Models for apical actomyosin organization and membrane organization. (A) Hypothetical model for surface topology and actomyosin organization in nonconfluent ECs. Actin filaments (red) form either thick bundles in bent MV or thinner structures (single filaments or thin bundles) that are not resolved as such by fluorescence microscopy (shown here below the plane of the membrane). Myosin (minifilaments) filaments (green) form a two-dimensional network below the apical membrane and are connected to both individual actin filaments and MV (indicated by bent actin filaments at MV roots). The plasma membrane (transparent orange) is tightly connected to MV. Bent MV could consist of a single bundle of actin filaments or of multiple tightly connected bundles oriented orthogonally to the plasma membrane (example shown in the foreground). (B) Schematic depiction of three types of mechanisms by which apical actomyosin dynamics influences the mobility and distribution of plasma membrane components.