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Liu X, Peng Y, Zhang X, Wang X, Chen W, Kou X, Liang H, Ren W, Khan MZ, Wang C. Coloration in Equine: Overview of Candidate Genes Associated with Coat Color Phenotypes. Animals (Basel) 2024; 14:1802. [PMID: 38929421 PMCID: PMC11200706 DOI: 10.3390/ani14121802] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2024] [Revised: 06/12/2024] [Accepted: 06/13/2024] [Indexed: 06/28/2024] Open
Abstract
Variation in coat color among equids has attracted significant interest in genetics and breeding research. The range of colors is primarily determined by the type, concentration, and distribution of melanin pigments, with the balance between eumelanin and pheomelanin influenced by numerous genetic factors. Advances in genomic and sequencing technologies have enabled the identification of several candidate genes that influence coat color, thereby clarifying the genetic basis of these diverse phenotypes. In this review, we concisely categorize coat coloration in horses and donkeys, focusing on the biosynthesis and types of melanin involved in pigmentation. Moreover, we highlight the regulatory roles of some key candidate genes, such as MC1R, TYR, MITF, ASIP, and KIT, in coat color variation. Moreover, the review explores how coat color relates to selective breeding and specific equine diseases, offering valuable insights for developing breeding strategies that enhance both the esthetic and health aspects of equine species.
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Affiliation(s)
| | | | | | | | | | | | | | | | - Muhammad Zahoor Khan
- Liaocheng Research Institute of Donkey High-Efficiency Breeding and Ecological Feeding, Liaocheng University, Liaocheng 522000, China
| | - Changfa Wang
- Liaocheng Research Institute of Donkey High-Efficiency Breeding and Ecological Feeding, Liaocheng University, Liaocheng 522000, China
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2
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Durward-Akhurst SA, Marlowe JL, Schaefer RJ, Springer K, Grantham B, Carey WK, Bellone RR, Mickelson JR, McCue ME. Predicted genetic burden and frequency of phenotype-associated variants in the horse. Sci Rep 2024; 14:8396. [PMID: 38600096 PMCID: PMC11006912 DOI: 10.1038/s41598-024-57872-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2023] [Accepted: 03/22/2024] [Indexed: 04/12/2024] Open
Abstract
Disease-causing variants have been identified for less than 20% of suspected equine genetic diseases. Whole genome sequencing (WGS) allows rapid identification of rare disease causal variants. However, interpreting the clinical variant consequence is confounded by the number of predicted deleterious variants that healthy individuals carry (predicted genetic burden). Estimation of the predicted genetic burden and baseline frequencies of known deleterious or phenotype associated variants within and across the major horse breeds have not been performed. We used WGS of 605 horses across 48 breeds to identify 32,818,945 variants, demonstrate a high predicted genetic burden (median 730 variants/horse, interquartile range: 613-829), show breed differences in predicted genetic burden across 12 target breeds, and estimate the high frequencies of some previously reported disease variants. This large-scale variant catalog for a major and highly athletic domestic animal species will enhance its ability to serve as a model for human phenotypes and improves our ability to discover the bases for important equine phenotypes.
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Affiliation(s)
- S A Durward-Akhurst
- Department of Veterinary Clinical Sciences, University of Minnesota, C339 VMC, 1353 Boyd Avenue, St. Paul, MN, 55108, USA.
