Genotype versus phenotype: conflicting results in mapping a lung tumor susceptibility locus to the G7c recombination interval in the mouse MHC class III region.

Susceptibility to chemically induced lung tumorigenesis has previously been mapped to a genomic interval of 27 kb in the MHC class III region of the mouse using two H2 (a/b) intra- H2 recombinants, B10.A(1R) and B10.A(2R). Three genes are located within this interval, G7e (encoding a viral envelope protein), G7a/ Vars2 (encoding valyl-tRNA synthetase), and G7c (a gene with unknown function). A 70 kb contig, spanning the 27 kb region and extending 20 kb either side, was constructed from lambda phage libraries with genomic inserts derived from mouse strains B10.A(1R) and B10.A(2R). The region was analyzed for single-nucleotide polymorphisms, which would facilitate further fine mapping of the interval. Analysis of the expression levels of the candidate genes did not reveal any difference between B10.A(1R) and B10.A(2R). In addition, no differences were found at the sequence level in the 27 kb interval except for an A to T transition in intron 7 of G7c. A database comparison of the sequence surrounding this polymorphism did not identify any DNA-binding or enhancer consensus sequence. In conclusion, the previously observed phenotype could not be associated with or assigned to any of the candidate genes G7e, G7a/ Vars2, or G7c, nor could any of the other susceptibility loci, which have been reported to map to this region ( Cps1, Acp, Orch1, and Igis1).