The Belt mutation in pigs is an allele at the Dominant white (I/KIT) locus

Genetic and Phenotypic Characteristics of Belted Pig Breeds: A Review

Belted pig breeds have unique, distinguishing phenotypic characteristics. This review summarises the current knowledge on pig breeds displaying a belted coat pattern. Belts of different widths and positions around the animal's trunk characterise specific pig breeds from all around the world. All the breeds included in the present paper have been searched through the FAO domestic animal diversity information system (DAD-IS), Every country was checked to identify all breeds described as having black or red piebald coat pattern variations. Advances in genomic technologies have made it possible to identify the specific genes and genetic markers associated with the belted phenotype and explore the genetic relationships between different local breeds. Thus, the origin, history, and production traits of these breeds, together with all the genomic information related to the mechanism of skin pigmentation, are discussed. By increasing our understanding of these breeds, we can appreciate the richness of our biological and cultural heritage and work to preserve the biodiversity of the world's animals.

Copy Number Variation on ABCC2-DNMBP Loci Affects the Diversity and Composition of the Fecal Microbiota in Pigs

Genetic variation in the pig genome partially modulates the composition of porcine gut microbial communities. Previous studies have been focused on the association between single nucleotide polymorphisms (SNPs) and the gut microbiota, but little is known about the relationship between structural variants and fecal microbial traits. The main goal of this study was to explore the association between porcine genome copy number variants (CNVs) and the diversity and composition of pig fecal microbiota. For this purpose, we used whole-genome sequencing data to undertake a comprehensive identification of CNVs followed by a genome-wide association analysis between the estimated CNV status and the fecal bacterial diversity in a commercial Duroc pig population. A CNV predicted as gain (DUP) partially harboring ABCC2-DNMBP loci was associated with richness (P = 5.41 × 10-5, false discovery rate [FDR] = 0.022) and Shannon α-diversity (P = 1.42 × 10-4, FDR = 0.057). The in silico predicted gain of copies was validated by real-time quantitative PCR (qPCR), and its segregation, and positive association with the richness and Shannon α-diversity of the porcine fecal bacterial ecosystem was confirmed in an unrelated F1 (Duroc × Iberian) cross. Our results advise the relevance of considering the role of host-genome structural variants as potential modulators of microbial ecosystems and suggest the ABCC2-DNMBP CNV as a host-genetic factor for the modulation of the diversity and composition of the fecal microbiota in pigs. IMPORTANCE A better understanding of the environmental and host factors modulating gut microbiomes is a topic of greatest interest. Recent evidence suggests that genetic variation in the pig genome partially controls the composition of porcine gut microbiota. However, since previous studies have been focused on the association between single nucleotide polymorphisms and the fecal microbiota, little is known about the relationship between other sources of genetic variation, like the structural variants and microbial traits. Here, we identified, experimentally validated, and replicated in an independent population a positive link between the gain of copies of ABCC2-DNMBP loci and the diversity and composition of pig fecal microbiota. Our results advise the relevance of considering the role of host-genome structural variants as putative modulators of microbial ecosystems and open the possibility of implementing novel holobiont-based management strategies in breeding programs for the simultaneous improvement of microbial traits and host performance.

Impact of KIT Editing on Coat Pigmentation and Fresh Meat Color in Yorkshire Pigs

The white coat color of Yorkshire pigs is caused by the dominant white I allele, which has been associated with at least one copy of the 450-kb duplication encompassing the entire KIT gene and a splice mutation (G > A) at the first base of intron 17. The splice mutation in KIT has an adverse effect on pigmentation in mice. Therefore, removing the 450 kb duplications harboring the KIT copy with splice mutations is expected to affect Yorkshire pig pigmentation. In this study, we describe the use of a Yorkshire pig kidney cell strain with the I^?/I^Be-ed genotype, previously created by CRISPR-Cas9, as donor cells for somatic cell nuclear transfer to generate gene-edited Yorkshire pigs. The removal of the 450 kb duplications harboring the KIT copy with splice mutation did not alter the white coat color of Yorkshire pigs, which was confirmed by the absence of fully mature melanocytes and melanin accumulation in the hair follicles. Except for the improved transcription of tyrosinase, and slight increase in microphthalmia transcription factor and tyrosinase-related protein 1 protein expression, there was no significant impact of the removal of splice mutations on genes and signaling pathways (PI3K/AKT) involved in melanogenesis. However, the removal of the 450 kb duplications harboring the KIT copy with splice mutation substantially improved fresh meat color accompanied by significantly increased red blood cell number, which merits further investigation. Our study provides new insights into the role of structural mutations of the KIT gene in the formation of white coat color and erythropoiesis in Yorkshire pigs.

Roan coat color in livestock

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.

Genetic diversity and population structure of six autochthonous pig breeds from Croatia, Serbia, and Slovenia

BACKGROUND

The importance of local breeds as genetic reservoirs of valuable genetic variation is well established. Pig breeding in Central and South-Eastern Europe has a long tradition that led to the formation of several local pig breeds. In the present study, genetic diversity parameters were analysed in six autochthonous pig breeds from Slovenia, Croatia and Serbia (Banija spotted, Black Slavonian, Turopolje pig, Swallow-bellied Mangalitsa, Moravka and Krskopolje pig). Animals from each of these breeds were genotyped using microsatellites and single nucleotide polymorphisms (SNPs). The results obtained with these two marker systems and those based on pedigree data were compared. In addition, we estimated inbreeding levels based on the distribution of runs of homozygosity (ROH) and identified genomic regions under selection pressure using ROH islands and the integrated haplotype score (iHS).

RESULTS

The lowest heterozygosity values calculated from microsatellite and SNP data were observed in the Turopolje pig. The observed heterozygosity was higher than the expected heterozygosity in the Black Slavonian, Moravka and Turopolje pig. Both types of markers allowed us to distinguish clusters of individuals belonging to each breed. The analysis of admixture between breeds revealed potential gene flow between the Mangalitsa and Moravka, and between the Mangalitsa and Black Slavonian, but no introgression events were detected in the Banija spotted and Turopolje pig. The distribution of ROH across the genome was not uniform. Analysis of the ROH islands identified genomic regions with an extremely high frequency of shared ROH within the Swallow-bellied Mangalitsa, which harboured genes associated with cholesterol biosynthesis, fatty acid metabolism and daily weight gain. The iHS approach to detect signatures of selection revealed candidate regions containing genes with potential roles in reproduction traits and disease resistance.

