Numerous mammalian cells contain abundant Zn2+ in their secretory granules. During stimulated secretion, Zn2+ is coreleased with other cargos into the extracellular medium, and the released Zn2+ can function as an important signal to modulate the biochemistry of neighboring cells or distant cells via paracrine or endocrine mechanisms. Despite the biological importance of granular Zn2+ activity, it remains challenging to monitor Zn2+ levels in the lumen of secretory granules with high specificity and sensitivity. To fill this technological gap, we have developed a class of cell membrane permeable fluorescent zinc granule indicators, ZIGIRs, that displayed more than 30-fold fluorescence enhancement upon Zn2+ binding. ZIGIRs are refractory to pH fluctuation down to pH 5 so they are ideally suited for measuring Zn2+ in acidic compartments including secretory granules. In pancreatic islet beta cells, ZIGIRs mark Zn2+-rich insulin granules with high specificity and reveal dynamic movements of individual insulin granules in living cells by time-lapse imaging. In addition to fluorescence microscopy, ZIGIRs are also compatible with flow cytometry to enable sorting of heterogenous beta cells based on their insulin granule contents. We expect ZIGIRs to have wide applications for studying the regulation, biogenesis, and trafficking of Zn2+-rich granules in living cells and for engineering beta cells with high insulin contents for treating diabetes

ZIGIRs for the fluorescence imaging of Zn2+ in secretory granules

2019 Spring National Meeting

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