Catherine G. Klein, PhD

With molecular biologic and molecular cytogenetic techniques, we study the mutagenic and epigenetic mechanisms that silence genes, including transgene expression in a unique set of mammalian cell lines. The G12 and G10 cell lines each contain a bacterial xanthine-guanine phosphoribosyl transferase (gpt) gene target that has been stably inserted into different chromosomal genome locations. These cell lines exhibit differing propensities for mutagenesis, deletions and epigenetic gene silencing by various oxidative carcinogens and clastogens, including x-rays, anticancer therapeutics, metals and traditionally nonmutagenic carcinogens such as diethylstilbestrol (DES). The assay offers the ability to analyze the epigenetic potential of other putative xenoestrogens or environmental toxicants, such as organic pesticides, environmental mixtures and nanoparticles. Using this assay system, the epigenetic silencing of the gpt transgene by DNA condensation, excess methylation and histone modifications were identified as important mechanisms for trangene silencing in carcinogenic nickel-induced G12 mutants. Epigenome arrays add complementary information about other genes and pathways that can be altered by a variety of environmental exposures.