crucial step in developing gene-manipulated mouse models. To date, techniques for
generating chimeric mice include direct microinjection of ES cells into the cavity of 3.5-d post-
coitum (dpc) blastocysts and aggregating or coculturing 2.5 dpc zona pellucida-free
(denuded) embryos with ES cells. We present here a procedure that is simple and
reproducible for mass producing (10–150 embryos/vial/time) chimeric embryos by …