Highly Dynamic and Sensitive NEMOer Calcium Indicators for Imaging ER Calcium Signals in Excitable Cells

Abstract

AbstractEndoplasmic/sarcoplasmic reticulum (ER/SR) sits at the heart of the calcium (Ca2+) signaling machinery, yet current genetically encoded Ca2+indicators (GECIs) lack the ability to detect elementary Ca2+release events from ER/SR, particularly in muscle cells. Here we report a set of organellar GECIs, termed NEMOer, to efficiently capture ER Ca2+dynamics with increased sensitivity and responsiveness. Compared to G-CEPIA1er, NEMOer indicators exhibit dynamic ranges that are an order of magnitude larger, which enables up to 5-fold more sensitive detection of Ca2+oscillation in both non-excitable and excitable cells. The ratiometric version further allows super-resolution monitoring of local ER Ca2+homeostasis and dynamics. Notably, the NEMOer-f variant enabled the inaugural detection of Ca2+blinks, elementary Ca2+releasing signals from the SR of cardiomyocytes, as well asin vivospontaneous SR Ca2+releases in zebrafish. In summary, the highly dynamic NEMOer sensors expand the repertoire of organellar Ca2+sensors that allow real-time monitoring of intricate Ca2+dynamics and homeostasis in live cells with high spatiotemporal resolution.