Establishment of thymoma-prone congenic rat strain, ACI.BUF/Mna-Tsr1/Tsr1

Purpose: To confirm the presence of the susceptible gene for the thymoma development in the region that was assumed by the previous linkage study by Oyabu et al. (J Natl Cancer Inst 91:279-282, 1999), we tried to establish a congenic strain of rats. Methods: Backcrossings between the BUF/Mna strain as a donor strain and the ACI/NMna strain as an inbred partner were repeated for 12 generations, examining whether rats had the thymoma development region, and then homozygous rats were yielded by mating among the heterozygotes. To detect the phenotypic expression, heterozygous ACI.BUF/Mna-Tsr1/+ (ACI-Tsr1/+) rats were generated by crossing female ACI.BUF/Mna-Tsr1/Tsr1 (ACI-Tsr1/Tsr1) rats with male ACI/NMna rats and were maintained for 24 months. Results: These ACI-Tsr1/+ rats produced thymoma in 71%, showing a dominant trait. The thymomas were of the lymphocyte predominant type, as those developed in rats of the original BUF/Mna strain. Conclusions: Thus, a new rat congenic strain, ACI-Tsr1/Tsr1, was established, revealing that thymoma develops in the dominant trait in ACI-Tsr1/+ rats.