Fig. 2

Dosage-dependent induction of kras^V12 expression and liver tumor induction and regression. (A) RT-PCR analysis of transgenic kras^V12 transcripts in the liver of 1-month-old driver-effector double-transgenic larvae after 3 days of mifepristone (RU486) induction at different concentrations. Induced and non-induced driver transgenics together with non-induced driver-effectors were used as negative controls. β-actin was used as loading control. 2-Off, treatment with 2 mM mifepristone followed by withdrawal for 7 or 14 days. (B) Tumor induction rates for 1-month-old driver-effector fish under different concentrations of RU486 (n=20 in each group). (C) Statistics of tumor incidence as determined by histopathological analysis on induced driver-effector transgenics after 1–4 weeks of 2 μM RU486 treatment. WT, wild type. (D) Liver tumor progression in driver-effector fish induced by 2 μM mifepristone. The four panels represent different stages of liver tumorigenesis starting from normal control liver on the left to hyperplastic liver (HL) (2 weeks), HCC (4 weeks) and hepatoblastoma in mixed HCC (8 weeks). Each panel contains brightfield and fluorescent images of gross liver morphology (top) and a relevant histological image (bottom). (E) Liver tumor regression after mifepristone withdrawal. Following treatment of 2 μM RU486 for 4 weeks, driver-effector fish developed EGFP-labeled HCC and their exposure to RU486 was then terminated. Histological sections from two representative fish after RU486 removal for 2 and 4 weeks are shown. Dotted areas showed tumor shrinkage with marked peripheral scarring, whereas asterisks indicate surrounding normal hepatic tissue. (+) and (–) indicate RU486-treated and untreated fish, respectively. Boxed areas are shown enlarged on the right. Scale bars: 100 μm.