CONCLUSIONS

Based on the estimation of population parameters obtained from three data sets, we showed the existence of relationships among the six pig breeds analysed here. Analysis of the distribution of ROH allowed us to estimate the level of inbreeding and the extent of homozygous regions in these breeds. The iHS analysis revealed genomic regions potentially associated with phenotypic traits and allowed the detection of genomic regions under selection pressure.

Whole-genome sequencing of European autochthonous and commercial pig breeds allows the detection of signatures of selection for adaptation of genetic resources to different breeding and production systems

Background

Natural and artificial directional selection in cosmopolitan and autochthonous pig breeds and wild boars have shaped their genomes and resulted in a reservoir of animal genetic diversity. Signatures of selection are the result of these selection events that have contributed to the adaptation of breeds to different environments and production systems. In this study, we analysed the genome variability of 19 European autochthonous pig breeds (Alentejana, Bísara, Majorcan Black, Basque, Gascon, Apulo-Calabrese, Casertana, Cinta Senese, Mora Romagnola, Nero Siciliano, Sarda, Krškopolje pig, Black Slavonian, Turopolje, Moravka, Swallow-Bellied Mangalitsa, Schwäbisch-Hällisches Schwein, Lithuanian indigenous wattle and Lithuanian White old type) from nine countries, three European commercial breeds (Italian Large White, Italian Landrace and Italian Duroc), and European wild boars, by mining whole-genome sequencing data obtained by using a DNA-pool sequencing approach. Signatures of selection were identified by using a single-breed approach with two statistics [within-breed pooled heterozygosity (H_P) and fixation index (F_ST)] and group-based F_ST approaches, which compare groups of breeds defined according to external traits and use/specialization/type.

Results

We detected more than 22 million single nucleotide polymorphisms (SNPs) across the 23 compared populations and identified 359 chromosome regions showing signatures of selection. These regions harbour genes that are already known or new genes that are under selection and relevant for the domestication process in this species, and that affect several morphological and physiological traits (e.g. coat colours and patterns, body size, number of vertebrae and teats, ear size and conformation, reproductive traits, growth and fat deposition traits). Wild boar related signatures of selection were detected across all the genome of several autochthonous breeds, which suggests that crossbreeding (accidental or deliberate) occurred with wild boars.

Conclusions

Our findings provide a catalogue of genetic variants of many European pig populations and identify genome regions that can explain, at least in part, the phenotypic diversity of these genetic resources.

Was the Cinta Senese Pig Already a Luxury Food in the Late Middle Ages? Ancient DNA and Archaeozoological Evidence from Central Italy

The Cinta senese is a pig breed, highly esteemed for its meat and derived products, characterized by a black coat with a typical white “belt” and documented by scant iconography, since the 13^th–14^th century in Italy. A piece of pottery showing a Cinta pig was found in the Graffignano castle (Northern Latium, Italy) dated 15th–16th centuries, spurring us to investigate the diet of the inhabitants. Ancient DNA analysis was carried out on 21 pig specimens on three nuclear SNPs: (1) g.43597545C>T, on the KIT gene, informative for the identification of the Cinta senese breed; (2) rs81460129, on an intergenic region in chr. 16, which discriminates between domestic pigs and wild boars, and; (3) a SNP on the ZFY/ZFX homologous genes, to determine the sex of the individuals. Our results indicate that the Cinta senese was present in Northern Latium in Late Medieval time, although it was not the only breed, and that pigs, including Cinta, interbred with wild boars, suggesting free-range breeding for all types of pigs. Moreover, the unexpected high proportion of young females may be considered as evidence for the wealth of the family inhabiting the castle.

Selection signatures in goats reveal copy number variants underlying breed-defining coat color phenotypes

Domestication and human selection have formed diverse goat breeds with characteristic phenotypes. This process correlated with the fixation of causative genetic variants controlling breed-specific traits within regions of reduced genetic diversity, so called selection signatures or selective sweeps. Using whole genome sequencing of DNA pools (pool-seq) from 20 genetically diverse modern goat breeds and bezoars, we identified 2,239 putative selection signatures. In two Pakistani goat breeds, Pak Angora and Barbari, we found selection signatures in a region harboring KIT, a gene involved in melanoblast development, migration, and survival. The search for candidate causative variants responsible for these selective sweeps revealed two different copy number variants (CNVs) downstream of KIT that were exclusively present in white Pak Angora and white-spotted Barbari goats. Several Swiss goat breeds selected for specific coat colors showed selection signatures at the ASIP locus encoding the agouti signaling protein. Analysis of these selective sweeps revealed four different CNVs associated with the white or tan (A^Wt), Swiss markings (A^sm), badgerface (A^b), and the newly proposed peacock (A^pc) allele. RNA-seq analyses on skin samples from goats with the different CNV alleles suggest that the identified structural variants lead to an altered expression of ASIP between eumelanistic and pheomelanistic body areas. Our study yields novel insights into the genetic control of pigmentation by identifying six functionally relevant CNVs. It illustrates how structural changes of the genome have contributed to phenotypic evolution in domestic goats.

Domestic animals have been selected for hundreds or sometimes even thousands of years for traits that were appreciated by their human owners. This process correlated with the fixation of causative genetic variants controlling breed-specific traits within regions of reduced genetic diversity, so called selection signatures or selective sweeps. We conducted a comprehensive screen for selection signatures in 20 phenotypically and genetically diverse modern goat breeds and identified a total of 2,239 putative selection signatures in our dataset. Follow-up experiments on selection signatures harboring known candidate genes for coat color revealed six different copy number variants (CNVs). Two of these CNVs were located in the 3’-flanking region of KIT and associated with a completely white coat color phenotype in Pak Angora goats and a white-spotted coat color phenotype in Barbari goats, respectively. The other four CNVs were located at the ASIP locus. They were associated with four different types of coat color patterning in seven Swiss goat breeds. Their functional effect is mediated by region-specific quantitative changes in ASIP mRNA expression. Our study illustrates how structural changes of the genome have contributed to phenotypic evolution in domestic goats.

