Subcellular localization of fluorescein-Trp25-exendin-4 in cultivated tumor β-cells of Rip1Tag2 mice 2 h after injection. Tumor beta-cells were incubated with fluorescein-Trp25-exendin-4 (A, green), anti-Rab5a (B, red, an anti-early endosome antibody), and nuclear DAPI stain (C, blue). Fluorescein-Trp25-exendin-4 was internalized into the cytoplasm and to a much lower degree into the nuclei of the tumor beta-cells. However, no strong co-localization was observed (D, merged picture). Scale bar, 10 μm.