Transgenic Expression of the piRNA-Resistant Masculinizer Gene Induces Female-Specific Lethality and Partial Female-to-Male Sex Reversal in the Silkworm,Bombyx mori

In bombyx mori (b. mori),fem pirna originates from the w chromosome and is responsible for femaleness. the fem pirna-piwi complex targets and cleaves mrnas transcribed from the masc gene. masc encodes a novel ccch type zinc-finger protein and is required for male-specific splicing of b. mori doublesex (bmdsx) transcripts. in the present study,several silkworm strains carrying a transgene,which encodes a fem pirna-resistant masc mrna (masc-r),were generated. forced expression of the masc-r transgene caused female-specific lethality during the larval stages. one of the masc-r strains weakly expressed masc-r in various tissues. females heterozygous for the transgene expressed male-specific isoform of the bombyx homolog of insulin-like growth factor ii mrna-binding protein (impm) and bmdsx. all examined females showed a lower inducibility of vitellogenin synthesis and exhibited abnormalities in the ovaries. testis-like tissues were observed in abnormal ovaries and,notably,the tissues contained considerable numbers of sperm bundles. homozygous expression of the transgene resulted in formation of the male-specific abdominal segment in adult females and caused partial male differentiation in female genitalia. these results strongly suggest that masc is an important regulatory gene of maleness in b. mori.