Gene discovery in the Old World Leishmania vector Phlebotomus perniciosus (Diptera, Psychodidae): de novo assembly and digital gene expression analysis of sexed transcriptomes from a laboratory strain and Ischia island natural populations.

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 are applying RNA-seq 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 defined a de novo reference transcriptome of about 50k transcripts which includes well conserved alternatively spliced transcripts of the doublesex (dsx) and fruitless (fru) ortholog genes, which are responsible in Drosophila of somatic sexual differentition and genetic control of courtship behaviour, respectively. Interestingly, an ortholog of the key switch gene of insect female sex determination, the transformer (tra) gene, is apparently absent in P. perniciosus transcriptome and the tra auxiliary factor transformer-2 (tra-2) is highly divergent respect to other dipteran tra-2 orthologs. These preliminary data suggest only a partial 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, the comparative and genome-wide analysis of haematofagy in Nematocera species and to develop new control methods for the sand fly vector species.