Distinct transgene activation in two K14CreER mouse lines. Skin sections (60 µm) from two mouse lines (as indicated at the left of the panel) injected with tamoxifen (100 µg/g body) or corn oil (carrier) at PD17 and sacrificed at PD21 were stained for X-Gal (blue). Note single-cell bulge labeling in hair follicles from the K14-CreER line with no leaky expression in the absence of tamoxifen (top). In contrast, the K14CreERT 2 line showed robust induction in all hair compartment including hair germ, as well as some leaky expression (bottom). Basement membrane around the bulge and hair germ marked with dotted lines. Bu, bulge; hg, hair germ; SG, sebaceous gland. Scale bar, 50 µm. N = 3 mice per transgenic line.