Evolutionarily conserved midbody reorganization precedes ring canal formation during gametogenesis

How canonical cytokinesis is altered during germ cell division to produce stable intercellular bridges called ring canals is poorly under-stood. Here, using time-lapse imaging in Drosophila , we observe that ring canal formation occurs via reorganization of the germline mid-body, a structure classically associated with its function in recruiting abscission-regulating proteins in complete cytokinesis. Germline midbodies reorganize from a focus into a ring rather than being discarded, and this transition is accompanied by changes in centralspindlin dynamics. The midbody-to-ring canal transformation is conserved in the Drosophila male and female germlines and during mouse and Hydra spermatogenesis. In Drosophila , ring canal formation depends on Citron kinase function in stark contrast to its role in abscission during somatic cell cytokinesis. Our results challenge existing models of ring canal formation, and provide important insights into broader functions of incomplete cytokinesis events across biological systems, such as those observed during development and disease states.