Transcriptomic analysis of the piRNA pathway in the Chagas disease vector Rhodnius prolixus

The piRNA pathway provides a defense system that protects the genome of metazoans from the deleterious effects caused by transposable elements mobilization. Core components of the pathway are the Piwi clade Argonaute proteins and the associated small non-coding RNAs termed piRNAs. In this study, we set to investigate the evolutionary conservation of the piRNA pathway in Rhodnius prolixus, a primary insect vector of the Chagas disease. First, we identified the Rhodnius orthologs of the proteins that act in the biogenesis and function of the piRNAs in the fruit fly Drosophila melanogaster ovary. Then, we employed transcriptomic analyses using total RNA extracted from previtellogenic stages of of Rhodnius’ oogenesis to determine their expression levels. Our study reveals that important enzymatic activities, including the three piwi orthologs (i.e. Rp-piwi2, Rp-piwi3 and Rp-ago3) and a vasa gene are expressed at substantial levels in Rhodnius ovaries. We also show the a fourth piwi ortholog, namely Rp-piwi1, is not expressed in early oogenesis and might be dispensable for Rhodnius adult female fertility. Finally, we unveil interesting differences between Drosophila and Rhodnius. For instance, the spnE gene, which is crucial for piRNA biogenesis in the fruit fly, is expressed at negligible levels in Rhodnius, where it might not be required for piRNA production. Our transcriptomic analyses also provide a full catalog of the genes expressed in Rhodnius ovaries and reveal that the current annotations of the Rhodnius genome do not fully reflect the actual structure and length of the transcripts expressed in this species. Thus, our study provides new insight in the evolution of the piRNA pathway and a valuable resource for future genomic and functional studies.