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 phase and basal return post-mitosis, yet its regulation remains incompletely understood in vertebrates, in part due to limited in vivo live-imaging models. In this methodological study, we adapted the zebrafish embryonic otic vesicle as an in vivo model to investigate cell division dynamics in simple columnar epithelium using high-resolution live imaging and genetic tools. We demonstrated 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 additionally analyzed the mouse epididymal epithelium, a simple columnar epithelial tissue, to allow cross-species comparison of nuclear migration dynamics. Together, these optimized in vivo vertebrate models uncover conserved and tissue-specific mechanisms underlying epithelial organization and function, and importantly, provide tools for deeper mechanistic dissection in the future.