Identification and Characterization of the Masculinizing Function of the Gene.

The () gene has been known to control sex development and dosage compensation in lepidopterans. However, it remains unclear whether its ortholog exists and plays the same roles in distantly related lepidopterans such as . To address this question, we cloned from (), which contains all essential functional domains of BmMasc, albeit with less than 30% amino acid sequence identity with BmMasc. Genomic PCR and qPCR analyses showed that is a Z chromosome-linked gene since its genomic content in males (ZZ) was two times greater than that in females (ZW). RT-PCR and RT-qPCR analyses revealed that expression was sex- and stage-biased, with significantly more transcripts in males and eggs than in females and other stages. Transfection of a mixture of three siRNAs of into a male embryonic cell line of led to the appearance of female-specific mRNA splicing isoforms of (), a downstream target gene of in the sex determination pathway. The knockdown of starting from the third instar larvae resulted in a shift of splicing from male to female isoforms, smaller male pupa and testes, fewer but larger/longer spermatocytes and sperm bundles, delayed pupation and internal fusion of the testes and follicles. These data demonstrate that functions as a masculinizing gene in the sex-determination cascade.