Coping with the inevitable: how cells repair a torn surface membrane

Disruption of the cell plasma membrane is a commonplace occurrence in many mechanically challenging, biological environments. 'Resealing' is the emerg ency response required for cell survival. Resealing is triggered by Ca2+ en tering through the disruption; this causes vesicles present in cytoplasm un derlying the disruption site to fuse rapidly with one another (homotypicall y) and also with the adjacent plasma membrane (heterotypically/exocytotical ly). The large vesicular products of homotypic fusion are added as a repara tive 'patch' across the disruption, when its resealing requires membrane re placement. The simultaneous activation of the local cytoskeleton supports t hese membrane fusion events. Resealing is clearly a complex and dynamic cel l adaptation, and, as we emphasize here, may be an evolutionarily primitive one that arose shortly after the ancestral eukaryote lost its protective c ell wall.