A Tale of 2 Species: What Do Canine Chromosomes Reveal about Humans?
They say dogs look like their owners. Now scientists are uncovering the genes that give dogs--and humans--their traits
A Tale of 2 Species: What Do Canine Chromosomes Reveal about Humans?
- Boxer Texas Belle, a white boxer, won't come if you call her—but not because she's disobedient. White boxers are prone to deafness. Elinor Karlsson and colleagues from the Broad Institute of Harvard University and the Massachusetts Institute of Technology identified a variation in the microphthalmia-associated transcription factor (MITF) gene in all 10 white boxers tested and zero of nine solid-colored ones. The gene helps control the development and function of melanocytes (pigment-producing cells) and controls the production of melanin—the pigment that dictates hair, eye and skin color. Melanocytes are also important in hearing.
The human connection: Waardenburg syndrome type 2 is a rare genetic disorder marked by pigment and hearing loss. It is caused by mutations in MITF, according to a study published November 1994 in Nature Genetics. ISTOCKPHOTO/lisegagne - Rhodesian ridgeback Dogs sport fur of all colors and textures. But the Rhodesian ridgeback's distinctive coif compelled Salmon Hillbertz and colleagues from the Swedish University of Agricultural Sciences to investigate the genes responsible for the spiny Mohawk. In their study, published November 2007 in Nature Genetics, the researchers concluded that duplications in the fibroblast growth factor genes FGF3, FGF4 and FGF19 cause the trademark hair ridge. The mutations also predispose the breed to dermoid sinus—a tunnel between the skin along the dog's spine and its spinal cord that results from an incomplete separation during development.
The human connection: Mutations in the genes encoding certain FGFs and their receptors are implicated in clefting syndromes like cleft palate, according to a study published March 2007 in Proceedings of the National Academy of Sciences. Mutations in FGFR2 (fibroblast growth factor receptor 2) have been linked to craniolacunia and the associated condition spina bifida—a birth defect caused by the incomplete closure of the embryonic neural tube. ISTOCKPHOTO/njgphoto - Beagle Some dog breeds are prone to obesity. Beagles, for example, need a lot of exercise and a strict diet to stay slim. A strong but coincidental selection for the gene FTO (for fat mass and obesity associated) has been observed in beagles, according to Akey. In this case researchers actually know more about the gene in humans than they do in dogs.
The human connection: A common variant in the FTO gene is associated with body mass index and is a risk factor for obesity in children and adults, according to a May 2007 publication in Science. ISTOCKPOTO/joshblake - Great Dane and Chihuahua In February 2010 George, a Great Dane from Arizona, was recognized by Guinness World Records as the tallest dog, standing 1.09 meters from paw to shoulder (the height of a six-year-old boy) and weighing 111 kilograms. The shortest dog, a long-haired Chihuahua called Boo Boo, stands just over 10 centimeters. Researchers from the National Institutes of Health implicated the gene encoding insulin-like growth factor 1 (IGF1) as the main player in dog size in a March 2010 review published in PLoS Biology. Another gene, PC2, is thought to define the ratio of leg length to width.
The human connection: IGF1 deficiency can lead to growth disorders. Laron syndrome—a type of dwarfism caused by mutations in the growth hormone receptor gene—is characterized by low IGF1 levels. Synthetic IGF1 is used to treat Laron syndrome and has also been used to enhance growth in normal children with short stature. ISTOCKPHOTO/globalp - Dachshund The dachshund's short legs and long body are what spawned the moniker "wiener dog". Using a multibreed gene association approach, Heidi Parker and her colleagues from the National Institutes of Health linked a retrogene—a piece of DNA copied back from RNA—encoding fibroblast growth factor 4 (FGF4) with disproportionately short limbs. In their study published August 2009 in Science the researchers theorized that abnormal expression of FGF4 in chondrocytes (cartilage cells) causes inappropriate activation of its receptors, leading to shorter limbs.
The human connection: A mutation in the gene encoding fibroblast growth factor receptor 3 is responsible for more than 95 percent of achondroplasia cases (the most common type of dwarfism) and up to 65 percent of hypochondroplasia (a form of short-limbed dwarfism), according to a study published December 2002 in Reviews in Endocrine and Metabolic Disorders. ISTOCKPHOTO/krakozawr - Shar-pei Some shar-peis are wrinklier than others. The more wrinkles the dog has, the higher the levels of mucin—a jellylike substance in the dermis of the skin—and hyaluronic acid—a chemical in the extracellular matrix (the space between cells). This prompted Joshua Akey from the University of Washington in Seattle to look for a wrinkle gene. He narrowed down the candidate pool to three genes that were highly selected for in shar-pei breeding—one of them was the gene encoding hyaluronic acid. After sequencing the gene HAS2 in shar-peis (32 wrinkled and 18 smooth), along with 94 dogs from 20 other breeds, Akey concluded that deletions in HAS2 were responsible for wrinkling. The study was published in the January 2010 issue of Proceedings of the National Academy of Sciences.
The human connection: Rare mutations in HAS2 cause severe cutaneous mucinosis—a condition marked by excessive mucin leading to folding and thickening of the skin, according to a study published January in 2000 in The Journal of Pediatrics. ISTOCKPHOTO/bogdansemenescu
