Hair growth determined by RSPO2 gene in multiple dog breeds

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Distinct eyebrows and moustache (so-called furnishings)

Improper coat (IC)

Shedding (MC5R and RSPO2 test combination)

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The coat appearance belongs clearly to the main morphologic distinctions among dogs of different breeds.

There are distinguished three main characteristic hair types of dogs:

• hair length - short/long
• presence/absence of curls
• presence/absence of traits: distinct moustache and eyebrows, characteristic for rough coated dogs

In 2009, Cadieu in cooperation with National Human Genome Research Institute (NIH) and other authors published an article about the results of research of genes participating in dog hair phenotype.
In connection with the hair type, different gene variations in genes RSPO2, FGF5 and KRT71 (encoding R-spondin-2, fibroblast growth factor-5 and keratin-71) have been found that together represent the majority of phenotypes of hair of purebred dogs.

Table (Cadieu et al. , 2009): hair phenotype and genotype

* TT genotype has not been found in this combination; however it probably induces a short-haired phenotype

According to the research, the rough-coated breeds with distinct eyebrows and moustache bear insertion in RSPO2. The appearance of dogs bearing insertion in RSPO2 and also the gene variation c.451C>T in KRT71 is similar to that of rough-coated, but the hair is longer and curlier. Dogs with long hair bear change c.284G>T in homozygous condition in FGF5 gene: If there is an insertion in RSPO2 in addition to this variation, the dogs have distinct moustache and brows and long smooth hair. Dogs with a combination of gene variations in FGF5 and KRT71 have long and curly hair. It is not surprising that the coat must be longer to be curly or wavy, and therefore breeds with such hair are homozygous for c.284G>T in FGF5. If the breed has a combination of all three gene variations, the hair is long, curly with distinct brows and moustache. None of these variations has been found in grey wolfs or in dog breeds with short hair.

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Distinct eyebrows and moustache (so-called furnishings)

According to Cadieu´s research, seven dog breeds with distinct eyebrows and moustache were subjected to RSPO2-gene test and it was found 167 bp insertion in the untranslated region (UTR) of RSPO2. In 297 of 298 dogs with furnishings, homozygous or heterozygous form of insertion was found and in all 406 dogs without distinct furnishings (eyebrows and moustache) the RSPO2 gene was present without insertion.
The eyebrow and moustache are dominantly inherited. That means that a dog with furnishings has insertion in RSPO2 on one or both alleles. A dog without furnishings carries two wild type alleles without presence of RSOP2 gene insertion.

Furnishings are important for the breeds:

• Brussels Griffon
• Chinese crested dog
• Dachshund
• German Shorthaired Pointer
• Irish Soft-Coated Wheaten Terrier

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Improper coat (IC)

Other manifestation of insertion in RSPO2-gene can be a non-standard fur in some dog breeds - improper coat (IC). For example, in Portuguese Water Dogs and Havana Dogs the wild type allele is responsible for IC-phenotype (Parker et al. 2010). Dogs with IC are homozygous for wild type allele. Dogs with standard fur type are carriers of one or two alleles with insertion.

Non-standard hair caused by RSPO2 was found in breeds:

• Portuguese Water Dog
• Bichon Havanese
• Havana silk dog
• Labradoodle

Improper coat (IC) is inherited in autosomal recessive trait. That means that IC will develop only in individuals, who inherit the wild-type allele from both parents and are homozygous for this allele. Heterozygous individuals (with one allele of wild –type and one inserted allele) will be only carriers of phenotype symptoms of IC. If two carries are mated, the litter will theoretically consist of 25 % offsprings with improper coat, 25 % will be carriers without phenotype symptoms and 50% offsprings will have typical coat. The genetic test identifies possible carries of IC. The occurrence of offsprings with IC in the litter can be avoided by targeted selection. To maintain the genetic variability, it is not necessary to exclude the heterozygotes from the breeding programmes.

Portuguese Water Dogs (PWD) show two basic variants of a coat, wavy and curly and both these variants are bred together. The thick coat covers the whole body evenly incl. face, top of the head and legs. However, within the PWD breed, an individual can be born that does not meet the expected coat standard, this phenomenon is known as Improper Coat (IC). The IC phenomenon is characterized by a non-standard coat with short hair on the head, face and legs. The whole body is covered by strong and rather flat or slightly wavy hair. The appearance of Portuguese Water Dogs with improper coat type is often compared with the flat or curly coated retrievers.

Although IC in PWD does not affect the health of dogs, it causes problems with their breeding, exhibiting or potential sale of offsprings, as these individuals do not meet the breed standards. Contrary to dogs with typical coat, the dogs of IC phenotype have underhair and lose their hair, which may present a limitation for breeders with respect to possible allergic reactions of people, who suffer from dog allergies. The frequency of wt allele in the American population of PWD has been calculated from randomly selected and genotypic samples and makes 12% (Parker et al. 2010).

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References:

Parker HG, Chase K, Cadieu E, Lark KG, Ostrander EA.: An insertion in the RSPO2 gene correlates with improper coat in the Portuguese water dog. J Hered. 2010 Sep-Oct;101(5):612-7.

Cadieu E, Neff M, Quignon P, Walsh K, Chase K, Parker HG, Vonholdt BM, Rhue A, Boyko A, Byers A, et al.: Coat variation in the domestic dog is governed by variants in three genes. 2009;326:150-153.