Actin Dynamics Drive Membrane Reorganization and Scission in Clathrin-Independent Endocytosis

Nascent transport intermediates detach from donor membranes by scission. This process can take place in the absence of dynamin, notably in clathrin-independent endocytosis, by mechanisms that are yet poorly defined. We show here that in cells scission of Shiga toxin-induced tubular endocytic membrane invaginations is preceded by cholesterol-dependent membrane reorganization and correlates with the formation of membrane domains on model membranes, suggesting that domain boundary forces are driving tubule membrane constriction. Actin triggers scission by inducing such membrane reorganization process. Tubule occurrence is indeed increased upon cellular depletion of the actin nucleator component Arp2, and the formation of a cortical actin shell in liposomes is sufficient to trigger the scission of Shiga toxin-induced tubules in a cholesterol-dependent but dynamin-independent manner. Our study suggests that membranes in tubular Shiga toxin-induced invaginations are poised to undergo actin-triggered reorganization leading to scission by a physical mechanism that may function independently from or in synergy with pinchase activity.