Whole genome sequence and analysis of the Marwari horse breed and its genetic origin

Unveiling the population genetic structure of Iranian horses breeds by whole-genome resequencing analysis

Preserving genetic diversity is pivotal for enhancing genetic improvement and facilitating adaptive responses to selection. This study focuses on identifying key genetic variants, including single nucleotide polymorphisms (SNPs), insertion/deletion polymorphisms (INDELs), and copy number variants (CNVs), while exploring the genomic evolutionary connectedness among seven Iranian horses representing five indigenous breeds: Caspian, Turkemen, DareShuri, Kurdish, and Asil. Using whole-genome resequencing, we generated 2.7 Gb of sequence data, with raw reads ranging from 1.2 Gb for Caspian horses to 0.38 Gb for Turkoman horses. Post-filtering, approximately 1.9 Gb of reads remained, with ~ 1.5 Gb successfully mapped to the horse reference genome (EquCab3.0), achieving mapping rates between 76.4% (Caspian) and 98.35% (Turkoman). We identified 2,909,816 SNPs in Caspian horses, constituting around 0.1% of the genome. Notably, 71% of these SNPs were situated in intergenic regions, while 8.5 and 6.8% were located upstream and downstream, respectively. A comparative analysis of SNPs between Iranian and non-Iranian horse breeds showed that Caspian horses had the lowest number of shared SNPs with Turkoman horses. Instead, they showed a closer genetic relationship with DareShuri, Quarter, Arabian, Standardbred, and Asil breeds. Hierarchical clustering highlighted Caspian horses as a distinct cluster, underscoring their distinctive genomic signature. Caspian horses exhibit a unique genetic profile marked by an enrichment of private mutations in neurological genes, influencing sensory perception and awareness. This distinct genetic makeup shapes mating preferences and signifies a separate evolutionary trajectory. Additionally, significant non-synonymous single nucleotide polymorphisms (nsSNPs) in reproductive genes offer intervention opportunities for managing Caspian horses. These findings reveal the population genetic structure of Iranian horse breeds, contributing to the advancement of knowledge in areas such as conservation, performance traits, climate adaptation, reproduction, and resistance to diseases in equine science.

Genome-Wide Single-Nucleotide Polymorphism-Based Genomic Diversity and Runs of Homozygosity for Selection Signatures in Equine Breeds

The horse, one of the most domesticated animals, has been used for several purposes, like transportation, hunting, in sport, or for agriculture-related works. Kathiawari, Marwari, Manipuri, Zanskari, Bhutia, Spiti, and Thoroughbred are the main breeds of horses, particularly due to their agroclimatic adaptation and role in any kind of strong physical activity, and these characteristics are majorly governed by genetic factors. The genetic diversity and phylogenetic relationship of these Indian equine breeds using microsatellite markers have been reported, but further studies exploring the SNP diversity and runs of homozygosity revealing the selection signature of breeds are still warranted. In our study, the identification of genes that play a vital role in muscle development is performed through SNP detection via the whole-genome sequencing approach. A total of 96 samples, categorized under seven breeds, and 620,721 SNPs were considered to ascertain the ROH patterns amongst all the seven breeds. Over 5444 ROH islands were mined, and the maximum number of ROHs was found to be present in Zanskari, while Thoroughbred was confined to the lowest number of ROHs. Gene enrichment of these ROH islands produced 6757 functional genes, with AGPAT1, CLEC4, and CFAP20 as important gene families. However, QTL annotation revealed that the maximum QTLs were associated with Wither's height trait ontology that falls under the growth trait in all seven breeds. An Equine SNP marker database (EqSNPDb) was developed to catalogue ROHs for all these equine breeds for the flexible and easy chromosome-wise retrieval of ROH along with the genotype details of all the SNPs. Such a study can reveal breed divergence in different climatic and ecological conditions.

