A method for labeling insulin-secreting pancreatic β-cells in human islets by using a genetically-encoded preproinsulin fluorescent protein reporter which targets an insulin fusion protein to correct insulin vesicles. The reporter system comprising an insulin and fluorescent protein construct provides real time tracking of secretory granules in live cells and allows for the accurate measuring of the level of secretion. The labeled cells are sorted by fluorescence-activated cell sorting to obtain purified insulin-secreting pancreatic β-cell pools from human islets. The β-cell pools are suitable for transplantation into the pancreas of diabetics in order to treat diabetes.
