Fig. 2. Pax6 activity is required for initiating and upregulating, but not for maintaining -enhancer-mediated expression. (A-C) Whole-mount views of E11.5 transgenic embryos in which the -enhancer drives gfp expression. (A) Normal gfp expression in -Cre-gfp; Pax6^+/+ (wild-type) embryo. Inset: 10 µm horizontal section revealing gfp expression in distal NR. (B) Reduced gfp levels in -Cre-gfp; Pax6^flox/flox where Pax6 is specifically eliminated from the distal (gfp⁺Cre⁺) NR. Note that the low fluorescence levels in B and inset, as well as in C were digitally enhanced to reveal expression. (C) No gfp expression can be detected in -Cre-gfp; Pax6^–/– (Pax6-null mutant) embryos. Arrowhead indicates eye rudiment in mutant embryo.