Spatial Expression Profiling of CreErT Transgenes

To determine the temporal and spatial expression profiles of the CreErT transgenes, we crossed the CreErT transgenic mice with Rosa26 reporter mice. The reporter mice express β-galactosidase in the presence of active Cre recombinase (Soriano, 1999 (link)). After three daily injections of tamoxifen 3 mg per 40 g body weight, the pancreas was embedded in OCT and sectioned for X-gal staining. Sections were postfixed with 0.25% glutaraldehyde in PBS and briefly washed with rinse solution (0.1 M phosphate buffer, pH 7.3, 0.1% deoxycholic acid, 0.2% NP-40, and 2 mM MgCl₂). X-gal staining was performed by incubating samples in staining buffer (2.5 mg/ml X-gal, 5 mM potassium ferricyanide, and 5 mM potassium ferrocyanide) overnight at 37°C and in some cases followed by counterstaining with nuclear fast red.