Gardel, M. L. — Page 2 | bioRxiv Science

bioRxiv2017

Formin-Dependent Adhesions Are Required For Invasion By Epithelial Tissues

Developing tissues change shape, and tumors initiate spreading, through collective cell motility. Conserved mechanisms by which tissues initiate motility into their surroundings are not known. We investigated cytoskeletal regulators during collective invasion by mouse tumor organoids and epithelial MDCK acini undergoing branching morphogenesis. Inhibition of formins, but not Arp2/3, prevented the formation of migrating cell fronts in both cell types. MDCK cells depleted of the formin protein Dia1 formed polarized acini and could execute planar cell motility, either within the acinus or in 2D scattering assays. However, Dia1 was required to form protrusions into the collagen matrix. Live imaging of actin, myosin, and collagen in control acini revealed adhesions that deformed individual collagen fibrils, while Dia1-depleted acini exhibited unstable adhesions with minimal collagen deformation. This work identifies Dia1-mediated adhesions as essential regulators of tissue shape changes, through their role in focal adhesion maturation.

cell biology↗

bioRxiv2017

Harnessing optogenetics to probe sub-cellular mechanics

The mechanics of the actin cytoskeleton regulates cell morphogenesis during essential physiological processes. While cellular contractility is known to be largely RhoA-dependent, the process by which localized biochemical signals are translated into cell-level responses is not well understood. Here we combine optogenetic control of RhoA in space and time, live cell imaging and traction force microscopy to investigate the dynamics of actomyosin-based force generation in adherent fibroblasts. Local activation of RhoA not only stimulates local recruitment of actin and myosin, but also leads to increased traction forces outside the activation region that rapidly propagate across the cell via stress fibers and drive actin flow towards the region of heightened RhoA. Surprisingly, the flow reverses direction when local RhoA activation stops. We identify zyxin as a regulator of stress fiber mechanics, as stress fibers are fluid-like without flow reversal in its absence. These experimental data are used to constrain a physical model, which demonstrates that stress fibers are elastic-like, even at time scales exceeding turnover of constituent proteins. Such molecular control of actin mechanics likely plays critical roles in regulation of morphogenic events.

biophysics↗