Cell-type-specific roles of Na+/K+ ATPase subunits in Drosophila auditory mechanosensation

Ion homeostasis is a fundamental cellular process particularly important in excitable cell activities such as hearing. It relies on the Na+/K+ ATPase (also referred to as the Na pump), which is composed of a catalytic alpha subunit and a beta subunit required for its transport to the plasma membrane and for regulating its activity. We show that alpha and beta subunits are expressed in Johnston's organ (JO), the Drosophila auditory organ. We knocked down expression of alpha subunits (ATP alpha and alpha-like) and beta subunits (nrv1, nrv2, and nrv3) individually in JO with UAS/Gal4-mediated RNAi. ATP alpha shows elevated expression in the ablumenal membrane of scolopale cells, which enwrap JO neuronal dendrites in endolymph-like compartments. Knocking down ATP alpha, but not alpha-like, in the entire JO or only in scolopale cells using specific drivers, resulted in complete deafness. Among beta subunits, nrv2 is expressed in scolopale cells and nrv3 in JO neurons. Knocking down nrv2 in scolopale cells blocked Nrv2 expression, reduced ATP alpha expression in the scolopale cells, and caused almost complete deafness. Furthermore, knockdown of either nrv2 or ATP alpha specifically in scolopale cells causes abnormal, electron-dense material accumulation in the scolopale space. Similarly, nrv3 functions in JO but not in scolopale cells, suggesting neuron specificity that parallels nrv2 scolopale cell-specific support of the catalytic ATP alpha. Our studies provide an amenable model to investigate generation of endolymph-like extracellular compartments.