Strain-dependent differences in DNA synthesis and gene expression in the regenerating livers of CB57BL/6J and C3H/HeJ mice.

C3H/HeJ (C3H) mice are approximately 50-fold more susceptible to liver-tumor induction than C57BL/6J (B6) mice. This difference is susceptibility is a consequence of allelic differences in hepatocarcinogen sensitivity (Hcs) genes that control the growth of preneoplastic lesions in the liver. We have shown previously that these two strains differ in their responses to partial hepatectomy, which acts as a promoter of hepatocarcinogenesis in B6 mice but not in C3H mice. To determine whether there are also strain-specific differences in normal regulation of hepatic growth, we compared liver regeneration in C3H and B6 mice at the levels of DNA synthesis and gene expression. Partial hepatectomy induced a cascade of controlled events resulting in the regeneration of the liver to its original mass 11 d after surgery. We observed a two-fold greater level of DNA synthesis in C3H mice relative to B6 mice during the first peak of DNA synthesis, which occurred 35 h after hepatectomy in both strains. While the c-fos transcript was readily induced in both strains, there was a reduction in the expression of the late response genes E2F1 and dihydrofolate reductase in the livers of B6 mice when compared with the expression of these transcripts in the livers of C3H mice. The differential regulation of E2F1 between B6 and C3H mice may indicate that the Hcs genes and E2F1 function in the same signal transduction pathway of normal growth control.