Efficiency of Isl1 ablation in stomachs of Isl1MCM/Delmutant mouse stomachs at E18.5. (A) Tamoxifen-inducible Cre recombinase excised DNA sequences flanked by two loxP sites. (B) Isl1 RNA levels were ablated in Isl1MCM/Del mutant stomachs as seen by semi-quantitative PCR. Isl1F/+mice showed a 592 base pair product whereas Isl1MCM/Del mice generated a 303 base pair product. (C) Isl1 was significantly down-regulated at the protein levels in Isl1MCM/Del mutant stomachs as shown by western blot. Expression of embryos at E11.5 was used as positive control. (D) Isl1 protein expression in Isl1F/+and Isl1MCM/Del embryonic pylorus. Isl1 expression was significantly reduced in Isl1MCM/Del embryonic stomachs, as seen by immunofluorescence. Images in Isl1F/+and Isl1MCM/Del were processed on the same slide and photographed at the same exposure. Enlarged images of the boxed areas are shown on the right side of the merged pictures. Yellow arrowheads show representative Isl1-positive cells, and white arrowheads show representative Isl1-negative cells. Yellow dotted lines mark the epithelial basement membrane. Scale bars: 50 μm.