title: Novel transgenic rat for in vivo genotoxicity assays using 6-thioguanine and Spi- selection.
abstract: Transgenic rodents are valuable models for investigating the genotoxicity of chemicals in vivo. Here, we report the establishment of a novel transgenic rat for genotoxicity analysis. In this model, about 10 copies of lambdaEG10 DNA carrying the gpt gene of E. coli and the red/gam genes of lambda phage are integrated per haploid genome of Sprague-Dawley rats at position 4q24-q31. After recovery of lambdaEG10 phage, point mutations in the gpt gene and deletions in the red/gam genes are identified by 6-thioguanine and Spi(-) selection, respectively. To examine the suitability of these rats for performing in vivo mutagenicity assays, rats were treated with single intraperitoneal injections of ethylnitrosourea (ENU; 100 mg/kg) or benzo[a]pyrene (B[a]P; 62.5 and 125 mg/kg), and the mutant frequencies (MFs) in the liver were determined 7 days after the treatment. ENU enhanced the gpt MF about 7-fold over the control while it did not significantly increase the Spi(-) MF. B[a]P increased both the gpt and Spi(-) MFs several-fold in a dose-dependent manner. To examine the kinetics of MF, ENU was administered (50 mg/kg/day for 5 successive days) and gpt MFs in the liver were determined 7, 21, 35, and 70 days after the last injection. The MF increased to 8-fold and 13-fold over the control at 7 and 35 days, respectively, after the last injection and then slightly declined at 70 days. These kinetics are similar to those reported for ENU-treated lacZ transgenic mice. This novel transgenic rat could be useful for investigating species differences between rats and mice in their response to genotoxic agents.
authors.affiliation: Pharmacology & Toxicology Research Laboratory, Meiji Seika Kaisha, Yokohama, Japan. Hiroyuki_Hayashi@meiji.co.jp
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Hayashi
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Kondo
authors.forename: Ken-ichi
authors.initials: K
authors.lastname: Masumura
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Shindo
authors.forename: Takehiko
authors.initials: T
authors.lastname: Nohmi
mesh_terms: D000818:Animals; D030801:Animals, Genetically Modified; D002874:Chromosome Mapping; D005038:Ethylnitrosourea / Q000633:toxicity*; D009152:Mutagenicity Tests; D009153:Mutagens / Q000633:toxicity*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012641:Selection, Genetic; D013866:Thioguanine
chemical_list: D009153:Mutagens; D013866:Thioguanine; D005038:Ethylnitrosourea