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 analyse focal contacts and GFP–tensin to study fibrillar adhesions reveals that both 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 medial ends of stationary focal contacts, contain α5β1 integrin and tensin but not other focal-contact components, and associate with fibronectin 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 transitions between focal contacts and fibrillar adhesions, with the ability of the matrix to deform functioning as a mechanical switch.