The mechanism of sex-specific splicing at the doublesex gene is different between Drosophila melanogaster and Bombyx mori

We have previously reported that Bmdsx, a homologue of the sex-determining gene, doublesex (dsx), was found to be sex-specifically expressed in variou s tissues at larval, pupal, and adult stages in the silkworm, Bombyx mori, and was alternatively spliced to yield male- and female-specific mRNAs. To reveal sex-specific differences in splicing patterns of Bmdsx pre-mRNA, the genomic sequence was determined and compared with male- and female-specifi c Bmdsx cDNA sequences. The open reading frame (ORF) consisted of five exon s. Exons 3 and 4 were specifically incorporated into the female type of Bmd sx mRNA. On the other hand, exon 2 was spliced to exon 5 to produce the mal e type mRNA of Bmdsx. As in the case of Drosophila dsx, the OD2 domain was separated by a female-specific intron into sex-independent and sex-dependen t regions. Sex-specific splicing occurred in equivalent positions in the Dr osophila dsx gene. However, unlike Drosophila dsx, the female-specific intr ons showed no weak 3' splice sites, and the TRA/TRA-2 binding site related sequences were not found in the female-specific exon, nor even in any other regions of the Bmdsx gene. Moreover, an in vitro splicing reaction consist ing of HeLa cell nuclear extracts showed that the female-type of Bmdsx mRNA represented the default splicing. These: findings suggest that the structu ral features of the sex-specific splicing patterns of Bmdsx pre-mRNA are si milar to those of Drosophila dsx but the regulation of sex-specific alterna tive splicing of Bmdsx pre-mRNA is different. (C) 2001 Elsevier Science Ltd . All rights reserved.