The Xoloitzcuintle Dog, which is also called the Mexican Hairless Dog or Xolo for short, is an ancient breed believed by the Aztecs to be sacred. Four thousand years ago, hairless Xoloitzcuintles may have been the models for pre-Colombian dog sculptures. Hairless Xoloitzcuintles are still prized by a small group of dog lovers, who attempt to breed only the hairless variant of the dog. Three-quarters of Xoloitzcuintle pups are born hairless. However, after 4000 years of selective breeding for hairlessness, one-fourth of newborn pups have coats. Scientists recently discovered why.
A gene mutation causes hairlessness in dogs
Hairlessness results from a genetic mutation in the dog’s DNA. Scientists used DNA from Chinese Crested Dogs, another breed with coated and hairless variants, to discover the mutated gene. Scientists discovered that the mutated gene was the blueprint for a protein that binds to DNA, which then controls the production of other proteins. The changes caused by the DNA mutation subsequently cause the dog to be hairless.
Hairless dogs also have bad teeth.
Hairless dogs also have problems with their teeth. Hairless dogs either have no teeth or their teeth are very weak. Most hairless dogs become toothless at some point in their lives. On the other hand, the coated hairless dogs (the one-fourth of hairless dogs that are born with hair) have strong, healthy teeth.
Hairless dogs must have one good copy of the gene to be born and survive.
Two copies of all genes are present in all dog and human cells. Generally, if one copy of a gene is mutated, the healthy copy will take its place. However, in the hairless gene, the healthy copy won’t replace the mutated copy. This means that dogs with one mutated and one healthy gene copy are hairless and dogs with two healthy gene copies have coats.
Pups with two mutated gene copies died before birth. This explains why breeders have not eliminated the coated variants of hairless breeds. All living hairless dogs must have one healthy gene copy to survive. The dogs must pass along the healthy gene in order for their offspring to survive.
A disease, ectodermal dysplasia, affects humans and dogs.
Since hairlessness and bad teeth always occur together and because at least one healthy copy of the gene is necessary for life, the scientists have concluded that the mutated gene plays an important role in the development of the body, which is most obviously seen in the hair and teeth. A human syndrome called ectodermal dysplasia causes people to have a condition very similar to that of hairless dogs.
Ectodermal dysplasia is a genetic disease caused by 150 different mutations in human DNA and occurs in both males and females of all races and ethnic groups. Children born with ectodermal dysplasia have malformed teeth and extremely sparse hair. The severity of the disease depends upon which mutation the child inherits.
Scientists seized the opportunity to study the similar mutation in dogs in order to gain understanding of the condition in humans. Knowledge gained from the dog might provide insights into how to cure or prevent ectodermal dysplasia. If this is true, dogs may be found to be a better “man’s best friend” than man ever knew.
References:
1. Dennis P. O'Brien, Gary S. Johnson, Robert D. Schnabel, Shahnawaz Khan, Joan R. Coates, Gayle C. Johnson, and Jeremy F. Taylor. Genetic Mapping of Canine Multiple System Degeneration and Ectodermal Dysplasia. Loci Journal of Heredity. (2005) Vol. 96. No. 7, 727-734. Website: http://jhered.oxfordjournals.org/cgi/reprint/96/7/727.
2. Cord Drögemüller, Elinor K. Karlsson, Marjo K. Hytönen, Michele Perloski, Gaudenz Dolf, Kirsi Sainio, Hannes Lohi, Kerstin Lindblad-Toh, Tosso Leeb. A Mutation in Hairless Dogs Implicates FOXI3 in Ectodermal Development. Science. (2008) Vol. 321. no. 5895, 1462. Website: http://www.ncbi.nlm.nih.gov/pubmed/18787161?ordinalpos=2&itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_DefaultReportPanel.Pubmed_RVDocSum
Linda Landon - Linda A. Landon, Ph.D. is a research scientist turned freelance writer. She recognizes the importance of clearly communicating science to ...
