Fig. 9. A model for cortactin- and dynamin-mediated fission of CCV. Step 1, binding of an extracellular ligand to its membrane receptor induces formation of a clathrin-coated pit and recruitment of dynamin to the neck of an invaginated vesicle where it is oligomerized to form a ring structure (for simplicity, only one dynamin ring is shown). The ligand/receptor interaction also triggers assembly of actin (orange line) by activation of WASP family proteins, the Arp2/3 complex and cortactin, resulting ultimately in a tight association of cortactin/Arp2/3 complex at a branched site (yellow circle). Step 2, while the actin polymerization is taking place, the SH3 domain of cortactin at a branching site becomes accessible for interaction with the PRD of dynamin at vesicles. Detail of the interactions between F-actin, cortactin, Arp2/3 complex and dynamin is presented. Step 3, elongation of actin filaments makes the complex of cortactin and dynamin away from the barbed end or its associated plasma membrane and eventually results in the separation of the vesicle from the plasma membrane (Step 4).