Fig. 5. A schematic diagram of Nes expression according to the cell-cycle-dependent morphological changes of neural progenitor cells in the developing cerebral cortex. (A) A schematic diagram of the stage-dependent thickening of the mouse cerebral wall based on Takahashi et al. (Takahashi et al., 1993). Cortical progenitor cells elongate as development proceeds from an early `neuroepithelial cell' to a mid-embryonic `radial glial cell' stage. The expression of Nes (green) was strong during the neurogenic stage, which accompanied obvious cerebral wall thickening and the prolonged G1 phase. (B) Cell-cycle-dependent morphological changes of mid-embryonic progenitor cells. At the beginning of the G1 phase, each progenitor cell generated at the ventricular surface is either connected to the pial surface (cell i) or lacking a pial process (cell ii). The daughter cell that inherited the pial process (cell i) elongates its process within a single cell cycle to match the cerebral wall thickening. The other daughter cell (cell ii) elaborates a new pial process, mainly during G1, and adopts the bipolar radial glial morphology by S phase. During mitosis, the cell body rounds up and the process becomes extremely thin. A model for the lineage-restriction of the progenitor cell is omitted for simplification. The expression of Nes (green) was observed concomitant with the elongation of the radial process during the G1 to S phases. At G2-M, Nes expression declined because of the phosphorylation of its upstream regulator class III POU protein, allowing the cells to undergo mitosis. Note that the duration of each cell cycle phase illustrated (G1, S, and G2-M) is according to those determined at E14 by Takahashi et al. (Takahashi et al., 1995). CP, cortical plate; IMZ, intermediate zone; VZ, ventricular zone.