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

Researchers Leif Andersson, Gregory Barsh, and colleagues discovered that the Dun camouflage color in horses was due to TBX3 expression in hair follicles, leading to asymmetric distribution of melanocytes and reduced pigment deposition. They found that most domestic horses exhibited a more intensely pigmented (non-dun) phenotype due to regulatory mutations impairing TBX3 expression, resulting in a more even distribution of melanocytes and pigment granules. They identified two alleles, non-dun1 and non-dun2, responsible for the non-dun color, with non-dun2 being a recent mutation and both Dun and non-dun1 alleles present in ancient horse DNA. This study highlighted a new developmental role for T-box genes and provided insights into hair follicle biology and pigmentation.