Fig. 3. Cell fate, proliferation, and death are perturbed in the Fgfr1^-/-; Fgfr2^-/- mutant. (A,B) BrdU incorporation and TUNEL analyses of E10.5 control and mutant telencephalons. Slightly lower rates of BrdU incorporation in the ventral telencephalon (A) and higher rates of cell death in the dorsal midline (B) are observed in the Fgfr1^-/-;Fgfr2^-/- mutant compared with controls. (C-F) Whole-mount in situ hybridization. The more anterior domain of Nkx2.1 expression in the forebrain is absent as early as E9.25 in the mutant. Arrowheads indicate the putative telencephalic-diencephalic ventral border. OS, optic stalk.