Bayesian mixed model analysis uncovered 21 risk loci for chronic kidney disease in boxer dogs.

Chronic kidney disease (CKD) affects 10% of the human population, with only a small fraction genetically defined. CKD is also common in dogs and has been diagnosed in nearly all breeds, but its genetic basis remains unclear. Here, we performed a Bayesian mixed model genome-wide association analysis for canine CKD in a boxer population of 117 canine cases and 137 controls, and identified 21 genetic regions associated with the disease. At the top markers from each CKD region, the cases carried an average of 20.2 risk alleles, significantly higher than controls (15.6 risk alleles). An ANOVA test showed that the 21 CKD regions together explained 57% of CKD phenotypic variation in the population. Based on whole genome sequencing data of 20 boxers, we identified 5,206 variants in LD with the top 50 BayesR markers. Following comparative analysis with human regulatory data, 17 putative regulatory variants were identified and tested with electrophoretic mobility shift assays. In total four variants, three intronic variants from the MAGI2 and GALNT18 genes, and one variant in an intergenic region on chr28, showed alternative binding ability for the risk and protective alleles in kidney cell lines. Many genes from the 21 CKD regions, RELN, MAGI2, FGFR2 and others, have been implicated in human kidney development or disease. The results from this study provide new information that may enlighten the etiology of CKD in both dogs and humans.

Heterochiasmy and the establishment of gsdf as a novel sex determining gene in Atlantic halibut.

Atlantic Halibut (Hippoglossus hippoglossus) has a X/Y genetic sex determination system, but the sex determining factor is not known. We produced a high-quality genome assembly from a male and identified parts of chromosome 13 as the Y chromosome due to sequence divergence between sexes and segregation of sex genotypes in pedigrees. Linkage analysis revealed that all chromosomes exhibit heterochiasmy, i.e. male-only and female-only meiotic recombination regions (MRR/FRR). We show that FRR/MRR intervals differ in nucleotide diversity and repeat class content and that this is true also for other Pleuronectidae species. We further show that remnants of a Gypsy-like transposable element insertion on chr13 promotes early male specific expression of gonadal somatic cell derived factor (gsdf). Less than 4.5 MYA, this male-determining element evolved on an autosomal FRR segment featuring pre-existing male meiotic recombination barriers, thereby creating a Y chromosome. Our findings indicate that heterochiasmy may facilitate the evolution of genetic sex determination systems relying on linkage of sexually antagonistic loci to a sex-determining factor.

The ZBED6-IGF2 axis has a major effect on growth of skeletal muscle and internal organs in placental mammals.

A single nucleotide substitution in the third intron of insulin-like growth factor 2 (IGF2) is associated with increased muscle mass and reduced subcutaneous fat in domestic pigs. This mutation disrupts the binding of the ZBED6 transcription factor and leads to a threefold up-regulation of IGF2 expression in pig skeletal muscle. Here, we investigated the biological significance of ZBED6-IGF2 interaction in the growth of placental mammals using two mouse models, ZBED6 knock-out (Zbed6-/-) and Igf2 knock-in mice that carry the pig IGF2 mutation. These transgenic mice exhibit markedly higher serum IGF2 concentrations, higher growth rate, increased lean mass, and larger heart, kidney, and liver; no significant changes were observed for white adipose tissues. The changes in body and lean mass were most pronounced in female mice. The phenotypic changes were concomitant with a remarkable up-regulation of Igf2 expression in adult tissues. Transcriptome analysis of skeletal muscle identified differential expression of genes belonging to the extracellular region category. Expression analysis using fetal muscles indicated a minor role of ZBED6 in regulating Igf2 expression prenatally. Furthermore, transcriptome analysis of the adult skeletal muscle revealed that this elevated expression of Igf2 was derived from the P1 and P2 promoters. The results revealed very similar phenotypic effects in the Zbed6 knock-out mouse and in the Igf2 knock-in mouse, showing that the effect of ZBED6 on growth of muscle and internal organs is mediated through the binding site in the Igf2 gene. The results explain why this ZBED6 binding site is extremely well conserved among placental mammals.

