(A) Schematic depiction of the Tet-Off STS transgenic system. (B) PCR genotyping using gene-specific primers for the detection of the FABP-tTA and TRE-STS transgenes. (C) Conditional STS transgene expression as determined by Northern blot analysis. STS full-length cDNA was used as the probe to detect transgene expression. The 18s rRNA was used as a loading control. (D) STS expression detected by immunohistochemistry in the liver and small intestine. (E) STS activity in the liver and small intestine. The enzymatic activity of STS was determined by an estrone sulfate conversion assay and was normalized to protein concentrations. Values are presented as the mean ± SD. N ≥ 4 for each group. ****, P < 0.0001. FABP, fatty acid binding protein; tTA, tetracycline-controlled transactivator; TRE, tetracycline response element; Pmin CMV, minimal human cytomegalovirus promoter. WT, wild-type mice; Tg, STS transgenic mice; LIV, liver; INT, small intestine; BAT, brown adipose tissue; WAT, white adipose tissue; DOX, doxycycline.