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First International Equine Gene Mapping Workshop
Kimberly S. Herbert, The Horse: Your Guide to Equine Health Care, Vol XII, No. 12. December, 1995.
Copyright 1995 THE BLOOD-HORSE, INC. All rights reserved.
Is there a gene that pre-disposes horses to having heaves (COPD)? Can we find a "speed gene" that will tell horse owners whether their potential runner inherited the propensity for speed found its family, or if it was not passed to that individual? Gait is a highly heritable trait. Can it be determined in a foal whether a certain gene or genes were passed on to allow an individual to have that extended, suspended trot that dressage owners crave in their mounts? Can it be determined if any disease or trait is heritable?
With the advances that will come in the next two or three years in gene mapping of the horse, those questions and others might be closer to having answers.
"It's basic research at this point," said Ernest Bailey, PhD, a professor in Veterinary Science at the Gluck Equine Research Center at the University of Kentucky. "Certain applications will come from this gene mapping project, and the knowledge will provide a tool to determine the genetic contribution of heredity to a disease and a basis to look for the specific gene."
"A gene map of the horse is a tool that will allow us to more finely dissect whether any heritable aspect of the horse," added Gus Cothran, PhD, director of the Equine Bloodtyping Research Laboratory at the University of Kentucky.
A large step forward occurred in Lexington, Ky., in late October. The first International Equine Gene Mapping Workshop was held, with Bailey as chairman. There were approximately 70 attendees from 20 countries participating in the workshop, with 25 different laboratories to be involved in the mapping project. Nine of the laboratories are located in the United States.
The gene map of the horse will provide signposts in the search for a specific gene that is associated with heritability of a trait or disease. There are 64 chromosomes in the horse-31 autosomes (there are two copies of each autosome) and two sex chromosomes. The goal is to have 300 markers (landmarks or signposts) for the gene map to identify areas on each chromosome. Currently, 129 markers have been identified, and Bailey estimated that 1,000 markers will be needed so that the best 300 can be selected and used on the map.
"If we wanted to investigate OCD or tying up, and we had a stallion with affected offspring, the map will allow us to identify the chromosome region with that gene," said Bailey.
"Normal genetic inheritance would say that each offspring has a 50/50 chance of inheriting any particular marker from the sire. If it is found out that the stallion's affected offspring inherit a certain section of genetic material from, say, chromosome 26, at least 95% of the time, then we know that the trait is associated with a gene or genes on that section of chromosome," said Bailey.
The gene map will give researchers those genetic markers-the signposts-to help locate an area on a specific chromosome that might be the hereditary basis for a certain trait or disease. Gene maps are available for many other animals, including man, cattle, sheep, pigs, chickens, and mice. Those gene maps will benefit the horse research because there is basic genetic material that is the same for all animals, although some genes have different expressions in different species. Also, the physical arrangement or association of the genes is generally conserved across different species.
If it is discovered that heaves in the horse is associated with an area on chromosome 3, and it is known that human chromosome 4 has homologues (corresponding areas) of that horse chromosome, then the more-detailed map of the human can be utilized to help locate the specific gene involved in heaves in the horse. Conversely, it could be that the equine heaves research would shed light on asthma in humans.
The human genome project is nearing completion. This is where not just signposts are being determined on chromosomes, but the location and naming of each gene on each chromosome is being undertaken.
One of the most productive items that resulted from the Equine Gene Mapping Workshop was that the cytogeneticists agreed on a standard nomenclature for horse chromosomes. Lack of concensus on this point has caused problems in other species research.
"So, when we speak of chromosome 26 in the Kentucky laboratory, the laboratory in Sweden will know precisely which chromosome we are talking about," said Bailey.
Agreement also was made on how to distribute the workload. For example, 15 horse reference families have been identified. DNA will be isolated from those family members and sent to the Gluck Equine Research Center for distribution to test laboratories. Test laboratories will apply for DNA, indicating how many genetic markers they will be testing. After testing, they will report their data to a central computer analysis laboratory, which probably will be the Veterinary Genetics Laboratory at the University of California, Davis. Laboratories are committed to identifying more than 900 markers in the next three years. There are several thousand markers used in other species.
There probably will be fewer than 100 people involved in the various laboratories worldwide in the equine gene mapping project. However, other U.S.-based laboratories and groups that had representatives at the workshop were Tufts University, Cornell University, Applied Biosystems Division of Perkin Elmer, University of Illinois, Stormont Laboratories California, Texas A&M University, Michigan State University, Shelterwood Laboratory Texas, National Cancer Institute, University of Minnesota, and the USDA. Foreign delegates included persons from Japan, Sweden, France, United Kingdom, Ireland, Norway, Belgium, Germany, Poland, Czech Republic, Thailand, Australia, New Zealand, south Africa, Canada, Italy, Switzerland, Denmark, and The Netherlands. The meeting was made possible by the Dorothy Russell Havemeyer Foundation, which is a New York foundation that supports equine research primarily through workshop meetings of scientists. The gene mapping workshop will be conducted annually over the next five years.
"We won't unlock all the secrets of the horse." said Bailey. "We'll just bring the important questions to the front."
-Kimberly S. Herbert