1. ^* Laboratory of Genetics, University of Wisconsin, Madison, Wisconsin 53706, USA
2. ^† Department of Pathology, University of Edinburgh, Teviot Place, Edinburgh EH8 9AG, UK
3. ^‡ Department of Molecular Biology, University of Edinburgh, Mayfield Road, Edinburgh EH9 3JR, UK
4. ^§ To whom correspondence should be addressed.

Abstract

Two recent developments suggest a route to predetermined alterations in mammalian germlines. These are, first, the characterization of mouse embryonic stem (ES) cells¹ that can still enter the germline after genetic manipulation in culture^2,3 and second, the demonstration that homologous recombination between a native target chromosomal gene and exogenous DNA can be used in culture to modify specifically the target locus⁴. We here use gene targetting functionally to correct the mutant hypoxanthine-guanine phosphoribosyl transferase (HPRT) gene in the ES cell line which has previously been isolated and used to produce an HPRT-deficient mouse⁵. This modification of a chosen gene in pluripotent ES cells demonstrates the feasibility of this route to manipulating mammalian genomes in predetermined ways.