Male determiner protein (M-factor) that controls male somatic sexual differentiation. Acts as a dominant factor that regulates the mRNA splicing of doublesex (dsx) or fruitless (fru) transcripts and promotes expression of male splice forms of dsx and fru. Male-specific expression. First detected 3 to 4 hours after oviposition, corresponding to the beginning of the syncytial blastoderm stage before sex is established. Feminized males, which display features such as the absence of one or both gonocoxites and gonostyli, or antennae with fewer and shorter setae than normal males. Mosquitoes shifts the alternative splicing of dsx and fru toward their female isoforms.