Propylnitrosourea-induced T-lymphomas in LEXF RI strains of rats: genetic analysis

Oral administration of propylnitrosourea (PNU) in drinking water induces high incidence of lympho-haemopoietic malignancies in rats. Previously we reported that F344 strain rats were highly susceptible to T-lymphomas, and LE/Stm rats, to erythro- or myeloid leukaemias. For analysis of the genetic factors determining types of diseases, we have established LEXF recombinant inbred strains of rats comprising 23 substrains, each derived from intercross between F344 and LE/Stm rats. Rats of 23 LEXF substrains were given PNU, and the development of tumours was observed. The overall incidence of haemopoietic tumours ranged from 100% to 66.7%, and the fractions of T-lymphomas, from 100% to 4%, showing a continuous spectrum. Based on the genetic profile published as a strain distribution pattern table for the LEXF, we screened the potential quantitative trait loci involved in determination of the types of disease and length of the latency period. Statistical calculation was performed using the Map Manager QT software developed by Manly. Four loci, on chromosome 4, 7, 10 and 18, were suggested to associate with the T-lymphoma susceptibility and three loci, on chromosome 1, 5 and 16, with the length of the latency period. These putative loci were further examined in backcross (F344 x LE)F1 x LE. Among seven loci suggested by the recombinant inbred study, three loci, on chromosome 5, 7 and 10, were significantly associated with T-lymphomas and another locus on chromosome 1, just weakly. These observations indicate that PNU-induced lymphomagenesis is a multifactorial genetic process involving a number of loci linked with susceptibility and resistance.