Regulatory Mutations in TBX3 Disrupt Asymmetric Hair Pigmentation That Underlies Dun Camouflage Color in Horses

The study explored the genetic basis of the Dun coat color in horses, characterized by pigment dilution and primitive markings, and linked it to the TBX3 transcription factor's expression in hair follicles. Researchers analyzed 1,814 horses, identifying three haplotypes: GG (Dun), AT (non-dun1), and A-del (non-dun2). Mutations in TBX3 led to asymmetric pigment deposition in Dun horses, while non-dun horses had more uniform pigmentation due to impaired TBX3 expression. The non-dun1 and non-dun2 alleles were responsible for the non-dun phenotype, with non-dun2 being a more recent mutation. The study concluded that TBX3 regulates pigment deposition in hair follicles, with its disruption leading to the non-dun phenotype, and suggested that the Dun phenotype served a camouflage function in wild equids.