Fig. 1. The patch hypothesis. (A) An undisturbed cell. The typical subcortical network of F-actin (red) and underlying lysosomes or yolk granules (blue) is emphasized. (B) A large disruption of the plasma membrane occurs. Ca²⁺ entering through the disruption initiates deopolymerization of the F-actin network and triggers accumulation of vesicles (lysosomes or yolk granules) powered by myosin and kinesin motor proteins. (C) The accumulating vesicles begin to fuse with one another to create large patch vesicles. (D) Continuing vesicle-vesicle fusion creates more and larger patch vesicles, while vesicle-plasma membrane fusions, now possible owing to dissolution locally of the F-actin barrier, add this membrane to the cell surface. (E) A patch of internal membrane added is thereby added. Resealing is now complete. (F) Post-resealing polymerization of F-actin and its contraction mediated by myosin restores subcortical network continuity.