Effects of Functional Depletion of on Male Development in the Sawfly, .

The () gene, which encodes a transcription factor, regulates sexual differentiation in insects. Sex-specific splicing of occurs to yield male- and female-specific isoforms, which promote male and female development, respectively. Thus, functional disruption of leads to an intersexual phenotype in both sexes. We previously identified a ortholog in the sawfly, . Similar to in other insects, in the sawfly yields different isoforms in males and females as a result of alternative splicing. The sawfly exploits a haplodiploid mode of reproduction, in which fertilized eggs develop into diploid females, whereas unfertilized eggs parthenogenetically develop into haploid males. In the present study, we knocked down the ortholog of () during several developmental stages with repeated double-stranded RNA (dsRNA) injections. Knockdown of via parental RNA interference (RNAi), which enables knockdown of genes in offspring embryos, led to a lack of internal and external genitalia in haploid male progeny. Additional injection of dsRNA targeting in these animals caused almost complete male-to-female sex reversal, but the resulting eggs were infertile. Notably, the same knockdown approach using diploid males obtained by sib-crossing caused complete male-to-female sex reversal; they were morphologically and behaviorally females. The same RNAi treatment did not affect female differentiation. These results indicate that in the sawfly is essential for male development and its depletion caused complete male-to-female sex reversal. This is the first demonstration of functional depletion of not causing intersexuality but inducing total sex reversal in males instead.