A targeting construct encoding a cre recombinase/mutated estrogen ligand binding-domain (cre/ERT2) fusion sequence and an Frt-flanked neo cassette was targeted to the Sox2 locus in V6.5 ES cells, so that cre was under control of endogenous Sox2 regulatory elements. Chimeric mice were bred to 129/SvJae wild-type animals to test for germline transmission and to establish stable lines. (J:177655)