The Genetic Basis of Piebald Coat Colour in Hucul Horses in the Context of White Markings and Crypto-Tobiano as a Breeding Problem in Poland

The aim of the study was to analyse the genetic basis of piebald coat colour in Hucul horses and to verify their coat colour in breeding records. Tests were performed with DNA purified from the whole blood samples of 242 Hucul horses with different coat colour patterns. DNA was analysed to identify an inversion in ECA3 (PCR). The results confirmed that the inversion on ECA3 is a direct factor determining piebald (tobiano) colour in the analysed Hucul horses. No inversion was observed in any of the solid coloured horses, but it was present in all the piebald ones. It was also identified in 18% (11 of 61) of the horses from the group of horses qualified in the passport as solid coloured with white markings. In fact, these horses had the tobiano gene that is phenotypically identifiable as crypto-tobiano, which may give the false impression of having white markings and lead to error when describing a horse. This is an important issue, in particular with regard to the breed standard, which eliminates Hucul horses with white markings from breeding.

Whole-Genome Resequencing Identifies KIT New Alleles That Affect Coat Color Phenotypes in Pigs

The Duroc × (Landrace × Large White) hybrid pig (DLY) is the most popular commercial pig used in the Chinese pig industry. DLY pigs are usually white but sometimes show colored phenotypes. Colored DLY pigs are not favored by slaughterhouses and retailers, thus causing certain economic losses to farmers in China. In this study, we first conducted a genome-wide association study and RNA sequencing to demonstrate that KIT variants are responsible for diversifying coat color phenotypes segregating in a DLY population. We then defined the precise sizes and locations of four duplications (DUP1-4), four candidate causative mutations at the KIT locus, in the pig reference genome using the whole-genome sequence data of representative colored individuals. The sequence data also enabled us to identify a list of new KIT alleles. By investigating the association between these new alleles and coat color phenotypes, we provide further evidence that DUP2 is another causative mutation for the solid white coat color in pigs. DUP1 (the KIT gene duplication), DUP2 and the splice mutation are all required for the manifestation of a solid white coat color. DUP4 had a more significant effect on the formation of the belt phenotype compared with DUP3. Given the necessity of DUP2 for the solid white coat color, we detected I^N/I^N homozygotes lacking DUP2 in Large White and Landrace pigs and found that French Landrace pigs had the highest frequency (8.98%) of I^N/I^N individuals. This study not only advances our understanding of the molecular mechanism of the color phenotype in pigs, but also establishes a simple and accurate method for the screening of KIT I^N/I^N homozygotes in Large White and Landrace that would cause colored DLY pigs.

Divergent Evolutional Mode and Purifying Selection of the KIT Gene in European and Asian Domestic Pig Breeds

The recent geographic expansion of wild boars and the even more recent development of numerous domestic pigs have spurred exploration on pig domestic origins. The porcine KIT gene has been showed to affect pleiotropic effects, blood parameters, and coat colour phenotypes, especially the white colour phenotype formation in European commercial breeds. Here, we described the use of SNPs to identify different selection patterns on the porcine KIT gene and the phylogenetic relationships of the inferred haplotypes. The phylogenetic tree revealed four clades in European and Asian wild and domestic pigs: two major clades with European and Asian origins and one minor clade with Iberian origins as well as the other minor clade in Asia, consistent with the major introgression of domestic Asian pigs in Europe around 18th -19th century. The domestication history of pigs, which occurred in the domestication centers (Europe and Asia), has also been demonstrated by mtDNA analysis. Furthermore, both Asian and European domestic pigs evolved under purifying selection. This study indicated that domestic pigs in Europe and Asia have different lineage origins but the porcine KIT gene was undergoing a purifying selection during their evolutional histories.

Remapping of the belted phenotype in cattle on BTA3 identifies a multiplication event as the candidate causal mutation

Background

It has been known for almost a century that the belted phenotype in cattle follows a pattern of dominant inheritance. In 2009, the approximate position of the belt locus in Brown Swiss cattle was mapped to a 922-kb interval on bovine chromosome 3 and, subsequently, assigned to a 336-kb haplotype block based on an animal set that included, Brown Swiss, Dutch Belted (Lakenvelder) and Belted Galloway individuals. A possible candidate gene in this region i.e. HES6 was investigated but the causal mutation remains unknown. Thus, to elucidate the causal mutation of this prominent coat color phenotype, we decided to remap the belted phenotype in an independent animal set of several European bovine breeds, i.e. Gurtenvieh (belted Brown Swiss), Dutch Belted and Belted Galloway and to systematically scan the candidate region. We also checked the presence of the detected causal mutation in the genome of belted individuals from a Siberian cattle breed.

Results

A combined linkage disequilibrium and linkage analysis based on 110 belted and non-belted animals identified a candidate interval of 2.5 Mb. Manual inspection of the haplotypes in this region identified four candidate haplotypes that consisted of five to eight consecutive SNPs. One of these haplotypes overlapped with the initial 922-kb interval, whereas two were positioned proximal and one was positioned distal to this region. Next-generation sequencing of one heterozygous and two homozygous belted animals identified only one private belted candidate allele, i.e. a multiplication event that is located between 118,608,000 and 118,614,000 bp. Targeted locus amplification and quantitative real-time PCR confirmed an increase in copy number of this region in the genomes of both European (Belted Galloway, Dutch Belted and Gurtenvieh) and Siberian (Yakutian cattle) breeds. Finally, using nanopore sequencing, the exact breakpoints were determined at 118,608,362 and 118,614,132 bp. The closest gene to the candidate causal mutation (16 kb distal) is TWIST2.

