Published online 9 January 2006. doi:10.1083/jcb1722iti3
The Rockefeller University Press, 0021-9525 $8.00
JCB, Volume 172, Number 2, 165-165
Sometimes size does matter
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 -smooth muscle actin (blue) joins stress fibers that are under a lot (top) but not less (bottom) tension.
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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 -smooth muscle actin (-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 -SMA. The question remains, however, as to what triggers incorporation of -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 physical forces and generated higher intracellular tension than did FAs of a more typical size. This higher tension in turn triggered -SMA recruitment to stress fibers, which did not occur in cells with smaller FAs.
The team is working to identify the cellular component that senses the increased tension in stress fibers and recruits -SMA. In the meantime, they are convinced that tension and size are intimately linked in the formation of supermature FAs and -SMA stress fibers.
Rabiya S. Tuma
rabiya@nasw.org
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Focal adhesion size controls tension-dependent recruitment of -smooth muscle actin to stress fibers
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