Immunostaining and morphometric evaluation Paraffin sections were incubated overnight with primary antibody (Key Resources Table). For each antibody, sections were stained and imaged in parallel such that the staining intensity reflects the protein expression. For quantification, images were captured systematically covering the whole section in confocal mode on a Zeiss LSM 710 microscope. Every cluster of insulin-stained cells (3–7 cells) or islet (8 or more cells)/section was evaluated; sections were coded and read blindly. For each age, 3–4 animals were evaluated for each staining. For human samples, sections from one block from the body of the pancreas from donors as listed in Key Resources Table.