Fig. 3.
Relationship between the cell body contact angle and the spread radius. (A) Confocal side views of cells at different times of spreading (Actin in red, paxillin in green, and nucleus in blue). Note the continuity of the actin cortex at the cell body–lamella junction (see also refs. 28 and 29 for superresolution imaging). (Scale bar: 10 μm.) (B) The spread radius R on fibronectin-coated substrates as a function of the cell body contact angle θ for control (black circles), 0.05 μm Lat-A (blue squares), and 8 μM Y-27632 (red diamonds). The radius Ra at which FAs start to grow corresponds to θ ≳ 90°, independently from actin polymerization or contractile myosin II activities, underlining the geometric triggering of FA growth. Consistently, the relationship between R and θ is maintained when cells are spreading on polylysine-coated substrates (red open circles), indicating that integrin signaling is not required. The pink stripes correspond to the SE on Ra.