A cassette encoding IRES-mnCre:GFP (an internal ribosome entry sequence (IRES), a Myc-tag and nuclear localization signals at the N-terminus of Cre recombinase, which is fused to green fluorescent protein followed by a SV40 polyadenylation sequence) was inserted just 3' of the termination codon in the last coding exon of the Ntsr1 gene via homologous recombination. The neomycin cassette was excised through crosses with animals broadly expressing Flp recombinase.