SEARCH

SEARCH BY CITATION

Keywords:

  • horse;
  • gene;
  • transcript;
  • RNA;
  • DNA;
  • microarray;
  • SNP;
  • exercise;
  • muscle

Summary

  1. Top of page
  2. Summary
  3. Introduction
  4. Genetic component of the performance traits: how to measure the heritability of the exercise variables and performance traits?
  5. New applications in equine genomics available after the recent genome publication
  6. Conclusion: genetic and genomics perspective in equine exercise
  7. Acknowledgements
  8. Conflicts of interest
  9. Manufacturers’ addresses
  10. References

Equine breeding selection has been developed by applying quantitative genetic methods for calculating the heritability of the complex traits such as performance in racing or sport competitions. With the great development of biotechnologies, equine molecular genetics has come of age. The recent sequencing of the equine genome by an international consortium was a major advance that will impact equine genomics in the near future. With the rapid progress in equine genetics, new applications in early performance evaluation and the detection of disease markers become available. Many new biomolecular tools will change management of horse selection, disease diagnosis and treatment. The purpose of this review is to present new developments in equine genetics and genomics for performance evaluation and health markers after a short summary of the previous knowledge about the genetic components of the exercise performance traits.


Introduction

  1. Top of page
  2. Summary
  3. Introduction
  4. Genetic component of the performance traits: how to measure the heritability of the exercise variables and performance traits?
  5. New applications in equine genomics available after the recent genome publication
  6. Conclusion: genetic and genomics perspective in equine exercise
  7. Acknowledgements
  8. Conflicts of interest
  9. Manufacturers’ addresses
  10. References

Equine breeding selection has been developed by applying quantitative genetic methods for calculating the heritability of the complex traits such as performance in racing or sport competitions. Genetic indices are now calculated routinely in different horse breeds in order to select the best stallions and mares according to a breeding plan with a well-defined genetic objective. Other exercise variables and disease characteristics have also been studied by the same quantitative genetic methods. With the great development of biotechnologies, the equine molecular genetics comes of age. The equine mitochondrial genome was sequenced in 1994 (Xu and Arnason 1994) and then partial genome sequencing was undertaken (Caetano et al. 1999; Milenkovic et al. 2002; Chowdhary et al. 2003). The recent equine genome sequencing by an international consortium (Wade et al. 2009) was a major advance that will impact equine genomics in the near future. With the rapid progress in equine genetics, new applications in early performance evaluation and the detection of disease markers become available. Many new biomolecular tools will change management of horse selection, disease diagnostics and treatment. In man, the research project HERITAGE family study provides continuous new knowledge and databases about the genes and quantitative trait loci (QTLs) related to exercise activity, health and performance. The last update of the gene list validated by experimental studies revealed 214 autosomal genes and quantitative trait loci and 7 others on the X chromosome (Bray et al. 2009). Moreover, there are 18 mitochondrial genes that have been shown to influence fitness and performance phenotypes. This important collection of genetic data related to exercise in man suggests that there will be great interest in studying equine genetics for performance evaluation and sports medicine applications.

The purpose of this review was to present new developments in equine genetics and genomics for performance evaluation and health markers after a short summary of previous knowledge about the genetic components of exercise performance traits.

Genetic component of the performance traits: how to measure the heritability of the exercise variables and performance traits?

  1. Top of page
  2. Summary
  3. Introduction
  4. Genetic component of the performance traits: how to measure the heritability of the exercise variables and performance traits?
  5. New applications in equine genomics available after the recent genome publication
  6. Conclusion: genetic and genomics perspective in equine exercise
  7. Acknowledgements
  8. Conflicts of interest
  9. Manufacturers’ addresses
  10. References

With the development of equine exercise physiology, more functional traits can be measured for early evaluation of exercise ability. The objective is to predict the level of performance that a young horse can reach by measuring some physiological characteristics during an exercise test. For breeding purposes, the heritability of each trait should be determined to know if it is useful for breeding selection. This section presents how to calculate the heritability and apply the method to some physiological and locomotor traits related to the equine exercise ability. Several exercise traits have been studied in different breeds: muscle fibre types, heart rate, blood lactate, gait, jump style and conformation.

Heritability calculation

Heritability estimates (h2) of exercise traits have been calculated in order to estimate the influence of genetic components andenvironment effects (i.e. nongenetic) on trait variability. Heritability is the ratio between genetic variance and the total variance including environmental effects. For each variable, the variance components are calculated using restricted maximum likelihood resolution (REML). The genetic variance is estimated by the following variance analysis model including fixed (known during the experiment) and random effects (unknown: animal genetic effect and error). The total variability of the trait is explained in the sum of fixed effects (for example: age, height, track, breed) and the random animal genetic effect:

  • image

Heritability values (h2) >0.4 indicate that 40% of the trait could be transmitted to offspring by mare and stallion. Forty percent represents a high percentage of genetic influence. Performance heritability estimates in racing and equestrian sports are: 0.15–0.55 for flat gallop racing, 0.17–0.26 for trot or pace racing, 0.05–0.28 for showjumping and 3-day eventing and 0.11 for dressage (Hintz 1980; Langlois 1980; Ricard et al. 2000). In addition, it was interesting to note that there is no genetic correlation or a little negative correlation between jumping ability and other other sport performance and gait variables. Heritability estimates are valid only for the breed for which they were calculated and they should be recalculated periodically if there is an ongoing breeding programme in the population. The heritabilities of the important traits are used to calculate genetic index using best linear unbiaised predictor (BLUP) method in sport horses in different countries (Ricard et al. 2000).

