Unchanged cell cycle kinetics in the PS cDKO embryonic brain. (A) Graphs show results of cumulative labeling with BrdU at E13.5 in PS cDKO (blue dotted line) and control embryos (black line). Least squares fit analysis of these rising phases (excluding data after giving 8.5 h of BrdU to embryos of both genotypes) yielded the trendlines and R2 values shown. Data points are means ± SEM of the proportions of BrdU-labeled cells, labeling index (LI), in the cortex of each embryo. (B) The growth fraction (GF), the length of S phase (Ts) and the length of the cell cycle (Tc) are calculated using the following equations. The intercept on the y-axis, Yi = GF (Ts/Tc); the time where the GF is maximal (Tm) = Tc-Ts ; the rate of increase (i.e. the slope) of the proportion of labeled cells = GF/Tc.