Common origin of transmissible venereal tumors (TVT) in dogs.

We determined the sequence of the 1.5-kb insert upstream to c-myc in the transmissible venereal tumor (TVT) of dogs. The sequence is highly homologous to the 3' region of the mammalian repetitive LINE element. The insert is bound by a 10-bp repeat indicating DNA transposition by a mechanism involving reverse transcriptase. We analyzed DNA of four TVT tumors from various geographical locations as well as normal canine DNA for the presence of the LINE insert. The results indicate that in all TVT tumors, but not in normal tissues, the same LINE insert was present upstream to c-myc. This result suggests that TVT tumors in various dogs may have a common cellular origin.