Genome wide analysis for genes involved in the lepidopteran insect sex determination cascade and its application to pest control

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We found that a Bombyx homolog of tra-2 is dispensable for the sex-specific splicing of Bmdsx pre-mRNA. Instead, a male-specific splice variant of Imp is involved in the male-specific splicing of Bmdsx. The male-specific expression of Imp is controlled by its autoregulatory function, whereby the protein product regulates the male-specific splicing of its own pre-mRNA. This suggests that Imp acts as the memory device for sex determination in the silkworm. In an attempt to identify the Fem gene of B. mori, we performed comparative analysis of de novo transcriptome assembly between male and female embryos at the sex-determining stage. Among 149 cDNAs that were expressed at more than eight-fold higher in females than in males, two cDNAs (FET-W1, FET-W2) were derived from genes located on the sex-determining region of the W chromosome. Knockdown of FETW-1 induced expression of male-type Bmdsx and ImpM in female eggs. These results suggest that FET-W1 is the most likely candidate for Fem.