Fig. 1.

Schematic illustration of the phases observed during fibroblast spreading (2). A suspended fibroblast is plated on a coated glass substrate (Top). The initial phase (P1) is characterized by rapid spreading driven by actin polymerization. This spreading is accompanied by gradual unfolding of membrane reservoirs and stretching out of the plasma membrane. The depletion of the membrane reservoir at the end of P1 leads to a transient increase in membrane tension (Middle). The increase in tension activates exocytosis and myosin contraction. Subsequent spreading (P2) is enabled by an increase in cell surface area due to the enhanced exocytic activity. This spreading phase is characterized by a gradual reduction in edge velocity and local cycles of protrusion and acto-myosin contraction (Bottom).