Figure 7.

The sequence of intracellular molecular events leading to ”membrane expansion”. In (a) the wrinkles are held in place (more detail in Figure 4). Following cleavage of ezin by activated µ-calpain (as shown in Figure 4), the tension in the membrane is relaxed and (c) shows that result on actin polymerisation, which can now proceed via the Brownian ratchet mechanism. In (d), actin polymerisation has progressed and branch points added such that the membrane made available by wrinkle detachment is pushed out. During phagocytosis, this would be coordinated to form a phagocytic cup, as a result of localised adhesion via integrin or antibody on the particle and during cell spreading coordinated to spread onto the contacting substrate.