Tension is required but not sufficient for focal adhesion maturation without a stress fiber template.
Bottom Line: As myosin II activity drives stress fiber assembly and enhanced tension at adhesions simultaneously, the extent to which adhesion maturation is driven by tension or altered actin architecture is unknown.We show that perturbations to formin and α-actinin 1 activity selectively inhibited stress fiber assembly at adhesions but retained a contractile lamella that generated large tension on adhesions.We propose that stress fiber assembly at the adhesion site serves as a structural template that facilitates adhesion maturation over a wide range of tensions.
Affiliation: Institute for Biophysical Dynamics, University of Chicago, Chicago, IL 60637, USA.Show MeSH
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Mentions: To explore the extent to which the organization of active myosin II within the lamella was affected by the inhibition of RSF assembly, we visualized the enzymatically active fraction of myosin II by immunofluorescence of myosin light chain (MLC) phosphorylated at serine 19 (pMLC; Adelstein and Conti, 1975) while also visualizing the F-actin cytoskeleton with fluorescent phalloidin (Fig. 2 A). In all populations, active myosin localized throughout the lamella primarily along transverse arcs (Fig. 2 A). We tested cell lysates for relative amounts of pMLC and total MLC via Western blotting (Fig. 2 B) and used densitometry to quantify the ratio of pMLC to MLC (Fig. 2 C). We found small reductions in the amount of MLC and pMLC but found no significant difference in the ratio of pMLC to MLC in both Dia-inhibited and Atn-1 KD cells. We speculate that this small reduction in active myosin may be a result of changes in biochemical signaling to Rho pathways caused by changes in lamellar organization or focal adhesions (Schwartz, 2010), but a definitive understanding would require further study.
Affiliation: Institute for Biophysical Dynamics, University of Chicago, Chicago, IL 60637, USA.