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Figure 1: Localization of STC-1 (receptor, ligand, and mRNA) and insulin ligand in mouse pancreatic islets. (a) and (b) show an example of in situ ligand binding (ISLB) to localize STC-1 receptors in adult mouse pancreas ((b) is higher magnification of (a)). High binding activity is evident over islet cells (dark purple). Comparatively low binding activity is evident over exocrine pancreatic acinar cells (Ex) and islet cell nuclei (arrow in (b)). The inset in (b) is a staining control. (c) shows the results of fluorescent immunocytochemistry (ICC) to colocalize STC-1 and insulin in adult mouse pancreatic islets, insulin (red), STC-1 (green), and insulin/STC-1 colocalization (merged in yellow). There was no immunoreactivity in surrounding exocrine tissue. The inset at lower left is an STC-1 staining control. (d) shows the distribution of STC-1 in the embryonic mouse pancreas (e17.5) as revealed by peroxidase immunocytochemistry. STC-1 immunoreactivity is evident in exocrine (Ex) acinar cells (arrow) but not in islet tissue (I). (e) shows the distribution of STC-1 receptors in a tissue section adjacent to that in (d) (e17.5). Weak binding activity is equally distributed in islet (I) and exocrine cells (Ex). (f) shows the distribution of STC-1 mRNA as revealed by digoxigenin-based in situ hybridization (ISH) in adult mouse pancreas. The hybridization signal obtained with antisense cRNA probe was confined for the most part to presumptive islet cell nuclei (red arrows). Weak hybridization signal was also evident over the cytoplasm of isolated acinar cells (black arrows). The inset panel is an adjacent section stained by ISH using a sense cRNA probe.