Muscle power: percentages of fast and slow myosin heavy chains of gluteus medius

Myosin heavy chain (MHC) percentages were measured in small muscle samples of 20–30 mg collected by microbiopsy under local anaesthesia in Anglo-Arabian horses. The analysis of slow MHC I and fast MHC IIA and IIX was performed using monoclonal antibodies with an ELISA method (Barrey et al. 1999a). The heritability of the percentage of fast MHC was 0.13 in Anglo-Arabian and 0.28 in Andalusian horses (Rivero and Barrey 2001). The relative area h2 of the fast muscle fibres was 0.12 in Anglo-Arabian and 0.15–0.23 in Andalusian horses for fast and slow fibres, respectively. The capillary density h2 in Andalusian horses was 0.20. The relationships with performance should be taken into account: muscular traits are significantly different between high and poor performers in racing and jumping horses.

Evaluation of cardiac and aerobic capacity

French trotters performed an exercise test at increasing speed. Heart rate and blood lactate were measured in order to determine speed related changes of these variables. The speed eliciting a heart rate of 200 beats/min (V200) and a blood lactate concentration of 4 mmol/l (VLa4) were calculated. The V200 h2 was higher (0.46) than the VLa4 h2 (0.10), which was more influenced by the training effect (Barrey et al. 1999b). For harness trotters, VLa4 is less heritable but more related to performance than V200 (Leleu et al. 2003).

Gait analysis

To measure kinetic and temporal variables of the walk, trot, gallop and jump the horses were equipped with the Equimetrix gait analysis system (Barrey and Galloux 1997; Barrey et al. 2001, 2002a). Two accelerometers were fixed with an elastic girth on the sternum ensuring that the transducer was held close to the horse's centre of gravity. The device recorded the dorso-ventral and longitudinal acceleration of the horse during the exercise and provided gait variables described in Tables 1 and 2. For the dressage gaits, the genetic effect of the breed was demonstrated in young horses of 3 European breeds: Hannover, Andalusian (PRE) and Selle Français (Barrey et al. 2002c). Heritability estimates of canter, gallop and jumping variables, such as take-off impulse were rather high: 0.23–0.52 (Barrey et al. 2002b; Barrey 2004). For equestrian sport horses, the use of gait variables, such as stride frequency, propulsion power and jump variables, is better indicated for early selection.

Table 1. Heritabilities (h2) of gait variables measured in Selle Français horses. Walk and trot were recorded in hand and canter under free condition. Canter heritabilities were higher than trot and walk heritabilities
Gait variablesWalk h2 (s.e.)Trot h2 (s.e.)Canter h2 (s.e.)
  1. NA, Nonavailable data.

Stride characteristics   
 Speed00.30 (0.14)NA
 Stride length00.29 (0.13)NA
 Stride frequency00.20 (0.15)0.32 (0.19)
Dorsoventral motion   
 Symmetry0.10 (0.08)0.12 (0.08)NA
 Regularity0.10 (0.13)0.12 (0.09)NA
 Displacement0.16 (0.12)0.14 (0.08)NA
 Dorsoventral activity0.41 (0.12)0.22 (0.10)0.50 (0.13)
 Gait rhythm0.29 (0.10)0.05 (0.07)NA
Longitudinal motion   
 Mean propulsion vector0.19 (0.07)0.20 (0.11)NA
 Propulsion duration0.69 (0.13)0.38 (0.15)NA
 Longitudinal activity00.44 (0.14)0.46 (0.20)
Table 2. Heritabilities (h2) of jump variables measured in Selle Français horses and Poney de Selle. The jumps were recorded under free condition. Jump heritabilities were higher than walk and trot heritabilities
TraitsHorsePony
Approach strides0.340.41
Take off force0.230.43
Jump flight0.300.42
Landing force0.520.40

Conformation

Using a 2D image analysis, it has been possible to measure French saddle horses and to calculate the heritability estimates of the main morphological traits. Conformation is poorly heritable in Selle Français horses and more heritable in Poney de Selle (Barrey et al. 2002a). In the 2 breeds, these conformation traits are poorly related to the sport performances. However, in a review of the conformation h2 obtained by other methods (judge scoring and direct measurements) and in other breeds, the heritabilities could be higher for some (Saastamoinen and Barrey 2000).