| | - J L Marlowe
- Department of Veterinary Clinical Sciences, University of Minnesota, C339 VMC, 1353 Boyd Avenue, St. Paul, MN, 55108, USA
| | - R J Schaefer
- Department of Veterinary Population Medicine, University of Minnesota, 225 VMC, 1365 Gortner Avenue, St. Paul, MN, 55108, USA
| | - K Springer
- Department of Veterinary Population Medicine, University of Minnesota, 225 VMC, 1365 Gortner Avenue, St. Paul, MN, 55108, USA
| | - B Grantham
- Interval Bio LLC, 408 Stierline Road, Mountain View, CA, 94043, USA
| | - W K Carey
- Interval Bio LLC, 408 Stierline Road, Mountain View, CA, 94043, USA
| | - R R Bellone
- Veterinary Genetics Laboratory, School of Veterinary Medicine, University of California-Davis, Davis, CA, USA
- Population Health and Reproduction and Veterinary Genetics Laboratory, School of Veterinary Medicine, University of California, Davis, CA, USA
| | - J R Mickelson
- Department of Veterinary and Biomedical Sciences, University of Minnesota, 295F Animal Science Veterinary Medicine Building, 1988 Fitch Avenue, St. Paul, MN, 55108, USA
| | - M E McCue
- Department of Veterinary Population Medicine, University of Minnesota, 225 VMC, 1365 Gortner Avenue, St. Paul, MN, 55108, USA
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McFadden A, Vierra M, Robilliard H, Martin K, Brooks SA, Everts RE, Lafayette C. Population Analysis Identifies 15 Multi-Variant Dominant White Haplotypes in Horses. Animals (Basel) 2024; 14:517. [PMID: 38338160 PMCID: PMC10854588 DOI: 10.3390/ani14030517] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2023] [Revised: 01/26/2024] [Accepted: 02/04/2024] [Indexed: 02/12/2024] Open
Abstract
The influence of a horse's appearance on health, sentimental and monetary value has driven the desire to understand the etiology of coat color. White markings on the coat define inclusion for multiple horse breeds, but they may disqualify a horse from registration in other breeds. In domesticated horses (Equus caballus), 35 KIT alleles are associated with or cause depigmentation and white spotting. It is a common misconception among the general public that a horse can possess only two KIT variants. To correct this misconception, we used BEAGLE 5.4-phased NGS data to identify 15 haplotypes possessing two or more KIT variants previously associated with depigmentation phenotypes. We sourced photos for 161 horses comprising 12 compound genotypes with three or more KIT variants and employed a standardized method to grade depigmentation, yielding average white scores for each unique compound genotype. We found that 7 of the 12 multi-variant haplotypes resulted in significantly more depigmentation relative to the single-variant haplotypes (ANOVA). It is clear horses can possess more than two KIT variants, and future work aims to document phenotypic variations for each compound genotype.
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Affiliation(s)
- Aiden McFadden
- Etalon Inc., Menlo Park, CA 94025, USA; (M.V.); (H.R.); (K.M.); (R.E.E.)
| | - Micaela Vierra
- Etalon Inc., Menlo Park, CA 94025, USA; (M.V.); (H.R.); (K.M.); (R.E.E.)
| | - Holly Robilliard
- Etalon Inc., Menlo Park, CA 94025, USA; (M.V.); (H.R.); (K.M.); (R.E.E.)
| | - Katie Martin
- Etalon Inc., Menlo Park, CA 94025, USA; (M.V.); (H.R.); (K.M.); (R.E.E.)
| | - Samantha A. Brooks
- Department of Animal Sciences, UF Genetics Institute, University of Florida, Gainesville, FL 32611, USA;
| | - Robin E. Everts
- Etalon Inc., Menlo Park, CA 94025, USA; (M.V.); (H.R.); (K.M.); (R.E.E.)
| | - Christa Lafayette
- Etalon Inc., Menlo Park, CA 94025, USA; (M.V.); (H.R.); (K.M.); (R.E.E.)
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McFadden A, Vierra M, Martin K, Brooks SA, Everts RE, Lafayette C. Spotting the Pattern: A Review on White Coat Color in the Domestic Horse. Animals (Basel) 2024; 14:451. [PMID: 38338094 PMCID: PMC10854722 DOI: 10.3390/ani14030451] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/25/2023] [Revised: 01/25/2024] [Accepted: 01/27/2024] [Indexed: 02/12/2024] Open
Abstract
Traits such as shape, size, and color often influence the economic and sentimental value of a horse. Around the world, horses are bred and prized for the colors and markings that make their unique coat patterns stand out from the crowd. The underlying genetic mechanisms determining the color of a horse's coat can vary greatly in their complexity. For example, only two genetic markers are used to determine a horse's base coat color, whereas over 50 genetic variations have been discovered to cause white patterning in horses. Some of these white-causing mutations are benign and beautiful, while others have a notable impact on horse health. Negative effects range from slightly more innocuous defects, like deafness, to more pernicious defects, such as the lethal developmental defect incurred when a horse inherits two copies of the Lethal White Overo allele. In this review, we explore, in detail, the etiology of white spotting and its overall effect on the domestic horse to Spot the Pattern of these beautiful (and sometimes dangerous) white mutations.
