Myosin1D directs circumferential F-actin flow to define cell chirality.

Eukaryotic cells possess intrinsic chirality in their structure, motility, and intracellular dynamics, known as cell chirality, which contributes to left-right asymmetric morphogenesis. However, the mechanisms underlying its formation remain elusive. In Drosophila, Myosin1D (Myo1D) and Myosin1C (Myo1C), respectively, dictate right-handed or left-handed chirality of the cell shape and body. Here, we report that Myo1D and Myo1C, respectively, directed clockwise and counterclockwise circumferential F-actin flows in Drosophila macrophages collaborating with Myosin2 (Myo2). Furthermore, Myo1C induced a random F-actin flow in an in vitro motility assay, whereas Myo1D triggered the self-organization of the F-actin ring rotating clockwise in the same conditions, implying that Myo1D assembles F-actin into a circular arrangement with barbed-end-to-pointed-end polarity aligned in a specific direction. We propose a model in which Myo1D induces the formation of F-actin structures aligned in such a polarized fashion within macrophages, and Myo2 rotates them clockwise. This model provides a molecular basis for the formation of cell and organ chirality.