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 emergency response required for cell survival. Resealing is triggered by Ca2+ entering through the disruption; this causes vesicles present in cytoplasm underlying the disruption site to fuse rapidly with one another (homotypically) and also with the adjacent plasma membrane (heterotypically/exocytotically). The large vesicular products of homotypic fusion are added as a reparative 'patch' across the disruption, when its resealing requires membrane replacement. The simultaneous activation of the local cytoskeleton supports these membrane fusion events. Resealing is clearly a complex and dynamic cell adaptation, and, as we emphasize here, may be an evolutionarily primitive one that arose shortly after the ancestral eukaryote lost its protective cell wall.