Sex determination in Aedes aegypti.

We proposed an hypothetical model for sex determination in Aedes that is presented here. In this model we hypothesized the existence of two different upstream regulators that we named SR-M and SR-F (SR is for Splicing Regulator, not necessarily an SR protein). In males a male-determining factor inhibits the SR-F protein required for the female-specific splicing of exon 5b and activates the SR-M protein required for the male-specific repression of exon 5a. It is also conceivable that the M could directly control the splicing of exon 5a. In any case, the result are the skipping of both female-specific dsx exons, with the production of a male-specific dsx isoform, and the default splicing of P1 exon, with the production of the male-specific fru isoform. In females the absence of the M leads to the default splicing of female-specific exons 5a and to the activation of the SR-F factor which in turn regulates the female-specific splicing of exon 5b. As a result two different female-specific DSX proteins are produced. However is still to be cleared how the repression of exon 5a is achieved in some but not all dsx female transcripts. The activation of the SR-F factor again in turn regulates the female-specific splicing of fru P1 exon and as a result the male-specific FRU protein is not produced. Hence we present a model with two different default splicing mode for dsx and fru gene and this is most probably the first case in the species studied till now. This could be better explained if we suppose that M factor is able to act directly on dsx gene but not on fru gene in males, due to the different binding sites we have identified (Nasonia dsxRE and dsxRE) . In the next future we will focus our attention on identification of the upstream regulators and their functional analysis to confirm or not our speculative hypotheses.