Bioinformatics and transcriptomics to uncover the sex determination in the sand fly species Phlebotomus perniciosus, a major Old World vector of Leishmania infantum.

In the Old World, the sand fly Phlebotomus perniciosus is the main vector of Leishmania infantum, the parasitic protozoan that causes visceral and cutaneous leishmaniases in humans and canine reservoir host, as well as, of known and emerging arboviruses considered relevant from an European public health perspective. P. perniciosus is widely distributed in the western Mediterranean Basin with the most important endemic focus of canine and human visceral leishmaniases of this area located in Italy, in the Campania region. We applied RNA-seq, de novo assembly and digital gene expression analysis to identify genes with sex-specific or sex-biased expression at a genome-wide level and to isolate genes involved in the sex determination pathway of the P. perniciosus. We assembled 55,393 high quality transcripts, of which 29,292 were unique, starting from adult whole body male and female pools. 11,736 transcripts had at least one functional annotation, including full-length low abundance salivary transcripts, 981 transcripts were classified as putative long non-coding RNAs and 244 transcripts encoded for putative novel proteins specific of the Phlebotominae sub-family. Differential expression analysis identified 8,590 transcripts significantly biased between sexes. Among them, we identified well conserved alternatively spliced transcripts of the transformer (tra), transformer-2 (tra-2), doublesex (dsx) and fruitless (fru) ortholog genes, which are responsible in Drosophila of somatic sexual differentition and genetic control of courtship behaviour. These preliminary data suggest a conservation of the sex determination cascade in this species. Our data could contribute to the study of the evolution of sex determination pathway in the under-studied Nematocera dipteran suborder and to the development of new control methods for sand fly vector species.