The Characteristics, Distribution, Function, and Origin of Alternative Lateral Horse Gaits

This article traces the characteristics, origin, distribution, and function of alternative lateral horse gaits, i.e., intermediate speed lateral-sequence gaits. Such alternative lateral gaits (running walk, rack, broken pace, hard pace, and broken trot) are prized by equestrians today for their comfort and have been found in select horse breeds for hundreds of years and even exhibited in fossil equid trackways. After exploring the evolution and development of alternative lateral gaits via fossil equid trackways, human art, and historical writings, the functional and genetic factors that led to the genesis of these gaits are discussed. Such gaited breeds were particularly favored and spread by the Scythians, Celts, Turks, and Spaniards. Fast and low-swinging hard pacing gaits are common in several horse breeds of mountainous areas of East and North Asia; high-stepping rack and running walk gaits are often displayed in European and North and South American breeds; the broken pace is found in breeds of Central Asia, Southeast Asia, West Asia, Western North America, and Brazil in South America; and the broken trot occurs in breeds of North Asia, South Asia, the Southern United States, and Brazil in South America, inhabiting desert or marshy areas.

Whole-genome sequencing and genomic analysis of Norduz goat (Capra hircus)

Artificial and natural selective breeding of goats has resulted in many different goat breeds all around the world. Norduz goat is one of these breeds, and it is a local goat breed of Turkey. The goats are favorable due to pre-weaning viability and reproduction values compared to the regional breeds. Development in sequencing technologies has let to understand huge genomic structures and complex phenotypes. Until now, such a comprehensive study has not been carried out to understand the genomic structure of the Norduz goats, yet. In the study, the next-generation sequencing was carried out to understand the genomic structure of Norduz goat. Real-time PCR was used to evaluate prominent CNVs in the Norduz goat individuals. Whole genome of the goat was constructed with an average of 33.1X coverage level. In the stringent filtering condition, 9,757,980 SNPs, 1,536,715 InDels, and 290 CNVs were detected in the Norduz goat genome. Functional analysis of high-impact SNP variations showed that the classical complement activation biological process was affected significantly in the goat. CNVs in the goat genome were found in genes related to defense against viruses, immune response, and cell membrane transporters. It was shown that GBP2, GBP5, and mammalian ortholog GBP1, which are INF-stimulated GTPases, were found to be high copy numbers in the goats. To conclude, genetic variations mainly in immunological response processes suggest that Norduz goat is an immunologically improved goat breed and natural selection could take an important role in the genetical improvements of the goats.

Sequence Variant in the TRIM39-RPP21 Gene Readthrough is Shared Across a Cohort of Arabian Foals Diagnosed with Juvenile Idiopathic Epilepsy

Juvenile idiopathic epilepsy (JIE) is a self-limiting neurological disorder with a suspected genetic predisposition affecting young Arabian foals of the Egyptian lineage. The condition is characterized by tonic-clonic seizures with intermittent post-ictal blindness, in which most incidents are sporadic and unrecognized. This study aimed to identify genetic components shared across a local cohort of Arabian foals diagnosed with JIE via a combined whole genome and targeted resequencing approach: Initial whole genome comparisons between a small cohort of nine diagnosed foals (cases) and 27 controls from other horse breeds identified variants uniquely shared amongst the case cohort. Further validation via targeted resequencing of these variants, that pertain to non-intergenic regions, on additional eleven case individuals revealed a single 19bp deletion coupled with a triple-C insertion (Δ19InsCCC) within the TRIM39-RPP21 gene readthrough that was uniquely shared across all case individuals, and absent from three additional Arabian controls. Furthermore, we have confirmed recent findings refuting potential linkage between JIE and other inherited diseases in the Arabian lineage, and refuted the potential linkage between JIE and genes predisposing a similar disorder in human newborns. This is the first study to report a genetic variant to be shared in a sub-population cohort of Arabian foals diagnosed with JIE. Further evaluation of the sensitivity and specificity of the Δ19InsCCC allele within additional cohorts of the Arabian horse is warranted in order to validate its credibility as a marker for JIE, and to ascertain whether it has been introduced into other horse breeds by Arabian ancestry.

