Conditional knockdown of transformer in sheep blow fly suggests a role in repression of dosage compensation and potential for population suppression

Abstract

The transformer (tra) gene is essential for female development in many insect species, including the Australian sheep blow fly, Lucilia cuprina. Sex-specific tra RNA splicing is controlled by Sex lethal (Sxl) in Drosophila melanogaster but is auto-regulated in L. cuprina. Sxl also represses X chromosome dosage compensation in female D. melanogaster. We have developed conditional Lctra RNAi knockdown strains using the tet-off system. Four strains did not produce females on diet without tetracycline and could potentially be used for genetic control of L. cuprina. In one strain, which showed both maternal and zygotic tTA expression, most XX transformed males died at the pupal stage. RNAseq and qRT-PCR analyses of mid-stage pupae showed increased expression of X-linked genes in XX individuals. These results suggest that Lctra promotes somatic sexual differentiation and inhibits X chromosome dosage compensation in female L. cuprina. However, XX flies homozygous for a loss-of-function Lctra knockin mutation were fully transformed and showed high pupal eclosion. Two of five X-linked genes examined showed a significant increase in mRNA levels in XX males. The stronger phenotype in the RNAi knockdown strain could indicate that maternal Lctra expression may be essential for initiation of dosage compensation suppression in female embryos.

Identification and functional analysis of the female determiner gene in the bean bug, Riptortus pedestris

“…More and more examples show that the sex‐specific lethality genes of the sex‐determination pathway not only function in sex determination, but also in X chromosome dosage compensation. In D. melanogaster and A. gambiae , sex‐specific lethality caused by loss‐of‐function mutations or knockdown of sex‐determination genes results from misregulation of dosage compensation 17,33–35 . We found that RNAi‐mediated knockdown of the expression of Rpfmd caused the female‐specific lethality.…”

“…In D. melanogaster and A. gambiae, sex-specific lethality caused by loss-of-function mutations or knockdown of sexdetermination genes results from misregulation of dosage compensation. 17,[33][34][35] We found that RNAi-mediated knockdown of the expression of Rpfmd caused the female-specific lethality. We therefore compared the autosomes and X chromosomes transcription of dsRpfmd female with that of dsgfp females, and found that X chromosome transcription in dsRpfmd females was significantly up-regulated, which in other species, was toxic and might cause the female-specific death, indicating that Rpfmd regulated the dosage compensation in R. pedestris (Fig.…”