How close are we to implementing gene targeting in animals other than the mouse?

Describes several significant contributions that bring us much closer to extending ‘‘gene targeting'' to mammalian species other than the mouse. Gene targeting now provides the means for creating new strains of mice with mutations in virtually any gene. First, the desired mutation is introduced into a cloned copy of the chosen gene by standard recombinant DNA technology. The mutation then is transferred to the genome of a pluripotent mouse embryo-derived stem (ES) cell by means of homologous recombination between the exogenous mutated DNA sequence and the cognate DNA sequence in the ES cell chromosome. By microinjection of ES cells containing the targeted mutation into blastocysts and allowing the embryo to come to term in foster mothers, chimeric mice can be generated that are capable of transmitting the targeted mutation to their offspring.