The evolution of Sex-linked barring alleles in chickens involves both regulatory and coding changes in CDKN2A.

Sex-linked barring is a fascinating plumage pattern in chickens recently shown to be associated with two non-coding and two missense mutations affecting the ARF transcript at the CDKN2A tumor suppressor locus. It however remained a mystery whether all four mutations are indeed causative and how they contribute to the barring phenotype. Here, we show that Sex-linked barring is genetically heterogeneous, and that the mutations form three functionally different variant alleles. The B0 allele carries only the two non-coding changes and is associated with the most dilute barring pattern, whereas the B1 and B2 alleles carry both the two non-coding changes and one each of the two missense mutations causing the Sex-linked barring and Sex-linked dilution phenotypes, respectively. The data are consistent with evolution of alleles where the non-coding changes occurred first followed by the two missense mutations that resulted in a phenotype more appealing to humans. We show that one or both of the non-coding changes are cis-regulatory mutations causing a higher CDKN2A expression, whereas the missense mutations reduce the ability of ARF to interact with MDM2. Caspase assays for all genotypes revealed no apoptotic events and our results are consistent with a recent study indicating that the loss of melanocyte progenitors in Sex-linked barring in chicken is caused by premature differentiation and not apoptosis. Our results show that CDKN2A is a major locus driving the differentiation of avian melanocytes in a temporal and spatial manner.

Complex inheritance of melanoma and pigmentation of coat and skin in Grey horses.

The dominant phenotype of greying with age in horses, caused by a 4.6-kb duplication in intron 6 of STX17, is associated with a high incidence of melanoma and vitiligo-like skin depigmentation. However, the progressive greying and the incidence of melanoma, vitiligo-like depigmentation, and amount of speckling in these horses do not follow a simple inheritance pattern. To understand their inheritance, we analysed the melanoma grade, grey level, vitiligo grade, and speckling grade of 1,119 Grey horses (7,146 measurements) measured in six countries over a 9-year period. We estimated narrow sense heritability (h(2)), and we decomposed this parameter into polygenic heritability (h(2) (POLY)), heritability due to the Grey (STX17) mutation (h(2) (STX17)), and heritability due to agouti (ASIP) locus (h(2) (ASIP)). A high heritability was found for greying (h(2) = 0.79), vitiligo (h(2) = 0.63), and speckling (h(2) = 0.66), while a moderate heritability was estimated for melanoma (h(2) = 0.37). The additive component of ASIP was significantly different from zero only for melanoma (h(2) (ASIP) = 0.02). STX17 controlled large proportions of phenotypic variance (h(2) (STX17) = 0.18-0.55) and overall heritability (h(2) (STX17)/h(2) = 0.28-0.83) for all traits. Genetic correlations among traits were estimated as moderate to high, primarily due to the effects of the STX17 locus. Nevertheless, the correlation between progressive greying and vitiligo-like depigmentation remained large even after taking into account the effects of STX17. We presented a model where four traits with complex inheritance patterns are strongly influenced by a single mutation. This is in line with evidence of recent studies in domestic animals indicating that some complex traits are, in addition to the large number of genes with small additive effects, influenced by genes of moderate-to-large effect. Furthermore, we demonstrated that the STX17 mutation explains to a large extent the moderate to high genetic correlations among traits, providing an example of strong pleiotropic effects caused by a single gene.

Constitutive activation of the ERK pathway in melanoma and skin melanocytes in Grey horses.

