Cadherin flow translates cortical chirality into left-right asymmetric cell division dynamics in Caenorhabditis...

Diverse strategies have evolved in bilaterians to establish left-right (L-R) asymmetry. One driver of L-R asymmetry conserved across phyla is the chiral mechanics of the actomyosin-rich cell cortex, a surface layer that governs cell shape and dynamics. However, how cortical chirality is converted into cellular L-R asymmetry remains obscure. Here, we identify cortical-flow-dependent chiral adhesion pattern formation as a key mechanism driving L-R symmetry breaking of cell division in the two-cell-stage Caenorhabditis elegans embryo. Using high-resolution 4D imaging, we show that the classical cadherin HMR-1 exhibits an early ventral flow followed by a later L-R asymmetric flow during cytokinesis. These ventral and chiral cadherin flows, driven by the extracellular matrix coat surrounding the embryos and by RhoA signaling, respectively, together generate a chiral cadherin pattern at the cell-cell contact. The chiral cadherin patch interacts asymmetrically with the cytokinetic contractile ring, selectively slowing its closure on the embryo's right side via inhibition of ring-directed cortical flow. Disrupting cadherin flow or its interaction with the ring abolishes the rightward displacement of the contractile ring-the earliest detectable L-R asymmetry in C. elegans development. Although cadherin flow is known to facilitate junctional remodeling across organisms, our findings reveal its unexpected role in translating cortical chirality into asymmetric cell division dynamics.