α-Spectrin and integrins act together to regulate actomyosin and columnarization, and to maintain a monolayered follicular epithelium

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 alpha-Spectrin and beta-Spectrin are essential to maintain a monolayered FE, but, contrary to previous work, spectrins are not required to control proliferation. Furthermore, spectrin mutant cells show differentiation and polarity defects only in the ectopic layers of stratified epithelia, similar to integrin mutants. Our results identify alpha-Spectrin and integrins as novel regulators of apical constriction-independent cell elongation, as alpha-Spectrin and integrin mutant cells fail to columnarize. Finally, we show that increasing and reducing the activity of the Rho1-Myosin II pathway enhances and decreases multilayering of alpha-Spectrin cells, respectively. Similarly, higher Myosin II activity enhances the integrin multilayering phenotype. This work identifies a primary role for alpha-Spectrin in controlling cell shape, perhaps by modulating actomyosin. In summary, we suggest that a functional spectrin-integrin complex is essential to balance adequate forces, in order to maintain a monolayered epithelium.