Calcium waves facilitate and coordinate the contraction of endfeet actin stress fibers in Drosophila interommatidial cells

Abstract

Actomyosin contraction shapes the Drosophila eyes panoramic view. The convex curvature of the retinal epithelium, organized in [~]800 close-packed ommatidia, depends upon a fourfold condensation of the retinal floor mediated by contraction of actin stress fibers in the endfeet of interommatidial cells (IOCs). How these tensile forces are coordinated is not known. Here, we discover a novel phenomenon: Ca2+ waves regularly propagate across the IOC network in pupal and adult eyes. Genetic evidence demonstrates that IOC Ca2+ waves are independent of phototransduction, but require inositol 1,4,5-triphosphate receptor (IP3R), suggesting these waves are mediated by Ca2+ releases from ER stores. Removal of IP3R disrupts stress fibers in IOC endfeet and increases the basal retinal surface by [~]40%, linking IOC waves to facilitating stress fiber contraction and floor morphogenesis. Further, IP3R loss disrupts the organization of a collagen IV network underneath the IOC endfeet, implicating ECM and its interaction with stress fibers in eye morphogenesis. We propose that coordinated Ca2+ spikes in IOC waves promote stress fiber contractions, ensuring an organized application of the planar tensile forces that condense the retinal floor. Summary StatementCa2+ waves have an important role in generating tensile forces to shape the Drosophila eyes convex curvature. Coordinated Ca2+ spikes facilitate actomyosin contractions at the basal endfeet of interommatidial cells.