Kraus Christopher, Schiffer Philipp H, Kagoshima Hiroshi, Hiraki Hideaki, Vogt Theresa, Kroiher Michael, Kohara Yuji, Schierenberg Einhard
Zoologisches Institut, Universität zu Köln, Cologne, NRW Germany.
Present Address: Institute for Genetics, Universität zu Köln, Cologne, NRW Germany.
Evodevo. 2017 Oct 18;8:16. doi: 10.1186/s13227-017-0081-y. eCollection 2017.
The free-living nematode is the closest known relative of with parthenogenetic reproduction. It shows several developmental idiosyncracies, for example concerning the mode of reproduction, embryonic axis formation and early cleavage pattern (Lahl et al. in Int J Dev Biol 50:393-397, 2006). Our recent genome analysis (Hiraki et al. in BMC Genomics 18:478, 2017) provides a solid foundation to better understand the molecular basis of developmental idiosyncrasies in this species in an evolutionary context by comparison with selected other nematodes. Our genomic data also yielded indications for the view that is a product of interspecies hybridization.
In a genomic comparison between , , other representatives of the genus and the more distantly related and , certain genes required for central developmental processes in like control of meiosis and establishment of embryonic polarity were found to be restricted to the genus . The mRNA content of early embryos was sequenced and compared with similar stages in and . We identified 350 gene families transcribed in the early embryo of but not in the other two nematodes. Looking at individual genes transcribed early in but not in and , we found that orthologs of most of these are present in the genomes of the latter species as well, suggesting heterochronic shifts with respect to expression behavior. Considerable genomic heterozygosity and allelic divergence lend further support to the view that may be the result of an interspecies hybridization. Expression analysis of early acting single-copy genes yields no indication for silencing of one parental genome.
Our comparative cellular and molecular studies support the view that the genus differs considerably from the other studied nematodes in its control of development and reproduction. The easy-to-culture parthenogenetic , with its high-quality draft genome and only a single chromosome when haploid, offers many new starting points on the cellular, molecular and genomic level to explore alternative routes of nematode development and reproduction.
自由生活的线虫是已知孤雌生殖的最亲近的亲属。它表现出一些发育特性，例如在繁殖方式、胚胎轴形成和早期卵裂模式方面（Lahl等人，《国际发育生物学杂志》50:393 - 397，2006年）。我们最近的基因组分析（Hiraki等人，《BMC基因组学》18:478，2017年）通过与选定的其他线虫进行比较，为在进化背景下更好地理解该物种发育特性的分子基础提供了坚实的基础。我们的基因组数据也为认为该线虫是种间杂交产物的观点提供了线索。
在该线虫与该属的其他代表物种以及亲缘关系更远的其他线虫之间进行基因组比较时，发现该线虫中一些中央发育过程所需的基因，如减数分裂控制和胚胎极性建立，仅限于该属。对该线虫早期胚胎的mRNA含量进行了测序，并与其他两种线虫的相似阶段进行了比较。我们鉴定出350个基因家族在该线虫早期胚胎中转录，但在其他两种线虫中不转录。查看在该线虫早期转录但在其他两种线虫中不转录的单个基因时，我们发现其中大多数的直系同源基因也存在于后两者的基因组中，这表明在表达行为方面存在异时性变化。相当程度的基因组杂合性和等位基因差异进一步支持了该线虫可能是种间杂交结果的观点。对早期起作用的单拷贝基因的表达分析未显示一个亲本基因组沉默的迹象。
我们的比较细胞和分子研究支持这样一种观点，即该属在线虫的发育和繁殖控制方面与其他研究的线虫有很大不同。易于培养的孤雌生殖的该线虫，拥有高质量的草图基因组且单倍体时只有一条染色体，在细胞、分子和基因组水平上提供了许多新的起点，以探索线虫发育和繁殖的替代途径。
