Characterization of the Gene BmEm4, a Homologue of Drosophila E(spl)m4, from the Silkworm, Bombyx mori

The Drosophila E(spl)m4 gene contains some highly conserved motifs (such as the Brd box, GY box, K box, and CAAC motif) in its 3′ untranslated region (3′ UTR). It was shown to be a microRNA target gene in Drosophila and to play an important role in the regulation of neurogenesis. We identified a homologue of the E(spl)m4 gene from Bombyx mori called BmEm4 and examined the expression patterns of BmEm4 mRNA and protein. There was a lack of correlation in the expression of the mRNA and protein between the different developmental stages, which raises the possibility of posttranscriptional regulation of the BmEm4 mRNA. Consistent with this idea is the finding that the 3′ UTR contains two putative binding sites for microRNAs. Moreover, given that the expression is the highest in the larval head, as confirmed by immunohistochemistry, we propose that BmEm4 may also be involved in the regulation of neurogenesis. Immunostaining indicated that BmEm4 is located primarily in the cytoplasm.