A missense mutation in PMEL17 is associated with the Silver coat color in the horse.
BACKGROUND
The Silver coat color, also called Silver dapple, in the horse is characterized by dilution of the black pigment in the hair. This phenotype shows an autosomal dominant inheritance. The effect of the mutation is most visible in the long hairs of the mane and tail, which are diluted to a mixture of white and gray hairs. Herein we describe the identification of the responsible gene and a missense mutation associated with the Silver phenotype.


RESULTS
Segregation data on the Silver locus (Z) were obtained within one half-sib family that consisted of a heterozygous Silver colored stallion with 34 offspring and their 29 non-Silver dams. We typed 41 genetic markers well spread over the horse genome, including one single microsatellite marker (TKY284) close to the candidate gene PMEL17 on horse chromosome 6 (ECA6q23). Significant linkage was found between the Silver phenotype and TKY284 (theta = 0, z = 9.0). DNA sequencing of PMEL17 in Silver and non-Silver horses revealed a missense mutation in exon 11 changing the second amino acid in the cytoplasmic region from arginine to cysteine (Arg618Cys). This mutation showed complete association with the Silver phenotype across multiple horse breeds, and was not found among non-Silver horses with one clear exception; a chestnut colored individual that had several Silver offspring when mated to different non-Silver stallions also carried the exon 11 mutation. In total, 64 Silver horses from six breeds and 85 non-Silver horses from 14 breeds were tested for the exon 11 mutation. One additional mutation located in intron 9, only 759 bases from the missense mutation, also showed complete association with the Silver phenotype. However, as one could expect to find several non-causative mutations completely associated with the Silver mutation, we argue that the missense mutation is more likely to be causative.


CONCLUSIONS
The present study shows that PMEL17 causes the Silver coat color in the horse and enable genetic testing for this trait.
Brunberg
Emma
E
Dept of Medical Biochemistry and Microbiology, Uppsala University, SE-751 24 Uppsala, Sweden. a1emmbru@stud.slu.se
Andersson
Leif
L
Cothran
Gus
G
Sandberg
Kaj
K
Mikko
Sofia
S
Lindgren
Gabriella
G
D000595:Amino Acid Sequence; D000818:Animals; D002874:Chromosome Mapping; D033481:Chromosomes, Mammalian / Q000235:genetics; D003001:Cloning, Molecular; D005260:Female; D005838:Genotype; D006200:Hair Color / Q000235:genetics*; D006736:Horses / Q000235:genetics*; D008297:Male; D008562:Membrane Glycoproteins / Q000235:genetics*; D008969:Molecular Sequence Data; D020125:Mutation, Missense / Q000235:genetics*; D010641:Phenotype; D011110:Polymorphism, Genetic / Q000235:genetics; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D012880:Skin Pigmentation / Q000235:genetics*; D058951:gp100 Melanoma Antigen
D008562:Membrane Glycoproteins; D058951:gp100 Melanoma Antigen