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Changes in nucleolar Ag stainability in NORs during rat hepatocarcinogenesis
180 1.2.10 Granger, M., M. Bichara, M. Daune and R.P.P. Fuchs, I.B.M.C. du CNRS, Laboratoire de Biophysique, 15 rue Ren6 Descartes, 67084 Strasbourg C6dex (France)
Survival and mutagenesis of a plasmid modified by a carcinogen (AAF) grown in E. coli strains deficient in mismatch repair Studies of the mutagenesis induced in the tetracycline resistance gene of pBR322 by the ultimate carcinogen N-acetoxy-N-2-acetylaminofluorene (-AAF) have shown that it depends upon the SOS mutator activity of the E. coli host. The mutations can be generated either at time of replication a n d / o r before replication somewhere along the repair pathways of the lesions. Our working hypothesis is that the mismatch correction system of E. coli is involved in the fixation of some of the mutations. Therefore, we have studied the survival and the induced mutagenesis of a plasmid modified by -AAF or its deacetylated form -AF grown in E. coli strains deficient in mismatch repair (mutH, routS, mutU). The survival of pBR322 modified by -AAF is found similar when grown either in a wild-type, a m u t H or a routS strain (37% survival: 13 A A F / p B R ) while it is considerably decreased in a mutU strain (37% survival: 5 A A F / p B R ) . The same observation is made with -AF with a 37% survival of 60 A F / p B R in a wild-type, m u t H or routS strain and 6 A F / p B R for the mutU strains. From these observations, we conclude that the m u t U gene product plays an important role in the repair of both -AAF and -AF adducts, presumably as part of the repair by the excision machinery. The m u t H and routS gene products are not involved in the AAF-induced mutagenesis while the m u t U gene product seems to play a crucial role. Therefore it seems that part of the genes involved in the mismatch correction system of E. coli is also involved in the fixation of mutations in a plasmid modified by AAF.
1.2.11 Kirsch-Volders, M. 1, A. Deleener 1 j. De Gerlache 2 and M. Lans 2, 1 Laboratory of Human Genetics, Vrije Universiteit Brussel, B-1050 Brussels, and z Laboratoire de Bioch6mie Toxicologique et Canc6rologique, Universit6 Catholique de Louvain, B-1200 Brussels (Belgium)
Changes in nucleolar Ag stainability in NORs during rat hepatocarcinogenesis Hepatocarcinogenesis was induced in young male Wistar rats by a modification of the Solt and Farber procedure: initiation by an acute dose of DENA (diethylnitrosamine, 200 mg/kg), followed by selection with a concentration of 0.03% of 2-AAF in the diet and CC14 (2 ml/kg: 1/1; v / v in corn oil), promotion by a 0.05% phenobarbital-supplemented diet. Hepatocytes were isolated by a liver perfusion from rats which had received a part of or the complete carcinogenic treatment; after silver staining, the nucleolar activity as estimated by the morphology of the nucleoli was analysed by distinguishing between ring-shaped nucleoli, nuclei with one or more small silver-stained granulae, nuclei with one or more compact nucleoli. The cytomorphological analysis showed that both DENA and phenobarbital modify the nucleolar activity of rat hepatocytes. The most important increase of nucleolar activity was observed immediately after a 2-day treatment with phenobarbital and after initiation with DENA and selection.
Survival and mutagenesis of a plasmid modified by a carcinogen (AAF) grown in E. coli strains deficient in mismatch repair Studies of the mutagenesis induced in the tetracycline resistance gene of pBR322 by the ultimate carcinogen N-acetoxy-N-2-acetylaminofluorene (-AAF) have shown that it depends upon the SOS mutator activity of the E. coli host. The mutations can be generated either at time of replication a n d / o r before replication somewhere along the repair pathways of the lesions. Our working hypothesis is that the mismatch correction system of E. coli is involved in the fixation of some of the mutations. Therefore, we have studied the survival and the induced mutagenesis of a plasmid modified by -AAF or its deacetylated form -AF grown in E. coli strains deficient in mismatch repair (mutH, routS, mutU). The survival of pBR322 modified by -AAF is found similar when grown either in a wild-type, a m u t H or a routS strain (37% survival: 13 A A F / p B R ) while it is considerably decreased in a mutU strain (37% survival: 5 A A F / p B R ) . The same observation is made with -AF with a 37% survival of 60 A F / p B R in a wild-type, m u t H or routS strain and 6 A F / p B R for the mutU strains. From these observations, we conclude that the m u t U gene product plays an important role in the repair of both -AAF and -AF adducts, presumably as part of the repair by the excision machinery. The m u t H and routS gene products are not involved in the AAF-induced mutagenesis while the m u t U gene product seems to play a crucial role. Therefore it seems that part of the genes involved in the mismatch correction system of E. coli is also involved in the fixation of mutations in a plasmid modified by AAF.
1.2.11 Kirsch-Volders, M. 1, A. Deleener 1 j. De Gerlache 2 and M. Lans 2, 1 Laboratory of Human Genetics, Vrije Universiteit Brussel, B-1050 Brussels, and z Laboratoire de Bioch6mie Toxicologique et Canc6rologique, Universit6 Catholique de Louvain, B-1200 Brussels (Belgium)
Changes in nucleolar Ag stainability in NORs during rat hepatocarcinogenesis Hepatocarcinogenesis was induced in young male Wistar rats by a modification of the Solt and Farber procedure: initiation by an acute dose of DENA (diethylnitrosamine, 200 mg/kg), followed by selection with a concentration of 0.03% of 2-AAF in the diet and CC14 (2 ml/kg: 1/1; v / v in corn oil), promotion by a 0.05% phenobarbital-supplemented diet. Hepatocytes were isolated by a liver perfusion from rats which had received a part of or the complete carcinogenic treatment; after silver staining, the nucleolar activity as estimated by the morphology of the nucleoli was analysed by distinguishing between ring-shaped nucleoli, nuclei with one or more small silver-stained granulae, nuclei with one or more compact nucleoli. The cytomorphological analysis showed that both DENA and phenobarbital modify the nucleolar activity of rat hepatocytes. The most important increase of nucleolar activity was observed immediately after a 2-day treatment with phenobarbital and after initiation with DENA and selection.