Differential actin-dependent localization modulates the evolutionarily conserved activity of Shroom family proteins

Shroom is an actin-associated determinant of cell morphol-ogy that is required for neural tube closure in both mice and frogs. Shroom regulates this process by causing apical constric-tion of epithelial cells via a pathway involvingmyosin II.Herewe report on characterization of the Shroom-related proteins Apxl andKIAA1202 and their role in cell architecture. Shroom,Apxl, and KIAA1202 exhibit differing abilities to interact with the actin cytoskeleton. In fibroblasts, Shroom readily associates with actin stress fibers and induces bundling, Apxl is found on cortical actin, and KIAA1202 is localized to a cytoplasmic pop-ulation of F-actin. In epithelial cells, Apxl andKIAA1202 do not induce apical constriction as Shroomdoes, but have the capacity to do so if targeted to the apical junctional complex. To deter-mine whether the activity of Shroom-like proteins is conserved in invertebrates, we have tested the ability of the lone Shroom