Figure 4.

(A) Schematic figure of three different kinds of intrinsic shapes of flexible membrane nanodomains: partly cylindrical, flat, and saddle-like. Nanodomains with C_1m > 0 and C_2m < 0 favor saddle-like membrane geometry found in the membrane neck connecting the daughter vesicle to the parent membrane (adapted from Reference [11]). (B) Some of the nanotubes forming between neighboring RT4 urothelial cells have vesicles at their free tips, as indicated by the arrows. Bar = 10 μm. (adapted from [75] -under the Creative Commons 3.0 License). (C) Schematic illustration of stabilization of membrane protrusions by accumulation of anisotropic membrane nanodomains in the tubular region. The cylindrical-shaped anisotropic membrane domains, once assembled in the membrane region of a nanotubular membrane protrusion, keep the protrusion mechanically stable even if the cytoskeletal components (actin filaments) are disintegrated (adapted from Reference [11]). (D) Numerically calculated equilibrium cell shapes for a two-component membrane of isotropic and anisotropic nanodomains with constraint of constant volume. From left to right, intrinsic mean curvature of isotropic membrane components is gradually increased, which results in a more pronounced isotropic-anisotropic segregation given by the color map. The color represents the fraction area covered by isotropic components. The fully blue color corresponds to a membrane composed of isotropic nanodomains only. The shift towards green and red colors indicates increased lateral density of the anisotropic components (adapted from Reference [67] under the Creative Commons 3.0 License). (E) Nanotube–vesicle network stained with the membrane dye DiO (adapted from Reference [39]). (F) The calculated equilibrium closed membrane shape obtained in a system of isotropic components and anisotropic components drawn without the inclusion of the entropy term (adapted from Reference [76]).