Mapping Trait Genes in Dogs Using the Dog as a Model Organism

Understanding the genetic background of a given phenotypic trait or disease has long intrigued scientists. Model organisms can be employed when it is not feasible or possible to find trait causality in human cohorts. This thesis reports the mapping of both a phenotypic trait (white spotting) and a disease (sensory ataxic neuropathy) in dogs, and in doing so highlights the potential of the dog as a model organism for mapping traits of relevance to human health and biology. For white spotting, a two-stage mapping approach was used to identify an associated genomic region, which contained only the microphtalmia-associated transcription factor (MITF) gene. Stage 1: a genome-wide association analysis in a single breed, taking advantage of the extensive within breed linkage disequilibrium (LD) and long haplotypes, identified a discrete region of approximately 1 Mb. Stage 2: finemapping in an additional breed presenting the same phenotype, exploiting the short LD and haplotypes shared across dog breeds, was used to narrow the region to about 100 kb. We functionally evaluated two candidate polymorphisms associated with MITF, a SINE insertion and a length polymorphism upstream of the melanocyte-specific transcription start site of MITF. The data indicated that both polymorphisms affect transcription from the MITF-M promoter. Sensory ataxic neuropathy (SAN) is a neurological disorder affecting a specific maternal lineage of Golden Retrievers. We identified a one base pair deletion in mitochondrial tRNA and through biochemical analyses of mitochondria and functional studies of the deletion, confirmed causality and the mitochondrial origin of SAN. This is one of the first mitochondrial disorders identified in dogs and we additionally developed a genetic test for the public to allow for the elimination of the disease from this breed. The genetic and functional analyses of both white spotting coat colour and SAN in dogs, which are controlled by mutations of the two different genomes, clearly demonstrate the utility of the canine model and establish a new role for man's best friend.