| Summary: | 碩士 === 國立中興大學 === 獸醫學系暨研究所 === 97 === Mouse mammary tumor virus (MMTV), an oncogenic B retrovirus, contributes to occurrence of breast cancer in mice, acquired horizontally through the milk (exogenous) to susceptible offspring or vertically through the germ line (endogenous provirus). The MMTV-like sequences have been found in human breast cancer, implicating the involvement of MMTV in human breast cancer. Dogs and cats with frequent human contacts were proposed to contribute to transmission of this virus between mouse and man; however, this hypothesis has not yet been defined. Hence, the goal of this study was to detect MMTV-like gene sequences in canine and feline mammary tumors. MMTV-like env and LTR sequence were amplified by means of nested PCR. The sequences of resultant DNA fragments were verified by direct automated sequencing. Moreover, we also examine clinical and pathological parameters by multivariate analysis, and find the association with the presence of the MMTV-like sequences.
In total of 124 samples from 113 dogs and 11 cats who had undergone surgery were obtained from 1995 to 2008 in Veterinary Medical Teaching Hospital, National Chung Hsing University. Specific MMTV-like env and LTR sequences were found in 3 (3.49%) and 16 (18.6%) of dogs with malignant mammary tumors, respectively. Besides this, specific MMTV-like env and LTR sequences were also detected in 2 (22.2%) and 2 (22.2%) of feline malignant mammary tumors, respectively. The homology of these sequences to MMTV identified from NIH 3T3 (MMTV-positive murine cell line) and MMTV-like sequences approximately range from 94% to 98%; however, a lower similarity (approximately 89%) was observed when MMTV-like LTR sequences from canine were aligned with those of MMTV identified from mouse (HeJ strain). Moreover, sequences of LTR present in 2 dogs (13.3%, 2/15) and sequences of LTR present in one cat (50.0%, 1/2), both in mammary tumor and in mammary normal tissue suggesting that it may be an endogenous origin. Nevertheless, it can’t be ruled out completely the possibility of the transmission from mice. The role of dog and cat plays in transmission of MMTV from mice to human remains unclear. In this respect, isolation of MMTV particles from such animals would be crucial.
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