Using homologous recombination in ES cells, a T2A sequence and a CreER(T2) fusion gene were inserted immediately downstream of the cholecystokinin B receptor locus (Cckbr) on chromosome 7. The targeting vector contained, from 5' to 3', a viral 2A oligopeptide sequence (T2A; mediates ribosomal skipping), a Cre recombinase gene, a bovine growth hormone polyA sequence, an frt site, a PGK-neo-polyA cassette, and an frt site. Founder mice were bred with Flpo-expressing mice to delete the PGK-neo-polyA cassette. (J:316161)