Fig. 6. The failure of olfactory bulb development in Foxg1-Cre/+; Fgfr1fx/fx mice involves a failure of cells in the anterior telencephalon to show decreased levels of proliferation. BrdU incorporation in E12.5 control (A,B) and mutant (A',B') telencephalons at the site of normal olfactory bulb development (A,A') and in the cerebral cortex (B,B'). Levels of BrdU incorporation are reduced at the anterior tip of the telencephalon in control whereas in the mutant levels remain high (arrowheads). Scale bar: 0.08 mm. (C) Quantitation of BrdU incorporation. Unlike cells in the anterior telencephalon of controls, cells in the anterior telencephalon of mutants continue to proliferate at rates comparable with those in neocortex (asterisk, P<0.0001).