Alpha-Spectrin and Integrins act together to regulate actomyosin and columnarization, and to maintain a mono-layered follicular epithelium

Abstract

The Spectrin cytoskeleton crosslinks actin to the membrane, and although it has been greatly studied in erythrocytes, much is unknown about its function in epithelia. We have studied the role of Spectrins during epithelia morphogenesis using the Drosophila follicular epithelium (FE). As previously described, we show that α-Spectrin and β-Spectrin are essential to maintain a mono-layered FE, but, contrary to previous work, Spectrins are not required to control proliferation. Furthermore, spectrin cells show differentiation and polarity defects only in the ectopic layers of stratified epithelia, similar to integrin mutants. Our results identify α-Spectrin and integrins as novel regulators of apical constriction-independent cell elongation, as α-spectrin and integrin cells fail to columnarize. Finally, we show that increasing and reducing the activity of the Rho1-myosin-II pathway enhances and decreases multi-layering of α-spectrin cells, respectively. Similarly, higher myosin-II activity enhances the integrin multi-layering phenotype. This work identifies a primary role for α-Spectrin in controlling cell shape, perhaps by modulating actomyosin. All together, we suggest that a functional Spectrin-Integrin complex is essential to balance adequate forces, in order to maintain a mono-layered epithelium.