Sarcoid is the most common skin cancer in horses. The etiology of the tumor is associated with BPV infection (BPV-1, -2, -13), which is an inducer of malignant transformation. The comparative genomic hybridization (CGH) technique identifying the unbalanced chromosome aberrations was used to analyze the genome of equine sarcoid cells and to diagnose the chromosome rearrangements involving large deletions or amplification. The results were based on the analysis of 100 metaphases and their karyograms as well as the diagram showing the average ratio of the intensity of the green to red fluorescence, using MetaSystems software (Isis). Based on a comparison of the fluorescence intensity ratios we found duplication in the subtelomeric regions of chromosome pairs 1, 4, 7, 8 and 23. Duplicated region of chromosome pair 1 also included the coding region of the rDNA. In the chromosome 23 next to the duplication occurring in the centromeric region of q arm (23q11) we also found the presence of deletions involving 23q18-23q19 region. For the chromosome pairs 25 to 31 and the X chromosome the software failed to generate CGH diagram, but on the individual karyograms we were able to observe fluorescence signals characteristic of duplication (red), in rDNA regions of chromosome pairs 28 and 31. The study showed that duplications of DNA present in the sarcoid cells are found mainly in the telomeric and rDNA regions. The presence of the duplication of telomeric regions is associated with increased activity of the telomerase enzyme, which is a hallmark of cancer cells, affecting the immortality of these cells. Accordingly, duplications of rDNA coding regions increase activity of nucleolar organizer region which is a tumor marker.
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