Spectrin coordinates cortical actomyosin organization and differentiation essential for a functional epithelial barrier

Cell shape and cell fate are tightly linked. However, how cortical cytoskeletal organization that controls cell shape connects to signaling and drives cell fate changes is still poorly understood. Here we used the skin epidermis as paradigm for spatiotemporally coordinated cell shape and fate changes. Upon induction of differentiation, epidermal stem cells stratify and increasingly flatten to form a functional barrier. Here, we identify spectrin, an actin-binding membrane cytoskeleton protein, as a major regulator of epidermal cell shape, signaling and differentiation to control the formation of a functional epithelial barrier. Loss of αII-spectrin (encoded by Sptan1 ) in the developing mouse epidermis inhibited suprabasal cell flattening, differentiation, and epidermal barrier function. Spectrin cortical localization required E-cadherin and actomyosin, while spectrin itself controls cortical actomyosin organization. In detail, using high resolution imaging and laser ablation revealed that spectrin was essential to form actin-based honeycomb-like cortical lattices that are essential to maintain cortical tension and structural integrity. We found that spectrin-dependent actomyosin organization controlled the activity and localization of the growth factor receptor EGFR, and the cation channel TRPV3, known to activate the enzyme transglutaminase essential for barrier function. Indeed, loss of spectrin, E-cadherin or actomyosin inhibition reduce TGM1 activity. Together, our results provide novel insights into how cortical organization and mechanics regulate cell shape and spatially activate signals necessary for differentiation and epithelial tissue function.