Date of Award

5-2023

Document Type

Thesis

Department

Genetics and Biochemistry

Abstract

The merle coat pattern is a pigmentary phenotype of dogs characterized by a dilute background with black patches. Merle is caused by a SINE insertion in PMEL17, a pigmentation gene expressed in melanocytes. The mutation causes aberrant splicing of transcripts and production of an abnormal protein. Harlequin is a dominant modifier of merle that further dilutes the background to white. Harlequin Great Danes have a heterozygous mutation impairing the ubiquitin-proteasome system, suggesting that the inability to degrade aberrant PMEL17 results in melanocyte death. Harlequin is not a recognized coat pattern of the Collie; however, a harlequin phenotype spontaneously appeared in a family of Finnish Collies. Pedigree analysis revealed an inheritance pattern consistent with a dominant modifier of merle occurring de novo in the proband. To identify the mutation, we generated 30X whole genome resequencing data from a second generation harlequin Collie. We identified over two million heterozygous variants and filtered for unique coding variants against 1400 canine genomes aligned to the CanFam3 reference genome. The remaining 155 variants were manually inspected in IGV revealing 10 candidate missense mutations. Sanger sequencing in family members revealed that none of the identified variants segregated with the harlequin phenotype. Future efforts will utilize newly available reference genomes to identify additional coding variants. The identification of novel mutations that cause harlequin patterning in merle dogs will provide insight into genes and sequences critical for proper functioning of the ubiquitin-proteasome system.

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