Proliferation defects are reversed in Foxg1-/- telencephalon if Pax6 levels are increased. (A,B) Coronal sections through the telencephalon of a wild-type (A) and a Foxg1-/- embryo (B) at E12.5 labelled with anti-BrDU (brown). Boxes 100 μm wide show the positions sampled in the wild-type dorsal telencephalon (A) and the whole telencephalon of embryos lacking Foxg1 (B). (C) Percentages of cells in S-phase are significantly lower in the Foxg1-/- telencephalon compared to the wild-type at rostral, central and caudal levels (mean ± s.e.m. In all three regions: wild-type, n = 3; Foxg1-/-, n = 4; Student's t-test, P < 0.01). In Foxg1-/-;Pax77 embryos, percentages of cells in S-phase are significantly increased compared to those in Foxg1-/- embryos at rostral (mean ± s.e.m, n = 4; Student's t-test, P < 0.05) and central (mean ± s.e.m, n = 4; Student's t-test, P < 0.01) but not at caudal levels.