GENETIC-MAPPING OF GENES REGULATING THE THYMUS SIZE IN BACKCROSS RATSBETWEEN THE LABORATORY BUF MNA STRAIN AND THE MITE STRAIN DERIVED FROM THE WILD RAT, RATTUS-NORVEGICUS/

The thymoma prone BUF/Mna (B) rat is a useful model for studying the g enes responsible for thymus enlargement during the stage of young grow th. Among the strains of rats, B rats have the largest thymuses at all stages of life. A locus, Ten-1, which contributes to thymus enlargeme nt in backcross (BC) rats between the B and WKY/NCrj (W) strains, was mapped on chromosome 1. To determine the precise location of the locus , {Bx(BxMITE)F1} BC rats were generated by crossing the B strain with the inbred MITE (M) strain, which was established from captured, Japan ese wild rats, and were examined by linkage study using polymerase cha in reaction with 67 microsatellite markers. Linkages with thymus enlar gement were found in genotypes of seven markers, BSIS, LSN, MYL2, IGF2 , PBPC2, D1Mgh11, and D1Mit6, by x(2)-test and Student's t-test, which confirmed the presence of the genetic locus associated with thymus en largement, Ten-1, in this region. Paradoxically,a suppressive locus, T su-1, to thymus enlargement was also found on chromosome 3, showing li nkages of phenotype of the small thymus with genotypes of SCN2A, CAT, D3Mit16, and D3Mit13. By analyses of MAPMAKER/EXP and MAPMAKER/QTL, Te n-1 was mapped at 4.6 cM proximal from IGF2 locus on chromosome 1 and Tsu-1 at 4.0 cM proximal from CAT locus on chromosome 3, respectively.