BACKGROUND: Constitutive activation of the ERK pathway, occurring in the vast majority of melanocytic neoplasms, has a pivotal role in melanoma development. Different mechanisms underlie this activation in different tumour settings. The Grey phenotype in horses, caused by a 4.6 kb duplication in intron 6 of Syntaxin 17 (STX17), is associated with a very high incidence of cutaneous melanoma, but the molecular mechanism behind the melanomagenesis remains unknown. Here, we investigated the involvement of the ERK pathway in melanoma development in Grey horses. METHODS: Grey horse melanoma tumours, cell lines and normal skin melanocytes were analyzed with help of indirect immunofluorescence and immunoblotting for the expression of phospho-ERK1/2 in comparison to that in non-grey horse and human counterparts. The mutational status of BRAF, RAS, GNAQ, GNA11 and KIT genes in Grey horse melanomas was determined by direct sequencing. The effect of RAS, RAF and PI3K/AKT pathways on the activation of the ERK signaling in Grey horse melanoma cells was investigated with help of specific inhibitors and immunoblotting. Individual roles of RAF and RAS kinases on the ERK activation were examined using si-RNA based approach and immunoblotting. RESULTS: We found that the ERK pathway is constitutively activated in Grey horse melanoma tumours and cell lines in the absence of somatic activating mutations in BRAF, RAS, GNAQ, GNA11 and KIT genes or alterations in the expression of the main components of the pathway. The pathway is mitogenic and is mediated by BRAF, CRAF and KRAS kinases. Importantly, we found high activation of the ERK pathway also in epidermal melanocytes, suggesting a general predisposition to melanomagenesis in these horses. CONCLUSIONS: These findings demonstrate that the presence of the intronic 4.6 kb duplication in STX17 is strongly associated with constitutive activation of the ERK pathway in melanocytic cells in Grey horses in the absence of somatic mutations commonly linked to the activation of this pathway during melanomagenesis. These findings are consistent with the universal importance of the ERK pathway in melanomagenesis and may have valuable implications for human melanoma research.

Copy number expansion of the STX17 duplication in melanoma tissue from Grey horses.

BACKGROUND: Greying with age in horses is an autosomal dominant trait, associated with loss of hair pigmentation, melanoma and vitiligo-like depigmentation. We recently identified a 4.6 kb duplication in STX17 to be associated with the phenotype. The aims of this study were to investigate if the duplication in Grey horses shows copy number variation and to exclude that any other polymorphism is uniquely associated with the Grey mutation. RESULTS: We found little evidence for copy number expansion of the duplicated sequence in blood DNA from Grey horses. In contrast, clear evidence for copy number expansions was indicated in five out of eight tested melanoma tissues or melanoma cell lines. A tendency of a higher copy number in aggressive tumours was also found. Massively parallel resequencing of the ~350 kb Grey haplotype did not reveal any additional mutations perfectly associated with the phenotype, confirming the duplication as the true causative mutation. We identified three SNP alleles that were present in a subset of Grey haplotypes within the 350 kb region that shows complete linkage disequilibrium with the causative mutation. Thus, these three nucleotide substitutions must have occurred subsequent to the duplication, consistent with our interpretation that the Grey mutation arose more than 2,000 years before present. CONCLUSIONS: These results suggest that the mutation acts as a melanoma-driving regulatory element. The elucidation of the mechanistic features of the duplication will be of considerable interest for the characterization of these horse melanomas as well as for the field of human melanoma research.

Bayesian model and selection signature analyses reveal risk factors for canine atopic dermatitis.

Canine atopic dermatitis is an inflammatory skin disease with clinical similarities to human atopic dermatitis. Several dog breeds are at increased risk for developing this disease but previous genetic associations are poorly defined. To identify additional genetic risk factors for canine atopic dermatitis, we here apply a Bayesian mixture model adapted for mapping complex traits and a cross-population extended haplotype test to search for disease-associated loci and selective sweeps in four dog breeds at risk for atopic dermatitis. We define 15 associated loci and eight candidate regions under selection by comparing cases with controls. One associated locus is syntenic to the major genetic risk locus (Filaggrin locus) in human atopic dermatitis. One selection signal in common type Labrador retriever cases positions across the TBC1D1 gene (body weight) and one signal of selection in working type German shepherd controls overlaps the LRP1B gene (brain), near the KYNU gene (psoriasis). In conclusion, we identify candidate genes, including genes belonging to the same biological pathways across multiple loci, with potential relevance to the pathogenesis of canine atopic dermatitis. The results show genetic similarities between dog and human atopic dermatitis, and future across-species genetic comparisons are hereby further motivated.

A novel canine reference genome resolves genomic architecture and uncovers transcript complexity.

