Fig. 8. Functional analyses of the early and late enhancers in the context of the Pax2 locus. (A) Structure of the Pax2 BAC #30, which contains an in-frame GFP insertion in exon 2 and extends at least 30 kb upstream of Pax2. A structurally different Pax2-GFP BAC (#76) gave rise to the same expression pattern as BAC #30. All mutant transgenes (#31-34) were derived from BAC #30. Nucleotide positions relative to the transcription start site indicate the extent of deletion. n.d., not determined. (B-F) Temporal expression pattern of the parental BAC #30. Strong GFP expression was observed in the metanephros (F) at E16.5. (G-K) The proximal but not distal enhancer of Pax2 is essential for late expression at the MHB (arrowhead). An oblique section (G) through the mesonephros of an E10 embryo revealed normal expression of transgene #32 in both the nephric duct (nd) and tubules (tub). (L-N) Before the four-somite stage, the early enhancer in the intermediate homology region is required for Pax2 expression in the MHB region. ad, adrenal gland; nt, neural tube; tb, tail bud.