Phenotypic trend, breeding value and heritability of biometric traits in Marwari horses

Analysis of phenotypic trend and estimation of inbreeding coefficient, breeding value and heritability of biometric traits was carried out for a total of 226 Marwari horses. The pedigree construct divided the entire population of 226 horses into 6 tiers spanning over a period of 30 years. The inbreeding coefficient of the herd was estimated to be 0.0017. The average height at withers, body length, heart girth and body weight of Marwari horses was 150.15±0.04 cm, 151.44±0.06 cm; 170.02±0.19 cm and 371.34±0.52 kg, respectively with non-significant effect of sex, tier and interaction of sex and tier. The Best Linear Unbiased Prediction (BLUP) estimate of breeding value for the height at withers (150.45 cm), body length (151.97 cm), heart girth (169.73 cm) and body weight (366.3 kg) for Marwari horses was -0.059 cm, -0.079 cm, 0.096 cm and 3.526 kg, respectively. The effect of sex and interaction of sex and tiers was non-significant but that of tier on the estimated breeding value for body weight was significant indicating that body weight received favour in breeding programme. The heritability of height at withers, body length, heart girth and body weight has been estimated to be 0.396±0.586, 0.370±0.777, 0.507±1.95 and 0.597±0.612, respectively. Negligible inbreeding and constant phenotype over decades indicated that the Marwari herd has been bred to maintain enough genetic variation and hence it can be the most reliable source of the stallions and mares for propagation and conservation of this legendry breed of horse which is getting diluted and declining at a faster rate.

Genomic Copy Number Variation Study of Nine Macaca Species Provides New Insights into Their Genetic Divergence, Adaptation, and Biomedical Application

Copy number variation (CNV) can promote phenotypic diversification and adaptive evolution. However, the genomic architecture of CNVs among Macaca species remains scarcely reported, and the roles of CNVs in adaptation and evolution of macaques have not been well addressed. Here, we identified and characterized 1,479 genome-wide hetero-specific CNVs across nine Macaca species with bioinformatic methods, along with 26 CNV-dense regions and dozens of lineage-specific CNVs. The genes intersecting CNVs were overrepresented in nutritional metabolism, xenobiotics/drug metabolism, and immune-related pathways. Population-level transcriptome data showed that nearly 46% of CNV genes were differentially expressed across populations and also mainly consisted of metabolic and immune-related genes, which implied the role of CNVs in environmental adaptation of Macaca. Several CNVs overlapping drug metabolism genes were verified with genomic quantitative polymerase chain reaction, suggesting that these macaques may have different drug metabolism features. The CNV-dense regions, including 15 first reported here, represent unstable genomic segments in macaques where biological innovation may evolve. Twelve gains and 40 losses specific to the Barbary macaque contain genes with essential roles in energy homeostasis and immunity defense, inferring the genetic basis of its unique distribution in North Africa. Our study not only elucidated the genetic diversity across Macaca species from the perspective of structural variation but also provided suggestive evidence for the role of CNVs in adaptation and genome evolution. Additionally, our findings provide new insights into the application of diverse macaques to drug study.

Signatures of selection analysis using whole-genome sequence data reveals novel candidate genes for pony and light horse types

Natural selection and domestication have shaped modern horse populations, resulting in a vast range of phenotypically diverse breeds. Horse breeds are classified into three types (pony, light, and draft) generally based on their body type. Understanding the genetic basis of horse type variation and selective pressures related to the evolutionary trend can be particularly important for current selection strategies. Whole-genome sequences were generated for 14 pony and 32 light horses to investigate the genetic signatures of selection of the horse type in pony and light horses. In the overlapping extremes of the fixation index and nucleotide diversity results, we found novel genomic signatures of selective sweeps near key genes previously implicated in body measurements including C4ORF33, CRB1, CPN1, FAM13A, and FGF12 that may influence variation in pony and light horse types. This study contributes to a better understanding of the genetic background of differences between pony and light horse types.

Transcriptome profiling of developing testes and spermatogenesis in the Mongolian horse

BACKGROUND

Horse testis development and spermatogenesis are complex physiological processes.

METHODS

To study these processes, three immature and three mature testes were collected from the Mongolian horse, and six libraries were established using high-throughput RNA sequencing technology (RNA-Seq) to screen for genes related to testis development and spermatogenesis.

RESULTS

A total of 16,237 upregulated genes and 8,641 downregulated genes were detected in the testis of the Mongolian horse. These genes play important roles in different developmental stages of spermatogenesis and testicular development. Five genes with alternative splicing events that may influence spermatogenesis and development of the testis were detected. GO (Gene ontology) and KEGG (Kyoto Encyclopedia of Genes and Genomes) pathway analyses were performed for functional annotation of the differentially expressed genes. Pathways related to "spermatogenesis," male gamete generation," "spermatid development" and "oocyte meiosis" were significantly involved in different stages of testis development and spermatogenesis.

