Identity of rearranged LINE/c-MYC junction sequences specific for the canine transmissible venereal tumor.

The canine transmissible venereal tumor is a naturally occurring neoplastic disease that affects the external genitalia of both sexes and is transmitted during coitus. Cytogenetic and immunologic studies demonstrated that tumors from different parts of the world are very similar, suggesting that they are transferred from one animal to another by the transplantation of viable cells. We found that the c-MYC oncogene was rearranged in this tumor by the insertion of a transposable genetic element sequence (known as LINE, long interspersed element) 5' to the first exon. The amplification of a DNA segment located in the junction of the LINE genome and c-MYC upstream sequences enabled the testing of the similarity of transmissible venereal tumor samples collected independently in different parts of the world. Oligonucleotide primers flanking the LINE/c-MYC junction were used to amplify a 340-base-pair segment and nested primers amplified a 280-base-pair segment. A fifth oligonucleotide used as a probe contained the actual junction sequence. All of the tumors analyzed revealed the existence of the specific bands, which were absent in normal canine DNA samples. The amplified segments obtained from all of the tumors analyzed were identical in size and nucleotide sequence, suggesting transmission of the original rearranged cell itself, as opposed to independent events of LINE insertion in a "hot spot."