Genetic Regulation of Development of Thymic Lymphomas Induced by N‐Propyl‐N‐nitrosourea in the Rat

To clarify the linkage between Hbb and Tls‐1 (thymic lymphoma susceptible‐1) loci and to investigate other loci concerned in thymic lymphomagenesis, the BUF/Mna rat, which is highly sensitive to the lymphomagenic activity of N‐propyl‐N‐nitrosourea (PNU), the WKY/NCrj rat, reported to be resistant, and their cross offspring were subjected to genetic analysis. F1 hybrid and backcross generations were raised from the 2 strains, and 6 genetic markers including Hbb were analyzed in individuals of the backcross generation. However, no linkage between Hbb and Tls‐1 loci could be demonstrated since WKY rats also developed a high incidence of thymic lymphomas in response to PNU. Nevertheless, thymic lymphomas developed more rapidly and reached a larger size in the BUF rats. F1 rats expressed a rather rapid and large tumor growth phenotype, while the [(WKY × BUF) × WKY] backcross generation consisted of rats with either rapidly growing or slowly growing tumors. It was thus concluded that rapid development of thymic lymphomas is determined by a gene, provisionally designated Tls‐3. Analysis of the relationship between 6 genetic markers and development of thymic lymphoma in the backcross generation demonstrated that the Tls‐3 locus is loosely linked to the Gc locus, suggesting a possible location on rat chromosome 14. Tls‐3 may not be identical with Tls‐1 and other genes known to be relevant to thymic tumors, but its relationship with Tls‐2 remains obscure.