A targeting vector was designed to insert an internal ribosomal entry site, nuclear-localized Cre recombinase gene, and polyA signal (IRES-Cre-pA) followed by an FRT-flanked PGK-Neo cassette into the 3' untranslated region of the cut-like homeobox 2 (Cux2) locus. Flp-mediated recombination removed the FRT-flanked PGK-Neo cassette.