New applications in equine genomics available after the recent genome publication

  1. Top of page
  2. Summary
  3. Introduction
  4. Genetic component of the performance traits: how to measure the heritability of the exercise variables and performance traits?
  5. New applications in equine genomics available after the recent genome publication
  6. Conclusion: genetic and genomics perspective in equine exercise
  7. Acknowledgements
  8. Conflicts of interest
  9. Manufacturers’ addresses
  10. References

The equine genome has been sequenced and annotated by an international consortium (Wade et al. 2009). The task has been conducted by the Broad Institute Sequencing Platform (Cambridge, Massachusetts, USA). The database is available online at: http://www.ncbi.nlm.nih.gov/genome/guide/horse/ (Figure 1).

image

Figure 1. Map viewer of the Equus caballus genome available on National Council of Biology Information (NCBI) web server at http://www.ncbi.nlm.nih.gov/genome/guide/horse/. View of the chromosome 10 where the glycogen synthase gene (GYS1) involved in the polysaccharide storage myopathy (PSSM), is located (McCue et al. 2008, Herszberg et al. 2009).

Download figure to PowerPoint

Briefly, the equine genome includes 20,322 predicted protein-coding genes according to the annotation process made by alignments and comparisons with the human, mouse and dog genomes. Some transcriptomic analysis showed that 87% of 18,039 genes can be detected using expression microarrays designed with equine probes. In order to have markers throughout the equine genome, a single nucleotide polymorphism (SNP) map was designed including a of total 106 SNP candidates with an average density of 1 SNP/2 kb. It was possible to discriminate 11 different breeds by genotyping a set of 1007 SNPs. This important equine genetic result allow production of new genetic investigations in various domains and design new genomic tools such as SNP chips (Equine SNP50)1 and expression microarrays2 to analyse gene expression and regulation.

Looking for genetic markers of performance, health and disease using a genome-wide scan

Using a genome-wide scan study with microsatellites markers or more recently SNP chips, it is now possible to identify some interesting genes linked to some performance traits or health troubles such as osteochondrosis (OC). Some small variations of the gene sequences such as a SNP can be detected and the association to interesting traits can be demonstrated by statistical tests. Then, if the genetic marker is close to an interesting candidate gene, it could be a way to discover the genetic determinism of a particular phenotype. Another application is to use the best informative SNP markers to genotype a subject in relation to a specific phenotype.

Because selection has been recent and intense in a closed population that stems from a small number of founder animals, Thoroughbreds represent a unique population, within which to identify genomic contributions to exercise-related traits. In a wide genome scan study of 112 Thoroughbred horses, Gu et al. (2009) identified some candidate racing performance genes by using 394 microsatellite markers. These genes were close to the genetic markers and were identified to be involved in energetic metabolism (alcohol dehydrogenase, ADHFE1; pyruvate dehydrogenase kinase 4, PDK4), mitochondrial respiration (mitochondrial fission regulator 1, MTFR1; COX cytochrome units), hypoxia (HIF1A), fatty acid oxidation (acyl-CoA synthetase short-chain family member 1, ACSS1), phosphoinositide-mediated signalling, insulin receptor signalling (PI3KR1), and muscle strength and integrity actin alpha 1, actinin alpha 2 and tenascin C genes (ACTA1, ACTN2, TNC).

Osteochondrosis is a major locomotor disorder in sport and racing horses. Several projects were started to detect genetic markers of this multifactorial joint disease affecting young horses. In a first study, Dierks et al. (2007) performed a genome-wide scan to detect QTLs for OC and osteochondrosis dissecans (OCD) in horses. The genetic marker set comprised 260 microsatellites. Data were collected from 211 Hanoverian Warmblood horses consisting of 14 paternal half-sib families. Traits used were OC (fetlock and/or hock joints affected), OCD (fetlock and/or hock joints affected), fetlock OC, fetlock OCD, hock OC and hock OCD. Genome-wide significant QTLs were located on equine chromosomes 2, 4, 5 and 16. QTLs for fetlock OC and hock OC partly overlapped on the same chromosomes, indicating that these traits may be genetically related. QTLs reached the chromosome-wide significance level on 8 different equine chromosomes: 2, 3, 4, 5, 15, 16, 19 and 21. This whole-genome scan was a first step toward the identification of candidate genome regions harbouring genes responsible for equine OC. In a second study, Lampe et al. (2009a) used 29 microsatellite markers distributed in chromosome 5 to refine the map positions of the QTL already identified for OC in the fetlock. Collagen type XXIV alpha 1 was identified as a potential functional candidate gene for the fetlock OC. In another chromosome-wide linkage analysis, Lampe et al. (2009b) revealed another QTL on chromosome 18 for OC in fetlock, hock or both joints, as well as for OCD in hock joints. Within this QTL for equine OC, the parathyroid hormone 2 receptor gene could be identified as a positional candidate gene. These last results are a further step toward the identification of genes responsible for OC in horses.

Using a new SNP chip (Equine SNP50)1, which includes 54,602 SNP markers distributed among the whole equine genome, other genome-wide scan projects are ongoing to detect SNP markers of showjumping and endurance race ability. Other projects are dealing with OC and larynx paralysis in French saddle horses and French Trotters.

Detecting the genes of performance, health and disease using genotyping

Using the genome database, comparative genomics and genome-wide scan results, it is now possible to identify some interesting genes variability linked to some performance traits such as gallop distance ability or health troubles such as polysaccharide storage myopathy (PSSM). Some small variations of the gene sequences such as a SNP can be related to the change of function of the gene in case of a mutation. By genotyping one identified SNP it is possible to make a genetic diagnosis of a disease such as PSSM or to predict a part of the performance trait such as the distance ability in racing.

