ABSTRACT
In the past few years, mouse embryonic stem (ES) cell-mediated transgenic technologies have revolutionized mammalian genetics. The choice of ES cells is very important for the aggregation method. We have tested several commonly used ES cell lines. Of them, R1 gave very consistent germline transmission with this method. The other lines, such as D3 and AB1, frequently gave chimeric embryos with strong ES cell contribution, but they died at birth. Targeted ES cells still have the developmental potential to contribute to all lineages of the developing embryo proper when they are introduced back to the in vivo environment. In vitro culture conditions must be optimal for ES cell aggregation, since the aggregates are cultured for at least 24 hours before they are transferred back into recipients. Aggregation of ES cells with blastomere stage embryos is a novel technique with a rapidly increasing popularity, as it has some important advantages over the ES cell injection method.