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Affiliation(s)
- Aiden McFadden
- Etalon Inc., Menlo Park, CA 94025, USA; (M.V.); (K.M.); (R.E.E.); (C.L.)
| | - Micaela Vierra
- Etalon Inc., Menlo Park, CA 94025, USA; (M.V.); (K.M.); (R.E.E.); (C.L.)
| | - Katie Martin
- Etalon Inc., Menlo Park, CA 94025, USA; (M.V.); (K.M.); (R.E.E.); (C.L.)
| | - Samantha A. Brooks
- Department of Animal Sciences, UF Genetics Institute, University of Florida, Gainesville, FL 32611, USA;
| | - Robin E. Everts
- Etalon Inc., Menlo Park, CA 94025, USA; (M.V.); (K.M.); (R.E.E.); (C.L.)
| | - Christa Lafayette
- Etalon Inc., Menlo Park, CA 94025, USA; (M.V.); (K.M.); (R.E.E.); (C.L.)
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Voß K, Blaj I, Tetens JL, Thaller G, Becker D. Roan coat color in livestock. Anim Genet 2022; 53:549-556. [PMID: 35811453 DOI: 10.1111/age.13240] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2021] [Revised: 06/20/2022] [Accepted: 06/22/2022] [Indexed: 11/27/2022]
Abstract
Since domestication, a wide variety of phenotypes including coat color variation has developed in livestock. This variation is mostly based on selective breeding. During the beginning of selective breeding, potential negative consequences did not become immediately evident due to low frequencies of homozygous animals and have been occasionally neglected. However, numerous studies of coat color genetics have been carried out over more than a century and, meanwhile, pleiotropic effects for several coat color genes, including disorders of even lethal impact, were described. Similar coat color phenotypes can often be found across species, caused either by conserved genes or by different genes. Even in the same species, more than one gene could cause the same or similar coat color phenotype. The roan coat color in livestock species is characterized by a mixture of white and colored hair in cattle, pig, sheep, goat, alpaca, and horse. So far, the genetic background of this phenotype is not fully understood, but KIT and its ligand KITLG (MGF) are major candidate genes in livestock species. For some of these species, pleiotropic effects such as subfertility in homozygous roan cattle or homozygous embryonic lethality in certain horse breeds have been described. This review aims to point out the similarities and differences of the roan phenotype across the following livestock species: cattle, pig, sheep, goat, alpaca, and horse; and provides the current state of knowledge on genetic background and pleiotropic effects.
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Affiliation(s)
- Katharina Voß
- Institute of Animal Breeding and Husbandry, University of Kiel, Kiel, Germany
| | - Iulia Blaj
- Institute of Animal Breeding and Husbandry, University of Kiel, Kiel, Germany
| | - Julia L Tetens
- Institute of Animal Breeding and Husbandry, University of Kiel, Kiel, Germany
| | - Georg Thaller
- Institute of Animal Breeding and Husbandry, University of Kiel, Kiel, Germany
| | - Doreen Becker
- Institute of Genome Biology, Research Institute for Farm Animal Biology (FBN), Dummerstorf, Germany
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Kvist L, Honka J, Niskanen M, Liedes O, Aspi J. Selection in the Finnhorse, a native all-around horse breed. J Anim Breed Genet 2020; 138:188-203. [PMID: 33226152 PMCID: PMC7894145 DOI: 10.1111/jbg.12524] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2020] [Revised: 10/20/2020] [Accepted: 11/01/2020] [Indexed: 12/19/2022]
Abstract
Selection by breeders modifies the morphology, behaviour and performance of domesticated species. Here, we examined signs of selection in Finnhorse, the only native horse breed in Finland. We first searched divergent genomic regions between Finnhorses and other breeds, as well as between different breeding sections of the Finnhorse with data from Illumina Equine SNP70 BeadChip, and then studied several of the detected regions in more detail. We found altogether 35 common outlier SNPs between Finnhorses and other breeds using two different selection tests. Many of the SNPs were located close to genes affecting coat colour, performance, size, sugar metabolism, immune response and olfaction. We selected genes affecting coat colour (KIT, MITF, PMEL), performance (MSTN) and locomotion (DMRT3) for a more detailed examination. In addition, we looked for, and found, associations with height at withers and SNPs located close to gene LCORL. Among the four breeding sections of Finnhorses (harness trotters, riding horses, draught horses and pony‐sized horses), a single SNP located close to the DMRT3 gene was significantly differentiated and only between harness trotters and pony‐sized horses.
