Sex determination in Bombyx mori

We describe here the current status and future prospects of sex-determination studies in the silkworm, Bombyx mori. The sex of Bombyx is strongly controlled by the presence of the W chromosome. Although several classical studies suggested that a presumptive feminizing gene (Fem) is located at a limited portion of the W chromosome, the Fem gene has not yet been cloned. Recently, the homologues of Drosophila sex determining gene doublesex was found in Bombyx and analysed. The doublesex in Bombyx (Bmdsx) is clearly regulated by sex-specific splicing, as is Drosophila doublesex. In spite of the fact that the upstream system in sex determination is very different between Drosophila and Bombyx, they may share a common downstream gene, doublesex. Future studies should try to locate the molecular cascade from the W chromosome to Bmdsx and identify the terminal sexspecific genes regulated by BmDSX.