Characterisation of the M-locus and functional analysis of the male-determining gene in the housefly

The housefly, Musca domestica, is an ideal model to study the evolution of sex determination and sex chromosomes as it harbours various sex determination systems. For instance, the dominant male determiner (M) is normally located on the Y-chromosome, but can also be present on different autosomes in natural populations. Recently, we identified Mdmd (Musca domestica male determiner) as the male-determining gene in a housefly strain with an M on chromosome 3. Mdmd is considered to be the functional male-determining gene as targeted disruption of it leads to female development. Mdmd is a paralog of the splicing regulatory gene CWC22. The goal of my thesis was to further analyse the genomic structure of the M-locus and the function of Mdmd. Multiple tandemly arranged copies of Mdmd were detected that show various levels of homology to each other. Of these variants only one copy appears to contain an intact open reading frame, which is assumed to be the coding sequence of Mdmd. Comparison of Mdmd protein sequences with its paralog CWC22/NCM revealed that Mdmd protein sequences have a close phylogenetic relationship with Md-NCM, suggesting that the male-determining gene Mdmd evolved from a single duplication event of Md-ncm. Moreover, a similar clustered organization of Mdmd copies is found in M-loci on different autosomes, indicating that amplification of sex determination genes and translocation of complex sex determination regions, may be an important process in sex chromosome evolution.