Canine Genomics and Genetics: Running with the Pack

The domestication of the dog from its wolf ancestors is perhaps the most complex genetic experiment in history, and certainly the most extensive. Beginning with the wolf, man has created dog breeds that are hunters or herders, big or small, lean or squat, and independent or loyal. Most breeds were established in the 1800s by dog fanciers, using a small number of founders that featured traits of particular interest. Popular sire effects, population bottlenecks, and strict breeding programs designed to expand populations with desirable traits led to the development of what are now closed breeding populations, with limited phenotypic and genetic heterogeneity, but which are ideal for genetic dissection of complex traits. In this review, we first discuss the advances in mapping and sequencing that accelerated the field in recent years. We then highlight findings of interest related to disease gene mapping and population structure. Finally, we summarize novel results on the genetics of morphologic variation

Leading the way: finding genes for neurologic disease in dogs using genome-wide mRNA sequencing

Because of dogs' unique population structure, human-like disease biology, and advantageous genomic features, the canine system has risen dramatically in popularity as a tool for discovering disease alleles that have been difficult to find by studying human families or populations. To date, disease studies in dogs have primarily employed either linkage analysis, leveraging the typically large family size, or genome-wide association, which requires only modest-sized case and control groups in dogs. Both have been successful but, like most techniques, each requires a specific combination of time and money, and there are inherent problems associated with each. Here we review the first report of mRNA-Seq in the dog, a study that provides insights into the potential value of applying high-throughput sequencing to the study of genetic diseases in dogs. Forman and colleagues apply high-throughput sequencing to a single case of canine neonatal cerebellar cortical degeneration. This implementation of whole genome mRNA sequencing, the first reported in dog, is additionally unusual due to the analysis: the data was used not to examine transcript levels or annotate genes, but as a form of target capture that revealed the sequence of transcripts of genes associated with ataxia in humans. This approach entails risks. It would fail if, for example, the relevant transcripts were not sufficiently expressed for genotyping or were not associated with ataxia in humans. But here it pays off handsomely, identifying a single frameshift mutation that segregates with the disease. This work sets the stage for similar studies that take advantage of recent advances in genomics while exploiting the historical background of dog breeds to identify disease-causing mutations

The IGF1 small dog haplotype is derived from Middle Eastern gray wolves

Abstract Background A selective sweep containing the insulin-like growth factor 1 (IGF1) gene is associated with size variation in domestic dogs. Intron 2 of IGF1 contains a SINE element and single nucleotide polymorphism (SNP) found in all small dog breeds that is almost entirely absent from large breeds. In this study, we surveyed a large sample of grey wolf populations to better understand the ancestral pattern of variation at IGF1 with a particular focus on the distribution of the small dog haplotype and its relationship to the origin of the dog. Results We present DNA sequence data that confirms the absence of the derived small SNP allele in the intron 2 region of IGF1 in a large sample of grey wolves and further establishes the absence of a small dog associated SINE element in all wild canids and most large dog breeds. Grey wolf haplotypes from the Middle East have higher nucleotide diversity suggesting an origin there. Additionally, PCA and phylogenetic analyses suggests a closer kinship of the small domestic dog IGF1 haplotype with those from Middle Eastern grey wolves. Conclusions The absence of both the SINE element and SNP allele in grey wolves suggests that the mutation for small body size post-dates the domestication of dogs. However, because all small dogs possess these diagnostic mutations, the mutations likely arose early in the history of domestic dogs. Our results show that the small dog haplotype is closely related to those in Middle Eastern wolves and is consistent with an ancient origin of the small dog haplotype there. Thus, in concordance with past archeological studies, our molecular analysis is consistent with the early evolution of small size in dogs from the Middle East. See associated opinion by Driscoll and Macdonald: http://jbiol.com/content/9/2/1

Population-based study of the association of variants in mismatch repair genes with prostate cancer risk and outcomes.