We present GSD_1.0, a high-quality domestic dog reference genome with chromosome length scaffolds and contiguity increased 55-fold over CanFam3.1. Annotation with generated and existing long and short read RNA-seq, miRNA-seq and ATAC-seq, revealed that 32.1% of lifted over CanFam3.1 gaps harboured previously hidden functional elements, including promoters, genes and miRNAs in GSD_1.0. A catalogue of canine "dark" regions was made to facilitate mapping rescue. Alignment in these regions is difficult, but we demonstrate that they harbour trait-associated variation. Key genomic regions were completed, including the Dog Leucocyte Antigen (DLA), T Cell Receptor (TCR) and 366 COSMIC cancer genes. 10x linked-read sequencing of 27 dogs (19 breeds) uncovered 22.1 million SNPs, indels and larger structural variants. Subsequent intersection with protein coding genes showed that 1.4% of these could directly influence gene products, and so provide a source of normal or aberrant phenotypic modifications.

Whole-genome sequencing of glioblastoma reveals enrichment of non-coding constraint mutations in known and novel genes.

BACKGROUND: Glioblastoma (GBM) has one of the worst 5-year survival rates of all cancers. While genomic studies of the disease have been performed, alterations in the non-coding regulatory regions of GBM have largely remained unexplored. We apply whole-genome sequencing (WGS) to identify non-coding mutations, with regulatory potential in GBM, under the hypothesis that regions of evolutionary constraint are likely to be functional, and somatic mutations are likely more damaging than in unconstrained regions. RESULTS: We validate our GBM cohort, finding similar copy number aberrations and mutated genes based on coding mutations as previous studies. Performing analysis on non-coding constraint mutations and their position relative to nearby genes, we find a significant enrichment of non-coding constraint mutations in the neighborhood of 78 genes that have previously been implicated in GBM. Among them, SEMA3C and DYNC1I1 show the highest frequencies of alterations, with multiple mutations overlapping transcription factor binding sites. We find that a non-coding constraint mutation in the SEMA3C promoter reduces the DNA binding capacity of the region. We also identify 1776 other genes enriched for non-coding constraint mutations with likely regulatory potential, providing additional candidate GBM genes. The mutations in the top four genes, DLX5, DLX6, FOXA1, and ISL1, are distributed over promoters, UTRs, and multiple transcription factor binding sites. CONCLUSIONS: These results suggest that non-coding constraint mutations could play an essential role in GBM, underscoring the need to connect non-coding genomic variation to biological function and disease pathology.

Regulatory mutations in TBX3 disrupt asymmetric hair pigmentation that underlies Dun camouflage color in horses.

Dun is a wild-type coat color in horses characterized by pigment dilution with a striking pattern of dark areas termed primitive markings. Here we show that pigment dilution in Dun horses is due to radially asymmetric deposition of pigment in the growing hair caused by localized expression of the T-box 3 (TBX3) transcription factor in hair follicles, which in turn determines the distribution of hair follicle melanocytes. Most domestic horses are non-dun, a more intensely pigmented phenotype caused by regulatory mutations impairing TBX3 expression in the hair follicle, resulting in a more circumferential distribution of melanocytes and pigment granules in individual hairs. We identified two different alleles (non-dun1 and non-dun2) causing non-dun color. non-dun2 is a recently derived allele, whereas the Dun and non-dun1 alleles are found in ancient horse DNA, demonstrating that this polymorphism predates horse domestication. These findings uncover a new developmental role for T-box genes and new aspects of hair follicle biology and pigmentation.

ZBED6 modulates the transcription of myogenic genes in mouse myoblast cells.

ZBED6 is a recently discovered transcription factor, unique to placental mammals, that has evolved from a domesticated DNA transposon. It acts as a repressor at the IGF2 locus. Here we show that ZBED6 acts as a transcriptional modulator in mouse myoblast cells, where more than 700 genes were differentially expressed after Zbed6-silencing. The most significantly enriched GO term was muscle protein and contractile fiber, which was consistent with increased myotube formation. Twenty small nucleolar RNAs all showed increased expression after Zbed6-silencing. The co-localization of histone marks and ZBED6 binding sites and the effect of Zbed6-silencing on distribution of histone marks was evaluated by ChIP-seq analysis. There was a strong association between ZBED6 binding sites and the H3K4me3, H3K4me2 and H3K27ac modifications, which are usually found at active promoters, but no association with the repressive mark H3K27me3. Zbed6-silencing led to increased enrichment of active marks at myogenic genes, in agreement with the RNA-seq findings. We propose that ZBED6 preferentially binds to active promoters and modulates transcriptional activity without recruiting repressive histone modifications.