CONCLUSION

Genes, pathways and alternative splicing events were identified with inferred functions in the process of spermatogenesis in the Mongolian horse. The identification of these differentially expressed genetic signatures improves our understanding of horse testis development and spermatogenesis.

The horse Y chromosome as an informative marker for tracing sire lines

Analysis of the Y chromosome is the best-established way to reconstruct paternal family history in humans. Here, we applied fine-scaled Y-chromosomal haplotyping in horses with biallelic markers and demonstrate the potential of our approach to address the ancestry of sire lines. We de novo assembled a draft reference of the male-specific region of the Y chromosome from Illumina short reads and then screened 5.8 million basepairs for variants in 130 specimens from intensively selected and rural breeds and nine Przewalski's horses. Among domestic horses we confirmed the predominance of a young'crown haplogroup' in Central European and North American breeds. Within the crown, we distinguished 58 haplotypes based on 211 variants, forming three major haplogroups. In addition to two previously characterised haplogroups, one observed in Arabian/Coldblooded and the other in Turkoman/Thoroughbred horses, we uncovered a third haplogroup containing Iberian lines and a North African Barb Horse. In a genealogical showcase, we distinguished the patrilines of the three English Thoroughbred founder stallions and resolved a historic controversy over the parentage of the horse 'Galopin', born in 1872. We observed two nearly instantaneous radiations in the history of Central and Northern European Y-chromosomal lineages that both occurred after domestication 5,500 years ago.

Whole genome sequencing analysis of horse populations inhabiting the Korean Peninsula and Przewalski's horse

BACKGROUND

The Jeju horse is an indigenous horse breed in Korea. However, there is a severe lack of genomic studies on Korean horse breeds.

OBJECTIVE

The objective of this study was to report genomic characteristics of domestic horse populations that inhabit South Korea (Jeju, Jeju crossbred, and Thoroughbred) and a wild horse breed (Przewalski's horse).

RESULTS

Using the equine reference genome assembly (EquCab 2.0), more than ~ 6.5 billion sequence reads were successfully mapped, which generated an average of 40.87-fold coverage throughout the genome. Using these data, we detected a total of 12.88 million SNPs, of which 73.7% were found to be novel. All the detected SNPs were deeply annotated to retrieve SNPs in gene regions using the RefSeq and Ensemble gene sets. Approximately 27% of the total SNPs were located within genes, whereas the remaining 73% were found in intergenic regions. Using 129,776 coding SNPs, we retrieved a total of 49,171 nonsynonymous SNPs in 12,351 genes. Furthermore, we identified a total of 10,770 deleterious nonsynonymous SNPs which are predicted to affect protein structure or function.

CONCLUSION

We showed numerous genomic variants from domestic and wild horse breeds. These results provide a valuable resource for further studies on functions of SNP-containing genes, and can aid in determining the molecular basis underlying variation in economically important traits of horses.

Comparative genome-wide survey of single nucleotide variation uncovers the genetic diversity and potential biomedical applications among six Macaca species

Macaca is of great importance in evolutionary and biomedical research. Aiming at elucidating genetic diversity patterns and potential biomedical applications of macaques, we characterized single nucleotide variations (SNVs) of six Macaca species based on the reference genome of Macaca mulatta. Using eight whole-genome sequences, representing the most comprehensive genomic SNV study in Macaca to date, we focused on discovery and comparison of nonsynonymous SNVs (nsSNVs) with bioinformatic tools. We observed that SNV distribution patterns were generally congruent among the eight individuals. Outlier tests of nsSNV distribution patterns detected 319 bins with significantly distinct genetic divergence among macaques, including differences in genes associated with taste transduction, homologous recombination, and fat and protein digestion. Genes with specific nsSNVs in various macaques were differentially enriched for metabolism pathways, such as glycolysis, protein digestion and absorption. On average, 24.95% and 11.67% specific nsSNVs were putatively deleterious according to PolyPhen2 and SIFT4G, respectively, among which the shared deleterious SNVs were located in 564–1981 genes. These genes displayed enrichment signals in the ‘obesity-related traits’ disease category for all surveyed macaques, confirming that they were suitable models for obesity related studies. Additional enriched disease categories were observed in some macaques, exhibiting promising potential for biomedical application. Positively selected genes identified by PAML in most tested Macaca species played roles in immune and nervous system, growth and development, and fat metabolism. We propose that metabolism and body size play important roles in the evolutionary adaptation of macaques.

