FIG. 3.
Forces driving apical constriction and epithelial folding. (a) Contraction pulses generated by the actomyosin network are initiated by Snail, whereas the contracted cell shape is stabilized by Twist. Adherens junctions assemble at the apical side into spot junctions when contraction initiates.184 (b) The modulation of tension at basal and apical sides drives the folding of epithelia. Tension generated at adherens junctions and actin (de)polymerization control YAP activity. The mechanical environment can influence (de)polymerization of actin filaments, which, in turn, affects tension exerted at the adherens junctions. Increases in F-actin and tension inhibit Hippo signaling and promote YAP activity.185 (c) Modulation of cell shape and density in response to matrix curvature changes leads to YAP nuclear export on crests and nuclear import in valleys.67