Fig. 1. The -enhancer is required for establishing a distal^high-proximal^low gradient of Pax6 activity in the neuroretina (NR). (A, top) Wild-type Pax6 genomic locus. Positions of the 1.8 kb fragment containing the -enhancer and the 0.4 kb P0 promoter used in the transgene constructs shown in B and Fig. 3I are indicated. (A, bottom) In the Pax6^lacZ allele lacZ/neo was inserted in frame with the translation start, replacing exon 4 to exon 6 (St-Onge et al., 1997), thereby eliminating the -enhancer. (B) Transgene driving gfp (and Cre) expression under control of -enhancer via P0 (see Marquardt et al., 2001). (C) Immunohistochemical detection of Pax6 in an E15.5 Pax6^lacZ/+ eye reveals normal distal^high-proximal^low gradient of Pax6 in the NR (arrowhead indicates distal high end of gradient). (D) In the same eye, ß-gal is uniformly distributed throughout the NR (open arrowhead). Relatively higher ß-gal levels are still found in corneal (ce) and lens epithelium (le), matching endogenous relative Pax6 levels in these tissues (see C). (E) gfp expression in transgenic mice carrying the construct shown in B. At E15.5, drives a sharp distoproximal gradient of gfp expression in the NR, matching the high end of the Pax6 gradient (arrowheads). onh, optic nerve head.

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