A new coat color mouse line for testing germline transmission of embryonic stem cells while retaining an inbred...

Most gene-targeted mice are produced on a mixed genetic background of C57BL/6 and substrains of 129/Sv. Mating chimeric mice containing 129/Sv-derived embryonic stem cells that are wild type at the agouti locus (A) in a nonagouti (a) donor genetic background with inbred C57BL/6 mice that are homozygous for the nonagouti allele allows the use of coat color to detect germline transmission. Agouti pups from such a cross indicate germline transmission of embryonic stem cell-derived genetic material. However, 129/Sv substrains and C57BL/6 are genetically and phenotypically quite different and, consequently, differing genetic contributions of the 2 backgrounds may influence the phenotype under investigation. To avoid this problem yet maintain the usefulness of the coat color system in detecting germline transmission, we have generated a new strain of mouse by selectively introducing the nonagouti locus into a 129/Sv inbred background. This mouse strain contains 129/Svderived genetic material almost entirely except for a small region surrounding the nonagouti allele. Germline transmission can be detected in the usual manner, but the agouti offspring will be almost identical to 129/Sv inbred mice. Thus, the system allows the generation of gene-targeted mutations on a 129/Sv genetic background.