Conclusions

Based on our findings and those of a previously published study that identified the same multiplication event, a quadruplication on bovine chromosome 3 between positions 118,608,362 and 118,614,132 bp is the most likely candidate causal mutation for the belted phenotype in cattle.

Electronic supplementary material

The online version of this article (10.1186/s12711-018-0407-9) contains supplementary material, which is available to authorized users.

A structural variant in the 5'-flanking region of the TWIST2 gene affects melanocyte development in belted cattle

Belted cattle have a circular belt of unpigmented hair and skin around their midsection. The belt is inherited as a monogenic autosomal dominant trait. We mapped the causative variant to a 37 kb segment on bovine chromosome 3. Whole genome sequence data of 2 belted and 130 control cattle yielded only one private genetic variant in the critical interval in the two belted animals. The belt-associated variant was a copy number variant (CNV) involving the quadruplication of a 6 kb non-coding sequence located approximately 16 kb upstream of the TWIST2 gene. Increased copy numbers at this CNV were strongly associated with the belt phenotype in a cohort of 333 cases and 1322 controls. We hypothesized that the CNV causes aberrant expression of TWIST2 during neural crest development, which might negatively affect melanoblasts. Functional studies showed that ectopic expression of bovine TWIST2 in neural crest in transgenic zebrafish led to a decrease in melanocyte numbers. Our results thus implicate an unsuspected involvement of TWIST2 in regulating pigmentation and reveal a non-coding CNV underlying a captivating Mendelian character.

Piebald Camels

Animal breeds are the diverse outcome of the thousands-year-long process of livestock domestication. Many of these breeds are piebald, resulting from the artificial selection by pastoralists of animals bearing a genetic condition known as leucism, and selected for their productive, behavioural, or aesthetical traits. Piebald dromedary camels have not been studied or discussed before, and their same existence is often overlooked. Based on fieldwork in Western Sahara, direct observations across Northern and East Africa and the Middle East, and a literature review, we address the morphological and behavioural traits, geographical distribution, taxonomy, and material and cultural importance of piebald (painted) camels. They are a hundreds-year-old camel breed used for caravans, as mounts, and for aesthetical and cultural reasons across Sudan, Niger, Mali, Mauritania, Western Sahara, and Morocco. While they are increasingly bred out of a pastoral context for tourism and entertainment in the Canary Islands, mainland Europe, and the USA, in part of their original African range, piebald camels are under threat due to wars, droughts, and demise of pastoral livelihoods. More research is needed about these 'beautiful and dignified' animals.

Estimation of genome-wide and locus-specific breed composition in pigs

Advances in pig genomic technologies enable implementation of new methods to estimate breed composition, allowing innovative and efficient ways to evaluate and ensure breed and line background. Existing methods to test for homozygosity at key loci involve test mating the animal in question and observing phenotypic patterns among offspring, requiring extensive resources. In this study, whole-genome pig DNA microarray data from over 8,000 SNP was used to profile the composition of U.S. registered purebred pigs using a refined linear regression method that enhances the interpretation of coefficients. In a simulation analysis, a strong correlation between true and estimated breed composition was observed (R² = 0.94). Applying these methods to 930 Yorkshire animals registered with the National Swine Registry, 95% were estimated to have a “genome-wide” Yorkshire breed composition of at least 0.825 or 82.5%, with similar performance for evaluating datasets of registered Duroc (n = 88) Landrace (n = 129), and Hampshire (n = 17) breeds. We also developed new methods to evaluate locus-based breed probabilities. Such methods have been applied to multi-locus SNP genotypes flanking the KIT gene known to predominantly control coat color, thereby inferring the probability that an animal has haplotypes in the KIT region that are predominant in white breeds. These methods have been adopted by the National Swine Registry as a means to identify purebred Yorkshire animals.

Domestic animals as models for biomedical research

Domestic animals are unique models for biomedical research due to their long history (thousands of years) of strong phenotypic selection. This process has enriched for novel mutations that have contributed to phenotype evolution in domestic animals. The characterization of such mutations provides insights in gene function and biological mechanisms. This review summarizes genetic dissection of about 50 genetic variants affecting pigmentation, behaviour, metabolic regulation, and the pattern of locomotion. The variants are controlled by mutations in about 30 different genes, and for 10 of these our group was the first to report an association between the gene and a phenotype. Almost half of the reported mutations occur in non-coding sequences, suggesting that this is the most common type of polymorphism underlying phenotypic variation since this is a biased list where the proportion of coding mutations are inflated as they are easier to find. The review documents that structural changes (duplications, deletions, and inversions) have contributed significantly to the evolution of phenotypic diversity in domestic animals. Finally, we describe five examples of evolution of alleles, which means that alleles have evolved by the accumulation of several consecutive mutations affecting the function of the same gene.

Platinum coat color in red fox (Vulpes vulpes) is caused by a mutation in an autosomal copy of KIT

The red fox (Vulpes vulpes) demonstrates a variety of coat colors including platinum, a common phenotype maintained in farm-bred fox populations. Foxes heterozygous for the platinum allele have a light silver coat and extensive white spotting, whereas homozygosity is embryonic lethal. Two KIT transcripts were identified in skin cDNA from platinum foxes. The long transcript was identical to the KIT transcript of silver foxes, whereas the short transcript, which lacks exon 17, was specific to platinum. The KIT gene has several copies in the fox genome: an autosomal copy on chromosome 2 and additional copies on the B chromosomes. To identify the platinum-specific KIT sequence, the genomes of one platinum and one silver fox were sequenced. A single nucleotide polymorphism (SNP) was identified at the first nucleotide of KIT intron 17 in the platinum fox. In platinum foxes, the A allele of the SNP disrupts the donor splice site and causes exon 17, which is part of a segment that encodes a conserved tyrosine kinase domain, to be skipped. Complete cosegregation of the A allele with the platinum phenotype was confirmed by linkage mapping (LOD 25.59). All genotyped farm-bred platinum foxes from Russia and the US were heterozygous for the SNP (A/G), whereas foxes with different coat colors were homozygous for the G allele. Identification of the platinum mutation suggests that other fox white-spotting phenotypes, which are allelic to platinum, would also be caused by mutations in the KIT gene.

