Parental RNAi-mediated knockdown of maleless gene expression in the codling moth Cydia pomonella

The maleless gene (mle) encodes one of the protein components of the "compensasome," which mediates dosage compensation of X-linked genes in Drosophila melanogaster. In this study, we isolated a mle cDNA homologue and performed parental RNAi knockdown experiments targeting mle expression in embryos. Injection of mle dsRNA in or near the ovaries of female codling moth pupae resulted in significantly reduced survival to adulthood relative to injected controls. This finding is consistent with the requirement of the mle gene product during female pupal development.

Eggs laid by mated adult females injected with mle dsRNA had a significantly reduced hatch rate relative to injected and uninjected controls. However, there was no statistically significant difference in the percentages of neonates surviving to pupal stage for all treatment groups and there was no statistically significant difference in the ratio of males to females produced for any treatment group.

These results suggests that the mle gene product does not play a role in dosage compensation in the codling moth. The possibility that dosage compensation of sex-linked genes does not occur in the Lepidoptera has been suggested by earlier investigations of Z-linked gene expression of genes or gene products in other lepidopteran species. This raises the question of what biological role the codling moth ortholog of the Drosophila mle gene is playing, and whether it functions in some other essential RNA-guided chromatin remodeling process.