Polysaccharide storage myopathy is an equine glycogenesis (metabolic myopathy) related to an abnormal glycogen accumulation. In man, 11 types of glycogenesis have been described, each containing several subtypes due to various gene mutations (Yoon 2006). In horses, it was first described in Quarter Horses (Valberg et al. 1992) and then in other breeds: Spanish Purebred horses, Belgian Draught horses, Morgan, Arabian, Standardbred, Warmbloods, ponies and mules (Quiroz-Rothe et al. 2002; Valentine and Cooper 2005; McCue et al. 2006, 2009; McCue and Valberg 2007). The common clinical signs of PSSM are poor performance, back soreness, exercise intolerance, gait disorders, generalised muscle atrophy, rhabdomyolysis, and spontaneous decumbency with inability to rise and episodic ‘colic’. A PSSM phenotype can be characterised by histological demonstration in striated muscle fibres of an accumulation of some periodic acid Schiff-positive amylase-resistant polysaccharides appearing ultrastructurally as glycogen-like particles (Firshman et al. 2006). In horses, a specific form of fatal glycogen storage disease was observed in a Quarter Horse foal where a nonsense mutation in codon 34 of the glycogen branching enzyme (GBE1) was identified (Ward et al. 2004). This PSSM form can be compared to human glycogenosis type IV where several mutations and deletions explain the total or partial deficiency of the GBE1 gene (Yoon 2006). In mature horses, a G-to-A mutation within the gene encoding glycogen synthase 1 (GYS1) has recently been observed in Quarter Horses and some Warmbloods (McCue et al. 2008; Herszberg et al. 2009). The PSSM mutation was identified in horses from 17 different breeds. The prevalence of the GYS1 mutation in PSSM horses was high in draught- (87%) and Quarter Horse-related breeds (72%) and lower in Warmbloods (18%) and other light horse breeds (24%), when diagnosis was based on grade 2 diagnostic criteria. Overall, the PSSM mutation was present in 16% of grade 1 and 70% of grade 2 PSSM horses. False-positive diagnosis, as well as the possibility of a second glycogenesis in horses with neuromuscular disease, might explain the absence of the GYS1 mutation in horses diagnosed with excessive glycogen accumulation in muscle. In some severe cases of PSSM, another gene mutation has been observed in the ryanodine receptor RYR1 that is responsible for an excess calcium release by the sarcoplasmic reticulum into the cytosol of the contracting muscle fibre (McCue et al. 2009). In addition to the clinical examination and muscular histology diagnosis, the genotyping of the genes GYS1 and RYR1 could be used to confirm the PSSM disease to establish a risk evaluation and to avoid the gene transmission to offspring.

Another example of genotyping in racing performance evaluation involves variants of the myostatin gene (MSTN), which are associated with muscle hypertrophy phenotypes in a range of mammalian species, most notably cattle, dogs, mice and man. Using a sample of registered Thoroughbred horses, Hill et al. (2010) have identified a novel MSTN sequence polymorphism that is strongly associated with best race distance among elite racehorses. The authors observed that the SNP C/C horses are suited to fast, short-distance races, C/T horses compete favourably in middle-distance races, and T/T horses have greater stamina for longer distance (Figure 2). Evaluation of retrospective racecourse performance (n = 142) and stallion progeny performance predict that C/C and C/T horses are more likely to be successful 2-year-old racehorses than T/T animals. This is the first study to demonstrate a relationship between a racing performance trait and a SNP gene variability.

image

Figure 2. Distribution of C/C (blue), C/T (red) and T/T (green) genotypes of the myostatin gene SNP among 179 listed race winning Thoroughbreds (Hill et al. 2010). The Thoroughbreds genotyped C/C (blue bars) are more adapted to race short distance (5–6 furlongs - 1000–1200 m). On the other hand, the Thoroughbreds genotyped T/T (green bars) are more adapted to race long distance gallop race (12–13 furlongs - 2400–2600 m). The Thoroughbred genotyped C/T have middle distance racing ability. © 2010 Hill et al.; with permission from Plos One.

Download figure to PowerPoint

Investigation of the phenotype by the analysis of gene expression and regulation

Gene expression and regulation determine most of the phenotype. The analysis of the cell transcriptome using DNA microarray provides qualitative and quantitative information about the up- and downregulated pathways involved during exercise. The collected data are massive and complex and should be studied by sophisticated data mining methods in order to extract only the informative data. The first transcriptomic studies in exercising horses were performed in the blood leucocytes of performers and disqualified endurance horses (Barrey et al. 2006) and in muscles of Thoroughbred racehorses in training (McGivney et al. 2009).

