Thomas M. Reid

Conversion of Congo red and 2-azoxyfluorene to mutagens following in vitro reduction by whole-cell rat cecal bacteria

Congo red, an azo dye derived from benzidine, and 2-azoxyfluorene, a derivative of 2-aminofluorene, were reduced during overnight incubation with a suspension of rat intestinal bacteria. High performance liquid chromatography and ultraviolet spectral analysis verified the presence of benzidine in extracts of the Congo red incubations and 2-aminofluorene in extracts of the 2-azoxyfluorene incubations. Extracts of the Congo red incubations were mutagenic toward Salmonella typhimurium TA1538 in the presence of a post-mitochondrial activating system, but Congo red was not mutagenic without this reductive pretreatment. Thus, the utility of the Ames test in screening for potential mutagens may be expanded by a reductive pretreatment utilizing cecal bacteria.

Nucleoli in a pronuclei-stage mouse embryo are represented by major satellite DNA of interconnecting chromosomes

OBJECTIVE To investigate the arrangement of chromosomes within pronuclei-stage mouse zygotes. DESIGN In vitro study. SETTING Academic medical center. PATIENT(S) None. INTERVENTION(S) None. MAIN OUTCOME MEASURE(S) Location of major alpha-satellite DNA, centromeres, and telomeres, and relative location of chromosomes. RESULT(S) Chromosomes appeared to be oriented inward by centromeres and to be interconnected by major alpha-satellite DNA, which appeared to be the sole DNA component of the nucleoli. This chromosomal arrangement persisted throughout interphase. Chromosomal painting failed to identify chromosomal ordering within pronuclei. CONCLUSION(S) Pronuclear nucleoli are represented by alpha-satellite sequences of interconnecting chromosomes that hold all chromosomes together during interphase. Chromosomes within the pronucleus are randomly positioned relative to each other.

Mutagenic and Biochemical Consequences of the Reaction of Arylamines with DNA

The carcinogenic activities of the arylamines have been linked to the abilities of the target tissues to transform these agents to derivatives that are capable of reacting with nucleic acid. Thus, the O-esterification of arylhydroxylamines and arylhydroxamic acids has been related to the production of C8 substituted guanine adducts and the subsequent formation of tumors (King, 1985). An important objective of attempts to elucidate the molecular mechanisms involved in tumorigenesis is the exploration of the extent to which these adducts perturb the processing and function of the DNA. The distortion imposed on DNA structure by bulky adducts can be manifested by mutagenic responses and changes in the metabolic disposition of the DNA (Singer and Grunberger, 1983). We have approached these phenomena in two ways by use of extrachromosomal DNA in E. coli cells. C8 adducts of 2-aminofluorene or 4-aminobiphenyl, and their N-acetylated derivatives have been studied (Figure 1). Our objectives have been to develop systems that might be used for comparison of structural differences on the mutagenic effects of site-specific arylamine DNA adducts and the biochemical effects these adducts have on DNA metabolism. Randomly modified DNA has been used in experiments designed to explore the effects of randomly introduced adducts on the ability of these vectors to be replicated, as well as mutagenic consequences. Single, site specific adducts have been employed to determine their mutagenic potentials.