(A) (a) Schematic of the mouse carbonic anhydrase I (mCA) locus with regions of DNA conserved between mouse and human (grey bars) and hypersensitive sites (numbers under the gene) identified. E= exon; e = erthyroid cell; c = colon; ec = both erythroid cell and colon. (b) Schematic of mCA Cre (CAC) transgene construct.. BspEI (B), NsiI (N), Sw (SwaI), X (XhoI), Sa (SacII) and S (SaII) restriction enzyme sites are indicated. (B) (a) Cre mRNA expression from the transgene measured in the proximal colon (CoP) of two transgenic lines (CAC5 and CAC6). (b) Survey of Cre mRNA expression in tissues from the CAC5 line. (C) (a) Whole mount staining for β-galactosidase (β-gal) in the intestine of 6 wk-old wild-type (WT) and CAC;R26R mice. Bar = 1 cm. (b) β-gal expression in colon (arrow) of E14.5 WT and CAC;R26R embryos, Bar = 1 cm. (D) (a) High magnification of β-gal staining in whole mount of proximal colon from CAC;R26R mice, Bar = 2 mm. β-gal expression in cryostat section of proximal colon: (b) Bar = 500 μm. (c) Bar = 100 μm.