Studying the Role of piRNA Pathway in Evolution of the Genome, Protein-coding Genes and Speciation

Species of the genus Drosophila have served as favorite models in speciation studies; however, genetic factors of interspecific reproductive incompatibility are underinvestigated. The study of the molecular mechanisms of hybrid sterility is important for both fundamental and applied points of view: it makes possible to clarify the evolutionary patterns of the speciation process and to develop an approach for increasing of hybrid reproduction potential. In this project we investigated the role of small noncoding piRNAs in postzygotic reproductive isolation and speciation using a model of closely related Drosophila species of the Simulans clade. Transposable elements are the main targets of piRNA. Components of the piRNA pathway evolve rapidly because organisms need to quickly adapt to the invasion of new transposable elements. Moreover, a number of studies demonstrates species- and sex-specific regulation of protein-coding genes by piRNA. Such features of the piRNA pathway can lead to the emergence and fixation of genomic differences and, as a consequence, reproductive barriers. In this project, we have developed an approach that allows us to search for protein-coding genes that are targets of piRNAs. Using this approach, we identified several novel piRNA targets in Drosophila gonads. In addition, we identified differential allele-specific expression of RDC complex components in the ovaries of D. melanogaster and D. simulans hybrids. We found that in the absence of the RDC complex from the D. melanogaster genome, the RDC complex from the D. simulans genome was able to mediate non-canonical transcription of double-stranded piRNA clusters in hybrid ovaries.