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 micrometers per hour. Fibrillar adhesions arise from the medial ends of stationary focal contacts, contain alpha5beta1 integrin and tensin but not other focal-contact components, and associate with fibronectin fibrils. Fibrillar adhesions translocate centripetally at a mean rate of 18 micrometers 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.