Champagne Gene - Inheritance and Expression

Inheritance and Expression

The champagne locus is on exon 2 of the SLC36A1 gene, which is on chromosome 14 (ECA14); a single nucleotide polymorphism (SNP) exchanges a C for a G at base 76 (c.188C>G) resulting in a missense mutation. On a protein level, this SNP is predicted to result in the replacement of a threonine with arginine at amino acid 63 (T63R). SLC36A1 is not associated with pigmentation phenotypes in other species, and its role in most tissues is poorly understood. SLC36A1 is a member of a loosely-united group of over 300 proteins responsible for active transport and facilitated diffusion called the Solute carrier family. Other members of this family include SLC45A2, which is responsible for pigmentation variations of many types in humans, as well as the cream coat color in horses; and SLC24A5, which is responsible for the Golden dilution in mice.

Dilution genes such as champagne and cream affect the nature or density of the pigments produced by melanocytes. On the other hand, genes in horses which produce white spotting, such as Frame and Sabino1, interrupt or limit the migration of melanocytes from the neural crest. In other words, the skin, eyes, and hair of horses with the champagne mutation do not lack melanocytes, melanosomes, or melanins, but rather exhibit hypomelanism. However, the specific role of SLC36A1 in pigmentation and how the champagne coat colors are created on a molecular level is not known. The researchers who identified the mutation in 2008 suggested that melanosome pH may be affected, which in turn might affect the processing of tyrosine, a critical element of melanogenesis.

There are two alleles in this series: the recessive, wildtype allele ch and the dominant CH. The CH allele represents the T63R SLC36A1 mutation.

• ch/ch recessive homozygotes are not affected by champagne and have no true champagne traits.
• CH/ch heterozygotes have one champagne allele, and one wildtype non-champagne allele. The skin is bright pink and the eyes bright blue at birth, darkening to freckled and hazel with age, respectively. Both red and black pigment in the hair are diluted.
• CH/CH homozygotes (homozygous champagnes) have no wildtype non-champagne alleles. Such horses are indistinguishable from heterozygotes, except that their freckles may slightly sparser and the coat slightly lighter.

The DNA test for champagne detects the c.188C>G mutation on SLC36A1.