Utilizing the Dog Genome in the Search for Novel Candidate Genes Involved in Glioma Development—Genome Wide Association Mapping followed by Targeted Massive Parallel Sequencing Identifies a Strongly Associated Locus

摘要

Gliomas are the most common form of malignant primary brain tumors in humans and second most common in dogs, occurring with similar frequencies in both species. Dogs are valuable spontaneous models of human complex diseases including cancers and may provide insight into disease susceptibility and oncogenesis. Several brachycephalic breeds such as Boxer, Bulldog and Boston Terrier have an elevated risk of developing glioma, but others, including Pug and Pekingese, are not at higher risk. To identify glioma-associated genetic susceptibility factors, an across-breed genome-wide association study (GWAS) was performed on 39 dog glioma cases and 141 controls from 25 dog breeds, identifying a genome-wide significant locus on canine chromosome (CFA) 26 (p = 2.8 x 10~(?8)). Targeted re-sequencing of the 3.4 Mb candidate region was performed, followed by genotyping of the 56 SNVs that best fit the association pattern between the re-sequenced cases and controls. We identified three candidate genes that were highly associated with glioma susceptibility: CAMKK2 , P2RX7 and DENR . CAMKK2 showed reduced expression in both canine and human brain tumors, and a non-synonymous variant in P2RX7 , previously demonstrated to have a 50% decrease in receptor function, was also associated with disease. Thus, one or more of these genes appear to affect glioma susceptibility. Author Summary Gliomas are devastating malignant brain tumors that are very rarely curable. Despite extensive research to define pathways and genes involved in the development of disease, there is still an urgent need to improve therapy. Some dog breeds have a considerable elevated risk of glioma, making the dog a suitable model for locating genes potentially of importance also for development of human glioma. In this study we defined a genomic region strongly associated with glioma in dogs. We also showed that this genomic region had likely been under selection in the dog breeds with the highest risk of developing glioma. Sometimes selection for breed specific traits results in amplification of disease causing mutations together with the variant selected for. We located three candidate genes in the identified region: CAMKK2 , P2RX7 and DENR . We performed further functional studies to evaluate the potential role of these genes in both canine and human glioma. By comparing normal and tumor tissue we could show that two of the genes— CAMKK2 and P2RX7 , were affected at the level of gene expression and protein structure, respectively. We propose that further investigation of all three genes could be of interest with potential benefit to both dog and human.