RNAseK is vital for epithelial function in Drosophila melanogaster

The transporting epithelial tissues comprising the Drosophila melanogaster alimentary and renal systems are known to share a common set of enriched genes sometimes referred to as the "epitheliome", reflecting their shared transport functions. Core amongst these genes are the vha genes, which encode subunits of the large Vacuolar-type ATPase (V-ATPase) proton pump complex. However, many of the non-vha components of the epitheliome remain broadly uncharacterised. Here, we explore the role of RNAseK, a gene identified during unbiased epithelial screens in Drosophila whose function within insects is not yet known, though evidence from mammalian systems suggest a role in supporting proton pump activity. We demonstrate computationally that RNAseK is strongly conserved across evolutionary history, and that expression is regulated by the highly epithelial-specific dCLEAR motif. Seeking to understand why epithelial expression is so emphasised, we have assayed the effects of RNAseK knockdown in different epithelia throughout the fly. Across hindgut, midgut, and Malpighian tubules, we note profound defects in gross tissue morphology, transport activity, and fly survival. Mechanistically, RNAseK co-localises apically with the V-ATPase subunit Vha55, and RNAseK knockdown phenotypes overlap with those caused by V-ATPase perturbation. These findings are consistent with a role for RNAseK in acidification-dependent epithelial transport and membrane homeostasis, although direct effects on V-ATPase biochemical activity or on other epithelial transport and junctional pathways remain to be tested.