Sub-nanomolar sensitive GZnP3 reveals TRPML1-mediated neuronal Zn2+ signals.

Although numerous fluorescent Zn2+ sensors have been reported, it is unclear whether and how Zn2+ can be released from the intracellular compartments into the cytosol due to a lack of probes that can detect physiological dynamics of cytosolic Zn2+. Here, we create a genetically encoded sensor, GZnP3, which demonstrates unprecedented sensitivity for Zn2+ at sub-nanomolar concentrations. Using GZnP3 as well as GZnP3-derived vesicular targeted probes, we provide the first direct evidence that Zn2+ can be released from endolysosomal vesicles to the cytosol in primary hippocampal neurons through the TRPML1 channel. Such TRPML1-mediated Zn2+ signals are distinct from Ca2+ in that they are selectively present in neurons, sustain longer, and are significantly higher in neurites as compared to the soma. Together, our work not only creates highly sensitive probes for investigating sub-nanomolar Zn2+ dynamics, but also reveals new pools of Zn2+ signals that can play critical roles in neuronal function. Numerous fluorescent Zn2+ sensors are available but most are unsuitable to detect physiological dynamics of cytosolic Zn2+. In this study, the authors present a genetically encoded sensor with sub-nanomolar sensitivity and show that Zn2 + is released from endolysosomal vesicles via TRPML1 in neurons.