Fig. 3. Analysis of cell-cycle kinetics. (A,B) Graphs show results of cumulative labelling with BrdU at (A) E12.5 and (B) E15.5 in Pax6^Sey/Sey and wild-type embryos, following the approach described by Nowakowski et al. (Nowakowski et al., 1989). Data points are means±s.e.m. of the proportions of BrdU-labelled cells in the cortex of each embryo. The proportions increased over 4.5 hours in E12.5 Pax6^Sey/Sey embryos (broken line in A) and over 8-8.5 hours in all other cases. Least squares fit analysis of these rising phases (i.e. excluding data after giving 8.5 hours of BrdU to Pax6^Sey/Sey embryos aged E12.5 and after giving 12.5 hours of BrdU to embryos of both genotypes aged E15.5) yielded the trendlines and r2 values shown. (C) The growth fraction (GF), the length of S phase (Ts) and the length of the cell cycle (Tc) are calculated using the equations of Nowakowski et al. (Nowakowski et al., 1989). The intercept on the y-axis=GFx(Ts/Tc); the time where the GF is maximal (Tm)=Tc-Ts; the rate of increase (i.e. the slope) of the proportion of labelled cells=GF/Tc. (D) Cell-cycle kinetics in wild-type and mutant telencephalon at E12.5 and E15.5. The circumference of each circle is proportional to the overall length of the cell cycle at the different stages. The wild-type cell cycle lengthens slightly between E12.5 and E15.5. In the mutant, overall cell-cycle length is significantly shorter than normal at E12.5 and longer than normal at E15.5. The proportion of time that the cells spend in S phase is not significantly different between mutant cortex and wild-type cortex at E12.5. However, by E15.5 the proportion of time in S phase is markedly increased in the mutant.