Dynein Recruitment to Nuclear Pores Activates Apical Nuclear Migration and Mitotic Entry in Brain Progenitor Cells

Abstract

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.

Nuclear pore complex tethers to the cytoskeleton

“…In these cells, nuclei undergo cell cycle dependent movement, and move towards the ventricular surface during G2, and then go through mitosis when the nuclei reach the surface. Interestingly, this movement is centrosome-independent (Tsai et al, 2010), and does not appear to involve the LINC complex (Hu et al, 2013). 3D structured illumination microscopy clearly showed that BicD2 (the Nup358-binding dynein/dynactin adaptor), dynein and dynactin localize to the cytoplasmic face of the NPC in G2, whereas CENP-F (required for Nup133-dependent dynein/dynactin recruitment) only binds later, in prophase.…”

“…Another interesting example of nuclear movement is in the radial glial progenitor cells involved in neuronal and glial development (Hu et al, 2013). In these cells, nuclei undergo cell cycle dependent movement, and move towards the ventricular surface during G2, and then go through mitosis when the nuclei reach the surface.…”

RANBP2 (RAN binding protein 2)

“…RGP nuclei migrate basally during G1, then apically during G2 via dynein, and eventually divide at the ventricular surface. Hu et al (2013) discovered that apical nuclear migration requires dynein recruitment at NPCs by two cooperating G2-specific mechanisms: the "RanBP2-BicD2" pathway acts first, and "Nup133-CENP-F" operates sequentially. This work identifies spatially regulated mechanisms, implying that only restricted regions of neurogenic tissues are permissive for mitosis: in this context, RANBP2 is essential for dynein control of apical nuclear migration, nuclear membrane remodelling and centrosome dynamics prior to mitosis.…”

Microcephaly as a cell cycle disease

“…Mitosis occurs only when the cell body is at the ventricular surface. 2 Once in G1, the nucleus migrates away from the ventricular surface through the narrow basal process of the cell, progresses through Sphase, and then returns to the ventricular surface during G2 for the next mitotic division (Fig. 1).…”

“…2,4 Early G2 nuclear envelope recruitment is activated by Cdk1 phosphorylation of the nucleoporin RanBP2, which, in turn, recruits BicD2, dynein, dynactin, and Lis1. Late G2 nuclear envelope recruitment involves another nucleoporin, Nup133, which recruits CENP-F once it has left the late G2 nucleus through an incompletely understood Cdk1-mediated mechanism.…”