(A) Immunostaining of a representative pancreatic section from wild-type mouse embryos at E12.5 showing immunostaining for pancreatic progenitor marker Pdx1 and neuropeptide Y (NPY) or the same section overlaid with glucagon (Pdx1: cyan; NPY: red; glucagon: green), showing exclusion of NPY from pancreatic progenitors. (B) Immunostaining of representative pancreatic sections from Ngn3-EGFP (EGFP expression driven by Neurogenin3 promoter to mark endocrine progenitors) embryos at E15.5, showing NPY (red), GFP (green), insulin (Ins; cyan) and overlay with DAPI (to counterstain the nuclei; blue). Arrows indicate cells with high GFP expression defining endocrine progenitors. (C) Immunostaining for NPY (red), glucagon (Glu; green), and insulin (cyan), with DAPI (blue) in fetal mouse (E17.5) and human (16 weeks pc/gestation) pancreatic sections. Larger arrows mark overlap of NPY with insulin, while smaller arrows mark overlap of NPY with glucagon. Scale bar: 50 μm. For A and B and mouse data in C, n = 4 animals.