Investigation into the pathogenesis of retinal dysplasia in the miniature schnauzer and English springer spaniel dog
Retinal dysplasia has been documented in many breeds of dogs. It has recently been hypothesized that Miniature Schnauzer dogs affected with retinal dysplasia and associated persistent hyperplastic primary vitreous have a decreased amount of Tfam and several mtDNA transcripts in the retina and RPE. Affected dogs were also hypothesized to have a decrease in leukocyte mtDNA compared to normal dogs. Additionally, using electron microscopy, these dogs were hypothesized to having decreased mitochondrial numbers and size with altered morphology in multiple tissues, including neutrophils. Due to these recent discoveries in this breed it has been proposed that retinal dysplasia could be the result of an altered energy supply to the retina and RPE. The objective of this study was to further investigate the pathogenesis of retinal dysplasia in the Miniature Schnauzer and English Springer Spaniel dog. The hypothesis of an altered Tfam gene sequence in affected Miniature Schnauzer dogs leading to a decreased amount of Tfam transcript in the retina and RPE was tested by amplifying, cloning and sequencing the coding, 5’ and 3’non-coding regions, and intron 1 of the Tfam gene from affected and normal Miniature Schnauzer dogs. Using transmission electron microscopy, affected and normal lymphocyte mitochondria were also objectively measured and quantified in this breed along with mitochondrial morphology assessment. In the English Springer Spaniel dog, the hypothesis of a decreased amount of leukocyte mtDNA in affected dogs was tested using real-time PCR. In addition, using transmission electron microscopy, affected and normal lymphocyte mitochondria were objectively measured and quantified in this breed with mitochondrial morphology assessment. Sequencing of the particular regions of the Miniature Schnauzer Tfam gene revealed no significant nucleotide changes between affected and normal dogs. Evaluation of lymphocyte mitochondrial size, number and morphology also revealed no significant differences between the two groups. In the English Springer Spaniel dog a relative decrease in leukocyte mtDNA did not exist in dogs affected with retinal dysplasia. Furthermore, evaluation of affected English Springer Spaniel dog lymphocyte mitochondria revealed no significant differences in mitochondrial number, surface area or morphology when compared to normal English Springer Spaniel dogs. To conclude, we failed to demonstrate a mutation in the areas of the Tfam gene sequenced in Miniature Schnauzers affected with retinal dysplasia and associated persistent hyperplastic primary vitreous. In contrast to previous findings of decreased leukocyte mtDNA in the affected Miniature Schnauzer dog, no evidence was found to support a relative decrease in leukocyte mtDNA in English Springer Spaniel dogs affected with retinal dysplasia. Furthermore, the hypothesis of altered mitochondrial size, number and morphology in affected dogs is not supported by this study. Further evaluation of mitochondria, mtDNA and mitochondrial gene expression within age-matched retina and RPE of Miniature Schnauzer and English Springer Spaniel dogs is necessary to determine if mitochondria and altered energy supply play a role in the pathogenesis of retinal dysplasia in these breeds.
Tfam, mitochondria, english springer spaniel, miniature schnauzer, retinal dysplasia
Master of Science (M.Sc.)
Small Animal Clinical Sciences
Small Animal Clinical Sciences