Demonstration of contractility of circumferential actin bundles and its morphogenetic significance in pigmented epithelium in vitro and in vivo.

Each pigmented epithelial cell bears circumferential actin bundles at its apical level when the pigmented epithelium is established in eyes in situ or in culture in vitro. Well-differentiated pigmented epithelia in culture were treated with a 50% glycerol solution containing 0.1 M KCl, 5 mM EDTA, and 10 mM sodium phosphate buffer, pH 7.2, for 24 h or more at 4 degrees C. When the glycerinated epithelium was transferred to the ATP solution, each cell constituting the epithelium began to contract. The epithelium was cleaved into many cell groups as a result of contraction of each cell. The periphery of each cell group was lifted to form a cup or vesicle and eventually detached from the substratum. However, those cells that had not adhered tightly and not formed a monolayer epithelium with typical polygonal cellular pattern contracted independently as observed in the glycerinated fibroblasts. Contraction of the glycerinated pigmented epithelial cells was inhibited by N-ethylmaleimide but not by cytochalasin B. ITP and UTP also effected the contraction of the glycerinated cells, but GTP and ADP did not. Ca2+ was not required. This contractile model of pigmented epithelium provides a useful experimental system for analyzing the function of actin in cellular morphogenesis.