Identification and characterization of the male-determining gene of the housefly, Musca domestica

Sexual propagation is one of the essential features of life. Sexually reproducing organisms are usually male or female, but the genetic mechanisms that determine the sexes are very diverse. The insect class illustrates this diversity with different chromosomal systems and sex determination genes. The housefly (Musca domestica) has different methods for sex determination which makes it an excellent model organism to study how different sex-determining mechanisms have evolved. The housefly has six pairs of chromosomes, and a male-determining gene (M-factor) can be present on the Y-chromosome (MY) or any of the other five chromosomes (MI, MII, MIII, MIV and MV). In this study, we compared the transcriptomes of male and female embryos and identified the male-determining gene, which we named Mdmd (for Musca domestica male determiner). Mdmd originated from a duplication of the spliceosomal factor gene CWC22. Mdmd is the same gene in different M-strains (MII, MIII, MV and MY) indicating that it translocated to different genomic sites in the M. domestica genome. Knockdown of Mdmd by embryonic RNA interference causes sex-reversal, M containing individuals develop as males with fully differentiated ovaries. This fundamental research with houseflies has led to a deeper understanding of the diversity and mechanisms of sex determination. It also has practical implications and may aid in the development of novel genetic systems to improve existing methods in control management of pest fly species and other harmful insects.