Male determiner protein (M-factor) that controls male somatic sexual differentiation (PubMed:28495751). Acts as a dominant factor that regulates the mRNA splicing of transformer (tra) and doublesex (dsx) transcripts and promotes expression of male splice forms of tra and dsx (PubMed:28495751). Probably acts as a component of the spliceosome C complex required for mRNA splicing factor and exon-junction complex (EJC) assembly (By similarity). Hinders eIF4AIII from non-specifically binding RNA and escorts it to the splicing machinery to promote EJC assembly on mature mRNAs (By similarity). Component of the spliceosome C complex. Specifically expressed in early male embryos. Zygotic expression first appears in 2- to 3-hour-old embryos (cellularized blastoderm stage). Expression is then maintained throughout male development until adulthood. Complete sex reversal to fertile females because flies exclusively express the female splice variants of transformer (tra) and doublesex (dsx). The M.domestica genome only codes for one male determiner Mdmd protein, which is encoded in the M region, and can be located at different loci on the genome (chromosomes II, III, V or Y). The M region contains a cluster of tandemly repeated Mdmd copies with only one intact copy: other copies are degenerate with large truncations and frameshifts and are assumed to be non-functional. The presence of multiple copies in the M region may preserve its integrity in a hostile non-recombining environment. This protein is encoded on chromosome III. Belongs to the CWC22 family. It's a thin line - Issue 201 of March 2018