Dynamics and segregation of cell-matrix adhesions in cultured fibroblasts

Here we use time-lapse microscopy to analyse cell-matrix adhesions in cells expressing one of two different cytoskeletal proteins, paxillin or tensin, tagged with green fluorescent protein (GFP), Use of GFP-paxillin to analys e focal contacts and GFP-tensin to study fibrillar adhesions reveals that b oth types of major adhesion are highly dynamic, Small focal contacts often translocate, by extending centripetally and contracting peripherally, at a mean rate of 19 micrometres per hour. Fibrillar adhesions arise from the me dial ends of stationary focal contacts, contain alpha(5)beta(1) integrin an d tensin but not other focal-contact components, and associate with fibrone ctin fibrils, Fibrillar adhesions translocate centripetally at a mean rate of 18 micrometres per hour in an actomyosin-dependent manner. We propose a dynamic model for the regulation of cell-matrix adhesions and for transitio ns between focal contacts and fibrillar adhesions, with the ability of the matrix to deform functioning as a mechanical switch.