Researchers discover "graying gene" in horses

News
Article

New research has uncovered gene responsible for graying speeds in horses, and a predisposition to melanoma

otsphoto/Adobe Stock

otsphoto/Adobe Stock

Researchers from Texas A&M’s College of Veterinary Medicine and Biomedical Sciences (VMBS) and Uppsala University in Sweden have discovered a gene that determines how horses change colors as they age.1 The discovery explains why some horses turn completely white as they grow older, while others remain a “dappled” gray color.1 The difference between fast- and slow-graying horses is the number of copies of the 4.6 kb intronic sequence within the gene Syntaxin 17 (STX 17).2 Slow-graying horses have a gene variant with 2 copies of the duplication (G2), while fast-graying horses have a gene variant with 3 (G3), along with a predisposition to melanoma.2

“There are horses that are born white because they carry a gene variant that is causing white coat color, but the great majority of white horses don’t have this gene variant,” Leif Andersson, PhD, a professor in the VMBS’ Department of Veterinary Integrative Biosciences, and at Uppsala University, said in a news release.1 “Instead, gray horses are born with normal coat pigment – like black or brown – that gradually lightens as they age and eventually becomes gray or white.”

Published in the journal Nature Communications, the study proved the presence of 2 variant alleles at the Gray locus in horses, in addition to the G1 wild-type allele.2 Of the variants, the G3 allele is more common and carries with it 3 copies of the 4.6 kb sequence.2 The G3 allele is associated with fast graying, eventually resulting in a white colored coat. Horses with the G2 allele carry 2 copies of the 4.6 kb sequence, gray slowly, and never become pure white.2

“Some horses, the ones that will eventually become white, begin to grow gray eyelashes and hairs at the base of the tail within the first week after birth,” Andersson explained.1 “A horse that is ‘slow graying’ will typically not show signs of gray until 5 to 7 years old.”

The significance of these findings goes beyond coat color. Horses with the G3 allele have a predisposition to melanoma, whereas horses with the G2 allele have a significantly lower incidence of melanoma, possibly as low as horses with neither variant.1,2,3 Andersson originally established the connection between duplicated STX17 and fast graying horses in 2008 study.3 At that time, they established that the duplicated sequence within STX17 played a key role in the development of melanocytes—cells that create pigmentation for skin, and host melanoma development.3

“Horses that are ‘fast graying’ are more likely to develop melanomas, whereas we don’t see an elevated risk in horses that are ‘slow graying,’” Andersson said.1 Researchers hope that this new understanding of coat colors and equine genetics will lead the way for future research on the prevention, and treatment, of melanomas in graying horses.1

References

  1. Texas A&M Researchers Discover Gene Variants That Determine Speed of Graying in Horses. News release. Texas A&M University College of Veterinary Medicine and Biomedical Sciences. September 19, 2024. Accessed September 20, 2024. https://vetmed.tamu.edu/news/press-releases/genes-behind-horse-graying/
  2. Rubin, CJ., Hodge, M., Naboulsi, R. et al. An intronic copy number variation in Syntaxin 17 determines speed of greying and melanoma incidence in Grey horses. Nat Commun 15, 7510 (2024). https://doi.org/10.1038/s41467-024-51898-2
  3. Good Karma: Aggie Veterinarians Save Horse From Life-Threatening Melanoma. News release. Texas A&M University College of Veterinary Medicine and Biomedical Sciences. January 10, 2024. Accessed September 23, 2024. https://vetmed.tamu.edu/news/press-releases/karma/
Recent Videos
Image Credit: © Przemyslaw Iciak - stock.adobe.com
© 2024 MJH Life Sciences

All rights reserved.