The targeting vector containied partial Rasgrf2 intron 29-33 sequence containing an frt3 site in intron 33, a partial Rasgrf2 exon 34 sequence up to (but not including) the endogenous stop codon, self-splicing T2A sequence in-frame with the Rasgrf2 coding sequence, a dCre fusion gene in-frame with the Rasgrf2 coding sequence, a bovine growth hormone polyA signal, an AttB site, a PGK-Neo-polyA cassette, an frt5 site, an mRNA splice acceptor, the 3' portion of the hygromycin gene with SV40 polyA signal, and an AttP site. The dCre fusion gene (destabilized Cre, hDHFR/Cre or ecDHFR/Cre) is Cre recombinase fused at its N terminus to the first 159 amino acids of the E. coli K-12 strain chromosomal dihydrofolate reductase gene (DHFR or folA) harboring the G67S mutation and modified to include the R12Y/Y100I destabilizing domain mutations. The targeting vector was electroporated into G4 ES cells. Correctly targeted ES cells were injected into recipient blastocysts. When treated with trimethoprim, cre reporter gene activity is observed at high levels in cortical layers 2/3 and other scattered cells of the cortex, hypothalamus, thalamus, and midbrain. (J:199220, J:220523)