PCP and Septins govern the polarized organization and mechanics of the actin cytoskeleton during convergent extension

Abstract

SummaryConvergent extension (CE) is a collective cell movement required for embryonic axis elongation, neural tube closure, and kidney tubule elongation. During CE, iterative cell intercalations drive the elongation of a tissue 1. In order to move, cells reorganize their actin cytoskeleton; the implication of actin regulators during CE, then, is expected. Interestingly, two other groups of proteins have been shown to be required for this cell behavior: Planar Cell Polarity proteins (PCP)2-4 and Septins5, both of which interact with the actin cytoskeleton 6-14. Disruption of any of these systems have substantial overlap in terms of embryonic phenotypes, but how they interact to govern CE is largely unknown15-17. Here, we find that PCP proteins and Septins sequester actomyosin activity, create flows of actin across the anterior side of cells, and bundle actin into a node and cable system that displays a planar polarized gradient of stiffness.Key findings-PCP- and Septin-dependent actin node and cable structures form and become anteriorized over time-Actin cytoskeletal reorganization correlates with PCP protein polarization.-Actomyosin flows are directed to anterior PCP puncta and PCP movement relies on actin turnover.-Septins localize to anterior nodes and bundle actin filaments into anterior actin cable.-PCP- and Septin-dependent anterior actin cables increase local cellular stiffness and create a planar polarized stiffness gradient across the cell.