepoxy fatty acids and associated soluble waxes. The wax components can trigger differentiation of germinating fungal spores into infection structures. The penetration of the fungus into the plant requires enzymatic degradation of the polyester and the underlying carbohydrate barriers. The polyesterase, called cutinase, is induced by the contact with the plant surface. The small amount of cutinase carried by the spore generates a small amount of cutin monomers upon contact with the host, and the unique monomers trigger expression of the cutinase gene. This transcriptional level control can be demonstrated with isolated nuclei. Upon incubation of nuclei with cutin monomer and a soluble protein factor from the fungus, cutinase transcription is selectively activated. Structure activity relationships showed that the cutinase transcription activation required all of the structural elements of the cutin monomer. The cutinase transcript generated by the isolated nuclei was identical in size to the cutinase mRNA induced in the fungal cultures, which indicated usual initiation and termination. Fungal infection triggers defense reaction in plants. Plant peroxidases were implicated in the defense response of plants to fungal attack and stress. A highly anionic peroxidase involved in suberization of cell walls in tomato plants in response to fungal attack was cloned and sequenced. It was observed that in resistant lines of tomato the expression of this anionic peroxidase was induced 1 day earlier than in susceptible lines.Key words: cutinase, cutin monomers, pectate lyase, Fusarium solani pisi, anionic peroxidase.
Genetic instability and aging: theories, facts, and future perspectives
Authors: Slagboom P. Eline , Vijg Jan
Published: April 2011

The fundamental mechanisms involved in the physiological deterioration observed with age in mammalian organisms have not yet been elucidated. It appears that random alterations in informational biomolecules and in their synthesis could be the basis of such physiological changes. There is, however, a lack of knowledge with respect to the frequency and characteristics of changes introduced in the cellular molecular machinery. Moreover, the driving force initiating the generation of such alterations and the order of events in which they occur are unknown at present. In this article, data concerning the hypothesis that the aging process is associated with widespread genetic instability are reviewed in the context of the complex interactions between the three major informational biomolecules, DNA, RNA, and protein. We conclude that the results obtained to date do not rule out the possibility that genetic instability in a wide sense is a major causal factor in a number of age-related phenomena. However, it appears that new strategies based on a new technology are ultimately necessary to elucidate the alterations in the intricately interwoven patterns of molecular control that could underlie the various aspects of the aging process. A first attempt is made to formulate the problems in this field and to provide some solutions.Key words: genetic instability, DNA and aging, gene expression, somatic mutations, DNA methylation, evolutionary aspects.
Probing Drosophila gene function by antisense RNA
Authors: Schuh Reinhard , Jäckle Herbert
Published: April 2011

The conventional technique for assigning a particular genetic function to a cloned transcription unit has relied on the rescue of the mutant phenotype by germ line transformation. An alternative approach is to mimic a mutant phenotype by the use of antisense RNA injections to produce phenocopies. This approach has been successfully used to identify genes involved in early pattern forming processes in the Drosophila embryo. At the time when antisense RNA is injected, the embryo develops as a syncytium composed of about 5000 nuclei which share a common cytoplasm. The gene interactions required to establish the body plan occur before cellularization at the blastoderm stage. Thus the nuclei and their exported transcripts are accessible to the injected antisense RNA. The antisense RNA interferes with the endogenous RNA by an as yet unidentified mechanism. The extent of interference is only partial and produces phenocopies with characteristics of weak mutant alleles. In our lab and others, this approach has been successfully used to identify several genes required for normal Drosophila pattern formation.Key words: Drosophila segmentation, phenocopy, antisense RNA, Krüppel gene.
Phenotypic expression of primary lesions of genetic material in Saccharomyces yeasts
Authors: Inge-Vechtomov Sergey G. , Repnevskaya Marina V.
Published: April 2011

"Illegitmate" mating of yeasts (α × α), either spontaneous or induced by uv light or ethyl methanesulfanate, in a selective system for "cytoduction" revealed that about 95% of cytoductants expressed their original (α) mating type. Inducing the mating by treating the recipient of cytoplasm with uv light reached two orders of magnitude. An additional copy of MATα in the α recipient almost completely eliminated the effect, which means that nonheritable mating type changes observed are formally recessive and are localized within MATα complex. About 1% of cytoductants obtained were nonmating types and some of them were identified as matα1 mutants. Rad18 mutant as a recipient showed a considerably elevated spontaneous frequency of illegitimate hybridization and cytoduction. The cytoductants also preserved the original mating type. These facts suggest that nonheritable changes of mating type are due to repairable primary (premutational) lesions in MATα genetic material. The significance of these results for understanding the mechanism of nonheritable variability is discussed.Key words: mating type, nonheritable changes, primary lesions, premutational events, Saccharomyces cerevisiae, repair.
DNA repair replication by soluble extracts from human lymphoid cell lines
Authors: Wood Richard D. , Robins Peter
Published: April 2011

