Imaging pancreatic β-cells in the intact pancreas

We have developed a method to visualize fluorescent protein-labeled β-cells in the intact pancreas through combined reflection and confocal imaging. This method provides a 3-D view of the β-cells in situ. Imaging of the pancreas from mouse insulin I promoter (MIP)-green (GFP) and red fluorescent protein (RFP) transgenic mice shows that islets, β-cell clusters, and single β-cells are not evenly distributed but are aligned along the large blood vessels. We also observe the solitary β-cells in both fetal and adult mice and along the pancreatic and common bile ducts. We have imaged the developing endocrine cells in the embryos using neurogenin-3 (Ngn3)-GFP mice crossed with MIP-RFP mice. The dual-color-coded pancreas from embryos (E15.5) shows a large number of green Ngn3-expressing proendocrine cells with a smaller number of red β-cells. The imaging technique that we have developed, coupled with the transgenic mice in which β-cells and β-cell progenitors are labeled with different fluorescent proteins, will be useful for studying pancreatic development and function in normal and disease states.