Tug-of-war by active gel shapes positioning symmetry in cell-sized compartment

Force generation powered by actin cytoskeleton is underlying a wide range of phenomena from heart beating to cell migration [1]. To understand the underlying physical principles, in vitro reconstruction of actin cytoskeleton in water-in-oil droplet has been developed as a cell model, in which spontaneous F-actin flow and actomyosin clusters were self-organized [2]. However, it remains unclear how the spatial positioning of these structure is determined. To understand actomyosin-mediated geometric positioning, we confined actomyosin droplets in quasi two-dimensional chamber. We find that periodic actomyosin waves move the cluster to center, while the cluster is towed to edge by percolation of radial actomyosin network. By considering time-lag between maturation of actomyosin cortex and that of percolated network, active gel model recovers size-dependent two-state cluster positioning, which will give insights into the nucleus and spindle positioning in vivo [3]. We revealed active role of physical confinement to control intracellular positioning through actin cytoskeleton.
[1] Murrell, M. et al. Nat. Rev. Mol. Cell Biol. 16, 486-498 (2015).
[2] Pinot, M. et al. Proc. Natl. Acad. Sci. USA 17, 11705-11710 (2012).
[3] Mogessie, B. et al. Annu. Rev. Cell Dev. Biol. 34, 381-403 (2018).