Chimera (genetics) - Mouse Chimeras

Mouse Chimeras

Chimeric mice are important tools in biological research, as they allow the investigation of a variety of biological questions in an animal that has two distinct genetic pools within it. These include insights into such problems as the tissue specific requirements of a gene, cell lineage, and cell potential. The general methods for creating chimeric mice can be summarized either by injection or aggregation of embryonic cells from different origins. The first chimeric mouse was made by Beatrice Mintz in the 1960s through the aggregation of eight cell stage embryos. Injection on the other hand was pioneered by Richard Gardner and Ralph Brinster who injected cells into blastocysts to create chimeric mice with germ lines fully derived from injected ES Cells. Mouse embryos both periimplantation and post implantation can contribute to a chimera. It is post implantation that ES cells from the inner cell mass of a blastocyst can contribute to all cell lineages of a mouse including the germ line. ES cells are also a useful tool in chimeras because genes can be mutated in them through the use of homologous recombination, thus allowing gene targeting. Since this discovery occurred in 1999, ES cells have become a key tool in the generation of specific chimeric mice.