Feeding induces CYP7A1 in humanized CYP7A1-tg mice. Total bile acid pool (A) and gallbladder bile acid composition (B) were determined in humanized CYP7A1-tg mice and wild type controls. C and D, human CYP7A1 mRNA levels in humanized CYP7A1-tg mice. Mice were fed chow or chow containing 5% cholestyramine or 2% cholesterol for 1 week. Human CYP7A1 mRNA was determined by real-time PCR. E, refeeding effect on human CYP7A1 mRNA expression in humanized CYP7A1-tg mice. Mice were fasted or refed for 3 h. Liver CYP7A1 mRNA was determined by real-time PCR. Results are expressed as mean ± S.E. (error bars), n = 3–4. *, statistical significance (p < 0.05). F, ChIP assay of the abundance of acetylated histone 3 (AcH3), trimethylated H3K9, and FoxO1 in the human CYP7A1 gene promoter of humanized CYP7A1-tg mice. Pooled liver samples from 3–4 mice were used in ChIP assays. Real-time PCR was done in triplicate, and mean values were plotted. Abbreviations for bile acids are as in Fig. 7.