Class I myosins direct circumferential F-actin flows to define cell chirality

Eukaryotic cells possess intrinsic chirality in their structure, motility, and intracellular dynamics, which are designated cell chirality. Cell chirality participates in the left-right asymmetric morphogenesis and tissue integrity. However, the mechanisms of cell chirality formation remain elusive. In Drosophila, two evolutionarily conserved myosin I genes, Myosin 1D (Myo1D) and Myosin 1C (Myo1C), respectively, dictate the dextral and sinistral chirality of the cells and body. Here, we reported that Myo1D and Myo1C respectively directed the clockwise and counterclockwise circumferential flow of F-actin in Drosophila macrophages. Both induced the corresponding circular cytoplasm flows and depended on Myosin2 (Myo2). In a modified in vitro motility assay using near-physiological actin concentrations, Myo1D triggered the self-organization of the F-actin ring (chiral F-actin ring) that rotated clockwise; conversely, Myo1C induced the random flow of F-actin. The chiral F-actin ring implied that the F-actin bundle was parallelly and annularly polarized concerning its barbed pointed end. Considering that Myo1D and Myo1C are localized to the dorsal plasma membrane of macrophages, Myo1D and Myo1C might organize the parallelly polarized F-actin in macrophages. Our results suggest that Myo2 might drive the clockwise circumferential flow of F-actin along its parallel and annular polarity induced by Myo1D, which may be a molecular basis of cell and organ chirality.