Figure 2: oRG cells divide horizontally to self-renew.
From: Mitotic spindle orientation predicts outer radial glial cell generation in human neocortex
(a) Time-lapse stills of a dividing oRG cell (blue arrowhead) in GW16 human fetal cortical slice labelled with Adeno-GFP. The cell undergoes MST and divides with a horizontal spindle orientation, producing an apical daughter (orange arrowhead) and a basal daughter (white arrowhead). The basal daughter retains the basal fibre and becomes a self-renewed oRG cell, while the apical daughter produces an apical process. Scale bar, 10 μm. (b) z-plane analysis of oRG cell in first frame of a, demonstrating lack of apical process. Scale bar, 10 μm. (c) z-plane analysis of daughter cells in last frame of a, demonstrating lack of apical process on basal daughter, and presence of apical process on apical daughter. Scale bar, 10 μm. (d) Image of oRG cell in fixed GW16 human fetal cortical oSVZ undergoing mitosis with a horizontal cleavage plane. Scale bar, 10 μm. (e) Schematic of oRG cells undergoing mitosis with vertical, oblique and horizontal cleavage planes. Cleavage plane angle was analysed with respect to the basal fibre of the dividing cell (or in the case of IP cells, with respect to the nearest basal fibre). (f) Time-lapse stills of IP cell (blue arrowhead) in a GW18 human fetal cortical slice that retracts its processes and rounds up to divide symmetrically, without undergoing MST or INM, to produce two daughter cells (white arrowheads). Spindle orientation was calculated with respect to the nearest radial fibre. Scale bar, 20 μm. (g) Image of IP cell in fixed GW16 human fetal cortical oSVZ undergoing mitosis with a horizontal spindle orientation. Scale bar, 5 μm. (h) Quantification of mitotic spindle orientations in i/oSVZ progenitors (oRG cells and IP cells) in fixed GW16 human fetal cortical slices. Cells used for calculation were in anaphase or telophase and displayed the following characteristics; oRG cells: pVim+, pH3+ cells in the iSVZ or oSVZ that displayed a basal fibre but no apical ventricular contact; IP cells: Tbr2+ cells in the iSVZ or oSVZ that were pVim+ and displayed no basal or apical fibre.
