Stalling interkinetic nuclear migration in curved pseudostratified epithelium of developing cochlea

Mouse vaginal development with lateral enlargement at late embryonic stages and caudal elongation after birth

Müllerian ducts give rise to the oviducts, uterus, cervix, and vagina. During female reproductive tract development in mice, the bilateral Müllerian duct epithelium grows caudally until reaching the urogenital sinus epithelium. This is followed by further caudal growth with the reduction of the urogenital sinus epithelium. Finally, the vaginal epithelium of adult mice is entirely derived from the Müllerian duct epithelium. Here, we explored the mechanisms underlying mouse vaginal development via cell proliferation, apoptosis, and lineage analyses. We found that at the late embryonic stages, apoptosis occurred at the attachment site of bilateral Müllerian duct epithelia below the cervix, resulting in bilateral lumen traffic. The Müllerian duct epithelium was enclosed by the urogenital sinus epithelium at their boundary region on embryonic day (E) 16.5, whereas the Müllerian duct epithelium encased the urogenital sinus epithelium at postnatal day (P) 0 through lateral enlargement. Lateral Müllerian duct enlargement was accompanied by focal ERK activation within the curved epithelial tips and the specific localization of mitotic nuclei on the luminal side of the Müllerian duct epithelial layer at E17.5. Descent of the Müllerian duct epithelium and shortening of the urogenital sinus epithelium occurred rapidly after birth, accompanied by cell proliferation in the Müllerian duct epithelium and its peripheral mesenchymal tissues as well as intense apoptosis in the urogenital sinus epithelium around their boundary region. Urogenital sinus epithelium was localized at the base of the vagina at P7. In conclusion, the mouse vagina develops laterally at the late embryonic stages and caudally after birth.

Stalling interkinetic nuclear migration in curved pseudostratified epithelium of developing cochlea

The bending of epithelial tubes is a fundamental process in organ morphogenesis, driven by various multicellular behaviours. The cochlea in the mammalian inner ear is a representative example of spiral tissue architecture where the continuous bending of the duct is a fundamental component of its morphogenetic process. Although the cochlear duct morphogenesis has been studied by genetic approaches extensively, it is still unclear how the cochlear duct morphology is physically formed. Here, we report that nuclear behaviour changes are associated with the curvature of the pseudostratified epithelium during murine cochlear development. Two-photon live-cell imaging reveals that the nuclei shuttle between the luminal and basal edges of the cell is in phase with cell-cycle progression, known as interkinetic nuclear migration, in the flat region of the pseudostratified epithelium. However, the nuclei become stationary on the luminal side following mitosis in the curved region. Mathematical modelling together with perturbation experiments shows that this nuclear stalling facilitates luminal-basal differential growth within the epithelium, suggesting that the nuclear stalling would contribute to the bending of the pseudostratified epithelium during the cochlear duct development. The findings suggest a possible scenario of differential growth which sculpts the tissue shape, driven by collective nuclear dynamics.