Establishment and characterization of a primary and a metastatic melanoma cell line from Grey horses.

The Grey horse phenotype, caused by a 4.6 kb duplication in Syntaxin 17, is strongly associated with high incidence of melanoma. In contrast to most human melanomas with an early onset of metastasis, the Grey horse melanomas have an extended period of benign growth, after which 50% or more eventually undergo progression and may metastasize. In efforts to define changes occurring during Grey horse melanoma progression, we established an in vitro model comprised of two cell lines, HoMel-L1 and HoMel-A1, representing a primary and a metastatic stage of the melanoma, respectively. The cell lines were examined for their growth and morphological characteristics, in vitro and in vivo oncogenic potential, chromosome numbers, and expression of melanocytic antigens and tumor suppressors. Both cell lines exhibited malignant characteristics; however, the metastatic HoMel-A1 showed a more aggressive phenotype characterized by higher proliferation rates, invasiveness, and a stronger tumorigenic potential both in vitro and in vivo. HoMel-A1 displayed a near-haploid karyotype, whereas HoMel-L1 was near-diploid. The cell lines expressed melanocytic lineage markers such as TYR, TRP1, MITF, PMEL, ASIP, MC1R, POMC, and KIT. The tumor suppressor p53 was strongly expressed in both cell lines, while the tumor suppressors p16 and PTEN were absent in HoMel-A1, potentially implicating significance of these pathways in the melanoma progression. This in vitro model system will not only aid in understanding of the Grey horse melanoma pathogenesis, but also in unraveling the steps during melanoma progression in general as well as being an invaluable tool for development of new therapeutic strategies.

A simple repeat polymorphism in the MITF-M promoter is a key regulator of white spotting in dogs.

The white spotting locus (S) in dogs is colocalized with the MITF (microphtalmia-associated transcription factor) gene. The phenotypic effects of the four S alleles range from solid colour (S) to extreme white spotting (s(w)). We have investigated four candidate mutations associated with the s(w) allele, a SINE insertion, a SNP at a conserved site and a simple repeat polymorphism all associated with the MITF-M promoter as well as a 12 base pair deletion in exon 1B. The variants associated with white spotting at all four loci were also found among wolves and we conclude that none of these could be a sole causal mutation, at least not for extreme white spotting. We propose that the three canine white spotting alleles are not caused by three independent mutations but represent haplotype effects due to different combinations of causal polymorphisms. The simple repeat polymorphism showed extensive diversity both in dogs and wolves, and allele-sharing was common between wolves and white spotted dogs but was non-existent between solid and spotted dogs as well as between wolves and solid dogs. This finding was unexpected as Solid is assumed to be the wild-type allele. The data indicate that the simple repeat polymorphism has been a target for selection during dog domestication and breed formation. We also evaluated the significance of the three MITF-M associated polymorphisms with a Luciferase assay, and found conclusive evidence that the simple repeat polymorphism affects promoter activity. Three alleles associated with white spotting gave consistently lower promoter activity compared with the allele associated with solid colour. We propose that the simple repeat polymorphism affects cooperativity between transcription factors binding on either flanking sides of the repeat. Thus, both genetic and functional evidence show that the simple repeat polymorphism is a key regulator of white spotting in dogs.

Sequence based analysis of U-2973, a cell line established from a double-hit B-cell lymphoma with concurrent MYC and BCL2 rearrangements.

