EDOUARD CADIEU
Hair any way you want it. Three genes lead to quite diverse canine coat
types as seen (left to right) in a smooth-coated Dachshund, Border
Terrier, Jack Russell Terrier mix, and Yorkshire Terrier.
Untangling Canine Coiffures
By Elizabeth Pennisi 27 August 2009
It doesn't take much, genetically, to turn the buzzcut of a
bloodhound into the silken mane of a bearded collie. Although
dog hair seems to come in an infinite variety of lengths,
thicknesses, and styles, most breeds' looks are dictated by the
particular versions of just three genes in that breed's genetic
makeup, according to a new study. That so few genes are
involved speaks to the power of artificial selection among dogs
and to the ability of just a few genetic changes to make a big
difference in appearance.
Ever since researchers pinpointed a gene for short stature in
purebred dogs, they have been mining canine genomic data for
genes underlying other traits. In the new study, Elaine
Ostrander of the National Human Genome Research Institute in
Bethesda, Maryland, and her colleagues sought to understand
such canine curiosities as why schnauzers have bushy eyebrows
and mustaches, poodles have the Shirley Temple look, and
basset hounds are clean-cut types.
The study, reported online today in Science, had three main
components. First, to begin to pin down some of the genes
involved, the researchers assessed genetic variation at about
50,000 spots in the genome of more than 100 dachshunds-which come in short-hair, long-hair, and wiry-hair varieties--and
correlated the sequence differences at those spots with the type
of hair. Variations at one spot on chromosome 13 were
associated with wiry hair, mustaches, and eyebrows--known as
furnishings among dog fanciers. With additional study, the
researchers pinpointed the gene responsible. Called R-spondin-
2, it encodes a protein that interacts with other proteins that are
important for the development of hair follicles and of hair-
follicle tumors that are often seen in dogs with mustaches.
With respect to hair length, the researchers confirmed that a
mutation in a gene called FGF5 coincides with long hair. They
determined that a base change that swaps an amino acid in the
FGF5 protein seems to be responsible. Looking at a larger set of
dog breeds, the researchers saw that change in 91% of the
long-haired dogs they evaluated, 4% of short-haired dogs, and
30% of dogs with medium length hair.
In the second part of the study, the researchers did a similar
genetic analysis with 76 Portuguese water dogs, about half with
curly hair and half with wavy hair. A mutation in a gene for
keratin, a protein found in hair, was associated with curliness.
The team had studied 903 dogs from 80 breeds to pin down
these mutations, and in the final part of the study, they
examined these and additional dogs to see how mutations at
these three genes worked together to produce various coat
types. Combinations of variations in R-spondin-2, FGF5, and
keratin genes explain the seven coat types that characterize
most of the dogs sampled, which represented 108 breeds.
Short-hair breeds such as basset hounds, for example, have
none of the three mutations; dogs with just the R-spondin-2
change had furnishings--picture an Australian terrier--and
those with that change and the change in FGF5 have furnishings
and long, soft coats, like bearded collies. All three mutations are
found in dogs with long, curly hair and mustaches--such as the
bichon Frisé.
That the same genes are at work in many breeds indicates that
these mutations are very old. "All the unique characteristics are
something that occurred once a long time ago and have been
preserved ever since," notes Gregory Acland, a geneticist at
Cornell College of Veterinary Medicine. When breeders shuffled
these genes, they created dogs with new types of coats.
Åke Hedhammar of the Swedish University of Agricultural
Sciences in Uppsala would now like to know how these genes
exert these effects and whether they are at work in other
species. That's a logical next step, says Acland: "Once you have
a candidate gene in one species, it's easier to ask if it's involved
in [a different] species."