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rce now sio d in bi-directional signaling unit of cell adhesion. 2013 Federation of European Biochemical Societies. Published by Elsevier B.V. All rights reserved. ellular bed as under on ECM, i tly regulat skeletal tension generation. In this study, we found that b1 integrin activation via inc fibronectin (FN) density or Mn2+ leads to enhanced genera cellular traction forces. We measured these forces by culturing cells on FN-functionalized arrays of uniformly spaced elastomeric microposts, a system we developed previously to enable studies of traction force dynamics [5,14]. Our data indicate that the activa-tion state of integrins is intimately connected to basic adherent cell behaviors like contractility, which has implications for improving our understanding of the regulation of cell shape, mechanics, and function. Abbreviations: b1KO, b1-integrin null mouse embryonic fibroblast; b3KO, b3-integrin null mouse embryonic fibroblast; BSA, bovine serum albumin; ECM, extracellular matrix; FA, focal adhesion; FN, fibronectin; LPA, lysophosphatidic acid; mPAD, micropost array detector; PDMS, polydimethylsiloxane; ROCK, Rho kinase