Generation and expression characterization of the Ai27, Ai32, Ai35 and Ai39 Cre-reporter lines. (a) Gene targeting vectors were designed to insert the Cre-dependent reporter cassettes into intron 2 of the Rosa26 locus. After obtaining germline-transmitted F1 mice, the PGK-neo selection cassette can be deleted by PhiC31-mediated recombination between the AttB and AttP sites, which combine into an AttL site, by breeding with a Rosa26-PhiC31 deleter line. (b) tdTomato, EYFP, and EGFP native fluorescence in Emx1-Cre;Ai27, Emx1-Cre;Ai32, Emx1-Cre;Ai35 and Emx1-Cre;Ai39 mice. Scale bar, 200 μm. (c) Confocal images of the CA1 pyramidal neurons in the same mice as in b, showing the cell membrane localization of tdTomato, EYFP and EGFP fluorescence. Scale bar, 20 μm. (d) Reporter gene mRNA expression in Emx1-Cre;Ai27, Emx1-Cre;Ai32, Emx1-Cre;Ai35 and Emx1-Cre;Ai39 mice (ages all ~P56), using in situ hybridization (Ai27, tdTomato riboprobe; Ai32, Ai35 and Ai39, EGFP/EYFP riboprobe). Scale bar, 200 μm.