Heteroplasmic Mutations and Polymorphisms in the Cyb Gene of Mitochondrial DNA in Canine Mast Cell Tumours

Defect in Mitochondrial NADH-Dehydrogenase Genes in Canine Mast Cell Tumours

Recent studies have demonstrated a significant role of mitochondrial DNA (mtDNA) defects in the pathogenesis of many human and some canine tumours. The aim of this study was to identify mutations in the ND2 and ND4 mitochondrial genes in canine mast cell tumours and determine their association with the process of neoplastic transformation and the phenotypic traits of dogs. In total, 136 gene sequences from 68 biological samples, including blood and neoplastic tissue samples from 34 dogs with diagnosed MCTs, were analysed. The study consisted in DNA sequencing of the ND2 and ND4 genes as well as bioinformatics and statistical analyses. For the first time, mutations in NADH-dehydrogenase genes were detected in dogs with MCTs. In total, 22 polymorphic loci and 19 mutations in the ND2 and ND4 genes were identified. The majority of the identified mutations were homoplasmic, and tumour heteroplasmy was detected in eight nucleotide positions in three dogs. Seven of the ND2 mutations and two of the ND4 mutations caused an amino acid change. The changes in non-synonymous protein-coding SNPs did not exert an adverse effect on proteins. A statistically significant correlation of the presence of mutations/polymorphisms with the sex, age, and size of the dogs and the tumour location was demonstrated. Polymorphisms and mutations in NADH-dehydrogenase genes, including mastocyte-specific changes, in canine mast cell tumours that had not been reported earlier in the literature were identified. Some of these changes may imply that these are the hotspot mutations in canine mast cell tumours. It cannot be excluded that the molecular changes are directly associated with the development of mast cell tumours, and further investigations are needed to verify whether they can become molecular markers of MCTs in the future.

Analysis of Mitochondrial Genome from Labrador (Canis lupus familiaris) with Mammary Gland Tumour Reveals Novel Mutations and Polymorphisms

The aim of the study was to find associations between the process of neoplastic transformation and mtDNA mutations/polymorphisms, i.e. factors with potential prognostic significance, and to determine their impact on the biochemical properties, as well as structural, and functional properties of proteins. Blood and neoplastic tissue samples were collected from a 9-year-old Labrador dog with a diagnosed malignant mammary tumour. Next-generation genome sequencing (NGS) of the entire mitochondrial genome was performed using Illumina technology, and bioinformatics analyses were carried out. This is the first report demonstrating the application of NGS in the analysis of the canine mtDNA genome in neoplastic disease. The proposed strategy is innovative and promising. For the first time in the literature, the sequence of 29 genes was analysed to determine their association with the prevalence of tumour. In total, 32 polymorphic loci and 15 mutations were identified. For the first time, as many as 24 polymorphisms and all the mutations have been described to be associated with the neoplastic process in dogs. Most polymorphisms/mutations were found in the D-loop (31% of the polymorphisms and 93% of the mutations) and the COX1 gene sequence (16% of the polymorphisms). Blood or cancer heteroplasmy was noted in 93% of the mutations. Four of the 18 polymorphisms detected in the protein-coding genes were non-synonymous polymorphisms that have not been described in the literature so far (m.T7593C in COX2, m.G8807A in COX3, m.A9911G in ND4L, and m.T13299A in ND5) but resulted in changes in amino acids in proteins. These mutations and polymorphisms can affect mitochondrial functions and may be a result of cell adaptation to the changes in the environment occurring during carcinogenesis. The replacement of “wild type” mtDNA by a mutated molecule may be an important phenomenon accompanying carcinogenesis.