Reassembly of contractile actin cortex in cell blebs

TLDR

Contractile actin cortex is involved in cell morphogenesis, movement, and cytokinesis, but its organization and assembly are poorly understood. The study aimed to measure the temporal sequence of protein recruitment to the membrane during cortex reassembly and to explore dependency relationships. Using the bleb cycle, where membrane detachment and retraction allow observation of protein recruitment, the authors examined how the cortex reassembles under the membrane. During bleb expansion actin was absent while submembranous cytoskeletal proteins were present; upon retraction ezrin first recruited, followed by actin, bundling proteins, and contractile components, completing a cage‑like cortex in ~30 s, with cytochalasin D blocking actin/α‑actinin recruitment but not ankyrin B/ezrin, and ezrin required for membrane tethering but not actin nucleation, while the Rho pathway was essential for assembly.

Abstract

Contractile actin cortex is involved in cell morphogenesis, movement, and cytokinesis, but its organization and assembly are poorly understood. During blebbing, the membrane detaches from the cortex and inflates. As expansion ceases, contractile cortex reassembles under the membrane and drives bleb retraction. This cycle enabled us to measure the temporal sequence of protein recruitment to the membrane during cortex reassembly and to explore dependency relationships. Expanding blebs were devoid of actin, but proteins of the erythrocytic submembranous cytoskeleton were present. When expansion ceased, ezrin was recruited to the membrane first, followed by actin, actin-bundling proteins, and, finally, contractile proteins. Complete assembly of the contractile cortex, which was organized into a cagelike mesh of filaments, took ∼30 s. Cytochalasin D blocked recruitment of actin and α-actinin, but had no effect on membrane association of ankyrin B and ezrin. Ezrin played no role in actin nucleation, but was essential for tethering the membrane to the cortex. The Rho pathway was important for cortex assembly in blebs.