A PI4KIIIα protein complex is required for cell viability during Drosophila wing development

Phosphatidylinositol 4 phosphate (PI4P) and phosphatidylinositol 4,5 bisphosphate [PI(4,5)P-2] are enriched on the inner leaflet of the plasma membrane and proposed to be key determinants of its function. PI4P is also the biochemical precursor for the synthesis of PI(4,5)P-2 but can itself also bind to and regulate protein function. However, the independent function of PI4P at the plasma membrane in supporting cell function in metazoans during development in vivo remains unclear. We find that conserved components of a multi-protein complex composed of phosphatidylinositol 4-kinase III alpha (PI4KIII alpha), TTC7 and Efr3 is required for normal vein patterning and wing development. Depletion of each of these three components of the PI4KIII alpha complex in developing wing cells results in altered wing morphology. These effects are associated with an increase in apoptosis and can be rescued by expression of an inhibitor of Drosophila caspase. We find that in contrast to previous reports, PI4KIII alpha depletion does not alter key outputs of hedgehog signalling in developing wing discs. Depletion of PI4KIII alpha results in reduced PI4P levels at the plasma membrane of developing wing disc cells while levels of PI(4,5)P-2, the downstream metabolite of PI4P, are not altered. Thus, PI4P itself generated by the activity of the PI4KIII alpha complex plays an essential role in supporting cell viability in the developing Drosophila wing disc.