The targeting vector contains a 5.5 kb 5 arm and a 3.5 kb 3arm. Lox71 and Lox2272 sites were inserted flanking the gene, where the cDNA was replaced with that encoding for an HA-tagged Ngn3 protein. The vector also contains a FRT-flanked Pgk-Puro-deltaTK cassette for positive selection by puromycin (targeting events) and negative selection by ganciclovir (RMCE events). (J:296396)