The nature of mitotic forces in epithelial monolayers

Epithelial cells undergo striking morphological changes during mitosis to ensure proper segregation of genetic and cytoplasmic materials. These morphological changes occur despite dividing cells being mechanically restricted by neighboring cells, indicating the need for extracellular force generation. While forces generated during mitotic rounding are well understood, forces generated after rounding remain unknown. Here, we identify two distinct stages of mitotic force generation that follow rounding: (1) protrusive forces along the mitotic axis that drive mitotic elongation, and (2) outward forces that facilitate post-mitotic re-spreading. Cytokinetic ring contraction of the mitotic cell, but not activity of neighboring cells, generates extracellular forces that propel mitotic elongation and also contribute to chromosome separation. Forces from mitotic elongation are observed in epithelia across many model organisms. Thus, forces from mitotic elongation represent a universal mechanism that powers mitosis in confining epithelia.