Characterization of γGT.Cre mice. (a) Plasmid map of the γGT.Cre transgene injected into B6 × SJL zygotes for the production of transgenic mice. (b) γGT.Cre transgenic mice express Cre transcripts only in the kidney and after postpartum day 7 (day P7), shown by Northern blot probed with cDNA encoding Cre and GAPDH. B, day of birth. (c) Immunofluorescent staining of a paraffin-embedded kidney section from γGT.Cre transgenic mice using antibody against Cre demonstrates staining in cortical proximal tubules but not in the medulla by confocal microscopy (×400); inset at higher power shows cortical tubular (CT) staining (×630). (d) R26R × γGT.Cre F1 hybrid mice express a recombination amplicon of approximately 575 bp’s (shown by PCR) (7, 8) in the kidney but not in the liver. bpA, poly A tail; Br, brain; Lu, lung; Ad, adrenal gland; Lv, liver; Sp, spleen; Mu, muscle; Kd, kidney.