A Novel Splice Variant of the Masculinizing Gene with piRNA-Cleavage-Site Defect Functions in Female External Genital Development in the Silkworm, .

In the silkworm, the sex-determination primary signal controls sex differentiation by specific binding of -derived piRNA to the cleavage site in mRNA, thus inhibiting protein production in the female. In this study, we identified a novel splicing isoform of , named , which lacks the intact sequence of the cleavage site, encoding a C-terminal truncated protein. Results of RT-PCR showed that was expressed in both sexes. Over-expression of and in female-specific cell lines showed that could be translated against the -piRNA cut. By RNA-protein pull-down, LC/MS/MS, and EMSA, we identified a protein BmEXU that specifically binds to an exclusive RNA sequence in compared to . Knockdown of resulted in abnormal morphology in female external genital and increased expression of the Hox gene , which similarly occurred by RNAi. These results suggest that the splice variant against -piRNA plays an important role in female external genital development, of which function is opposite to that of full-length . Our study provides new insights into the regulatory mechanism of sex determination in the silkworm.