Analysis of genome-wide copy number variations in Chinese indigenous and western pig breeds by 60 K SNP genotyping arrays

Copy number variations (CNVs) represent a substantial source of structural variants in mammals and contribute to both normal phenotypic variability and disease susceptibility. Although low-resolution CNV maps are produced in many domestic animals, and several reports have been published about the CNVs of porcine genome, the differences between Chinese and western pigs still remain to be elucidated. In this study, we used Porcine SNP60 BeadChip and PennCNV algorithm to perform a genome-wide CNV detection in 302 individuals from six Chinese indigenous breeds (Tongcheng, Laiwu, Luchuan, Bama, Wuzhishan and Ningxiang pigs), three western breeds (Yorkshire, Landrace and Duroc) and one hybrid (Tongcheng×Duroc). A total of 348 CNV Regions (CNVRs) across genome were identified, covering 150.49 Mb of the pig genome or 6.14% of the autosomal genome sequence. In these CNVRs, 213 CNVRs were found to exist only in the six Chinese indigenous breeds, and 60 CNVRs only in the three western breeds. The characters of CNVs in four Chinese normal size breeds (Luchuan, Tongcheng and Laiwu pigs) and two minipig breeds (Bama and Wuzhishan pigs) were also analyzed in this study. Functional annotation suggested that these CNVRs possess a great variety of molecular function and may play important roles in phenotypic and production traits between Chinese and western breeds. Our results are important complementary to the CNV map in pig genome, which provide new information about the diversity of Chinese and western pig breeds, and facilitate further research on porcine genome CNVs.

Genome-wide analysis reveals artificial selection on coat colour and reproductive traits in Chinese domestic pigs

Pigs from Asia and Europe were independently domesticated from c. 9000 years ago. During this period, strong artificial selection has led to dramatic phenotypic changes in domestic pigs. However, the genetic basis underlying these morphological and behavioural adaptations is relatively unknown, particularly for indigenous Chinese pigs. Here, we performed a genome-wide analysis to screen 196 regions with selective sweep signals in Tongcheng pigs, which are a typical indigenous Chinese breed. Genes located in these regions have been found to be involved in lipid metabolism, melanocyte differentiation, neural development and other biological processes, which coincide with the evolutionary phenotypic changes in this breed. A synonymous substitution, c.669T>C, in ESR1, which colocalizes with a major quantitative trait locus for litter size, shows extreme differences in allele frequency between Tongcheng pigs and wild boars. Notably, the variant C allele in this locus exhibits high allele frequency in most Chinese populations, suggesting a consequence of positive selection. Five genes (PRM1, PRM2, TNP2, GPR149 and JMJD1C) related to reproductive traits were found to have high haplotype similarity in Chinese breeds. Two selected genes, MITF and EDNRB, are implied to shape the two-end black colour trait in Tongcheng pig. Subsequent SNP microarray studies of five Chinese white-spotted breeds displayed a concordant signature at both loci, suggesting that these two genes are responsible for colour variations in Chinese breeds. Utilizing massively parallel sequencing, we characterized the candidate sites that adapt to artificial and environmental selections during the Chinese pig domestication. This study provides fundamental proof for further research on the evolutionary adaptation of Chinese pigs.

Endogenous retrovirus insertion in the KIT oncogene determines white and white spotting in domestic cats

The Dominant White locus (W) in the domestic cat demonstrates pleiotropic effects exhibiting complete penetrance for absence of coat pigmentation and incomplete penetrance for deafness and iris hypopigmentation. We performed linkage analysis using a pedigree segregating White to identify KIT (Chr. B1) as the feline W locus. Segregation and sequence analysis of the KIT gene in two pedigrees (P1 and P2) revealed the remarkable retrotransposition and evolution of a feline endogenous retrovirus (FERV1) as responsible for two distinct phenotypes of the W locus, Dominant White, and white spotting. A full-length (7125 bp) FERV1 element is associated with white spotting, whereas a FERV1 long terminal repeat (LTR) is associated with all Dominant White individuals. For purposes of statistical analysis, the alternatives of wild-type sequence, FERV1 element, and LTR-only define a triallelic marker. Taking into account pedigree relationships, deafness is genetically linked and associated with this marker; estimated P values for association are in the range of 0.007 to 0.10. The retrotransposition interrupts a DNAase I hypersensitive site in KIT intron 1 that is highly conserved across mammals and was previously demonstrated to regulate temporal and tissue-specific expression of KIT in murine hematopoietic and melanocytic cells. A large-population genetic survey of cats (n = 270), representing 30 cat breeds, supports our findings and demonstrates statistical significance of the FERV1 LTR and full-length element with Dominant White/blue iris (P < 0.0001) and white spotting (P < 0.0001), respectively.

Genome-wide association study identifies quantitative trait loci affecting hematological traits in an F2 intercross between Landrace and Korean native pigs

Changes affecting the status of health and robustness can bring about physiological alterations including hematological parameters in swine. To identify quantitative trait loci (QTL) associated with eight hematological traits (one leukocyte trait, six erythrocyte traits and one platelet trait), we conducted a genome-wide association study using the PorcineSNP60K BeadChip in a resource population derived from an intercross between Landrace and Korean native pigs. A total of 36 740 SNPs from 816 F2 progeny were analyzed for each blood-related trait after filtering for quality control. Data were analyzed by the genome-wide rapid association using mixed model and regression (GRAMMAR) approach. A total of 257 significant SNPs (P < 1.36 × 10(-6) ) on SSC3, 6, 8, 13 and 17 were identified for blood-related traits in this study. Interestingly, the genomic region between 17.9 and 130 Mb on SSC8 was found to be significantly associated with red blood cell, mean corpuscular volume and mean corpuscular hemoglobin. Our results include the identification of five significant SNPs within five candidate genes (KIT, IL15, TXK, ARAP2 and ERG) for hematopoiesis. Further validation of these identified SNPs could give valuable information for understanding the variation of hematological traits in pigs.

