The coding region for a nuclear-localized beta-galactosidase (nLacZ; using an SV40 nuclear localization signal) was targeted to the Fzd1 locus by homologous recombination. The nLacZ sequences replace the Fzd2 open reading frame. A LoxP-flanked neo selectable marker used for ES cell selection was removed by subsequent crossing to a mouse line expressing germline Cre recombinase. Sequences from the E coli tetracycline resistance gene (TetR) are included immediately 3' of the nLacZ sequences and are part of the 3' untranslated region of the nLacZ transcript. (J:159434)