BACKGROUND: Mismatch repair (MMR) gene activity may be associated with prostate cancer risk and outcomes. This study evaluated whether single nucleotide polymorphisms (SNP) in key MMR genes are related to prostate cancer outcomes. METHODS: Data from two population-based case-control studies of prostate cancer among Caucasian and African-American men residing in King County, Washington were combined for this analysis. Cases (n = 1,458) were diagnosed with prostate cancer in 1993 to 1996 or 2002 to 2005 and were identified through the Seattle-Puget Sound Surveillance Epidemiology and End Results cancer registry. Controls (n = 1,351) were age-matched to cases and were identified through random digit dialing. Logistic regression was used to assess the relationship between haplotype-tagging SNPs and prostate cancer risk and disease aggressiveness. Cox proportional hazards regression was used to assess the relationship between SNPs and prostate cancer recurrence and prostate cancer-specific death. RESULTS: Nineteen SNPs were evaluated in the key MMR genes: five in MLH1, 10 in MSH2, and 4 in PMS2. Among Caucasian men, one SNP in MLH1 (rs9852810) was associated with overall prostate cancer risk [odds ratio, 1.21; 95% confidence interval (95% CI), 1.02, 1.44; P = 0.03], more aggressive prostate cancer (odds ratio, 1.49; 95% CI, 1.15, 1.91; P < 0.01), and prostate cancer recurrence (hazard ratio, 1.83; 95% CI, 1.18, 2.86; P < 0.01), but not prostate cancer-specific mortality. A nonsynonymous coding SNP in MLH1, rs1799977 (I219V), was also found to be associated with more aggressive disease. These results did not remain significant after adjusting for multiple comparisons. CONCLUSION: This population-based case-control study provides evidence for a possible association with a gene variant in MLH1 in relation to the risk of overall prostate cancer, more aggressive disease, and prostate cancer recurrence, which warrants replication

Revisiting the missing protein-coding gene catalog of the domestic dog

<p>Abstract</p> <p>Background</p> <p>Among mammals for which there is a high sequence coverage, the whole genome assembly of the dog is unique in that it predicts a low number of protein-coding genes, ~19,000, compared to the over 20,000 reported for other mammalian species. Of particular interest are the more than 400 of genes annotated in primates and rodent genomes, but missing in dog.</p> <p>Results</p> <p>Using over 14,000 orthologous genes between human, chimpanzee, mouse rat and dog, we built multiple pairwise synteny maps to infer short orthologous intervals that were targeted for characterizing the canine missing genes. Based on gene prediction and a functionality test using the ratio of replacement to silent nucleotide substitution rates (<it>d</it>_N/<it>d</it>_S), we provide compelling structural and functional evidence for the identification of 232 new protein-coding genes in the canine genome and 69 gene losses, characterized as undetected gene or pseudogenes. Gene loss phyletic pattern analysis using ten species from chicken to human allowed us to characterize 28 canine-specific gene losses that have functional orthologs continuously from chicken or marsupials through human, and 10 genes that arose specifically in the evolutionary lineage leading to rodent and primates.</p> <p>Conclusion</p> <p>This study demonstrates the central role of comparative genomics for refining gene catalogs and exploring the evolutionary history of gene repertoires, particularly as applied for the characterization of species-specific gene gains and losses.</p

No evidence of BRCA2 mutations in chromosome 13q-linked Utah high-risk prostate cancer pedigrees

<p>Abstract</p> <p>Background</p> <p>Germline mutations in the <it>BRCA2 </it>gene have been suggested to account for about 5% of familial prostate cancer; mutations have been reported in 2% of early onset (i.e., ≤ 55 years) prostate cancer cases and a segregating founder mutation has been identified in Iceland (999del5). However, the role of <it>BRCA2 </it>in high risk prostate cancer pedigrees remains unclear.</p> <p>Findings</p> <p>We examined the potential involvement of <it>BRCA2 </it>in a set offive high-risk prostate cancer pedigrees in which all prostate cases were no more distantly related than two meioses from another case, and the resulting cluster contained at least four prostate cancer cases. We selected these five pedigrees from a larger dataset of 59 high-risk prostate cancer pedigrees analyzed in a genome-wide linkage screen. Selected pedigrees showed at least nominal linkage evidence to the <it>BRCA2 </it>region on chromosome 13q. We mutation screened all coding regions and intron/exon boundaries of the <it>BRCA2 </it>gene in the youngest prostate cancer case who carried the linked 13q segregating haplotype, as well as in a distantly related haplotype carrier to confirm any segregation. We observed no known protein truncating <it>BRCA2 </it>deleterious mutations. We identified one non-segregating <it>BRCA2 </it>variant of uncertain significance, one non-segregating intronic variant not previously reported, and a number of polymorphisms.</p> <p>Conclusion</p> <p>In this set of high-risk prostate cancer pedigrees with at least nominal linkage evidence to <it>BRCA2</it>, we saw no evidence for segregating <it>BRCA2 </it>protein truncating mutations in heritable prostate cancer.</p

Analysis of recently identified prostate cancer susceptibility loci in a population-based study: Associations with family history and clinical features.

