Abstract
BackgroundCurly horses present a variety of curl phenotypes that are associated with various degrees of curliness of coat, mane, tail and ear hairs. Their origin is still a matter of debate and several genetic hypotheses have been formulated to explain the diversity in phenotype, including the combination of autosomal dominant and recessive alleles. Our purpose was to map the autosomal dominant curly hair locus and identify the causal variant using genome-wide association study (GWAS) and whole-genome sequencing approaches.ResultsA GWAS was performed using a Bayesian sparse linear mixed model, based on 51 curly and 19 straight-haired French and North American horses from 13 paternal families genotyped on the Illumina EquineSNP50 BeadChip. A single strong signal was observed on equine chromosome 11, in a region that encompasses the type I keratin gene cluster. This region was refined by haplotype analysis to a segment including 36 genes, among which are 10 keratin genes (KRT-10, -12, -20, -23, -24, -25, -26, -27, -28, -222). To comprehensively identify candidate causal variants within all these genes, whole-genome sequences were obtained for one heterozygous curly stallion and its straight-haired son. Among the four non-synonymous candidate variants identified and validated in the curly region, only variant g.21891160G>A in the KRT25 gene (KRT25:p.R89H) was in perfect agreement with haplotype status in the whole pedigree. Genetic association was then confirmed by genotyping a larger population consisting of 353 horses. However, five discordant curly horses were observed, which carried neither the variant nor the main haplotype associated with curliness. Sequencing of KRT25 for two discordant horses did not identify any other deleterious variant, which suggests locus rather than allelic heterogeneity for the curly phenotype.ConclusionsWe identified the KRT25:p.R89H variant as responsible for the dominant curly trait, but a second dominant locus may also be involved in the shape of hairs within North American Curly horses.
Highlights
Horses present a variety of curl phenotypes that are associated with various degrees of curliness of coat, mane, tail and ear hairs
First described by Crow and Sioux Native American tribes as early as 1801 during winter horse counting [1], Curly horses present a variety of coat curl phenotypes associated with diverse degrees of curliness which can range from “minimal” scattered curled hair up to extremely dense “micro curled” permanent coat as observed in certain Missouri Fox Trotter lines (Fig. 1)
A Bayesian sparse linear mixed model (BSLMM) [9] was applied to the Illumina EquineSNP50 BeadChip genotyping data of 51 curly and 19 straight-haired French and North American horses from 13 different paternal families. This hybrid genome-wide association study (GWAS) analysis approach combines a was observed in 46 out of the 51 curly animals, whereas it was absent from the 19 straight-haired animals
Summary
Horses present a variety of curl phenotypes that are associated with various degrees of curliness of coat, mane, tail and ear hairs. Their origin is still a matter of debate and several genetic hypotheses have been formulated to explain the diversity in phenotype, including the combination of autosomal dominant and recessive alleles. First described by Crow and Sioux Native American tribes as early as 1801 during winter horse counting [1], Curly horses present a variety of coat curl phenotypes associated with diverse degrees of curliness which can range from “minimal” scattered curled hair up to extremely dense “micro curled” permanent coat as observed in certain Missouri Fox Trotter lines (Fig. 1). The mane and tail hairs present particular phenotypes ranging from curly to wavy or sometimes resembling dreadlocks [3]. Horses are claimed to Morgenthaler et al Genet Sel Evol (2017) 49:85
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