Figure 1

Appropriate ventricular zone (VZ) output requires greater than 5% neural progenitor cell (NPC) death. (A, B) Two simple cell decision paradigms are used to identify a plausibility window and calculate viable levels of NPC death. Beginning at 'P' and following the arrows clockwise, in model D_G1 (A) the NPC population P_i-1is doubled at the i^thmitosis, then NPC death, 'D,' and differentiation, 'Q,' are imposed, so that the P population for the subsequent cell cycle (CC) is given by P _i = 2(1 - d _i - q _i )P_i-1. (B) In model D_G2 dying NPCs are removed from the NPC population prior to doubling the population, and P _i = (1 - q _i )2(1 - d _i )P_i-1. (C, D) Model output from P₀ = 550,000. VZ output (total Q cells, y-axis) is plotted after 11 CCs when the indicated fraction of NPCs die at each CC (Death, x-axis). The window of plausible VZ output, between 1 × 10⁷ and 2.72 × 10⁷, is indicated by dashed lines. (C) Using model D_G1, the center of the plausible VZ output range (total Q cells = 1.86 × 10⁷) corresponds to 19% NPC death, as indicated by the solid line that descends from plotted VZ output to the x-axis. (D) Similarly, the center of the plausibility window using model D_G2 corresponds to 17% NPC death.