Differences in the genetic control of early egg development and reproduction between and its parthenogenetic relative .

BACKGROUND

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.

RESULTS

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.

CONCLUSIONS

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.