BACKGROUND: Double-hit lymphoma is a complex and highly aggressive sub-type of B-cell lymphoma, which has recently been classified and is an area of active research interest due to the poor prognosis for patients with this disease. It is characterized by the presence of both an activating MYC chromosomal translocation and a simultaneous additional oncogenic translocation, often of the BCL2 gene. Recently, a cell line was established from a patient with this complex lymphoma and analyzed using conventional tools revealing it contains both MYC and BCL2 translocation events. FINDINGS: In this work, we reanalyzed the genome of the cell line using next generation whole genome sequencing technology in order to catalogue translocations, insertions and deletions which may contribute to the pathology of this lymphoma type. CONCLUSIONS: We describe the cell line in much greater detail, and pinpoint the exact locations of the chromosomal breakpoints. We also find several rearrangements within cancer-associated genes, which were not found using conventional tools, suggesting that high throughput sequencing may reveal novel targets for therapy, which could be used concurrently with existing treatments.

Identification of a melanocyte-specific, microphthalmia-associated transcription factor-dependent regulatory element in the intronic duplication causing hair greying and melanoma in horses.

Greying with age in horses is an autosomal dominant trait, characterized by hair greying, high incidence of melanoma and vitiligo-like depigmentation. Previous studies have revealed that the causative mutation for this phenotype is a 4.6-kb intronic duplication in STX17 (Syntaxin 17). By using reporter constructs in transgenic zebrafish, we show that a construct containing two copies of the duplicated sequence acts as a strong enhancer in neural crest cells and has subsequent melanophore-specific activity during zebrafish embryonic development whereas a single copy of the duplicated sequence acts as a weak enhancer, consistent with the phenotypic manifestation of the mutation in horses. We further used luciferase assays to investigate regulatory regions in the duplication, to reveal tissue-specific activities of these elements. One region upregulated the reporter gene expression in a melanocyte-specific manner and contained two microphthalmia-associated transcription factor (MITF) binding sites, essential for the activity. Microphthalmia-associated transcription factor regulates melanocyte development, and these binding sites are outstanding candidates for mediating the melanocyte-specific activity of the element. These results provide strong support for the causative nature of the duplication and constitute an explanation for the melanocyte-specific effects of the Grey allele.

ZBED6: The birth of a new transcription factor in the common ancestor of placental mammals.

A DNA transposon integrated into -the genome of a primitive mammal some 200 million years ago and, millions of years later, it evolved an essential function in the common ancestor of all placental mammals. This protein, now named ZBED6, was recently discovered because a mutation disrupting one of its binding sites, in an intron of the IGF2 gene, makes pigs grow more muscle. These findings have revealed a new mechanism for regulating muscle growth as well as a novel transcription factor that appears to be of major importance for transcriptional regulation in placental mammals.

Sex-linked barring in chickens is controlled by the CDKN2A /B tumour suppressor locus.

Sex-linked barring, a common plumage colour found in chickens, is characterized by black and white barred feathers. Previous studies have indicated that the white bands are caused by an absence of melanocytes in the feather follicle during the growth of this region. Here, we show that Sex-linked barring is controlled by the CDKN2A/B locus, which encodes the INK4b and ARF transcripts. We identified two non-coding mutations in CDKN2A that showed near complete association with the phenotype. In addition, two missense mutations were identified at highly conserved sites, V9D and R10C, and every bird tested with a confirmed Sex-linked barring phenotype carried one of these missense mutations. Further work is required to determine if one of these or a combined effect of two or more CDKN2A mutations is causing Sex-linked barring. This novel finding provides the first evidence that the tumour suppressor locus CDKN2A/B can affect pigmentation phenotypes and sheds new light on the functional significance of this gene.

A cis-acting regulatory mutation causes premature hair graying and susceptibility to melanoma in the horse.

In horses, graying with age is an autosomal dominant trait associated with a high incidence of melanoma and vitiligo-like depigmentation. Here we show that the Gray phenotype is caused by a 4.6-kb duplication in intron 6 of STX17 (syntaxin-17) that constitutes a cis-acting regulatory mutation. Both STX17 and the neighboring NR4A3 gene are overexpressed in melanomas from Gray horses. Gray horses carrying a loss-of-function mutation in ASIP (agouti signaling protein) had a higher incidence of melanoma, implying that increased melanocortin-1 receptor signaling promotes melanoma development in Gray horses. The Gray horse provides a notable example of how humans have cherry-picked mutations with favorable phenotypic effects in domestic animals.