Barrey et al. (2006) analysed the gene expressions by using DNA microarrays in order to study the physiological adaptations and metabolic disorders in endurance horses. In order to show that genes are modulated in leucocytes in relationship with performance and clinical status of the horses, gene expression in leucocytes, haematological and biochemical parameters were compared between successful and disqualified endurance horses. Blood samples were collected at rest and just after a 140–160 km endurance race in 2 groups of horses: 10 continuing successfully and 10 disqualified at a vet-gate for metabolic disorders. Total RNA was extracted from the total blood cells, checked for purity, amplified and hybridised using mouse cDNA microarrays including 15,264 unique genes. Differential gene expressions were studied by hybridisation of each sample collected at the end of the race vs. the control sample collected before the race. Some significant differences were observed in the haematology and biochemistry of the 2 groups. In the disqualified group, rhabdomyolysis was confirmed with CK 13,124 u/l and AST 1242 u/l. The list of 726 (including 603 annotated genes) significant genes was filtered according to a high P value cut-off (P<0.00001). Among them, 130 were upregulated (expression ratio >1.5) and 288 were downregulated (<1/1.5). Analysis of variance revealed 62 genes differentially expressed (P<0.05) in disqualified and successful horses. The expression levels of 28 and 50 genes were significantly correlated (r2>0.75) with CK and AST levels in the disqualified group, respectively. The gene ontology classification showed that more genes were upregulated in the successful than in the disqualified horses. More genes were downregulated in the disqualified horses. Long exercise induced many significant gene modulations in leucocytes and many of them are involved in inflammation signalling. Some genes were expressed in relationship with the clinical phenotype observed in the disqualified horses: inflammation, rhabdomyolysis and haemolysis. Some of these genes could be interesting markers and/or candidates of poor performance or pathologies.

McGivney et al. (2009) suggested that exercise stimulates immediate early molecular responses as well as delayed responses during recovery, resulting in a return to homeostasis and enabling long-term adaptation. Global gene expression changes in equine skeletal muscle following exercise have not been reported. Therefore, to identify novel genes and key regulatory pathways responsible for exercise adaptation the authors used equine-specific cDNA microarrays to examine global mRNA expression in skeletal muscle from a cohort of Thoroughbred horses (n = 8) at 3 time points following a single bout of treadmill exercise. Skeletal muscle biopsies were taken from the gluteus medius before exercise, immediately after and 4 h after exercise. While only 2 genes had increased expression after exercise (P<0.05), by 4 h after exercise, 932 genes had increased (P<0.05) and 562 genes had decreased expression (P<0.05). Functional analysis of genes differentially expressed during the recovery phase (4 h after exercise) revealed an over-representation of genes localised to the actin cytoskeleton and with functions in the MAPK signalling, focal adhesion, insulin signalling, mTOR signalling, p53 signalling and type II diabetes mellitus pathways. After the exercise, an over-representation of genes involved in the stress response, metabolism and intracellular signalling was observed. These findings suggest that protein synthesis, mechanosensation and muscle remodelling contribute to skeletal muscle adaptation towards improved integrity and hypertrophy. This was the first study to characterise global mRNA expression profiles in equine skeletal muscle using an equine-specific microarray platform. Novel genes and mechanisms are revealed that are temporally expressed following exercise in the equine skeletal muscle transcriptome.

More recently, muscle diseases such as PSSM (Barrey et al. 2009) and recurrent exertional rhabdomyolysis (RER) were investigated using transcriptomic analysis (Jayr 2009). Several cases of myopathies have been observed in the Cob Normand breed, with muscle histology examinations revealing that some families suffer from PSSM. It is assumed that a gene expression signature related to PSSM should be observed at the transcriptional level because the glycogen storage disease could also be linked to other dysfunctions in gene regulation. Therefore, the functional genomic approach could be conducted in order to provide new knowledge about the metabolic disorders related to PSSM. It was proposed to explore the PSSM muscle fibre metabolic disorders by measuring gene expression in relationship with the histological phenotype. Genotypying analysis of GYS1 mutation revealed 2 homozygous (AA) and 5 heterozygous (GA) PSSM horses. In the PSSM muscles, histological data revealed positive amylase resistant abnormal polysaccharides, inflammation, necrosis, lipomatosis and active regeneration of fibres. Ultrastructural evaluation revealed a decrease of mitochondrial number and structural disorders. Extensive accumulation of an abnormal polysaccharide displaced and partially replaced mitochondria and myofibrils. The severity of the disease was higher in the 2 homozygous PSSM horses. Gene expression analysis revealed that 129 genes were significantly modulated (P<0.05). The following genes were upregulated >2 fold: IL18, CTSS, LUM, CD44, FN1, GST01. The most down-regulated genes were the following: mitochondrial tRNA, SLC2A2, PRKC alpha, VEGF alpha. Data mining analysis showed that protein synthesis, apoptosis, cellular movement, growth and proliferation were the main cellular functions significantly associated with the modulated genes (P<0.05). Several upregulated genes, especially IL18, revealed a severe muscular inflammation in PSSM muscles. The upregulation of glycogen synthase kinase-3 (GSK3B) in its active form could be responsible for glycogen synthase (GYS1) inhibition and hypoxia-inducible factor (HIF1A) destabilisation (Figure 3). The main disorders observed in PSSM muscles could be related to mitochondrial dysfunctions, glycogenesis inhibition and the chronic hypoxia of the PSSM muscles.

image

Figure 3. Relationships between inflammatory process, inhibition of glycogen synthase and hypoxia according to data mining analysis of PSSM transcriptomic results (Barrey et al. 2009). The up-regulation of the glycogen synthase kinase (GSK3β) under its active form was responsible for the glycogen synthase (GYS1) inhibition. The upregulation of GSK3β has another effect on hypoxia and low capillarisation of the PSSM muscle. Phosphorylation of GSK3β increases the HIF1α destabilisation, which is degraded in the proteosome. Consequently, the low expression of HIF1α downregulates VEGFα expression, which contributes to a poor capillarisation and increases chronic hypoxia of the regenerated muscle fibres. The PubMed ID of the related publications found by the data mining analysis were indicated on the figure. © 2009 Barrey et al.; with permission from BioMed Central Ltd.

