Origins of Nuclear Genomes in Hybrid Unisexual Salamanders

克里斯蒂娜·M·斯波尔斯基托马斯·M·乌泽尔博士。费城自然科学院的克里斯蒂娜·M·斯波尔斯基和托马斯·M·乌泽尔获得了研究火蜥蜴基因组印记和异常生殖生活方式相互作用的研究经费。鼹鼠蜥蜴(Ambystoma属)包括各种克隆繁殖的血统，几乎完全是雌性。这种克隆雌性是有性繁殖物种之间的杂交，可能是不育的。然而，克隆雌性能够繁殖，并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，但最类似于一个种组的线粒体DNA，而核遗传物质(染色体中包含的DNA)类似于另一个物种组中的两个种。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保存在所谓的cdna文库中。其中两个核基因(血清白蛋白和蛇毒蛋白)将从这些文库中分离出来并进行测序。这些序列将被用来设计和测试允许鉴定克隆个体基因组组成的引物。克隆繁殖的鼹鼠蜥蜴的线粒体基因组是独特的，表明这些谱系已经存在了300-500万年。根据进化论，这比预期的时间要长得多，因为有害突变的逐渐积累最终应该会注定任何严格意义上的克隆谱系灭绝。线粒体DNA的长期独立生存所带来的悖论表明，在有性繁殖而不是克隆繁殖中，克隆火蜥蜴的核染色体组偶尔会被有性种雄性的核染色体组所取代。基因组特异性引物将允许对这种染色体替换发生的频率进行评估。尽管克隆生殖具有短期优势，但这些数据对有性生殖的持久性理论很重要。比较线粒体和核DNA的变异性，将为评估自然选择对克隆谱系中这两种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.