Fig. 1. The structure of transgenes (A-C) and the mating scheme (D). The Pdx1Cre transgene has the Cre-coding region directly fused to the SalI-SmaI region of the 5' promoter region of Pdx1. The Pdx1-Cre-ER^TM has the Cre-ER^TM ATG fused with the Pdx1 ATG (A). The Ngn3-Cre construct directly fuses the Cre-coding region to the 6.5 kb upstream sequence of Ngn3. The Ngn3-Cre-ER^TM has the Cre-ER^TM ATG fused with the Ngn3 ATG directly (B). Promoters and introns are represented by red lines, untranslated regions by red boxes and coding regions by blue boxes. The transgene polyadenylation signal, which is from the large T antigen polyA region, is noted by black boxes. The yellow and green boxes represent the coding regions of Cre or Cre-ER^TM. The reporter used is the Z/AP transgenic line (C) (Lobe et al., 1999). When Pdx1-Cre or Ngn3-Cre strain is crossed with reporters, no further manipulation is needed (D1). When Pdx1-Cre-ER^TM or Ngn3-Cre-ER^TM is used, tamoxifen (TM) is injected at different embryonic or postnatal days as indicated (D2). HPAP staining was examined 3-8 weeks after birth.