Zebrafish otic vesicle and mouse epididymis as model systems for studying columnar epithelial cell division.

Epithelial cell division maintains tissue architecture through coordinated nuclear migration, cell shape changes, and spindle orientation. In columnar epithelia, interkinetic nuclear migration (INM) involves apical nuclear translocation in G2 and basal return post-mitosis, yet its regulation and physiological significance remain understudied due to limited live imaging in vivo models. We adapted the zebrafish embryonic otic vesicle as an in vivo model to study epithelial division dynamics using high-resolution live imaging and genetic tools. We find that apical INM initiates in mid-to-late G2 and is driven by dynein, not myosin II. Mitotic rounding is achieved via actomyosin-mediated basolateral constriction while maintaining basal attachment. Inhibiting myosin II impairs rounding and planar division, causing apical retention of daughter cells, suggesting planar division ensures proper integration. We extend our analysis to the mouse epididymis epithelium, comparing nuclear migration, cell shape, and spindle orientation across species. Our work introduces optimized in vivo models and reveals conserved and tissue-specific mechanisms maintaining structure and function of columnar epithelia.