Origins of Nuclear Genomes in Hybrid Unisexual Salamanders

DEB-0075856克里斯蒂娜M.托马斯·M·斯波尔斯基UzzellDrs.克里斯蒂娜M. Spolsky和托马斯M.美国费城自然科学院的Uzzell博士获得了一笔研究经费，用于研究蝾螈基因组印记和不寻常的生殖生活方式之间的相互作用。 鼹鼠蝾螈（Ambystoma属）包括各种几乎完全是雌性的克隆繁殖谱系。这种无性繁殖的雌性是有性繁殖物种之间的杂交种，并且可能是不育的。然而，克隆雌性能够繁殖，并且具有广泛的地理范围，它们是常见的。克隆形式的线粒体DNA，虽然不同，最相似的是在一个物种在一个物种组的Ambystoma，而核遗传物质（DNA中包含的染色体）类似于在另一个物种组的两个物种。该奖项将用于从选定的有性物种和克隆个体的组织中获得遗传物质。所有编码蛋白质的基因都将被保存在所谓的cDNA文库中。将从这些文库中分离两个核基因（血清白蛋白和丝氨酸蛋白酶抑制剂）并测序。这些序列将被用来设计和测试引物，以鉴定克隆个体的基因组组成。克隆繁殖的鼹鼠蝾螈的线粒体基因组是独特的，表明这些谱系已经存在了3-5百万年。这比进化理论预期的要长得多，因为有害突变的逐渐积累最终会使任何严格的无性系灭绝。线粒体DNA的长期独立生存所带来的矛盾，考虑到理论上预期的短暂生存，表明克隆蝾螈的核染色体组偶尔会被有性繁殖而不是克隆繁殖的雄性物种的核染色体组所取代。基因组特异性引物将允许评估这种染色体替换发生的频率。尽管克隆繁殖具有短期优势，但这些数据对有性繁殖持续性的理论很重要。线粒体和核DNA变异的比较将为评价自然选择在克隆谱系中对这两种DNA的相对影响提供依据。

DEB-0075856Christina M. SpolskyThomas M. UzzellDrs. Christina M. Spolsky and Thomas M. Uzzell of the Academy of Natural Sciences, Philadelphia, have been awarded a grant to study the interaction of genomic imprinting and unusual reproductive lifestyles in salamanders. Mole salamanders (genus Ambystoma) include a variety of clonally-reproducing lineages that are almost exclusively female. Such clonal females are hybrids between sexually reproducing species, and might be expected to be sterile. Nevertheless, the clonal females are capable of reproducing and have broad geographic ranges in which they are common. The mitochondrial DNA of the clonal forms, although distinct, most resembles that in a species in one species group of Ambystoma, whereas the nuclear genetic material (DNA contained in chromosomes) resembles that of two species in another species group. This award will be used to obtain genetic material from tissues of selected sexual species and clonal individuals. All the genes that encode proteins will be archived in so-called cDNA libraries. Two of the nuclear genes (serum albumin and serpin) will be isolated from these libraries and sequenced. These sequences will be used to design and test primers that permit identification of the genomic composition of clonal individuals.The mitochondrial genomes of clonally-reproducing mole salamanders are distinctive, and suggest that these lineages have existed for 3-5 million years. This is far longer than expected according to evolutionary theory, because gradual accumulation of deleterious mutations should eventually doom any strictly clonal lineage to extinction. The paradox posed by the long independent survival of the mitochondrial DNA given the brief survival expected from theory suggests that occasionally nuclear chromosome sets of the clonal salamanders are replaced, in sexual rather than clonal reproduction, by nuclear chromosome sets from males of sexual species. Genome-specific primers will permit an assessment of the frequency with which such chromosomal replacements occur. The data are important for theories about the persistence of sexual reproduction despite the short-term advantages of clonal reproduction. Comparison of variability in mitochondrial and nuclear DNA will provide a basis for evaluating the relative effects of natural selection on these two kinds of DNA in the clonal lineages.