Experiment
Authors used congenic line analysis to confirm the existence of an alcohol consumption QTL named Eac2 (ethyl alcohol consumption QTL 2) at 42.5 cM on mouse Chromosome 6. Congenic line B6.BALB-(D6Mit275-D6Mit134) carries BALB/cJ-derived chromosome 6 donorDNA from 25.5 cM - 57.5 cM on a C57BL/6ByJ genetic background. Congenic animals display significantly decreased consumption of 12% alcohol in a 2-bottle free choice alcohol preference test compared to background strain C57BL/6ByJ. This difference in alcohol preference was more pronounced in males.
A genome scan to detect possible genetic contamination in the B6.BALB-(D6Mit275-D6Mit134) congenic was negative after 402 polymorphic SNPs were screened. It was estimated the Eac2 critical region spans 75 Mb -122 Mb on chromosome 6. This region contains 404 genes. Grm7 at 110.6 Mb displays genotype-dependent correlation with cis-regulated gene expression. In addition, 218 intronic SNPs were detected in the Grm7 genetic sequence between BALB/cJ and C57BL/6 andone SNP was located in the Grm7 promoter region. Background strain C57BL/6J displays decreased Grm7 transcript abundance compared to donor strain BALB/cJ. Comparison of alcohol consumption and SNPs between inbred strains C57BL/6J, AKR/J, BALB/cJ, A/J,DBA/2J, 129/SvJ, and C3H/J showed a high correlation for Nfu1 (36 cM) and Aak1 (35.5 cM), and relatively high correlation for Grm7.
Further support for Grm7 as a candidate gene for Eac2 was demonstrated in an F2 cross involving alcohol-preferring (I5B25A)and alcohol-non-preferring (C5B3) quasi-cogenic RQI strains derived from C57BL/6ByJ and BALB/cJ. F2 animals were genotyped for an SNP marker located in intron 7 of Grm7. Homozygosity for C57BL/6ByJ-derived alleles at this SNP was associated with increased alcohol consumption compared to F2 animals homozygous for BALB/cJ alleles. This finding is consistent with the genotype-phenotype correlation observed in B6.BALB-(D6Mit275-D6Mit134) congenic animals. Authors indicate linkage analysis in this cross eliminated Nfu1, Aak1, and Chchd4 as potential candidates for Eac2.
Significant correlation between eQTL cis-regulation in mouse hippocampus and genotype was detected for Sox5 with LOD=31.56 in BXD recombinant inbred strains and LOD=3 in CXB recombinant inbred strains.
Previously identified alcohol-related QTLs mapping near Eac2 include Eila2 (36.5 cM), Etlm3 (30 cM), Rear1 (36.5 cM), Bits2 (37 cM), and Taste5 (48 cM).
Analysis Tools