Fig. 2. Localization of Foxg1-driven Cre expression and strategy for generating Fgf8 conditional knockouts. (A) X-gal staining of R26R^lacZ/+;Foxg1^Cre/+ embryos at E9.5, E10.5 and E12.5. Top panels show whole-mount images and bottom panels show corresponding sections from embryos processed as whole mounts. At E9.5, staining is detected in forebrain (FB) and olfactory placode (arrows). At E10.5, staining is observed at rim of invaginating nasal pit (NP; arrows). OC, optic cup. At E12.5, prominent staining is observed in OE. Scale bars: 500 µm in the top panels; 200 µm in the bottom panels. (B) Fgf8^flox/flox,Foxg1^+/+ females were crossed with Fgf8^d2,3/+;Foxg1^Cre/+ males and embryos genotyped with three different primer sets to detect different alleles: Fgf8-flox and wild-type (F1 and F2), Fgf8-d2,3 (F1 and F3) and Cre (C1 and C2). One-quarter of offspring had the Fgf8^d2,3/flox;Foxg1^Cre/+ (mutant) genotype.