Sometimes size does matter

During myofibroblast differentiation in vitro, “supermature” focal adhesions (FAs) arise due to increased physical stress, report Goffin et al. (page 259). Additionally, increased tension induces accumulation of α-smooth muscle actin (α-SMA) in stress fibers that are anchored at these FAs.

In vivo, the extracellular matrix rearranges and increases in rigidity in response to wounding. This change, along with the release of growth factors, induces fibroblasts to take on a contractile phenotype, including expression of α-SMA. The question remains, however, as to what triggers incorporation of α-SMA into stress fibers in these cells.

When differentiated myofibroblasts were cultured on flexible substrates, FAs remained relatively small. However when the cells were grown on rigid substrates, supermature FAs formed. Once formed, supermature FAs were able to withstand substantially larger...