Mutations in the agouti (ASIP), the extension (MC1R), and the brown (TYRP1) loci and their association to coat color phenotypes in horses (Equus caballus).

This research article analyzes the genetic basis of different coat colors in horses, focusing on mutations in three specific genes. The findings show an 11-bp deletion in one of these genes is completely associated with a specific coat color across different breeds and implies its alteration can lead to a loss-of-function mutation.

Study Focus and Methods

• The focus of this study is on determining the genetic basis of different coat colors in horses. Specifically, the researchers were interested in studying mutations in three genes—agouti (ASIP), extension (MC1R), and brown (TYRP1)—and how these mutations relate to differing coat color phenotypes in horses.
• Cross-species techniques were used to clone, sequence, and characterize the equine melanocortin-1-receptor (MC1R) and agouti-signalling-protein (ASIP) genes. A partial sequencing of tyrosinase-related protein 1 (TYRP1) was also completed.
• The researchers then examined coding sequences and parts of the flanking regions in these genes on 40 horses and applied the identified mutations to a total of 120 horses.

Detailed Observations

• The studied panel included 22 different horse breeds with 11 different coat colors. When comparing a large genomic fragment of MC1R among the 11 coat color phenotypes, the researchers found no sequence difference aside from the known chestnut allele.
• Upon analyzing a long genomic fragment of ASIP, they discovered two intronic base substitutions and point mutation in the untranslated region (UTR). They also found an 11-bp deletion in exon 2, which was associated with a recessive black coat color in horses.

Conclusions and Implications

• The 11-bp deletion found in the ASIP gene is assumed to initiate a frameshift, altering the regular coding sequence and causing what is known as a loss-of-function mutation. This finding is interesting because it suggests that a mutation in this gene could change the horse’s coat color.
• An analysis of TYRP1 revealed a base substitution that unknown function and an SNP was found in intron 2.
• The exploration of these gene mutations provides insight into the biology and evolution of horse coat color and could be a basis for further research in horse breeding and the genetic basis of coat colors in other animal species as well.