ZIGIR, a Granule-Specific Zn2+ Indicator, Reveals Human Islet α Cell Heterogeneity

Numerous mammalian cells contain abundant Zn2+ in their secretory granules, yet available Zn2+ sensors lack the desired specificity and sensitivity for imaging granular Zn2+. We developed a fluorescent zinc granule indicator, ZIGIR, that possesses numerous desired properties for live cell imaging, including >100-fold fluorescence enhancement, membrane permeability, and selective enrichment to acidic granules. The combined advantages endow ZIGIR with superior sensitivity and specificity for imaging granular Zn2+. ZIGIR enables separation of heterogenous β cells based on their insulin content and sorting of mouse islets into pure α cells and β cells. In human islets, ZIGIR facilitates sorting of endocrine cells into highly enriched α cells and β cells, reveals unexpectedly high Zn2+ activity in the somatostatin granule of some δ cells, and uncovers variation in the glucagon content among human α cells. We expect broad applications of ZIGIR for studying Zn2+ biology and Zn2+-rich secretory granules and for engineering β cells with high insulin content for treating diabetes. [Display omitted] •ZIGIR is a fluorescent Zn2+ indicator that selectively labels Zn2+-rich granules•ZIGIR imaging tracks granule dynamics and exocytosis with high sensitivity•ZIGIR enables sorting of human or mouse islet α cells and β cells with high purity•ZIGIR reveals human α cell heterogeneity defined by distinct glucagon content Ghazvini Zadeh et al. develop a fluorescent zinc indictor, ZIGIR, that labels Zn2+-rich secretory granules with high specificity and sensitivity. ZIGIR tracks trafficking and exocytosis of native granules, enables sorting of islet α cells and β cells with high purity, and reveals human α cell heterogeneity and high Zn2+ activity in the human somatostatin granule.