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Affiliation(s)
- Laura Kvist
- Department of Ecology and Genetics, University of Oulu, Oulu, Finland
| | - Johanna Honka
- Department of Ecology and Genetics, University of Oulu, Oulu, Finland
| | - Markku Niskanen
- Research Unit of History, Culture and Communications, University of Oulu, Oulu, Finland
| | - Oona Liedes
- Department of Ecology and Genetics, University of Oulu, Oulu, Finland
| | - Jouni Aspi
- Department of Ecology and Genetics, University of Oulu, Oulu, Finland
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Coat Color Roan Shows Association with KIT Variants and No Evidence of Lethality in Icelandic Horses. Genes (Basel) 2020; 11:genes11060680. [PMID: 32580410 PMCID: PMC7348759 DOI: 10.3390/genes11060680] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2020] [Revised: 06/18/2020] [Accepted: 06/19/2020] [Indexed: 11/26/2022] Open
Abstract
Roan (Rn) horses show a typical seasonal change of color. Their body is covered with colored and white hair. We performed a descriptive statistical analysis of breeding records of Icelandic horses to challenge the hypothesis of roan being lethal in utero under homozygous condition. The roan to non-roan ratio of foals from roan × roan matings revealed homozygous roan Icelandic horses to be viable. Even though roan is known to be inherited in a dominant mode and epistatic to other coat colors, the causative mutation is still unknown. Nevertheless, an association between roan phenotype and the KIT gene was shown for different horse breeds. In the present study, we identified KIT variants by Sanger sequencing, and show that KIT is also associated with roan in the Icelandic horse breed.
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Merkies K, Paraschou G, McGreevy PD. Morphometric Characteristics of the Skull in Horses and Donkeys-A Pilot Study. Animals (Basel) 2020; 10:E1002. [PMID: 32521777 PMCID: PMC7341236 DOI: 10.3390/ani10061002] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2020] [Revised: 05/27/2020] [Accepted: 06/05/2020] [Indexed: 12/12/2022] Open
Abstract
Horses and donkeys belong to the genus Equus, but important differences exist between the species, many of which affect their management and welfare. This study compared skull morphology between horses and donkeys. Horse (n = 14) and donkey (n = 16) heads were obtained post-mortem, sectioned sagittally close to the midline, and photographed for subsequent measurement of various skull structures. Skull, cranial, nasal, and profile indices were calculated for topographical comparisons between the species. The olfactory bulb area (OBA), OB pitch (the angle between the hard palate and the OB axis), and whorl location (WL) were also measured. A General Linear Model determined the main effect of species with Sidak's multiple comparisons of species' differences among the various measurements. There was no species difference in cranial or nasal indices (p > 0.13), but donkeys had a larger cranial profile than horses (p < 0.04). Donkeys had a smaller OBA (p < 0.05) and a steeper OB pitch (p < 0.02) than horses. The WL corresponded to the level of the OB in horses but was extremely rostral in donkeys (p < 0.0001). These results show clear differentiation in skull morphology between horses and donkeys. This may be useful in validating other physiological and behavioural differences between horses and donkeys.
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Affiliation(s)
- Katrina Merkies
- Department of Animal Biosciences, University of Guelph, Guelph, N1G 2W1 ON, Canada
- Campbell Centre for the Study of Animal Welfare, University of Guelph, Guelph, N1G 2W1 ON, Canada
| | | | - Paul Damien McGreevy
- Sydney School of Veterinary Science, Faculty of Science, University of Sydney, Sydney, NSW 2006, Australia;
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