Summary Radial glial progenitors (RGPs) are elongated epithelial cells which give rise to neurons, glia, and adult stem cells during brain development. RGP nuclei migrate basally during G1, apically using cytoplasmic dynein during G2, and undergo mitosis at the ventricular surface. By live imaging of in utero electroporated rat brain, we find that two distinct G2-specific mechanisms for dynein nuclear pore recruitment are essential for apical nuclear migration. The “RanBP2-BicD2” and “Nup133-CENP-F” pathways act sequentially, with Nup133 or CENP-F RNAi arresting nuclei close to the ventricular surface in a pre-mitotic state. Forced targeting of dynein to the nuclear envelope rescues nuclear migration and cell cycle progression, demonstrating that apical nuclear migration is not simply correlated with cell cycle progression from G2 to mitosis, but rather, is a required event. These results reveal that cell cycle control of apical nuclear migration occurs by motor recruitment, and identify a role for nucleus- and centrosome-associated forces in mitotic entry.

Summary Dynein recruitment to the nuclear envelope is required for pre-mitotic nucleus-centrosome interactions in nonneuronal cells, and for apical nuclear migration in neural stem cells. In each case, dynein is recruited to the nuclear envelope (NE) specifically during G2, via two nuclear pore-mediated mechanisms involving RanBP2-BicD2 and Nup133-CENP-F. The mechanisms responsible for cell cycle control of this behavior are unknown. We now find that Cdk1 serves as a direct master controller for NE dynein recruitment in neural stem cells and HeLa cells. Cdk1 phosphorylates conserved sites within RanBP2 and activates BicD2 binding and early dynein recruitment. Late recruitment is triggered by a Cdk1-induced export of CENP-F from the nucleus. Forced NE targeting of BicD2 overrides Cdk1 inhibition, fully rescuing dynein recruitment and nuclear migration in neural stem cells. These results reveal how NE dynein recruitment is cell cycle regulated, and identify the trigger mechanism for apical nuclear migration in the brain.

Brain neural stem cells (RGPs) undergo a mysterious form of cell cycle-entrained “interkinetic” nuclear migration (INM), driven apically by cytoplasmic dynein and basally by the kinesin KIF1A, which has recently been implicated in human brain developmental disease. To understand the consequences of altered basal INM and the roles of KIF1A in disease, we performed constitutive and conditional RNAi and expressed mutant KIF1A in E16-P7 rat RGPs and neurons. RGPs inhibited in basal INM still showed normal cell cycle progression, though neurogenic divisions were severely reduced. Postmitotic neuronal migration was independently disrupted at the multipolar stage, accompanied by premature ectopic expression of neuronal differentiation markers. Similar effects were unexpectedly observed throughout the layer of surrounding control cells, mimicked by Bdnf or Dcx RNAi, and rescued by BDNF application. These results identify novel, sequential, and independent roles for KIF1A and provide an important new approach for reversing the effects of human disease.

Highlights d Spindles reorient from oblique to planar during growth, driving symmetric outcomes d Stress-and aging-mediated activation of JNK promotes planar spindles d JNK interacts with Wdr62 and represses Kif1a expression to promote planar spindles d Restoring oblique spindles in old flies extends lifespan

Tissue regeneration after injury requires coordinated regulation of stem cell activation, division, and daughter cell differentiation, processes that are increasingly well understood in many regenerating tissues. How accurate stem cell positioning and localized integration of new cells into the damaged epithelium are achieved, however, remains unclear. Here, we show that enteroendocrine cells coordinate stem cell migration towards a wound in the Drosophila intestinal epithelium. In response to injury, enteroendocrine cells release the N-terminal domain of the PTK7 orthologue, Otk, which activates non-canonical Wnt signaling in intestinal stem cells, promoting actin-based protrusion formation and stem cell migration towards a wound. We find that this migratory behavior is closely linked to proliferation, and that it is required for efficient tissue repair during injury. Our findings highlight the role of non-canonical Wnt signaling in regeneration of the intestinal epithelium, and identify enteroendocrine cell-released ligands as critical coordinators of intestinal stem cell migration.