Organization of mouse Tbx21 gene and transgene constructs. (A) Genomic organization of Tbx21 gene on mouse chromosome 11. Exons are indicated by boxes with numbers: purple boxes indicate the open reading frame; and light blue boxes represent 5'- and 3'-non-translated regions. (B) Nucleotide sequence identity plots of human, rhesus, dog and rat Tbx21 genes compared with mouse ortholog by using the VISTA program . Highly conserved regions (> 80% identity) in 5'-flanking sequences and introns are shown in pink. Mitral and tufted cell-specific enhancer (MCE; 307 bp) is present at ~3 kb upstream from the transcription start site of Tbx21 gene. (C) Transgene constructs. 5'-flanking regions of Tbx21 gene with different lengths (5.0, 2.6 and 1.0 kb: yellow) were fused to a membrane-targeted Venus complementary DNA (cDNA) (gV: green) to generate Tbx5.0gV, Tbx2.6gV and Tbx1.0gV transgenes. Highly conserved 307-bp sequence (MCE: red) and SV40 minimal promoter (blue) were fused with gapVenus cDNA to generate MCE-gV transgene. 5.0-kb 5'-flanking region of Tbx21 gene was fused with synaptopHluorin cDNA (spH: dark blue) in order to generate Tbx-spH transgene.