Fig. 7. Cooperation between Otx1 and Otx2 under FM and FM2 enhancers. (A) Histological features of a series of double mutants at E12.5; the genotype of each mutant is indicated at the left. Among mutants not shown, defects were either absent or subtle in Otx2^FM2/FM2, Otx1^+/–Otx2^+/FM2, Otx1^–/–, Otx2^+/–, Otx2^FM/FM2, Otx1^+/–Otx2^+/FM, Otx2^FM/FM, Otx1^+/–Otx2^FM2/FM2 and Otx1^–/–Otx2^+/FM2 mutants. Otx1^+/–Otx2^FM2/– was affected to the same extent as Otx2^FM/– (f); furthermore, defects in Otx1^+/–Otx2^FM/– were as severe as those in Otx1^–/–Otx2^FM/FM (h). Arrowheads indicate the position of the isthmus. Scale bars: 400 µm. (B) Marker analysis of the defects in Otx1^–/–Otx2^FM/FM at E10.5; Otx2 (a), Pax6 (b), Fgf8 (c) and Emx2 (d) expression. See Fig. 3C for the expression in wild-type embryos. Arrows in a and b indicate residual Otx2- and Pax6-positive domains, respectively. Scale bars: 400 µm.