How Synergy of Actin Assembly-Disassembly and Myosin Motors Drives Cell Shape Changes

Abstract

Cell motility and division are complex mechanisms that involve drastic cell shape changes. A crucial role is played by the actin cortex, which, together with the molecular motor myosin, regulates the production of cellular tension (1). A better understanding of the interplay between actin network dynamics and myosin-driven contractility is necessary to elucidate the detailed mechanism of contraction in a dynamic, out of equilibrium, constantly polymerizing and depolymerizing actin structure. In order to dissect this dual actin-myosin contribution we make advantage of biomimetic systems: cell-sized liposomes indeed offer the possibility to retain only the essential players involved in contraction mechanisms and to finely control the physical and biochemical conditions to mimic cell-like shape changes (2).Particularly we study acto-myosin contraction mechanisms on cell-sized doublets, which enable overcoming the spherical symmetry of single liposomes: with this geometry, shape changes, and hence tension build-up, can be fully characterised by recording contact angle variations. A polymerizing actin network is built at the outer surface of doublets. A fluorescently labelled actin is used and simultaneous detection of phase contrast and fluorescence images allow following actin cortex dynamics and further shape changes induced by the addition of myosin motors (3). A micropipette aspiration technique is also adopted to further characterize these cell-like shape changes (4).This reconstituted doublet system allows us to decouple biochemical and physical aspects of actin network dynamics and fully dissect the dual role of actin and myosin contractility, thus significantly improving our understanding of acto-myosin driven cell shape changes.1.Blanchoin L et al. Physiol Rev 2014, 94:235-263.2.Murrell M et al. Nat Rev Mol Cell Biol. 2015, 16(8):486-98.3.Carvalho K et al. Proc Natl Acad Sci U S A. 2013, 110(41):16456-16461.4.Campillo C et al. Biophys J 2013, 104:1248-1256.