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Repairing a torn cell surface: make way, lysosomes to the rescue

Department of Cellular Biology and Anatomy, Institute of Molecular Medicine and Genetics, Medical College of Georgia, Augusta, GA 30904, USA

View larger version (91K): [in a new window]   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.

View larger version (113K): [in a new window]   Fig. 2. Staining of a resealed fibroblast with antibodies against a luminal domain of the lyososome-specific protein, Lamp-1. The right hand side of this cell was severed when the culture dish it was growing in was scratched with a needle (the red streak on the right indicates the needle path). Staining with anti-Lamp-1 was then performed on the living, resealed cell, limiting detection to surface exposed antigen only. Surface exposure of Lamp-1, indicated by the staining, is evident over the resealed disruption site. This provides strong evidence that the local exocytotic response evoked by a disruption utilizes lysosomes. (Photomicrograph courtesy of Norma Andrews, Yale University.)

View larger version (65K): [in a new window]   Fig. 3. (A) Post sealing repair of wound-related damage to the cortical F-actin network. A Xenopus oocyte injected with fluorescent actin was wounded (circular profile) with a laser and then imaged at intervals of 3 minutes. An intensely labeled zone of F-actin assembly is seen around the wound site in the first panel and, in subsequent panels, is seen to contract, purse-string-style, restoring continuity to the cortical actin network. (B) Experimental analysis of the zone of actin polymerization indicates that it contains at its interface with the wound site a `contractile array' consisting of F-actin and myosin 2. Finger-like, polymerization-dependent protrusions of F-actin extend into the wound site and may facilitate final closure. (Micrographs and drawing courtesy of C. Mandato and W. Bement, University of Wisconsin.)