A chromosome 17 locus is involved in dorsal pigmentation in hooded Long-Evans Agouti rats.

The hooded coat pattern in laboratory rats is produced by recessive alleles of the h (Kit) locus on chromosome 14. A quantitative trait locus (QTL) on chromosome 17 has been previously identified as a potential modifier locus of dorsal pigmentation in hooded Long-Evans Agouti (LEA) rats. To validate the contribution of this chromosome 17 locus, we analyzed an (LEA × F344) F2 population and identified distinct genetic determinants of dorsal and ventral pigmentation. Genome-wide QTL mapping identified a major locus influencing dorsal pigmentation on chromosome 17 near D17Rat2 exceeding a highly significant level. In contrast, ventral pigmentation showed a distinct genetic pattern from dorsal pigmentation, although no genome-wide significant loci were identified. We established an F344-TyrC line (non-albino hooded F344) and generated congenic rats carrying an LEA-derived chromosome 17 segment on an F344 background. Congenic rats heterozygous for the LEA-derived chromosome 17 segment showed a marked increase in dorsal pigmented coat area compared to hooded F344 rats (55% vs. 40%). Boundary marker analysis refined the interval to 0-6.8 Mbp. Collectively, the findings indicate that the LEA allele on chromosome 17 increases dorsal but not ventral pigmentation even in the heterozygous state. This refinement of the genetic architecture of hooded coat patterns provides a valuable resource for identifying genes responsible for region-specific pigmentation in rats.