Bhattarai, A.; McGhie, E. W.; Woo, J. C.; Niraula, S.; Rosetti, P.; Kim, J. M.; Popoola, E.; Johnson, R.

Heterogeneity and complexity of cytoskeletal structures, and how these are regulated, is poorly understood. Here we use cells of the Drosophila pupal eye as models to explore diversity in the actin cytoskeleton. We found that different F-actin structures emerge in primary, secondary, and tertiary pigment cells as they mature. Primary cells became characterized by dense accumulations of apical F-actin that we termed Apical Ribs of Actin Fibers (ARAFs). The formins Diaphanous and Dishevelled Associated Activator of Morphogenesis are essential for generation of ARAFs, which are connected into a network by alpha-Actinin, the villin Quail, and Spectrins, and linked to the apical membrane by Quail and Spectrins. ARAFs are contractile, stress-fiber-like, and connect to adherens junctions. Impairing ARAFs indicated that this network maintains cortical tension and is crucial for primary cells to achieve their characteristic shapes. Our evaluation of the three-dimensional shape of primary cells reveals that ARAFs are essential for the rounding and elevation of the apical membrane. Hence, a toolkit of conserved actin regulatory proteins builds and maintains a network of apical stress fibers that governs the morphology of the cell.