The smooth movement of gaited horses results from a genetic mutation that can be found worldwide, according to a recent study published Tuesday in the journal Animal Genetics. The international research team contributing to the study included Dr. Leif L. Andersson, Texas A&M University Department of Veterinary Integrative Biosciences, College of Veterinary Medicine and Biomedical Sciences.
The free-access paper, entitled “Worldwide frequency distribution of the ‘Gait keeper’ mutation in the DMRT3 gene,” (2014, doi: 10.1111/age.12120) was first published online: 21 Jan. 2014, co-authored by Promerová, M., Andersson, L. S., Juras, R., Penedo, M. C. T., Reissmann, M., Tozaki, T., Bellone, R., Dunner, S., Hoín, P., Imsland, F., Imsland, P., Mikko, S., Modr, D., Roed, K. H., Schwochow, D., Vega-Pla, J. L., Mehrabani-Yeganeh, H., Yousefi-Mashouf, N., G. Cothran, E., Lindgren, G. and Andersson, L. — variously of Uppsala University, Uppsala Sweden; Department of Animal Breeding and Genetics, Swedish University of Agricultural Sciences, Uppsala, Sweden; Department of Veterinary Integrative Biosciences, College of Veterinary Medicine and Biomedical Sciences, Texas A&M University, College Station, TX; Veterinary Genetics Laboratory, School of Veterinary Medicine, University of California, Davis; Breeding Biology and Molecular Genetics, Faculty of Agriculture and Horticulture, Humboldt University, Berlin, Germany; Genetic Analysis Department, Laboratory of Racing Chemistry, Utsunomiya, Tochigi, Japan; Department of Biology, University of Tampa, Florida; Veterinary Faculty, Universidad Complutense de Madrid, Spain; Institute of Animal Genetics, CEITEC, University of Veterinary and Pharmaceutical sciences, Brno, Czech Republic; Menntaskolinn vid Hamrahlid, Iceland; Department of Pathology and Parasitology, Faculty of Veterinary Medicine, CEITEC, University of Veterinary and Pharmaceutical sciences, Brno, Czech Republic; nstitute of Parasitology, Biology Centre of Academy of Sciences of the Czech Republic; Department of Basic Sciences & Aquatic Medicine, Norwegian School of Veterinary Science, Oslo, Norway; Laboratorio de Investigación Aplicada, Cría Caballar de las Fuerzas Armadas, 14080, Cordoba, Spain; and the Department of Animal Science, University of Tehran, Iran.
The researchers note that for centuries, domestic horses have represented an important means of transport and served as working and companion animals, and although their role in transportation is less important today, many horse breeds are still subject to intense selection based on their pattern of locomotion.
They cite one striking example of such a selected trait being the ability of a horse to perform additional gaits other than the common walk, trot and gallop. Those could be four-beat ambling gaits, which are particularly smooth and comfortable for the rider, or pace, used mainly in racing. Gaited horse breeds occur around the globe, suggesting that gaitedness is an old trait, selected for in many breeds.
The co-authors cite a recent study that discovered that a nonsense mutation in DMRT3 has a major impact on gaitedness in horses and is present at a high frequency in gaited breeds and in horses bred for harness racing.
In the Animal Genetics article they report a study of the worldwide distribution of this mutation in which they genotyped 4396 horses representing 141 horse breeds for the DMRT3 stop mutation. The researchers say more than half (2749) of these horses also were genotyped for a SNP situated 32 kb upstream of the DMRT3 nonsense mutation because these two SNPs are in very strong linkage disequilibrium. They show that the DMRT3 mutation is present in 68 of the 141 genotyped horse breeds at a frequency ranging from 1% to 100%, and also that the mutation is not limited to a geographical area, but is found worldwide. Breeds with a high frequency of the stop mutation (>50%) are either classified as gaited or bred for harness racing.
“We have previously demonstrated that a single mutation in the DMRT3 gene has a large impact on gaitedness in horses, and it was therefore named ‘Gait keeper,’” comments Dr. Leif Andersson, a Texas A&M University Institute for Advanced Study Faculty Fellow collaborating with researchers at the College of Veterinary Medicine & Biomedical Sciences (CVM) in a TAMUTimes release. “This gene codes for a protein in a specific subset of neurons in the spinal cord that coordinates the movements of the animal’s legs. The mutated version of the gene causes a truncation of the DMRT3 protein, a genetic ‘mistake’ that allows horses to pace and amble.”
“The CVM has a reputation as a world leader in genomic research,” says Dr. Eleanor M. Green, Carl B. King Dean of Veterinary Medicine. “The collaborative efforts of our genomic scientists will continue to make an impact, not only in the equine industry through studies such as this one, but also in other species, including humans, through the application of the lessons learned from this investigative approach. This study is yet another example of contributions to One Health.”
This recent research shows that the mutation arose only once and then spread across the world via positive selection, Dr. Andersson observes. In other words, early humans probably noticed that some horses had the ability to move in unique ways, and they then selected those horses for breeding, most likely because they offered a smoother, more comfortable ride, called a “running walk” in some breeds. Horse breeds that are known to perform these “ambling gaits” are referred to as “gaited,” and the researchers found that the mutated version of the gene is common in these breeds. They analyzed genes of 4396 horses from 141 breeds and found that the mutation is spread across Eurasia from Japan to the British Isles, in Iceland, in South and North America, and in breeds from South Africa.
“During such ambling gaits the horse has at least one foot on the ground, which means that the vertical movement of the rider is minimal,” Dr. Andersson says. “For instance, Paso Fino is a breed from Latin America in which the frequency of the ‘Gait keeper’ mutation is nearly 100 percent. It is claimed that the Paso Fino gait is so smooth that you can have a glass of wine in your hand without letting it spill!”
“Now that we have the genetic tools with enough power, we are beginning to find unexpected insights into how genes influence movement,” said Dr. E. Gus Cothran, a clinical professor in the Department of Veterinary Integrative Biosciences at the CVM and another of the article’s authors. “Dr. Andersson and I are hoping to continue this work with the goal of understanding how other genes can influence the basic gait pattern inferred by DMRT3.”
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