Copy number variations in Friesian horses and genetic risk factors for insect bite hypersensitivity

Background

Many common and relevant diseases affecting equine welfare have yet to be tested regarding structural variants such as copy number variations (CNVs). CNVs make up a substantial proportion of total genetic variability in populations of many species, resulting in more sequence differences between individuals than SNPs. Associations between CNVs and disease phenotypes have been established in several species, but equine CNV studies have been limited. Aim of this study was to identify CNVs and to perform a genome-wide association (GWA) study in Friesian horses to identify genomic loci associated with insect bite hypersensitivity (IBH), a common seasonal allergic dermatitis observed in many horse breeds worldwide.

Results

Genotypes were obtained using the Axiom® Equine Genotyping Array containing 670,796 SNPs. After quality control of genotypes, 15,041 CNVs and 5350 CNV regions (CNVRs) were identified in 222 Friesian horses. Coverage of the total genome by CNVRs was 11.2% with 49.2% of CNVRs containing genes. 58.0% of CNVRs were novel (i.e. so far only identified in Friesian horses). A SNP- and CNV-based GWA analysis was performed, where about half of the horses were affected by IBH. The SNP-based analysis showed a highly significant association between the MHC region on ECA20 and IBH in Friesian horses. Associations between the MHC region on ECA20 and IBH were also detected based on the CNV-based analysis. However, CNVs associated with IBH in Friesian horses were not often in close proximity to SNPs identified to be associated with IBH.

Conclusions

CNVs were identified in a large sample of the Friesian horse population, thereby contributing to our knowledge on CNVs in horses and facilitating our understanding of the equine genome and its phenotypic expression. A clear association was identified between the MHC region on ECA20 and IBH in Friesian horses based on both SNP- and CNV-based GWA studies. These results imply that MHC contributes to IBH sensitivity in Friesian horses. Although subsequent analyses are needed for verification, nucleotide differences, as well as more complex structural variations like CNVs, seem to contribute to IBH sensitivity. IBH should be considered as a common disease with a complex genomic architecture.

Electronic supplementary material

The online version of this article (10.1186/s12863-018-0657-0) contains supplementary material, which is available to authorized users.

Transformation of animal genomics by next-generation sequencing technologies: a decade of challenges and their impact on genetic architecture

For more than a quarter of a century, sequencing technologies from Sanger's method to next-generation high-throughput techniques have provided fascinating opportunities in the life sciences. The continuing upward trajectory of sequencing technologies will improve livestock research and expedite the development of various new genomic and technological studies with farm animals. The use of high-throughput technologies in livestock research has increased interest in metagenomics, epigenetics, genome-wide association studies, and identification of single nucleotide polymorphisms and copy number variations. Such studies are beginning to provide revolutionary insights into biological and evolutionary processes. Farm animals, such as cattle, swine, and horses, have played a dual role as economically and agriculturally important animals as well as biomedical research models. The first part of this study explores the current state of sequencing methods, many of which are already used in animal genomic studies, and the second part summarizes the state of cattle, swine, horse, and chicken genome sequencing and illustrates its achievements during the last few years. Finally, we describe several high-throughput sequencing approaches for the improved detection of known, unknown, and emerging infectious agents, leading to better diagnosis of infectious diseases. The insights from viral metagenomics and the advancement of next-generation sequencing will strongly support specific and efficient vaccine development and provide strategies for controlling infectious disease transmission among animal populations and/or between animals and humans. However, prospective sequencing technologies will require further research and in-field testing before reaching the marketplace.

Ancient genomes revisit the ancestry of domestic and Przewalski’s horses

The Eneolithic Botai culture of the Central Asian steppes provides the earliest archaeological evidence for horse husbandry, ~5500 years ago, but the exact nature of early horse domestication remains controversial. We generated 42 ancient-horse genomes, including 20 from Botai. Compared to 46 published ancient- and modern-horse genomes, our data indicate that Przewalski’s horses are the feral descendants of horses herded at Botai and not truly wild horses. All domestic horses dated from ~4000 years ago to present only show ~2.7% of Botai-related ancestry. This indicates that a massive genomic turnover underpins the expansion of the horse stock that gave rise to modern domesticates, which coincides with large-scale human population expansions during the Early Bronze Age.

