Fig. 7.
Influence of the exit behavior of precursors cells on proportions of successive generations (generation profiles). After differentiative divisions one or both daughter cells quit the cell cycle and lead to high proportions of heavily labeled FG neurons (bottom pathway). After proliferative divisions, daughter cells remain in the cell cycle, and this leads to low numbers of FG neurons. During early stages of corticogenesis, when the proliferative pool is increasing, the percentage of differentiative divisions is low (top pathway). At later stages, high rates of differentiative divisions (bottom pathway) lead to a steady decline in the precursor pool. Ventricular regions characterized by high rates of differentiative division (i.e., high LF) lead to large numbers of heavily labeled FG neurons immediately after the pulse and low numbers of SG neurons. Thus, differences in the ratio between FG and SG neurons reflect the differences in the rate of differentiative divisions.