A Focal Adhesion Protein-Based Mechanochemical Checkpoint Regulates Cleft Progression During Branching Morphogenesis

Cleft formation is the initial step of branching morphogenesis in many organs. We previously demonstrated that ROCK 1 regulates a nonmuscle myosin II-dependent mechanochemical checkpoint to transition initiated clefts to progressing clefts in developing submandibular salivary glands. Here, we report that ROCK-mediated integrin activation and subsequent formation of focal adhesion complexes comprise this mechanochemical checkpoint. Inhibition of ROCK1 and nonmuscle myosin II activity decreased integrin 01 activation in the cleft region and interfered with localization and activation of focal adhesion complex proteins, such as focal adhesion kinase (FAX). Inhibition of FAX activity also prevented cleft progression, by disrupting recruitment of the focal adhesion proteins talin and vinculin and subsequent fibronectin assembly in the cleft region while decreasing ERK1/2 activation. These results demonstrate that inside-out integrin signaling leading to a localized recruitment of active FAX-containing focal adhesion protein complexes generates a mechanochemical checkpoint that facilitates progression of branching morphogenesis. Developmental Dynamics 240:2069-2083, 2011. (C) 2011 Wiley-Liss, Inc.