Engineering of NEMO as calcium indicators with large dynamics and high sensitivity

Genetically encoded calcium indicators (GECIs) are indispensable tools for real-time monitoring of intracellular calcium signals and cellular activities in living organisms. Current GECIs face the challenge of suboptimal peak signal-to-baseline ratio (SBR) with limited resolution for reporting subtle calcium transients. We report herein the development of a suite of calcium sensors, designated NEMO, with fast kinetics and wide dynamic ranges (>100-fold). NEMO indicators report Ca^2+ transients with peak SBRs around 20-fold larger than the top-of-the-range GCaMP6 series. NEMO sensors further enable the quantification of absolution calcium concentration with ratiometric or photochromic imaging. Compared with GCaMP6s, NEMOs could detect single action potentials in neurons with a peak SBR two times higher and a median peak SBR four times larger in vivo, thereby outperforming most existing state-of-the-art GECIs. Given their high sensitivity and resolution to report intracellular Ca^2+ signals, NEMO sensors may find broad applications in monitoring neuronal activities and other Ca^2+-modulated physiological processes in both mammals and plants.

Jia Li, Ziwei Shang, Jia-Hui Chen, Wenjia Gu, Li Yao, Xin Yang, Xiaowen Sun, Liuqing Wang, Tianlu Wang, Siyao Liu, Jiajing Li, Tingting Hou, Dajun Xing, Donald L. Gill, Jiejie Li, Shi-Qiang Wang, Lijuan Hou, Yubin Zhou, Ai-Hui Tang, Xiaohui Zhang, Youjun Wang