A targeting vector was designed to insert (from 5' to 3') a glial cell line derived neurotrophic factor (Gdnf) cDNA, an internal ribosomal entry sequence 2 (IRES2), cre/ERT2 coding sequence, an SV40 polyA sequence, and a neomycin selection cassette into exon 2 of the Gdnf gene (J:206853)