A system is described in which extracts from human cells can perform repair replication on DNA damaged by ultraviolet light or chemical carcinogens. Whole cell extracts from lymphoid cell lines are incubated with damaged plasmid DNA circles at 30 °C in the presence of ATP and the four deoxynucleoside triphosphates. Repair synthesis is monitored by the incorporation of α-32P-dATP into closed circular plasmid molecules. Analysis of the time course of the reaction suggests that the slowest step in repair is incision, rather than polymerization or ligation. The size of repair patches inserted into ultraviolet-irradiated DNA during a reaction was estimated by substitution of thymidine triphosphate with 5-bromodeoxyuridine triphosphate and sedimentation in alkaline cesium chloride gradients. Patches with heterogeneous sizes of less than 120 bases were observed.Key words: DNA repair, human cells, ultraviolet light, cell extracts.
Formation of differentiation pattern in Dictyostelium discoideum
Authors: Takeuchi Ikuo , Tasaka Masao
Published: April 2011

Aggregation of an apparently homogenous population of Dictyostelium discoideum cells brings about differentiation within a tissue of two types of presumptive cells, prestalk and prespore cells. They appear in a certain proportion and at fixed locations. Prespore cells begin to appear when the aggregate forms the tip and a major class of prespore genes are first expressed at this stage. A class of prestalk genes are also expressed at the same stage, the others being expressed a little earlier or later. Reconstruction of the differentiation pattern with cells dissociated from the tissue is brought about by sorting out of prestalk and prespore cells, without accompanying changes in cell type. Prestalk cells sort out as a result of differential chemotaxis rather than differential adhesiveness. When vegetative cells are allowed to differentiate within an aggregate cultured in roller tubes, the process of pattern formation coincides with that of the pattern reconstruction, supporting the idea of pattern formation based on nonpositional cell differentiation and subsequent cell sorting. Within an aggregate developing on an agar surface, however, prespore cells first appear in the basal part, favoring the idea of pattern formation due to positional information. A possible means of overcoming the apparent contradiction is suggested.Key words: cell differentiation, cell sorting, pattern formation, Dictyostelium discoideum.
Molecular genetic aspects of sex determination in Drosophila melanogaster
Authors: Baker B. S. , Burtis K. , Goralski T. , Mattox W. , Nagoshi R.
Published: April 2011

The molecular analyses of three of the regulatory genes (transformer (tra), doublesex (dsx), and transformer-2 (tra-2)) controlling sexual differentiation in Drosophila have demonstrated that the control of RNA processing has a major role in regulating somatic sexual differentiation. The activities of both the tra and dsx genes are controlled at the level of RNA processing. In the case of tra the use of different splice acceptor sites results in a functional transcript being produced only in females, whereas at dsx the use of different splice acceptor sites in the two sexes results in the production of transcripts that encode different proteins in males and females. The tra-2 gene has been shown to be necessary for the processing of the dsx pre-mRNA in females and the conceptual translation of a tra-2 cDNA shows that it encodes a protein with similarity to a family of RNA-binding proteins which includes known splicesome components. We previously suggested that the pattern of sexual differentiation and dosage compensation characteristic of a male was a default regulatory state. The findings reviewed here provide a molecular basis for this default expression in males as well as an insight into how females differ from males in control of the expression of these genes. For both the tra and dsx genes the molecular basis of their male (default) state of expression appears to be the processing of their transcripts by the housekeeping RNA splicing machinery. In females the specification of the alternative pattern of splicing at both tra and dsx is by the sex determination regulatory genes that function upstream of them in this regulatory cascade. It seems likely that the activities of these sex determination regulatory genes in females do not provide all of the information that is necessary for proper splicing of the transcripts of the genes downstream of them. Rather we imagine that the products of the Sxl, tra, and tra-2 genes are acting to impose a specificity on the basic cellular splicing machinery.Key words: Drosophila melanogaster, sex determination, sexual differentiation.
Transgenic mice to study T-cell receptor gene regulation and repertoire formation
Authors: Steinmetz Michael , Blüthmann Horst , Ryser Stefan , Uematsu Yasushi
Published: April 2011

