Toward the evaluation of function in genetic variability: characterizing human SNP frequencies and establishing BAC-transgenic mice carrying the human CYP1A1_CYP1A2 locus.
Interindividual differences in human CYP1A1 and CYP1A2 expression appear to be associated with variability in risk toward various types of environmental toxicity and cancer. These two genes are oriented head-to-head on human chromosome 15; the 23.3-kb spacer region might contain distinct regulatory regions for CYP1A1 and distinct regulatory regions for CYP1A2, or the regulatory regions for the two genes might overlap one another. From 24 unrelated subjects of five major, geographically-isolated subgroups, we resequenced both genes (all exons and all introns) plus some 3' flanking sequences and the entire spacer region (39.6 kb total); 85 SNPs were found, 49 of which were not currently in the National Center for Biotechnology Information (NCBI) database. Of the 57 double-hit SNPs, we carried out SNP-typing in 94 Africans, 96 Asians, and 83 Caucasians and found striking ethnic differences in SNP frequencies and haplotype evolution; the two CYP1A1 SNPs and the one CYP1A2 SNP that are most commonly used in epidemiological studies were shown not to be representative haplotype tag SNPs across these three human subgroups. Four BAC-transgenic mouse lines, carrying the human CYP1A2 and 15,190 bp of 5' flank, expressed only negligible basal or inducible CYP1A2 mRNA. A fifth BAC-transgenic mouse line, carrying both the human CYP1A1 and CYP1A2 genes and ample amounts of 3' flanking sequences, plus all of the spacer region--in the absence of the mouse Cyp1a1 or Cyp1a2 genes--expressed the human CYP1A1 and CYP1A2 mRNA, protein and enzyme activities in liver and nonhepatic tissues very similar to that of the mouse. Comparison of this hCYP1A1_1A2 transgenic line with hCYP1A1_1A2 lines carrying other common human haplotypes will enable us to evaluate function in human CYP1A1_CYP1A2 locus variability, with regard to toxicity and cancer caused by combustion products.