Mechanical self-organization of the actin cytoskeleton in artificial cells.

The actin cytoskeleton generates diverse cellular functions, including intracellular positioning, symmetry breaking, and cell migration, through dynamic self-organization. Despite extensive molecular characterization of actin-binding proteins, the physical principles by which local molecular interactions give rise to cell-scale organization remain incompletely understood. Artificial cells provide a powerful platform for addressing this question because they enable precise control over molecular composition, geometry, and physical boundary conditions while minimizing the complexity inherent to living cells. In this review, we describe how artificial cell systems have been used to investigate the emergence of actin-dependent intracellular organization and motility. Using the cytoplasmic extracts of Xenopus eggs encapsulated within cell-sized water-in-oil droplets surrounded by a phospholipid membrane, we reconstructed actomyosin-driven intracellular positioning and spontaneous cell-like migration. By combining quantitative molecular perturbations with theoretical modeling, these studies revealed how competing actomyosin structures, stochastic network formation, and mechanical coupling between the actin cytoskeleton and the membrane collectively determine intracellular organization and directional movement. These findings illustrate how constructive approaches using artificial cells can uncover general physical principles governing the self-organization of cellular architecture and function. This review article is an extended version of the Japanese article, reconstitution of actin cytoskeletal functions in cell-sized confinement, published in SEIBUTSU BUTSURI Vol. 65 p. 192-196 (2025).