Download figure to PowerPoint

Recently, microRNAs (miRNAs) were detected in muscle and blood and could be interesting markers of diseases in the near future, as has already been presented in human cancer prognostics (Calin et al 2006). MicroRNAs are small, endogenous, noncoding, interfering RNA molecules of 18–25 nucleotides that are regarded as major regulators in eukaryotic gene expression. They play a role in developmental timing, cellular differentiation, signalling and apoptosis pathways. Because of the central function of miRNAs in the proliferation and differentiation of the myoblasts demonstrated in mice and man, it is assumed that they could be present in equine muscles and their expression profile may be related to the muscle status. Several miRNA candidates (miRNA-1, 23, 30, 133, 181, 188, 195, 206, 339, 375) were significantly detected in the normal and pathological muscles and some other miRNAs in blood samples collected in PSSM cases (Barrey et al. 2010). This first study on muscular miRNAs profiles in equine myopathies indicated that it is possible to discriminate pathological from control horses according to their miRNA profile. The RER miRNA profile was more specific and contrasted than the PSSM miRNA profile.

Conclusion: genetic and genomics perspective in equine exercise

  1. Top of page
  2. Summary
  3. Introduction
  4. Genetic component of the performance traits: how to measure the heritability of the exercise variables and performance traits?
  5. New applications in equine genomics available after the recent genome publication
  6. Conclusion: genetic and genomics perspective in equine exercise
  7. Acknowledgements
  8. Conflicts of interest
  9. Manufacturers’ addresses
  10. References

With the great development of the genomic technologies many new applications will soon be available for the horse industry: candidate genes responsible for diseases and performance, genotyping, diagnostic tools and treatments. The first genotype test for racing distance ability is now available for flat racing early evaluation. The diagnostic of PSSM myopathy by genotyping is routinely applied. Within 5 years, other genotyping methods will be available for early performance evaluation and genetic diseases diagnostic and risk evaluation like in osteochondrosis. Perhaps new genomic treatments will be designed to treat some myopathies and other metabolic diseases as are now applied in man. The drawback of the biotechnologies’ availability will be illicit use for doping using muscular transgenesis for example. Hopefully, research projects are already going on to detect this new type of genomic doping both in man and horses.

