SENSITIVITY OF THE PHI-X174 AM3 ALLELE IN RELATION TO THE ENDOGENOUS HPRT GENE FOR DETECTING MUTATION IN TRANSGENIC MICE

Transgenic mice have been developed containing multiple, chromosomally integrated copies of the Phi X174 am3 allele that serve as reporters for in vivo mutation at a single A:T basepair. In this study, we exami ned the relative sensitivity of the am3 transgene For detecting the in vivo mutagenicity of N-ethyl-N-nitrosourea (ENU). Three-week-old male Phi X174 mice were treated with 0, 40, and 160 mg/kg of ENU. After 1, 3, 6, and 9 weeks, animals were killed, their spleens removed, and is olated splenocytes were used to measure mutant frequencies (MFs) in bo th the am3 allele and the endogenous Hprt gene. For animals treated wi th 40 mg/kg of ENU, the Hprt assay detected an average 22-fold increas e over background, while the am3 MFs averaged threefold above backgrou nd. With the 160 mg/kg dose, the Hprt assay detected a 54-fold average increase, while a sixfold average increase above background was found for the transgenic locus. We conclude that the sensitivity of the am3 assay to ENU was compromised by the presence of ex vivo mutations. Ad justment of am3 MFs to exclude these ex vivo mutants could enhance the sensitivity of the assay. Environ. Mol. Mutagen. 32:229-235, 1998 (C) 1998 Wiley-Liss, Inc.