CONGENIC STRAINS FOR GENES AFFECTING COLON TUMORS

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The overall goal of this proposal is to test which regions of the mouse genome, identified in preliminary experiments, have an effect on the number of colon tumors induced by a standard treatment with 1,2- dimethylhydrazine dihydrochloride (DMH). In an early study on sensitivity to DMH-induced colon tumors (Evans et al. 1977), the most sensitive strain was ICR/Ha (I), with 60/60 animals having large numbers of tumors after DMH treatment, while the most resistant strain was C57BL/6Ha (B), with 0/90 having tumors. All 68 1XB Fl hybrid animals developed tumors. In a backcross, (IXB)XB, 46/117 animals developed tumors. The IBB backcross has been repeated and tumors were detected in 40 of 122 progeny. SSR-PCR using primer pairs (Dietrich et al. 1992) has detected variation between strains 1 and B for 41% of the primer pairs tested. The 122 progeny have been typed for 90 loci with at least two loci per autosome. The data suggest that tumor formation is controlled by several genetic loci. The major locus, Ccs-1, on central Chr 12 was linked to Dl2Mit6 (p <0.001). Other genetic tests identified loci on Chrs 2, 3, 5,7, 9, 10, 14, 15 and 16. To determine whether or not the loci at the eleven genetic regions identified in the backcross affect DMH-induced tumor formation in mice, it is proposed to generate congenic strains in which, for each suspected locus, the allele from the sensitive strain is placed on the background of the resistant strain. The reciprocal congenic, in which the allele from the resistant strain is placed on the background of the sensitive strain, will -also be made. A total of 22 congenic strains are proposed. Animals from each of these congenic strains will be treated with DMH and the effect of each allele, in both the homozygous and heterozygous state, on tumor - susceptibility will be determined. Double congenic strains will be made and used to determine how pairs of loci interact. In the course of this work, the number of backcross progeny will be increased, which will improve the statistics of linkage and increase the number of tumor-bearing animals. Tumor DNA from different congenic strains will be used to test for loss of heterozygosity of candidate genes. Tumor RNA will be used to determine expression of candidate genes. DNA from existing inbred strains and existing congenic strains will be typed for loci used to obtain the framework map, especially those loci in the eleven identified regions, to identify strains differing at only l or 2 of these loci. Animals from these strains will be treated with DMH to determine the effects of alleles from these regions.