References

  1. Top of page
  2. Summary
  3. Introduction
  4. Genetic component of the performance traits: how to measure the heritability of the exercise variables and performance traits?
  5. New applications in equine genomics available after the recent genome publication
  6. Conclusion: genetic and genomics perspective in equine exercise
  7. Acknowledgements
  8. Conflicts of interest
  9. Manufacturers’ addresses
  10. References
  • Barrey, E. and Galloux, P. (1997) Analysis of the equine jumping technique by accelerometry. Equine vet. J., Suppl. 23, 45-49.
  • Barrey, E., Valette, J.P., Jouglin, M., Blouin, C. and Langlois, B. (1999a) Heritability of percentage of fast myosin heavy chains in skeletal muscles and relationship with performance. Equine vet. J., Suppl. 30, 289-292.
  • Barrey, E., Courouce, A., Langlois, B., Blouin, C. and Auvinet, B. (1999b) Genetic component of exercise test parameters in French Trotters: first estimations. In: Conference on Equine Sports Medicine and Science, Ed: A. Lindner, Cordoba. pp 219-224.
  • Barrey, E., Evans, S.E., Evans, D.L., Curtis, R.A., Quinton, R. and Rose, R.J. (2001) Locomotion evaluation for racing in Thoroughbreds. Equine vet. J., Suppl. 33, 99-103.
  • Barrey, E., Desliens, F., Blouin, C. and Langlois, B. (2002a) Heritabilities of gait characteristics: application for breeding in dressage. In: Conference on Equine Sports Medicine and Science 2002, The Elite Dressage and Three-Day-Event Horse, Ed: A. Lindner. pp 91-95.
  • Barrey, E., Desliens, F., Blouin, C. and Langlois, B. (2002b) Mesures du modèle, des allures et du saut des étalons nationaux par la méthode Equimétrix. 27èmes Journées de la Recherche équine, Les Haras Nationaux, Paris. pp 157-176.
  • Barrey, E., Desliens, F., Poirel, D., Biau, S., Lemaire, S., Rivero, J.L. and Langlois, B. (2002c) Early evaluation of dressage ability in different breeds. Equine vet. J., Suppl. 34, 319-324.
  • Barrey, E. (2004) Influence of genetics in equine exercise physiology. 9th Annual Congress, European College of Sport Science, Clermont-Ferrand, Abstracts book. p 119.
  • Barrey, E., Mucher, E., Robert, C., Amiot, F. and Gidrol, X. (2006) Gene expression profiling in blood cells of endurance horses completing competition or disqualified due to metabolic disorder. Equine vet. J., Suppl. 36, 43-49.
  • Barrey, E., Mucher, E., Jeansoule, N., Larcher, T., Guigand, L., Herszberg, B., Chaffaux, S., Guérin, G., Mata, X., Benech, P., Canale, M., Alibert, O., Maltere, P. and Gidrol, X. (2009) Gene expression profiling in equine polysaccharide storage myopathy revealed inflammation, glycogenesis inhibition, hypoxia and mitochondrial dysfunctions. BMC vet. Res. 7, 29.
  • Barrey, E., Bonnamy, B., Barrey, E., Barrey, E.J., Mata, X., Chaffaux, S. and Guérin, G. (2010) Muscular microRNA expressions in healthy and myopathic horses suffering from polysaccharide storage myopathy or recurrent exertional rhabdomyolysis. Equine vet. J., Suppl. In Press.
  • Bray, M.S., Hagberg, J.M., Pérusse, L., Rankinen, T., Roth, S.M., Wolfarth, B. and Bouchard, C. (2009) The human gene map for performance and health-related fitness phenotypes: the 2006-2007 update. Med. Sci. Sports Exerc. 41, 35-73.
  • Calin, G.A. and Croce, C.M. (2006) MicroRNA signatures in human cancers. Nat. Rev. Cancer 6, 857-866.
  • Caetano, A.R., Shiue, Y.L., Lyons, L.A., O’Brien, S.J., Laughlin, T.F., Bowling, A.T. and Murray, J.D. (1999) A comparative gene map of the horse (Equus caballus). Genome Res. 9, 1239-1249.
  • Chowdhary, B.P., Raudsepp, T., Kata, S.R., Goh, G., Millon, L.V., Allan, V., Piumi, F., Guérin, G., Swinburne, J., Binns, M., Lear, T.L., Mickelson, J., Murray, J., Antczak, D.F., Womack, J.E. and Skow, L.C. (2003) The first-generation whole-genome radiation hybrid map in the horse identifies conserved segments in human and mouse genomes. Genome Res. 13, 742-751. Erratum: Genome Res. 13, 1258.
  • Dierks, C., Löhring, K., Lampe, V., Wittwer, C., Drögemüller, C. and Distl, O. (2007) Genome-wide search for markers associated with osteochondrosis in Hanoverian Warmblood horses. Mamm. Genome 18, 739-747.
  • Firshman, A.M., Valberg, S.J., Bender, J.B., Annandale, E.J. and Hayden, D.W. (2006) Comparison of histopathologic criteria and skeletal muscle fixation techniques for the diagnosis of polysaccharide storage myopathy in horses. Vet. Pathol. 43, 257-269.
  • Gu, J., Orr, N., Park, S.D., Katz, L.M., Sulimova, G., Sulimova, G., MacHugh, D.E. and Hill, E.W. (2009) A genome scan for positive selection in Thoroughbred horses. PLoS ONE 4, e5767.
  • Herszberg, B., McCue, M.E., Larcher, T., Mata, X., Vaiman, A., Chaffaux, S., Chérel, Y., Valberg, S.J., Mickelson, J.R. and Guérin, G. (2009) A GYS1 gene mutation is highly associated with polysaccharide storage myopathy in Cob Normand draught horses. Anim. Genet. 40, 94-96.
  • Hill, E.W., Gu, J., Eivers, S.S., Fonseca, R.G., McGivney, B.A., Govindarajan, P., Orr, N., Katz, L.M. and MacHugh, D.A. (2010) Sequence polymorphism in MSTN predicts sprinting ability and racing stamina in Thoroughbred horses. PLoS ONE 5, e8645.
  • Hintz, R.L. (1980) Genetics of performance in the horse. J. anim. Sci. 51, 582-594.
