Analysis of proliferation and cell cycle in the Fgf15 mutants. (a-i) Comparison of the rate of proliferation of the neuronal progenitors at E14.5 in coronal hemisections from Fgf15+/+ (left column) and Fgf15-/- (right column) embryos. The number of neuronal progenitors undergoing mitosis was evaluated by PH3+ immunofluorescence (a, b); quantification of the PH3+ cells in the VZ and SVZ is shown in (c) (n = 3; p = 0.0019, Student's t-test, indicated by * and **; see Materials and methods). The analysis of the cell cycle length (d, e) (quantification in (f)) and of the number of neuronal progenitors exiting the cell cycle (Q fraction) (f, g) (quantification in (i)) were performed at E14.5 by double labeling with IdU and BrdU (n = 3; p = 0.001, Student's t-test, indicated by *; see Materials and methods). The rectangles in a-b, d-e, g-h indicate the sampled bins. The error bars indicate the standard deviations. MUT, mutant; SVZ, subventricular zone; VZ, ventricular zone; WT, wild type.