Purpose: Two recent genome-wide association studies have highlighted several SNPs purported to be associated with prostate cancer risk. We investigated the significance of these SNPs in a population-based study of Caucasian men, testing the effects of each SNP in relation to family history of prostate cancer and clinicopathological features of disease. Experimental Design: We genotyped 13 SNPs in 1,308 prostate cancer patients and 1,267 unaffected controls frequency matched to cases by five-year age groups. The association of each SNP with disease risk and stratified by family history of prostate cancer and clinicopathological features of disease was calculated using logistic and polytomous regression. Results: These results confirm the importance of multiple previously reported SNPs in relation to prostate cancer susceptibility; 11 of the 13 SNPs were significantly associated with risk of developing prostate cancer. However, none of the SNP associations were of comparable magnitude to that associated with having a first-degree family history of the disease. Risk estimates associated with SNPs rs4242382 and rs2735839 varied by family history, while risk estimates for rs10993994 and rs5945619 varied by Gleason score. Conclusions: Our results confirm that several recently identified SNPs are associated with prostate cancer risk; however the variant alleles only confer a low to moderate relative risk of disease and are generally not associated with more aggressive disease features

Association of FGFR4 genetic polymorphisms with prostate cancer risk and prognosis

The fibroblast growth factor receptor 4 (FGFR4) is thought to be involved in many critical cellular processes and has been associated with prostate cancer risk. Four single nucleotide polymorphisms within or near FGFR4 were analysed in a population-based study of 1458 prostate cancer patients and 1352 age-matched controls. We found no evidence to suggest that any of the FGFR4 SNP genotypes were associated with prostate cancer risk or with disease aggressiveness, Gleason score or stage. A weak association was seen between rs351855 and prostate cancer-specific mortality. Subset analysis of cases that had undergone radical prostatectomy revealed an association between rs351855 and prostate cancer risk. While our results confirm an association between FGFR4 and prostate cancer risk in radical prostatectomy cases, they suggest that the role of FGFR4 in disease risk and outcomes at a population-based level appears to be minor

Canine Population Structure: Assessment and Impact of Intra-Breed Stratification on SNP-Based Association Studies

In canine genetics, the impact of population structure on whole genome association studies is typically addressed by sampling approximately equal numbers of cases and controls from dogs of a single breed, usually from the same country or geographic area. However one way to increase the power of genetic studies is to sample individuals of the same breed but from different geographic areas, with the expectation that independent meiotic events will have shortened the presumed ancestral haplotype around the mutation differently. Little is known, however, about genetic variation among dogs of the same breed collected from different geographic regions.In this report, we address the magnitude and impact of genetic diversity among common breeds sampled in the U.S. and Europe. The breeds selected, including the Rottweiler, Bernese mountain dog, flat-coated retriever, and golden retriever, share susceptibility to a class of soft tissue cancers typified by malignant histiocytosis in the Bernese mountain dog. We genotyped 722 SNPs at four unlinked loci (between 95 and 271 per locus) on canine chromosome 1 (CFA1). We showed that each population is characterized by distinct genetic diversity that can be correlated with breed history. When the breed studied has a reduced intra-breed diversity, the combination of dogs from international locations does not increase the rate of false positives and potentially increases the power of association studies. However, over-sampling cases from one geographic location is more likely to lead to false positive results in breeds with significant genetic diversity.These data provide new guidelines for association studies using purebred dogs that take into account population structure

Widespread, long-term admixture between grey wolves and domestic dogs across Eurasia and its implications for the conservation status of hybrids

Hybridisation between a domesticated species and its wild ancestor is an important conservation problem, especially if it results in the introgression of domestic gene variants into wild species. Nevertheless, the legal status of hybrids remains unregulated, partially because of the limited understanding of the hybridisation process and its consequences. The occurrence of hybridisation between grey wolves and domestic dogs is well-documented from different parts of the wolf geographic range, but little is known about the frequency of hybridisation events, their causes and the genetic impact on wolf populations. We analysed 61K SNPs spanning the canid genome in wolves from across Eurasia and North America and compared that data to similar data from dogs to identify signatures of admixture. The haplotype block analysis, which included 38 autosomes and the X chromosome, indicated the presence of individuals of mixed wolf-dog ancestry in most Eurasian wolf populations, but less admixture was present in North American populations. We found evidence for male-biased introgression of dog alleles into wolf populations, but also identified a first-generation hybrid resulting from mating between a female dog and a male wolf. We found small blocks of dog ancestry in the genomes of 62% Eurasian wolves studied and melanistic individuals with no signs of recent admixed ancestry, but with a dog-derived allele at a locus linked to melanism. Consequently, these results suggest that hybridisation has been occurring in different parts of Eurasia on multiple timescales and is not solely a recent phenomenon. Nevertheless, wolf populations have maintained genetic differentiation from dogs, suggesting that hybridisation at a low frequency does not diminish distinctiveness of the wolf gene pool. However, increased hybridisation frequency may be detrimental for wolf populations, stressing the need for genetic monitoring to assess the frequency and distribution of individuals resulting from recent admixture