Cremello Gene Found

Researchers at the Laboratoire de Genetique Biochimique et de Cytogenetique in the Institut National de la Recherche Agronomique (INRA) at the Centre de Recherche de Jouy-en-Josas, France, recently identified the gene that produces the cremello coat color in the horse. The cremello color is a dilution of all basic coat colors, and produces a pale (cream) to an almost white coat in a horse with pink skin and blue eyes (resulting in a blue-eyed cream horse, or BEC). The cremello color has been considered undesirable by certain breed registries, some of which have denied registration to cremello horses. This breakthrough will allow breeders to plan more precise breedings in the hope of producing or avoiding the cremello coat color, and it will also allow breed registries to confirm the genotype (genetic makeup) for coat color of horses being registered.

The three-year study was first published in Genetics, Selection, Evolution. It identified that a mutation in the membrane-associated transport protein (MATP) gene causes the cream coat color; however, it's not precisely known how the mutation works. Scientists were able to zero in on this gene due to known mutations in fish, mice, and humans that cause depigmentation related to a form of albinism. According to Gerard Guerin, PhD, research scientist in charge of horse molecular genetics at INRA, the researchers hypothesize that the MATP gene encodes a transporter protein (which transports nutrients through a membrane) that regulates the production of melanin, or pigments.

According to authors working on the gene in different species, the cream mutation results in a change in the makeup of the transmembrane protein. During this change, the amino acid asparagine is produced instead of aspartic acid. This mutation in animals heterozygous for the cremello gene produces the diluted colors for buckskin on a bay background and palomino on a chestnut background, and the cremello color in the homozygous condition (double mutant).

Guerin; Denis Mariat, PhD, an INRA researcher; and Sead Taourit, a senior scientist, have worked on the genetics of basic coat colors, and became interested in the dilution genes, such as the cremello gene.

"For the 'cream gene,' we were asked by a French association--Association francaise du poney Connemara--to identify this gene," says Guerin. "This color is present in the (Connemara) breed and is diversely appreciated because of the color itself, but also because some breeders believe the horses have vision problems, which has still to be demonstrated. There is a debate in the International Connemara Association whether to include these cream animals in the main register of the breed or not."

The researchers developed a molecular test to detect the cream gene in DNA found in the blood or hair. Guerin says the test will help owners identify heterozygous carriers of the gene (those able to pass on the cremello gene to offspring). "The test is most useful in cases where the gene is masked by another color, such as black or gray, or when the color is difficult to define as in dark buckskins or light palominos," he says. "Our perspective is to give a precise genotype identity of most of the colors encountered in the horse."

The Veterinary Genetics Laboratory at the University of California, Davis, also offers a test to detect the cream gene. For more information, call 530/752-2211.

Guerin and his colleagues expanded on research done at UC-Davis in 2001 that found an association between the cream color and molecular markers present on chromosome 21 among those that were spread over the whole genome. They combined this knowledge with information from genetic research in other species on a few genes known to cause similar color patterns. Once the gene was identified, they used sequencing (the process of determining the exact order of the chemical building blocks) in animals of different coat colors. The sequence in the MATP gene for all BEC animals differs from other coat colors, supporting the researchers' hypothesis that the MATP gene produces the cremello coat color.

The MATP mutation is the fourth causal mutation for coat color identified in horses. The other mutations involve the chestnut, overo lethal white, and black colors.

About the Author

Sarah Evers Conrad

Sarah Evers Conrad has a bachelor’s of arts in journalism and equine science from Western Kentucky University. As a lifelong horse lover and equestrian, Conrad started her career at The Horse: Your Guide to Equine Health Care magazine. She has also worked for the United States Equestrian Federation as the managing editor of Equestrian magazine and director of e-communications and served as content manager/travel writer for a Caribbean travel agency. When she isn’t freelancing, Conrad spends her free time enjoying her family, reading, practicing photography, traveling, crocheting, and being around animals in her Lexington, Kentucky, home.

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