Transgenic mice have been obtained with genes coding for an αβ T-cell receptor that recognizes the male-specific antigen H-Y in association with the Db class I major histocompatibility complex molecule. Most if not all of the T-cells express the β chain encoded by the transgene and show allelic exclusion of endogenous β genes. In contrast, the expression of the α transgene does not completely block rearrangement and formation of functional endogenous α genes. In H-2b transgenic female mice the transgenic T-cell receptor is functionally expressed on at least 30% of CD8+ peripheral T-lymphocytes as indicated by their ability to lyse male target cells. Also in transgenic H-2b male mice a large proportion of peripheral T-cells appear to express the transgenic receptor. However, these cells do not react with male target cells because they show only low level or no expression of CD8 cell interaction molecules. Tolerance is established in the male transgenic thymus through deletion of CD4+CD8+ immature thymocytes.Key words: transgenic mice, immune system, T-lymphocytes, T-cell receptor, tolerance, CD8 surface antigen, enhancer, gene rearrangement, allelic exclusion.
Structure, organization, and expression of the 16-kDa heat shock gene family of Caenorhabditis elegans
Authors: Candido E. P. M. , Jones D. , Dixon D. K. , Graham R. W. , Russnak R. H. , Kay R. J.
Published: April 2011

Exposure of the nematode Caenorhabditis elegans to a heat shock results in the induction of a number of genes not normally expressed in the animals under normal growth conditions. Among these are a family of genes encoding 16 kDa heat shock proteins (hsp16s). The major hsp16 genes have been cloned and characterized, and found to reside at two clusters in the C. elegans genome. One cluster contains two distinct genes, hsp16-1 and hsp16-48, arranged in divergent orientations separated by only 348 base pairs (bp). An identical pair, duplicated and inverted with respect to the first pair, is located 415 bp away. This cluster, located on chromosome V, therefore contains four genes as two identical pairs within less than 4 kilobases of DNA, and the pairs form the arms of a large inverted repeat. A second pair of genes, hsp16-2 and hsp16-41, constitutes a second hsp16 locus with an organization very similar to that of the hsp16-1/48 locus, except that it is not duplicated. Comparisons of the derived amino acid sequences show that hsp16-1 and hsp16-2 form a closely related pair, as do hsp16-41 and hsp16-48. These hsps show extensive sequence identity with the small hsps of Drosophila, as well as with mammalian alpha-crystallins. The coding region of each gene is interrupted by a single intron of approximately 50 bp, in a position homologous to that of the first intron in a mouse alpha-crystallin gene. The compact intergenic regions of both hsp16 loci contain a TATA element and a heat shock element (HSE) for each member of the pair, and are very similar in sequence overall. Expression studies, however, show that the level of transcripts from the hsp16-2/41 pair may be up to 14-fold higher on a per gene basis, as the level of RNA from the hsp16-1/48 pair, depending upon the induction conditions and developmental stage. This difference in message levels seems to be due to differences in the kinetics of inactivation of the genes rather than in transcription rates or rates of mRNA turnover. Distinct DNAseI hypersensitive sites are present upstream of each HSE in chromatin when the genes are inactive; these disappear and the whole intergenic region seems to become DNAse sensitive when the genes are maximally active.Key words: heat shock, 16-kDa polypeptides, gene structure, transcription, DNAseI hypersensitive sites, Caenorhabditis elegans.
Variation in natural populations of Drosophila as revealed by four-cutter analysis
Authors: Aguadé Montserrat
Published: April 2011

Four-cutter restriction enzyme analysis, a recently developed electroblotting technique, enables the survey of restriction site and insertion–deletion polymorphism in natural populations at a fine level of resolution. Using this technique, the distribution of polymorphism among geographically isolated populations of Drosophila melanogaster and in different structural–functional domains of the genome has been studied. A summary of these results is presented and discussed. Recent investigations of molecular variation within and between different chromosome arrangements in Drosophila are presented. Levels of variation in different regions of the X chromosome of D. melanogaster are also discussed.Key words: populations, DNA polymorphisms, Drosophila, restriction enzymes.
Expression vectors for human adenosine deaminase gene therapy
Authors: Moore Kateri A. , Fletcher Frederick A. , Alford Raye Lynn , Villalon Deborah K. , Hawkins Dianne H. , MacGregor Grant R. , Caskey C. Thomas , Belmont John W.
Published: April 2011

Somatic gene transfer offers a possible new approach for treatment of human genetic disease. Defects affecting blood-forming tissues are candidates for therapies involving transfer of genetic information into hematopoietic stem cells. Adenosine deaminase (ADA) deficiency is being used as a model disease for which gene transfer techniques can be developed and evaluated. We describe here the construction and testing of 20 retroviral vectors for their ability to transfer and express human ADA in vitro and in vivo via a mouse bone marrow transplantation model. After infection of primary bone marrow with one of these vectors (pΔNN2ADA), human ADA was detected in 60–85% of spleen colonies at day 14 and maintained long term in the blood of fully reconstituted mice. This system offers the opportunity to assess methods for increasing efficiency of gene transfer, for regulation of expression of foreign genes in hematopoietic progenitors, and for long-term measurement of the stability of expression in these cells.Key words: gene therapy, adenosine deaminase, retrovirus vectors, immunodeficiency.
Protein engineering with synthetic Escherichia coli amber suppressor genes
Authors: Miller Jeffrey H. , Kleina Lynn G. , Masson Jean-Michel , Normanly Jennifer , Abelson John
Published: April 2011