Accumulating mutations in series of haplotypes at the KIT and MITF loci are major determinants of white markings in Franches-Montagnes horses

Coat color and pattern variations in domestic animals are frequently inherited as simple monogenic traits, but a number are known to have a complex genetic basis. While the analysis of complex trait data remains a challenge in all species, we can use the reduced haplotypic diversity in domestic animal populations to gain insight into the genomic interactions underlying complex phenotypes. White face and leg markings are examples of complex traits in horses where little is known of the underlying genetics. In this study, Franches-Montagnes (FM) horses were scored for the occurrence of white facial and leg markings using a standardized scoring system. A genome-wide association study (GWAS) was performed for several white patterning traits in 1,077 FM horses. Seven quantitative trait loci (QTL) affecting the white marking score with p-values p≤10(-4) were identified. Three loci, MC1R and the known white spotting genes, KIT and MITF, were identified as the major loci underlying the extent of white patterning in this breed. Together, the seven loci explain 54% of the genetic variance in total white marking score, while MITF and KIT alone account for 26%. Although MITF and KIT are the major loci controlling white patterning, their influence varies according to the basic coat color of the horse and the specific body location of the white patterning. Fine mapping across the MITF and KIT loci was used to characterize haplotypes present. Phylogenetic relationships among haplotypes were calculated to assess their selective and evolutionary influences on the extent of white patterning. This novel approach shows that KIT and MITF act in an additive manner and that accumulating mutations at these loci progressively increase the extent of white markings.

Signatures of diversifying selection in European pig breeds

Following domestication, livestock breeds have experienced intense selection pressures for the development of desirable traits. This has resulted in a large diversity of breeds that display variation in many phenotypic traits, such as coat colour, muscle composition, early maturity, growth rate, body size, reproduction, and behaviour. To better understand the relationship between genomic composition and phenotypic diversity arising from breed development, the genomes of 13 traditional and commercial European pig breeds were scanned for signatures of diversifying selection using the Porcine60K SNP chip, applying a between-population (differentiation) approach. Signatures of diversifying selection between breeds were found in genomic regions associated with traits related to breed standard criteria, such as coat colour and ear morphology. Amino acid differences in the EDNRB gene appear to be associated with one of these signatures, and variation in the KITLG gene may be associated with another. Other selection signals were found in genomic regions including QTLs and genes associated with production traits such as reproduction, growth, and fat deposition. Some selection signatures were associated with regions showing evidence of introgression from Asian breeds. When the European breeds were compared with wild boar, genomic regions with high levels of differentiation harboured genes related to bone formation, growth, and fat deposition.

The domestic pig, an important source of protein worldwide, was domesticated from the ancestral wild boar in multiple locations throughout the world. In Europe, local types were developed following domestication, but phenotypically distinct breeds only arose in the eighteenth century with the advent of systematic breeding. Recently developed molecular tools for pigs (as well as other livestock species) now allow a genetic characterisation of breed histories, including identification of regions of the genome that have been under selection in the establishment of breeds. We have applied these tools to identify genomic regions associated with breed development in a set of commercial and traditional pig breeds. We found strong evidence of genetic differentiation between breeds near genes associated with traits that are used to define breed standards, such as ear morphology and coat colour, as well as in regions of the genome that are associated with pork production traits. It is well documented that crosses with Asian pigs have been used to modify European breeds. We have found evidence of genetic influence from Asian pigs in European breeds, again in regions of the genome associated with breed standard characteristics, including ear shape and coat colour, as well as production traits.

Identification of genome-wide copy number variations among diverse pig breeds by array CGH

Background

Recent studies have shown that copy number variation (CNV) in mammalian genomes contributes to phenotypic diversity, including health and disease status. In domestic pigs, CNV has been catalogued by several reports, but the extent of CNV and the phenotypic effects are far from clear. The goal of this study was to identify CNV regions (CNVRs) in pigs based on array comparative genome hybridization (aCGH).

Results

Here a custom-made tiling oligo-nucleotide array was used with a median probe spacing of 2506 bp for screening 12 pigs including 3 Chinese native pigs (one Chinese Erhualian, one Tongcheng and one Yangxin pig), 5 European pigs (one Large White, one Pietrain, one White Duroc and two Landrace pigs), 2 synthetic pigs (Chinese new line DIV pigs) and 2 crossbred pigs (Landrace × DIV pigs) with a Duroc pig as the reference. Two hundred and fifty-nine CNVRs across chromosomes 1–18 and X were identified, with an average size of 65.07 kb and a median size of 98.74 kb, covering 16.85 Mb or 0.74% of the whole genome. Concerning copy number status, 93 (35.91%) CNVRs were called as gains, 140 (54.05%) were called as losses and the remaining 26 (10.04%) were called as both gains and losses. Of all detected CNVRs, 171 (66.02%) and 34 (13.13%) CNVRs directly overlapped with Sus scrofa duplicated sequences and pig QTLs, respectively. The CNVRs encompassed 372 full length Ensembl transcripts. Two CNVRs identified by aCGH were validated using real-time quantitative PCR (qPCR).

Conclusions

Using 720 K array CGH (aCGH) we described a map of porcine CNVs which facilitated the identification of structural variations for important phenotypes and the assessment of the genetic diversity of pigs.

Exclusion of candidate genes for coat colour phenotypes of the American mink (Neovison vison)

In a previous project, we screened the American mink Bacterial Artificial Chromosome library, CHORI-231, for genes potentially involved in various coat colour phenotypes in the American mink. Subsequently, we 454 sequenced the inserts containing these genes and developed microsatellite markers for each of these genes. Here, we describe a lack of association between three different 'roan-type' phenotypes represented by Cross, Stardust and Cinnamon in American mink and six different genes that we considered to be potentially linked to these phenotypes. Thus, c-KIT (HUGO-approved symbol KIT), ATOH-1 (HUGO-approved symbol ATOH1) and POMC were excluded as potential candidates for these three phenotypes. In addition, MITF and SLC24A5 were excluded for Cross and Cinnamon, and KITL (HUGO-approved symbol KITLG) for Cross and Stardust. Although most of these genes have been implicated as the cause of similar phenotypes in other mammals, including horses, pigs, cows, dogs, cats, mice and humans, they do not appear to be responsible for comparable phenotypes found in American mink.

