Genetic dissection of murine susceptibilities to liver and lung tumors based on the two-stage concept of carcinogenesis

Fibroblast growth factor 15 deficiency impairs liver regeneration in mice

Fibroblast growth factor (FGF) 15 (human homolog, FGF19) is an endocrine FGF highly expressed in the small intestine of mice. Emerging evidence suggests that FGF15 is critical for regulating hepatic functions; however, the role of FGF15 in liver regeneration is unclear. This study assessed whether liver regeneration is altered in FGF15 knockout (KO) mice following 2/3 partial hepatectomy (PHx). The results showed that FGF15 KO mice had marked mortality, with the survival rate influenced by genetic background. Compared with wild-type mice, the KO mice displayed extensive liver necrosis and marked elevation of serum bile acids and bilirubin. Furthermore, hepatocyte proliferation was reduced in the KO mice because of impaired cell cycle progression. After PHx, the KO mice had weaker activation of signaling pathways that are important for liver regeneration, including signal transducer and activator of transcription 3, nuclear factor-κB, and mitogen-activated protein kinase. Examination of the KO mice at early time points after PHx revealed a reduced and/or delayed induction of immediate-early response genes, including growth-control transcription factors that are critical for liver regeneration. In conclusion, the results suggest that FGF15 deficiency severely impairs liver regeneration in mice after PHx. The underlying mechanism is likely the result of disrupted bile acid homeostasis and impaired priming of hepatocyte proliferation.

Genomic instability of murine hepatocellular carcinomas with low and high metastatic capacities

AIM: To investigate the frequency of genomic instability in murine hepatocellular carcinoma (HCC) cell lines Hca/A2-P(P) and Hca/163-F(F) with low and high metastatic capacity, and to explore its association with the occurrence and metastasis of hepatocellular carcinomas.

METHODS: Forty microsatellite markers were randomly selected to examine P and F cells for genomic instability using PCR-simple sequence length polymorphism (PCR-SSLP) analysis.

RESULTS: Allelic genes on the chromosomes of P cell line with thirty informative microsatellite loci were paralleled to those of inbred strain C₃H mouse, while those of F cell line with 28 loci were paralleled to those of inbred strain C₃H mice. The frequency of microsatellite alterations was 37.5% and 42.5% in P cell line and F cell line, respectively. There were different alterations of allelic band 9 at loci between P and F cells, among which, the frequency of microsatellite alterations was most commonly seen on chromosomes 3, 7, 11 and 16.

CONCLUSION: Genomic instability in mouse chromosomes 3, 7, 11 and 16 may play a more important role in the development and progression of HCC in mice. It is suggested that these two sub-clones derived from a same hepatic tumor in homozygous mouse present different genetic features.

Complications associated with genetic background effects in models of experimental epilepsy

To elucidate the genetic influences contributing to susceptibility to seizure disorders, researchers have long used selected lines and inbred strains of rodents. In recent years, the use of genetically altered mice as models of complex human disease has revolutionized biomedical research into the genetics of disease pathogenesis and potential therapeutic interventions. In particular, the study of transgenic and gene-deleted (knockout) mice can provide important insights into the in vivo function and interaction of specific gene products. While a variety of inbred mouse mutations have been used to directly evaluate the genetic basis of seizure disorders, data obtained from such genetically altered mice must be interpreted carefully. An increasing number of scientific articles have reported that the phenotype of a given single gene mutation in mice can be modulated by the genetic background of the inbred strain in which the mutation is maintained. This effect is attributable to so-called modifier genes, which act in combination with the causative gene. In this review, the author points out the importance of considering the genetic background of the strain used to create these animal models, the potential problems with interpretation of phenotype, and solutions to selecting an appropriate mouse model of experimental epilepsy. Despite these potential limitations, knockout mice provide a powerful tool for understanding the genetic and neurobiological mechanisms contributing to experimental epilepsy.

Five quantitative trait loci affecting 4-nitroquinoline 1-oxide-induced tongue cancer in the rat

In our previous study, Dark-Agouti (DA) rats were found to be highly susceptible to 4-nitroquinoline 1-oxide (4NQO)-induced tongue carcinoma (TC), whereas Wistar / Furth (WF) rats were barely susceptible. Interval mapping analysis of reciprocal backcross rats showed two quantitative trait loci (QTL) on rat chromosomes (RNO) 1 and 19. In the present study, a composite interval mapping analysis was applied to 4NQO-induced TC in 130 (DA x WF) F2 rats, demonstrating five independent QTL, Tongue squamous cell carcinoma 1 - 5 (Tscc1 - 5), responsible for phenotypic differences in the size and number of TCs in the two strains. Two of these QTL were mapped on RNO1, and the others were mapped on RNO4, 14, and 19. The DA allele at these loci consistently yielded semidominant susceptibility to TC. Out of the five loci detected in this F2 generation, Tscc1 and 2 were identical to Stc1 and Rtc1 described in our previous study, but the other three were novel. We propose a new nomenclature consistent with their function. Genome-wide screening of the F2 progeny also suggested the presence of three additional QTL on RNO5, 6, and 10. The possible roles of these loci in tongue carcinogenesis are discussed.

Paradoxical effects of phenobarbital on mouse hepatocarcinogenesis

Phenobarbital was the first tumor promoter for rodent liver to be associated with the 2-stage or initiation-promotion concept of carcinogenesis. In rats and mice preinitiated with genotoxic carcinogens, phenobarbital administration increases the number of hepatocellular tumors by approximately 5-fold despite its nongenotoxicity. However, in mice phenobarbital occasionally exhibits strong inhibitory effects on hepatocarcinogenesis initiated with the potent carcinogen diethylnitrosamine. Both positive and negative effects of phenobarbital on hepatocytic proliferation and apoptosis, which are mechanistically involved in the promotion stage of hepatocarcinogenesis, have been described. These complex outcomes of phenobarbital treatment and their effects on hepatocarcinogenesis in mice raise serious issues regarding extrapolation of experimental data from laboratory animals to human risk assessment. Recent work suggests that the paradoxical actions of phenobarbital on hepatocarcinogenesis can be understood by consideration of qualitative diversity in initiated lesions and differential responses to promotion stimulus.