Generation of Tac2-Cre mice. Top, schematic diagram of the gene targeting strategy used to insert Cre into the wildtype Tac2 locus. The Tac2-Cre targeting vector included Cre directly downstream of the Tac2 ATG codon sequence, an FRT-flanked neomycin positive selection cassette, and a DTA negative selection cassette. XbaI sites and the expected sizes of the resulting DNA fragments are indicated. Below, Southern blot analyses for verification of correct targeting of Tac2 locus. Southern blot with XbaI and external probes confirmed correctly targeted homologous recombination events. The 12 kb WT band is seen in all lanes, and two correctly targeted and distinct 7 Kb bands represent the targeted allele at the 5' and 3' homology arms.