Copy number variation in the genomes of domestic animals

Copy number variation (CNV) might be one of the main contributors to phenotypic diversity and evolutionary adaptation in animals and plants, employing a wide variety of mechanisms, such as gene dosage and transcript structure alterations, to modulate organismal plasticity. In the past 4 years, considerable advances have been made in the characterization of the genomic architecture of CNV in domestic species. First, low-resolution CNV maps were produced for cattle, goat, sheep, pig, dog, chicken, duck and turkey, showing that these structural polymorphisms comprise a significant part of these genomes. Furthermore, CNVs have been associated with several pigmentation (white coat in horse, pig and sheep) and morphological (late feathering and pea comb in chicken) traits, as well as with susceptibility to a wide array of diseases and developmental disorders, for example osteopetrosis, anhidrotic ectodermal dysplasia, copper toxicosis, intersexuality, cone degeneration, periodic fever and dermoid sinus, among others. In the future, development of high-resolution tools for CNV detection and typing combined with the implementation of databases integrating CNV, QTL and gene expression data will be essential to identify and measure the impact of this source of structural variation on the many phenotypes that are relevant to animal breeders and veterinary practitioners.

Colours of domestication

During the last decade, coat colouration in mammals has been investigated in numerous studies. Most of these studies addressing the genetics of coat colouration were on domesticated animals. In contrast to their wild ancestors, domesticated species are often characterized by a huge allelic variability of coat-colour-associated genes. This variability results from artificial selection accepting negative pleiotropic effects linked with certain coat-colour variants. Recent studies demonstrate that this selection for coat-colour phenotypes started at the beginning of domestication. Although to date more than 300 genetic loci and more than 150 identified coat-colour-associated genes have been discovered, which influence pigmentation in various ways, the genetic pathways influencing coat colouration are still only poorly described. On the one hand, similar coat colourations observed in different species can be the product of a few conserved genes. On the other hand, different genes can be responsible for highly similar coat colourations in different individuals of a species or in different species. Therefore, any phenotypic classification of coat colouration blurs underlying differences in the genetic basis of colour variants. In this review we focus on (i) the underlying causes that have resulted in the observed increase of colour variation in domesticated animals compared to their wild ancestors, and (ii) the current state of knowledge with regard to the molecular mechanisms of colouration, with a special emphasis on when and where the different coat-colour-associated genes act.

A 6-bp deletion in the TYRP1 gene causes the brown colouration phenotype in Chinese indigenous pigs

Brown coat colour has been described in Chinese-Tibetan, Kele, and Dahe pigs. Here, we report the identification of a causal mutation underlying the brown colouration. We performed a genome-wide association study (GWAS) on Tibetan and Kele pigs, and found that brown colours in Chinese breeds are controlled by a single locus on pig chromosome 1. By using a haplotype-sharing analysis, we refined the critical region to a 1.5-Mb interval that encompasses only one pigmentation gene: tyrosinase-related protein 1 (TYRP1). Mutation screens of sequence variants in the coding region of TYRP1 revealed a strong candidate causative mutation (c.1484_1489del). The protein-altering deletion showed complete association with the brown colouration across Chinese-Tibetan, Kele, and Dahe breeds by occurring exclusively in brown pigs (n=121) and lacking in all non-brown-coated pigs (n=745) from 27 different breeds. The findings provide the compelling evidence that brown colours in Chinese indigenous pigs are caused by the same ancestral mutation in TYRP1. To our knowledge, this study gives the first description of GWAS identifying causal mutation for a monogenic trait in the domestic pig.

Testes bioquímico (albumina e proteína de ligação da vitamina D) e molecular (gene KIT) para detecção de marcadores genéticos para pelagem tobiana em cavalos Pampa e Paint

Foram utilizados 159 cavalos Pampa, registrados na Associação Brasileira dos Criadores de Cavalo Pampa, e um grupo-controle, de 32 cavalos da raça Paint, ambos os grupos provenientes de plantéis de diferentes regiões brasileiras, com o objetivo de comparar os testes bioquímico e molecular para detecção de marcadores genéticos para pelagem tobiana em cavalos Pampa. Houve diferença significativa (P<0,001) entre os testes bioquímico e molecular, nos cavalos Pampa, mas o mesmo fato não ocorreu com os da raça Paint. Os resultados mostraram que o marcador molecular (KIT) foi mais eficiente na identificação dos prováveis cavalos homozigotos do que os marcadores bioquímicos albumina (Al) e proteína de ligação da vitamina D (Gc), em ambas as raças.

Genetic heterogeneity at the bovine KIT gene in cattle breeds carrying different putative alleles at the spotting locus

According to classical genetic studies, piebaldism in cattle is largely influenced by the allelic series at the spotting locus (S), which includes the S(H) (Hereford pattern), S(+) (non-spotted) and s (spotted) alleles. The S locus was mapped on bovine chromosome 6 in the region containing the KIT gene. We investigated the KIT gene, analysing its variability and haplotype distribution in cattle of three breeds (Angus, Hereford and Holstein) with different putative alleles (S(+), S(H) and s respectively) at the S locus. Resequencing of a whole of 0.485 Mb revealed 111 polymorphisms. The global nucleotide diversity was 0.087%. Tajima's D-values were negative for all breeds, indicating putative directional selection. Of the 28 inferred haplotypes, only five were observed in the Hereford breed, in which one was the most frequent. Coalescent simulation showed that it is highly unlikely (P < 10E-6) to obtain this low number of haplotypes conditionally on the observed number of segregating SNPs. Therefore, the neutral model could be rejected for the Hereford breed, suggesting that a selection sweep occurred at the KIT locus. Twelve haplotypes were inferred in Holstein and Angus. For these two breeds, the neutral model could not be rejected. High heterogeneity of the KIT gene was confirmed from a phylogenetic analysis. Our results suggest a role of the KIT gene in determining the S(H) allele(s) in the Hereford, but no evidence of selective sweep was obtained in Holstein, suggesting that complex mechanisms (or other genes) might be the cause of the spotted phenotype in this breed.

