MOLECULAR GENETICS OF CD TOXICITY

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The long-term goal of this project is to identify and characterize the gene(s) responsible for interindividual differences in response to cadmium (Cd++). Cadmium is a widespread environmental pollutant and is classifed as an IARC "Category I" human carcinogen. Cadmium can also cause severe renal toxicity and cardiovascular disease. Genetic differences in susceptibility to cadmium toxicity have been suggested in humans, whereas in inbred mice there are unequivocal genetic data. Resistance to cadmium-induced testicular damage was reported in 1973 to be associated with a single recessive gene, named Cdm, found on mouse chromosome (Chr) 3. With the help of recent advances in the Mouse Genome Project and studying semiquantitative histological parameters, we have now corroborated the original 1973 data and, using polymorphic microsatellite markers, have refined the chromosomal location of the Cdm gene from more than 24 centiMorgans (cM) to 0.64 cM (estimated 40-80 genes). We have used recombinant inbred lines generated from C57BL/6J (B6, resistant) and DBA/2J (D2, sensitive) inbred mice to determine that the Cdm gene maps between microsatellite markers D3Mit110 and D3Mit255. There is strong evidence that Cd++ exerts its toxic effects by causing cell type-specific oxidative stress which can result in the covalent modification of cellular macromolecules or disruption of the cell cycle-leading to enhanced cell division, apoptosis or growth arrest. We will locate and identify the Cdm gene, and our hypothesis is that the Cdm gene encodes a protein in specific cell types that plays an important role in cadmium-induced disruption of cellular redox homeostasis. Thus, we propose to [1] narrow the Cdm-gene-containing region on Chr 3, by identifying single nucleotide polymorphisms (SNPs) between B6 and D2 mice, and then determining the genotype of these new markers in the BXD14/Ty mouse ; [2] sequence portions of the Cdm-gene- containing region and identify a BAC clone that will confer testicular sensitivity to Cd++ on a resistant B6 mouse background; and [3] identify the Cdm gene from the genomic sequences produced in Spec.Aims number 1 and number 2. Although toxicity to numerous heavy metals is well known, molecular mechanisms have yet to be uncovered - in humans or laboratory mammals. These studies will enhance our understanding of heavy metal toxicity by identifying and characterizing, for the first time, a major gene responsible for susceptibility to cadmium-induced toxicity.