Membrane rupture and independent extension of sister membranes drive cytokinesis in C. elegans embryos

Cell division, the physical separation of a cell into two daughter cells, is classically thought to require continuous plasma membrane invagination driven by equatorial contractile forces. Here, we challenge this paradigm by uncovering an unexpected mechanism in C. elegans embryos: the plasma membrane ruptures as early as metaphase. Instead of invaginating as a continuous sheet, the separated membranes extend independently to partition the cytoplasm. The membrane rupture and independent extension of sister membranes create membrane discontinuities—widely observed in electron microscopy (EM) sections. Without plasma membrane coverage, the exposed cytoplasmic regions are shielded either by plasma membrane from neighboring, likely kinship, cells or extracellular matrix components, preventing massive leakage. Our findings overturn the long-standing assumption that cytokinesis requires persistent membrane integrity, and offer fresh insights into cell division, particularly in fast dividing embryonic cells.