A new mouse embryonic stem cell line with good germ line contribution and gene targeting frequency

The use of gene targeting in embryonic stem (ES) cells provides an attractive method for the introduction of genetic alterations into the mammalian germ line. For this ES cell system to operate efficiently the cell lines used should ideally show a high frequency of gene targeting and should contribute readily to the germ line of chimaeric animals. Our early gene targeting experiments were carried out in the hypoxanthine phosphoribosyltransferase (HPRT) deficient ES cell line, E14TG2a. For alternative gene targeting strategies and improved germ line transmission frequencies, we isolated a new ES cell line, HM-1, directly from HPRT-deficient strain 129 mice that had been produced by blastocyst injection of E14TG2a cells.