FIGURE 2. Specificity and dose dependence of recombination.

a, HPAP expression is specific to islets. A section from the pancreas of a RIP–CreER;Z/AP mouse injected with tamoxifen 2 days before sacrifice and stained for insulin (brown) and HPAP (blue). HPAP⁺ cells are found in islets and are absent from acini and ducts. Original magnification, 50. Scale bar, 100 m. Note that co-staining for insulin and HPAP results in a dark blue to black colour. b, HPAP labelling within islets is specific to -cells. A confocal image of a section similar to a, stained for DNA (4,6-diamidino-2-phenylindole (DAPI); blue), insulin (green) and HPAP (red). All HPAP⁺ cells also express insulin (orange in the lower-right panel). Note that insulin-negative islet cells (for example, glucagon-positive cells) do not express HPAP (arrowheads). Original magnification, 400. c, HPAP⁺ cells (red) do not express non--cell markers (green). DNA is stained with DAPI (blue). Original magnification for the DBA and amylase staining, 200; for the glucagon, somatostatin and pp staining, 400. d, The degree of HPAP labelling in islets is dependent on the dose of tamoxifen (TM). Shown are sections of the pancreas from adult RIP–CreER;Z/AP mice, injected with the indicated dose of tamoxifen. Slides were stained for HPAP (dark blue) and counterstained with haematoxylin. Original magnification, 100. Scale bar, 50 m.