Department of Biology, Indiana University, Bloomington, IN 47405, USA.
Proc Natl Acad Sci U S A. 2012 Jan 17;109(3):858-63. doi: 10.1073/pnas.1119667109. Epub 2012 Jan 3.
Although transitions from sexual to asexual reproduction are thought to have important evolutionary consequences, little is known about the mechanistic underpinnings of these changes. The cyclical parthenogen Daphnia pulex is a powerful model in which to address these issues because female-limited meiosis suppression can be transmitted to sexual individuals via males, providing the opportunity for genetic dissection of the trait. A previous study identified genomic regions differentiating obligately asexual females from their sexual counterparts, and a candidate gene within one such region, encoding the meiotic cohesin Rec8, is the subject of this investigation. The D. pulex genome contains three Rec8 loci, all of which are quite polymorphic. However, at one of the loci, all obligately asexual clones carry an allele containing an identical upstream insertion of a transposable element as well as a frameshift mutation, both of which are completely absent from sexual lineages. The low level of variation within the insertion allele across all asexual lineages suggests that this element may be in the process of spreading through the species, and abrogation or modification of Rec8 function is possibly responsible for converting meiotically reproducing lineages into obligate asexuals.
虽然从有性生殖到无性生殖的转变被认为具有重要的进化后果，但人们对这些变化的机制基础知之甚少。周期性的孤雌生殖的溞属（Daphnia pulex）是一个强大的模型，可以用来解决这些问题，因为雌性限制作减数分裂的抑制可以通过雄性传递给有性个体，从而为该特征的遗传剖析提供机会。先前的研究确定了区分强制性无性雌性与其有性对应物的基因组区域，并且该区域内的一个候选基因，即编码减数分裂黏合蛋白 Rec8 的基因，是本研究的主题。溞属（Daphnia pulex）基因组包含三个 Rec8 基因座，所有这些基因座都非常多态。然而，在一个基因座上，所有强制性无性克隆都携带一个等位基因，该等位基因包含一个可转座元件的相同上游插入以及一个移码突变，而这些在有性谱系中完全不存在。所有无性谱系中插入等位基因内的低变异水平表明，该元件可能正在通过物种传播，并且 Rec8 功能的缺失或修饰可能负责将有性繁殖谱系转化为强制性无性。
