Fig. 2.

Inducibility of reporter expression by doxycycline (Dox) in 2 different types of double transgenic mice. The UPII-rtTA line and the low-copied UPII-rtTA-M2 line were intercrossed separately with a transgenic reporter line in which tetracycline-responsive elements (TRE) drive the expression of an enhanced green fluorescent protein (EGFP; see materials and methods for details). A: RT-PCR analysis of EGFP expression. Single (TRE-EGFP) and double transgenic (rtTA/TRE-EGFP vs. rtTA-M2/TRE-EGFP) mice either received regular diet (uninduced or U) or the same diet supplemented with Dox (induced or I). Note the total absence of EGFP induction by Dox in the rtTA/TRE-EGFP double transgenic mice (top; lanes 7 and 8), and in stark contrast, the strong induction of EGFP (400-bp band) in the rtTA-M2/TRE-EGFP double transgenic mice (3rd panel; lanes 7 and 8). B: fluorescent microscopy of frozen bladder section from a Dox-treated (for 1 mo) rtTA/TRE-EGFP double transgenic mouse showing the lack of green fluorescence in urothelium (a), whereas bladder section from a rtTA-M2/TRE-EGFP mouse showed strong nuclear green fluorescence (b). The sections were counterstained with a pan-uroplakin antibody (red) and DAPI (blue).