Mutation induction in relation to organ specificity, 2) mutation induction during development, 3) systemic effect of somatic mutations of age-related degenerative diseases, and 4) tumor progression from pre- neoplastic to neoplastic growth in relation to genomic stability. A recoverable vector transgenic approach can be used to deal with some of these issues. Use of vectors that only detect a limited array of genetic alterations give increased sensitivity in kinetic studies, require fewer data points, and uncover specific mutagenicity that may go undetected with targets that respond to a broad spectrum. For example, the A:T base pair plays an extremely important role in induced mutagenicity in mammals, but the effect of mutagens on the A:T target is often masked by C pG mutagenicity in transgenic systems that detect a broad spectrum of genetic alterations. Initially, the well characterized am3 mutation of phiX174 is used as a transgene to evaluate substitutions at the A:T base pair. An inbred line of C57BL6/J mice was established that is homozygous for phiX174 in a tandem array and free of detrimental effect from the insertion. Reversions via one transition and two transversions are detected by selection among progeny phage recovered from the transgenic animals. The vector can be recovered from the genomic DNA, and both recovery and putative mutation frequencies are independent of any endogenous variation in the CpG methylation between host animals and tissues. The level of CpG methylation increases progressively with the number of generations removed from the founder animal. To maintain high recovery of the vector from animals from subsequent generations it was necessary to develop a bacterial strain with a high methylation tolerance level for recovery of PhiX174 from the mammalian DNA. The spontaneous reverse mutation frequencies of am3 in the vector isolated from in testis, liver and spleen seems to be close to the same namely approximately 1 per million of recovered vectors. After treatment with ethyl nitrosourea the mutation frequency varied greatly between animals. This variation may indicate a strong clonial nature of the mutations.

National Institute of Health (NIH)
National Institute of Environmental Health Sciences (NIEHS)
Intramural Research (Z01)
Project #
Application #
Study Section
Special Emphasis Panel (TB)
Project Start
Project End
Budget Start
Budget End
Support Year
Fiscal Year
Total Cost
Indirect Cost
United States
Zip Code
Samet, Jonathan M; DeMarini, David M; Malling, Heinrich V (2004) Biomedicine. Do airborne particles induce heritable mutations? Science 304:971-2
Weaver, Robert P; Malling, Heinrich V (2003) The in vivo but not the in vitro am3 revertant frequencies increase linearly with increased ethylnitrosourea doses in spleen of mice transgenic for phiX174 am3, cs70 using the single burst assay. Mutat Res 534:1-13
Cosentino, Lidia; Malling, Heinrich V; Heddle, John A (2002) Response of the phiX174 am3, cs70 transgene to acute and chronic ENU exposure: implications for protocol design. Mutat Res 518:113-21
Valentine, Carrie R; Montgomery, Beverly A; Miller, Scott G et al. (2002) Characterization of mutant spectra generated by a forward mutational assay for gene A of Phi X174 from ENU-treated transgenic mouse embryonic cell line PX-2. Environ Mol Mutagen 39:55-68
Malling, H V; Delongchamp, R R (2001) Direct separation of in vivo and in vitro am3 revertants in transgenic mice carrying the phiX174 am3, cs70 vector. Environ Mol Mutagen 37:345-55
Delongchamp, R R; Valentine, C R; Malling, H V (2001) Estimation of the average burst size of Phix174 am3, cs70 for use in mutation assays with transgenic mice. Environ Mol Mutagen 37:356-60
Delongchamp, R R; Malling, H V; Chen, J B et al. (1999) An estimator of the mutant frequency in assays using transgenic animals. Mutat Res 440:101-8
Malling, H V (1999) Frederick J. de Serres: the years at the Research Triangle Park (1972-1995). Mutat Res 437:69-75
Malling, H V; Newbold, R R; Lewis, S et al. (1999) Mutagenesis of a single AT basepair in mice transgenic for PhiX174 am3, cs70. II. Brain. Mutat Res 444:85-95