Micron-scale supramolecular myosin arrays help mediate cytoskeletal assembly at mature adherens junctions.

Epithelial cells assemble specialized actomyosin structures at E-Cadherin-based cell-cell junctions, and the force exerted drives cell shape change during morphogenesis. The mechanisms that build this supramolecular actomyosin structure remain unclear. We used ZO-knockdown MDCK cells, which assemble a robust, polarized, and highly organized actomyosin cytoskeleton at the zonula adherens, combining genetic and pharmacologic approaches with superresolution microscopy to define molecular machines required.

Good Fences Make Good Neighbors: Crumbs Regulates Rho-Kinase Dynamics to Assemble a Tissue Boundary.

Boundary formation between nascent tissues prevents cell mixing, powering morphogenesis. In this issue of Developmental Cell, Sidor et al. (2020) describe a novel mechanism whereby the homophilic adhesion protein Crumbs regulates planar-polarized assembly of actomyosin cables at tissue boundaries by affecting dynamics of membrane recruitment of the myosin regulator Rho-kinase.

CRMP-1 enhances EVL-mediated actin elongation to build lamellipodia and the actin cortex.

Cells can control actin polymerization by nucleating new filaments or elongating existing ones. We recently identified CRMP-1 as a factor that stimulates the formation of actin comet tails, thereby implicating it in actin assembly. We now show that CRMP-1 is a major contributor to actin assembly in epithelial cells, where it works with the Ena/VASP family member EVL to assemble the actin cytoskeleton in the apical cortex and in protruding lamellipodia.

Collapsin Response Mediator Protein-1 Regulates Arp2/3-dependent Actin Assembly.

Listeria monocytogenes is a bacterial parasite that uses host proteins to assemble an Arp2/3-dependent actin comet tail to power its movement through the host cell. Initiation of comet tail assembly is more efficient in cytosol than it is under defined conditions, indicating that unknown factors contribute to the reaction. We therefore fractionated cytosol and identified CRMP-1 as a factor that facilitates Arp2/3-dependent Listeria actin cloud formation in the presence of Arp2/3 and actin alone.