Using homologous recombination, a cre/ERT2-IRES-EGFP cassette was inserted immediately upstream of the translation start ATG codon in exon 2 of the tenascin C gene. A neo selection marker flanked by frt sites followed the cre cassette. EGFP expression is similar to endogenous Tnc expression in the kidney inner medulla interstitial cells. No significant cre-dependent reporter activity is observed in absence of tamoxifen treatment.