Early diagnosis of mammary gland tumors is a challenging task in animals, especially in unspayed dogs. Hence, this study investigated the role of microsatellite instability (MSI), MMR gene mRNA transcript levels and SNPs of MMR genes in canine mammary gland tumors (CMT). A total of 77 microsatellite (MS) markers in 23 primary CMT were selected from four breeds of dogs. The results revealed that 11 out of 77 MS markers were unstable and showed MSI in all the tumors (at least at one locus), while the other markers were stable. Compared to the other markers, the ABC9TETRA, MEPIA, 9A5, SCNA11 and FJL25 markers showed higher frequencies of instability. All CMT demonstrated MSI, with eight tumors presenting MSI-H. The RT-qPCR results revealed significant upregulation of the mRNA levels of cMSH3, cMLH1, and cPMSI, but downregulation of cMSH2 compared to the levels in the control group. Moreover, single nucleotide polymorphisms (SNPs) were observed in the cMSH2 gene in four exons, i.e., 2, 6, 15, and 16. In conclusion, MSI, overexpression of MMR genes and SNPs in the MMR gene are associated with CMT and could be served as diagnostic biomarkers for CMT in the future.
Keywords: MMR system; canine mammary gland tumors; microsatellite instability; polymorphism.