Male determiner protein (M-factor) that controls male somatic sexual differentiation. Acts as a dominant factor that regulates the mRNA splicing of doublesex (dsx) transcripts and promotes expression of male splice forms of dsx. Expression is male-specific. Transcription begins in embryos between 2 and 2.5 hours after oviposition, before blastoderm formation, and expression and continues throughout the life of the mosquito. Expression precedes establishment of sex-specific splicing of dsx by up to 6 hours. Male-specific lethality in embryos.