Characterisation of Muta™Mouse λgt10-lacZ transgene: evidence for in vivo rearrangements

The multicopy λgt10-lacZ transgene shuttle vector of Muta™Mouse serves as an important tool for genotoxicity studies. Here, we describe a model for λgt10-lacZ transgene molecular structure, based on characterisation of transgenes recovered from animals of our intramural breeding colony. Unique nucleotide sequences of the 47 513 bp monomer are reported with GenBank® assigned accession numbers. Besides defining ancestral mutations of the λgt10 used to construct the transgene and the Muta™Mouse precursor (strain 40.6), we validated the sequence integrity of key λ genes needed for the Escherichia coli host-based mutation reporting assay. Using three polymerase chain reaction (PCR)-based chromosome scanning and cloning strategies, we found five distinct in vivo transgene rearrangements, which were common to both sexes, and involved copy fusions generating ∼10 defective copies per haplotype. The transgene haplotype was estimated by Southern hybridisation and real-time–polymerase chain reaction, which yielded 29.0 ± 4.0 copies based on spleen DNA of Muta™Mouse, and a reconstructed CD2F1 genome with variable λgt10-lacZ copies. Similar analysis of commercially prepared spleen DNA from Big Blue® mouse yielded a haplotype of 23.5 ± 3.1 copies. The latter DNA is used in calibrating a commercial in vitro packaging kit for E.coli host-based mutation assays of both transgenic systems. The model for λgt10-lacZ transgene organisation, and the PCR-based methods for assessing copy number, integrity and rearrangements, potentially extends the use of Muta™Mouse construct for direct, genomic-type assays that detect the effects of clastogens and aneugens, without depending on an E.coli host, for reporting effects

Mutagenicity of comfrey (Symphytum Officinale) in rat liver

Comfrey is a rat liver toxin and carcinogen that has been used as a vegetable and herbal remedy by humans. In order to evaluate the mechanisms underlying its carcinogenicity, we examined the mutagenicity of comfrey in the transgenic Big Blue rat model. Our results indicate that comfrey is mutagenic in rat liver and the types of mutations induced by comfrey suggest that its tumorigenicity results from the genotoxicity of pyrrolizidine alkaloids in the plant

Molecular mechanism of hepatocellular injury in alpha 1 antitrypsin deficiency

Liver injury in PiZZ Α 1 -antitrypsin (Α 1 -AT) deficiency probably results from toxic effects of the abnormal Α 1 -AT molecule accumulating within the ER of liver cells. However, only 12–15% of individuals with this same genotype develops liver disease. Therefore, we predicted that other genetic traits that determine the net intracellular accumulation of the mutant Α 1 -AT molecule would also determine susceptibility to liver disease. To address this prediction, we transduced skin fibroblasts from PiZZ individuals with liver disease or without liver disease with amphotropic recombinant retroviral particles designed for constitutive expression of the mutant Α 1 -AT Z gene. Human skin fibroblasts do not express the endogenous Α 1 -AT gene but presumably express other genes involved in postsynthetic processing of secretory proteins. The results show that expression of human Α 1 -AT M gene was conferred on each fibroblast cell line. Compared to the same cell line transduced with the wild-type Α 1 -AT M gene, there was selective intracellular accumulation of the mutant Α 1 -AT Z protein in each case. However, there was a marked delay in degradation of the mutant Α 1 -AT Z protein after it accumulated in the fibroblasts from ZZ individuals with liver disease (“susceptible hosts”) as compared to those without liver disease (“protected hosts”). Appropriate disease controls showed that the lag in degradation in susceptible hosts is specific for the combination of PiZZ phenotype and liver disease. Biochemical characteristics of Α 1 -AT Z degradation in the protected hosts were found to be similar to those of a common ER degradation pathway previously described in model experimental cell systems for T-cell receptor Α subunits and asialoglycoprotein receptor subunits, therefore, raising the possibility that the lag in degradation in the susceptible host is a defect in this common ER degradation pathway. Thus, these data provide evidence that other genetic traits that affect the fate of the abnormal Α 1 -AT Z molecule, at least in part, determine susceptibility to liver disease. These data also validate a system for elucidating the biochemical/genetic characteristics of these traits and for examining the relevance to human disease of pathways for protein dÉradation in the ER.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/38411/1/1840210638_ftp.pd