Seven novel KIT mutations in horses with white coat colour phenotypes

White coat colour in horses is inherited as a monogenic autosomal dominant trait showing a variable expression of coat depigmentation. Mutations in the KIT gene have previously been shown to cause white coat colour phenotypes in pigs, mice and humans. We recently also demonstrated that four independent mutations in the equine KIT gene are responsible for the dominant white coat colour phenotype in various horse breeds. We have now analysed additional horse families segregating for white coat colour phenotypes and report seven new KIT mutations in independent Thoroughbred, Icelandic Horse, German Holstein, Quarter Horse and South German Draft Horse families. In four of the seven families, only one single white horse, presumably representing the founder for each of the four respective mutations, was available for genotyping. The newly reported mutations comprise two frameshift mutations (c.1126_1129delGAAC; c.2193delG), two missense mutations (c.856G>A; c.1789G>A) and three splice site mutations (c.338-1G>C; c.2222-1G>A; c.2684+1G>A). White phenotypes in horses show a remarkable allelic heterogeneity. In fact, a higher number of alleles are molecularly characterized at the equine KIT gene than for any other known gene in livestock species.

Characterization of the porcine KIT ligand gene: expression analysis, genomic structure, polymorphism detection and association with coat colour traits

Kit ligand (KITLG) is the ligand for the type III receptor tyrosine kinase KIT. Studies of the KIT/KITLG pathway in a number of mammalian species have shown that it is important for the development of stem cell populations in haematopoietic tissues, germ cells in reproductive organs and the embryonic migrating melanoblasts that give rise to melanocytes. Consequently, mutations in the pathway may result in a range of defects including anaemia, sterility and de-pigmentation. The cDNA sequence of the porcine KITLG gene has been reported previously, and is an attractive candidate locus for moderating coat colour in pigs. In this paper we report the gene structure and physical mapping of the porcine gene. We also report the identification of polymorphisms in the gene, one of which was used to confirm linkage to chromosome 5. Preliminary RNA expression studies using a panel of tissues have shown that in addition to the known variant lacking exon 6, there is alternative splicing of exon 4. However, little evidence was found for the KITLG gene being linked to variation in colour in a Meishan x Large White cross.

An accurate method for quantifying and analyzing copy number variation in porcine KIT by an oligonucleotide ligation assay

BACKGROUND

Aside from single nucleotide polymorphisms, copy number variations (CNVs) are the most important factors in susceptibility to genetic disorders because they affect expression levels of genes. In previous studies, pyrosequencing, mini-sequencing, real-time PCR, invader assays and other techniques have been used to detect CNVs. However, the higher the copy number in a genome, the more difficult it is to resolve the copies, so a more accurate method for measuring CNVs and assigning genotype is needed.

RESULTS

PCR followed by a quantitative oligonucleotide ligation assay (qOLA) was developed for quantifying CNVs. The accuracy and precision of the assay were evaluated for porcine KIT, which was selected as a model locus. Overall, the root mean squares of bias and standard deviation of qOLA were 2.09 and 0.45, respectively. These values are less than half of those in the published pyrosequencing assay for analyzing CNV in porcine KIT. Using a combined method of qOLA and another pyrosequencing for quantitative analysis of KIT copies with spliced forms, we confirmed the segregation of KIT alleles in 145 F1 animals with pedigree information and verified the correct assignment of genotypes. In a diagnostic test on 100 randomly sampled commercial pigs, there was perfect agreement between the genotypes obtained by grouping observations on a scatter plot and by clustering using the nearest centroid sorting method implemented in PROC FASTCLUS of the SAS package. In a test on 159 Large White pigs, there were only two discrepancies between genotypes assigned by the two clustering methods (98.7% agreement), confirming that the quantitative ligation assay established here makes genotyping possible through the accurate measurement of high KIT copy numbers (>4 per diploid genome). Moreover, the assay is sensitive enough for use on DNA from hair follicles, indicating that DNA from various sources could be used.

CONCLUSION

We have established a high resolution quantification method using an oligonucleotide ligation assay to measure CNVs, and verified the reliability of genotype assignment for random animal samples using the nearest centroid sorting method. This new method will make it more practical to determine KIT CNV and to genotype the complicated Dominant White/KIT locus in pigs. This procedure could have wide applications for studying gene or segment CNVs in other species.

Influence of the dominant white/KIT genotypes on the reproductive organs of pigs

Based on earlier studies with mice and pigs, the possible pleiotropic effects of the individual porcine Dominant White/KIT genotypes on the size, histological parameters, and surface features of the ovaries; on the size, histological characteristics, and volume of the testes; and on the occurrence of abnormal epididymal sperm cells were studied in two F2 generations of an intercross between Hampshire boars and Hungarian Large White sows. The KIT genotypes were determined by a PCR-RFLP method. The ovarian diameters of gilts of various KIT genotypes did not differ significantly (P=0.292), and the II pigs had the smallest diameters. The proportion of the investigated follicular types among the different KIT genotypes did not differ significantly (P=0.329-0.919), and the highest numbers of degenerated and atretic follicles were found in the ovaries of II genotype pigs, which also exhibited the highest proportion of primary follicles. The testis volume in the II homozygote white genotype boars (249.5 cm(3)) was significantly (P<0.01) larger than in the Ii (205.4 cm(3)) and ii (197.5 cm(3)) boars. Bodyweight and age significantly (P<0.01) affected testicular volume. KIT genotypes had no profound effect on the proportion of the various epididymal sperm abnormalities, and ii type boars showed the highest (nonsignificant) numbers of primary abnormalities. The changes in abnormal sperm cell frequency were linear to the changes in bodyweight and testis volume. We were unable to demonstrate disadvantageous effects of the KIT genotypes on the investigated ovarian, testicular, and epididymal sperm characteristics. Therefore the reproductive traits of white colored pigs examined in this study are no worse than those of pigmented breeds.