Studying actin-induced cell shape changes using Giant Unilamellar Vesicles and reconstituted actin networks

Abstract

Cell shape changes that are fuelled by the dynamics of the actomyosin cytoskeleton control cellular processes such as motility and division. However, the mechanisms of interplay between cell membranes and actomyosin are complicated to decipher in the complex environment of the cytoplasm. Using biomimetic systems offers an alternative approach to studying cell shape changes in assays with controlled biochemical composition. Biomimetic systems allow quantitative experiments that can help to build physical models describing the processes of cell shape changes. This article reviews works in which actin networks are reconstructed inside or outside cell-sized Giant Unilamellar Vesicles (GUVs), which are models of cell membranes. We show how various actin networks affect the shape and mechanics of GUVs and how some cell shape changes can be reproduced in vitro using these minimal systems.

Keywords: actin; biomimetism; cytoskeleton; membranes.

Figure 1.. Schematics of biomimetic systems made of GUVs coupled to actin filaments formed without NPFs.

GUVs coupled to F-actin in the outside (A) and inside (B) configurations; GUVs encapsulating F-actin in the presence of crosslinkers (C) α-actinin; (D,E) fascin that induces bundles or rings in the lumen of the GUV (F) GUVs encapsulating F-actin in the presence of myosin II motors.

Figure 2.. Schematics of biomimetic systems made of GUVs coupled to dynamic F-actin networks nucleated by the Arp2/3 complex.

In the outside configuration: reconstitution of actin-rich membrane domains (A), filopodia-like protrusions (B), filopodia-like protrusions and endocytic pits-like structures (C), global GUV deformation (D), and actin-coated nanotubes (E); In the inside configuration: reconstitution of Arp2/3-generated networks allows forming a cortex-like structure (F); studies on the effect of the cortex on GUV spreading (G) and on membrane dynamics by nanotube pulling experiments (H). Actomyosin networks coupled to the GUV surface (I) or GUVs doublets (J) show myosin-induced shape changes; Encapsulation of Arp2/3 generated actin networks comprising myosin II motors which then induce membrane protrusions (K,L).