Regulation of interkinetic nuclear migration by cell cycle‐coupled active and passive mechanisms in the developing brain

A hallmark of neurogenesis in the vertebrate brain is the apical–basal nuclear oscillation in polarized neural progenitor cells. Known as interkinetic nuclear migration (INM), these movements are synchronized with the cell cycle such that nuclei move basally during G1‐phase and apically during G2‐phase. However, it is unknown how the direction of movement and the cell cycle are tightly coupled. Here, we show that INM proceeds through the cell cycle‐dependent linkage of cell‐autonomous and non‐autonomous mechanisms. During S to G2 progression, the microtubule‐associated protein Tpx2 redistributes from the nucleus to the apical process, and promotes nuclear migration during G2‐phase by altering microtubule organization. Thus, Tpx2 links cell‐cycle progression and autonomous apical nuclear migration. In contrast, in vivo observations of implanted microbeads, acute S‐phase arrest of surrounding cells and computational modelling suggest that the basal migration of G1‐phase nuclei depends on a displacement effect by G2‐phase nuclei migrating apically. Our model for INM explains how the dynamics of neural progenitors harmonize their extensive proliferation with the epithelial architecture in the developing brain. In proliferating neural epithelia, cells undergo interkinetic nuclear migration: stereotyped cell cycle‐dependent movements in the apico‐basal plane. The microtubule‐binding protein Tpx2 is here shown to regulate the G2‐phase basal‐to‐apical migration, while passive displacement effects are responsible for basally directed movements.