Epithelial cell chirality emerges through the dynamic concentric pattern of actomyosin cytoskeleton

Abstract

The chirality of tissues and organs is essential for their function and development. Tissue-level chirality derives from the chirality of individual cells that comprise the tissue, and cellular chirality is considered to emerge through the organization of chiral molecules within the cell. However, the principle of how molecular chirality leads to cellular chirality is still unclear. To address this question, we experimentally studied the chiral behaviors of isolated epithelial cells derived from a carcinoma line and developed a theoretical understanding of how their behaviors arise from molecular-level chirality. We first found that the nucleus rotates, and the cytoplasm circulates in a clockwise direction in a cell. During the rotation, actin and myosin IIA are organized into stress fibers with a vortex-like chiral orientation at the ventral side of the cell periphery, simultaneously forming thin filaments with a concentric orientation at the dorsal level of the cell. Lattice light-sheet microscopy showed that these concentric filaments moved in a clockwise direction, suggesting their potential involvement in the rotation of intracellular components. On the other hand, when stress fibers with chiral orientations were removed by drug treatment, cells still exhibited intracellular rotation, implying that the cells generate rotational force without any macroscopic cell-scale chiral orientational order of the cytoskeleton. To elucidate how concentric actomyosin filaments induce chiral rotation, we analyzed a hydrodynamic model considering the microscopic chirality of actomyosin filaments. Our experiments and theory suggest that cell chirality emerges driven by the microscopic chirality of actomyosin rather than the macroscopic chiral orientational order.Significance statementCell chirality, the fundamental asymmetry of cells, originates from molecular chirality, and plays a crucial role in establishing the left-right asymmetry of organs and tissues. Active torque induced by the cytoskeleton has been implicated in the mechanism behind cell chirality. However, the precise organization of molecular-scale torque driving cell chirality remains elusive. In our study, we observed a clockwise rotational motion of the nucleus and cytoplasm in singly isolated epithelial cells derived from a colorectal carcinoma line. Our investigation suggests that the non-chiral structure formed by actin and myosin II is responsible for driving cell chirality. Our theory, based on active hydrodynamics, further suggests that the concentric orientation of actomyosin induces the clockwise cytoplasmic flow.