We have constructed synthetic genes encoding different Escherichia coli suppressor tRNAs for use in amino acid substitution studies and protein engineering. We used oligonucleotides to assemble the genes for different tRNAs with the anticodon 5′ CTA 3′. The suppressor genes are expressed from a synthetic promoter derived from the promoter sequence of the E. coli lipoprotein gene. The genes have been used to suppress an amber mutation in a protein coding sequence, and the resulting altered protein has been subjected to sequence analysis to determine the nature of the amino acid inserted at the amber site. Twelve amino acids can now be added in response to the amber codon. We have employed these suppressors to study amino acid substitutions in the lac repressor.Key words: synthetic tRNA, amber suppressor, protein engineering, lac repressor, Escherichia coli.
Variation in structure and expression of ribosomal DNA loci in wheat
Authors: Flavell R. B.
Published: April 2011

Ribosomal RNA genes are organised in tandem arrays at complex loci called nucleolus organisers. The structure of a locus and of a wheat rRNA gene is described in detail. Active or potentially active genes are in the nucleolus during interphase, while inactive genes are excluded from the nucleolus. Genetic variation exists within a species for the number of the rRNA genes at a locus and also for the structure of the intergenic, regulatory DNA. This variation can affect the activity of a locus, relative to that of another in the same cell and the proportion of the rRNA genes at a locus included in the nucleolus. The active loci are enriched with genes that are not methylated at specific CpG residues in the intergenic regulatory DNA and that are in a chromatin conformation accessible to DNase I. A model is presented that attempts to relate the structural variation between genes to the differential expression and nucleolar organisation of the rRNA genes at different loci. The model is based on the affinity of proteins, in limiting concentration, to specific regulatory DNA sequences. These sequences are subject to change as a result of mechanisms that can spread mutations through a locus. The resulting variation, which may not be eliminated by selection unless it is very deleterious and accounts for a large part of the total rDNA, may be one reason why plants maintain a large excess of ribosomal RNA genes.Key words: nucleolus, ribosomal RNA gene, methylation.
The Brassica self-incompatibility multigene family
Authors: Dwyer Kathleen G. , Chao Anna , Cheng Betty , Chen Che-Hong , Nasrallah June B.
Published: April 2011

The pollen–stigma interaction of self-incompatibility in Brassica species is controlled by a single genetic locus, the S locus. This locus encodes the S locus specific glycoproteins of the stigma. Hybridization of restriction enzyme digested genomic DNA isolated from homozygous strains of Brassica with cDNA probes encoding these glycoproteins yields a pattern of multiple fragments of varying size and intensity. The presence of S sequences as multiple related copies in the Brassica oleracea genome has been verified by the cloning of several different genomic regions containing S homology. Probes capable of distinguishing between S gene copies have been obtained and have demonstrated that two such copies are expressed. Characterization of additional probes specific for S gene copies will permit the study of the expression of the other copies, and the analysis of the genomic organization of the self-incompatibility multigene family.Key words: self-incompatibility, Brassica, cDNA probes.
Molecular genetic analysis of the maize Suppressor-mutator element's epigenetic developmental regulatory mechanism
Authors: Fedoroff Nina , Banks Jo Ann , Masson Patrick
Published: April 2011

The genetic mechanism underlying the developmental regulation of the maize Suppressor-mutator element has been analyzed by molecular and genetic techniques. The element is subject to inactivation by a negative, epigenetic mechanism that results in the methylation of C residues in the vicinity of the element's transcription start site. Fully methylated elements are genetically and transcriptionally silent (cryptic), while hypomethylated elements are active. Partially methylated elements, designated programable, exhibit a variety of developmental expression programs. The element encodes a positive regulatory gene product which activates element expression and promotes reprograming of the element by interfering with methylation of the element's 5′ end.Key words: maize transposable element, Suppressor-mutator element, developmental regulation.
The male gamete as a tool in the genetic improvement of cereals
Authors: Picard E.
Published: April 2011

This review surveys recent developments in the use of male gametes for the genetic improvement of cereals. It focuses mainly on the production of doubled haploids and their use in breeding programmes but also discusses gametoclonal variaton, in vitro selection through anther or pollen culture, and genetic transformation using the pollen tube as a vehicle for foreign DNA.Key words: male gamete, haploids, doubled haploids, cereals, gametoclonal variation, in vitro selection, pollen-mediated genetic transformation.