A homologue of the Drosophila doublesex gene is transcribed into sex-specific mRNA isoforms in the silkworm, Bombyx mori

The doublesex (dsx) gene is known as the final gene of the sex-determining cascade in Drosophila melanogaster. We have isolated a homologue of dsx in the silkworm, Bombyx mori, which has an epistatic feminizing gene located o n the W chromosome. RT-PCR analysis indicated that B, mori dsx (Bmdsx) was transcribed in all the examined tissues, and the size of the amplified prod ucts was different between males and females. In Northern blot hybridizatio n of poly(A)(+) RNA, the Bmdsx probe also detected a band with a sex-specif ic size difference. The male-specific cDNA lacked the sequence between 713 and 961nt of the female-specific cDNA. An RNase protection assay indicated that this sequence was male-specifically removed from the Bmdsx pre-mRNA. S outhern blot analysis showed that Bmdsx is present at a single copy in the genome. These results suggested that the primary Bmdsx transcript is altern atively spliced to yield male- and female-specific mRNA isoforms. These sex -specific isoforms encode polypeptides with a common amino terminal sequenc e but sex-specific carboxyl termini. DNA binding domain (DM domain) of BmDS X has 80% identity with D. melanogaster DSX proteins. These results suggest the Bmdsx would also regulate sexual differentiation, as does the Drosophi la dsx gene. (C) 2001 Elsevier Science Inc. All rights reserved.