Fig. 2. Inhibition of myosin II causes the formation of F-actin-rich protrusions at the surface of epithelial cysts. (A,B) Caco-2 (A) or SK-CO15 (B) cells were embedded for 72 hours into 3D Matrigel in the presence of either vehicle or the myosin II inhibitors blebbistatin (100 µM) or Y27632 (20 µM) and analyzed for cyst morphology by fluorescent labeling for F-actin. Vehicle-treated Caco-2 and SK-CO15 cells formed spherical cysts with smooth surfaces, whereas cysts grown in the presence of myosin II inhibitors developed radiating F-actin protrusions (arrows). (C,D) SK-CO15 cells were transfected with either control or NMMIIA-specific siRNA and, 72 hours later, were analyzed for NMMIIA expression (C) and morphology of 3D cysts (D). NMMIIA knockdown caused a significant decrease in the level of NMMIIA and induced the formation of numerous F-actin-rich surface spikes. ^*P<0.05.