  • Jayr, L. (2009) Predisposition à la rhabdomyolyse d’effort chez le Trotteur Français: Analyse Génomique. Thèse vétérinaire ENV Alfort. Presented 24th September, pp 84.
  • Lampe, V., Dierks, C. and Distl, O. (2009a) Refinement of a quantitative trait locus on equine chromosome 5 responsible for fetlock osteochondrosis in Hanoverian warmblood horses. Anim. Genet. 40, 553-555.
  • Lampe, V., Dierks, C., Komm, K. and Distl, O. (2009b) Identification of a new quantitative trait locus on equine chromosome 18 responsible for osteochondrosis in Hanoverian warmblood horses. J. anim. Sci. 87, 3477-3481.
  • Langlois, B. (1980) Heritability of racing ability in Thoroughbreds - a review. Livestock Prod. Sci. 7, 583-594.
  • Leleu, C., Cotrel, C. and Barrey, E. (2003) Relationships between locomotor test and racing performances in Standardbreds. In: 54th Annual Meeting of the European Association for Animal Production, Horse Production, Rome. Abstract H2.9.
  • McCue, M.E. and Valberg, S.J. (2007) Estimated prevalence of polysaccharide storage myopathy among overtly healthy Quarter Horses in the United States. J. Am. vet. med. Ass. 231, 746-750.
  • McCue, M.E., Ribeiro, W.P. and Valberg, S.J. (2006) Prevalence of polysaccharide storage myopathy in horses with neuromuscular disorders. Equine vet. J., Suppl. 36, 340-344.
  • McCue, M.E., Valberg, S.J., Jackson, M., Borgia, L., Lucio, M. and Mickelson, J.R. (2009) Polysaccharide storage myopathy phenotype in quarter horse-related breeds is modified by the presence of an RYR1 mutation. Neuromuscul.. Disord. 19, 37-43.
  • McCue, M.E., Valberg, S.J., Miller, M.B., Wade, C., DiMauro, S., Akman, H.O. and Mickelson, J.R. (2008) Glycogen synthase (GYS1) mutation causes a novel skeletal muscle glycogenosis. Genomics 91, 458-466.
  • McGivney, B.A., Eivers, S.S., MacHugh, D.E., MacLeod, J.N., O’Gorman, G.M., Park, S.D., Katz, L.M. and Hill, E.W. (2009) Transcriptional adaptations following exercise in Thoroughbred horse skeletal muscle highlights molecular mechanisms that lead to muscle hypertrophy. BMC Genom. 30, 638.
  • McGowan, C.M., McGowan, T.W. and Patterson-Kane, J.C. (2009) Prevalence of equine polysaccharide storage myopathy and other myopathies in two equine populations in the United Kingdom. Vet. J. 180, 330-336.
  • Milenkovic, D., Oustry-Vaiman, A., Lear, T.L., Billault, A., Mariat, D., Piumi, F., Schibler, L., Cribiu, E. and Guérin, G. (2002) Cytogenetic localization of 136 genes in the horse: comparative mapping with the human genome. Mamm. Genome 13, 524-534.
  • Quiroz-Rothe, E., Novales, M., Aguilera-Tejero, E. and Rivero, J.L. (2002) Polysaccharide storage myopathy in the M. longissimus lumborum of showjumpers and dressage horses with back pain. Equine vet. J. 34, 171-176.
  • Ricard, A., Bruns, E. and Cunningham, E.P. (2000) Genetics of performance traits. In: Genetics of the horse, Eds: A.T.Bowling and A.Ruvinsky, CABI Publishing, New York. pp 411-438.
  • Rivero, J.L. and Barrey, E. (2001) Heritabilities and genetic and phenotypic parameters for gluteus medius muscle fibre type composition, fibre size and capillaries in purebred Spanish horses. Livestock Prod. Sci. 72, 233-241.
  • Saastamoinen, M.T. and Barrey, E. (2000) The genetics of the horse: 16 conformation and physiological traits: Their evaluation and heritability. In: The genetics of the horse, Eds: A.T.Bowling and A.Ruvinsky, CABI Publishing, New York. pp 441-472.
  • Valberg, S.J., Cardinet, G.H. 3rd, Carlson, G.P. and DiMaruro, S. (1992) Polysaccharide storage myopathy associated with recurrent exertional rhabdomyolysis in horses. Neuromusc. Disord. 2, 351-359.
  • Valentine, B.A. and Cooper, B.J. (2005) Incidence of polysaccharide storage myopathy:necropsy study of 225 horses. Vet. Pathol. 42, 823-837.
  • Wade, C.M., Giulotto, E., Sigurdsson, S., Zoli, M., Gnerre, S., Imsland, F., Lear, T.L., Adelson, D.L., Bailey, E., Bellone, R.R., Blöcker, H., Distl, O., Edgar, R.C., Garber, M., Leeb, T., Mauceli, E., MacLeod, J.N., Penedo, M.C., Raison, J.M., Sharpe, T., Vogel, J., Andersson, L., Antczak, D.F., Biagi, T., Binns, M.M., Chowdhary, B.P., Coleman, S.J., Della Valle, G., Fryc, S., Guérin, G., Hasegawa, T., Hill, E.W., Jurka, J., Kiialainen, A., Lindgren, G., Liu, J., Magnani, E., Mickelson, J.R., Murray, J., Nergadze, S.G., Onofrio, R., Pedroni, S., Piras, M.F., Raudsepp, T., Rocchi, M., Røed, K.H., Ryder, O.A., Searle, S., Skow, L., Swinburne, J.E., Syvänen, A.C., Tozaki, T., Valberg, S.J., Vaudin, M., White, J.R., Zody, M.C., Broad Institute Genome Sequencing Platform; Broad Institute Whole Genome Assembly Team, Lander, E.S. and Lindblad-Toh, K. (2009) Genome sequence, comparative analysis, and population genetics of the domestic horse. Science 326, 865-867.
  • Ward, T.L., Valberg, S.J., Adelson, D.L., Abbey, C.A., Binns, M.M. and Mickelson, J.R. (2004) Glycogen branching enzyme (GBE1) mutation causing equine glycogen storage disease IV. Mamm. Genome 15, 570-577.
  • Xu, X. and Arnason, U. (1994) The complete mitochondrial DNA sequence of the horse, Equus caballus: Extensive heteroplasmy of the control region. Gene 148, 357-362.
  • Yoon, S.S. (2006) Glycogen storage disease: Clinical, biochemichal and molecular heterogeneity. Semin. Pediatr. Neurol. 13, 115-120.