Highly Variable Genomic Landscape of Endogenous Retroviruses in the C57BL/6J Inbred Strain, Depending on Individual Mouse, Gender, Organ Type, and Organ Location

Transposable repetitive elements, named the "TREome," represent ~40% of the mouse genome. We postulate that the germ line genome undergoes temporal and spatial diversification into somatic genomes in conjunction with the TREome activity. C57BL/6J inbred mice were subjected to genomic landscape analyses using a TREome probe from murine leukemia virus-type endogenous retroviruses (MLV-ERVs). None shared the same MLV-ERV landscape within each comparison group: (1) sperm and 18 tissues from one mouse, (2) six brain compartments from two females, (3) spleen and thymus samples from four age groups, (4) three spatial tissue sets from two females, and (5) kidney and liver samples from three females and three males. Interestingly, males had more genomic MLV-ERV copies than females; moreover, only in the males, the kidneys had higher MLV-ERV copies than the livers. Perhaps, the mouse-, gender-, and tissue/cell-dependent MLV-ERV landscapes are linked to the individual-specific and dynamic phenotypes of the C57BL/6J inbred population.

Ancient genomic changes associated with domestication of the horse

The domestication of the horse was a seminal event in human cultural evolution. Libradoet al.obtained genome sequences from 14 horses from the Bronze and Iron Ages, about 2000 to 4000 years ago, soon after domestication. They identified variants determining coat color and genes selected during the domestication process. They could also see evidence of admixture with archaic horses and the demography of the domestication process, which included the accumulation of deleterious variants. The horse appears to have undergone a different type of domestication process than animals that were domesticated simply for food.

Science, this issue p.442

Identification of copy number variations in three Chinese horse breeds using 70K single nucleotide polymorphism BeadChip array

Copy number variation (CNV), an essential form of genetic variation, has been increasingly recognized as one promising genetic marker in the analysis of animal genomes. Here, we used the Equine 70K single nucleotide polymorphism genotyping array for the genome-wide detection of CNVs in 96 horses from three diverse Chinese breeds: Debao pony (DB), Mongolian horse (MG) and Yili horse (YL). A total of 287 CNVs were determined and merged into 122 CNV regions (CNVRs) ranging from 199 bp to 2344 kb in size and distributed in a heterogeneous manner on chromosomes. These CNVRs were integrated with seven existing reports to generate a composite genome-wide dataset of 1558 equine CNVRs, revealing 69 (56.6%) novel CNVRs. The majority (69.7%) of the 122 CNVRs overlapped with 438 genes, whereas 30.3% were located in intergenic regions. Most of these genes were associated with common CNVRs, which were shared by divergent horse breeds. As many as 60, 42 and 91 genes overlapping with the breed-specific ss were identified in DB, MG and YL respectively. Among these genes, FGF11, SPEM1, PPARG, CIDEB, HIVEP1 and GALR may have potential relevance to breed-specific traits. These findings provide valuable information for understanding the equine genome and facilitating association studies of economically important traits with equine CNVRs in the future.

InCoB2014: mining biological data from genomics for transforming industry and health

The 13th International Conference on Bioinformatics (InCoB2014) was held for the first time in Australia, at Sydney, July 31-2 August, 2014. InCoB is the annual scientific gathering of the Asia-Pacific Bioinformatics Network (APBioNet), hosted since 2002 in the Asia-Pacific region. Of 106 full papers submitted to the BMC track of InCoB2014, 50 (47.2%) were accepted in BMC Bioinformatics, BMC Genomics and BMC Systems Biology supplements, with three papers in a new BMC Medical Genomics supplement. While the majority of presenters and authors were from Asia and Australia, the increasing number of US and European conference attendees augurs well for the international flavour of InCoB. Next year's InCoB will be held jointly with the Genome Informatics Workshop (GIW), September 9-11, 2015 in Tokyo, Japan, with a view to integrate bioinformatics communities in the region.