Fig. 11

Model for sex determination in sand flies. In female embryos, a maternal tra mRNA or TRA protein, and a maternal auxiliary TRA-2 protein led to the activation of a positive feedback autoregulative loop. The early TRA and TRA-2 proteins drive the female-specific splicing of the zygotically transcribed tra pre-mRNA so that new TRA protein can be produced. The newly synthesized protein controls the maintenance of tra autoregulation and the female-specific splicing of dsx and fru pre-mRNAs leading to female development. In male embryos, tra autoregulation is impaired by a male-specific factor, resulting in absence of the TRA protein, determining the male-specific splicing of the dsx and fru genes and thus inducing male development. The mechanism by which tra autoregulation is exerted in sand flies (as well as in the other insect species) is unknown. However, the absence of the TRACAM domain in sand fly TRAs led us to hypothesize that a different TRA region is involved in the control of the autoregulation or that a novel and unknown auxiliary protein could act, in parallel to TRA-2, to regulate sex-specific alternative splicing of tra, dsx and fru pre-mRNA in insects