Germline transmission of a transferred human chromosome 21 fragment in transchromosomal mice

We generated transchromosomal (Tc) mice containing a human chromosome 21 fr agment (hCF21) using mouse embryonic stem (ES) cells with the transferred h CF21. Here we report breeding analyses that test the maintenance rate of th e hCF21 in Tc mice of two different genetic backgrounds, MCH (ICR) and C57B L/6. Fluorescence in situ hybridization and polymerase chain reaction-based DNA analyses revealed that the structure of the hCF21 fragment including t he CBR1, SIM2, HLCS, and D21S268 markers, was approximately 5Mb in size, an d was transmitted at least to the F3 generation. Though the retention rate of the hCF21 was variable among individual mice, for example, 21%-92% in br ain and 10%-92% in tail fibroblasts, the C57BL/6 background yielded a highe r retention rate than did the MCH (ICR). These results suggest that the hCF 21 could be maintained stably in Tc mice, depending on the genetic backgrou nd. The panel of Tc mice will be a useful model to investigate the function of genes on the hCF21 fragment in various tissues through germinal transmi ssion.