Far-red fluorescent genetically encoded calcium ion indicators.

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Nat Commun. 2025 Apr 07;16(1):3318. doi: 10.1038/s41467-025-58485-z

Far-red fluorescent genetically encoded calcium ion indicators. GENIE

Dalangin R, Jia BZ, Qi Y, Aggarwal A, Sakoi K, Drobizhev M, Molina RS, Patel R, Abdelfattah AS, Zheng J, Reep D, Hasseman JP, Team GENIE, Zhao Y, Wu J, Podgorski K, Tebo AG, Schreiter ER, Hughes TE, Terai T, Paquet M, Megason SG, Cohen AE, Shen Y, Campbell RE

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Abstract

Genetically encoded calcium ion (Ca) indicators (GECIs) are widely-used molecular tools for functional imaging of Ca dynamics and neuronal activities with single-cell resolution. Here we report the design and development of two far-red fluorescent GECIs, FR-GECO1a and FR-GECO1c, based on the monomeric far-red fluorescent proteins mKelly1 and mKelly2. FR-GECOs have excitation and emission maxima at ~596 nm and ~644 nm, respectively, display large responses to Ca in vitro (ΔF/F = 6 for FR-GECO1a, 18 for FR-GECO1c), are bright under both one-photon and two-photon illumination, and have high affinities (apparent K = 29 nM for FR-GECO1a, 83 nM for FR-GECO1c) for Ca. FR-GECOs offer sensitive and fast detection of single action potentials in neurons, and enable in vivo all-optical manipulation and measurement of cellular activities in combination with optogenetic actuators.

Preprint: https://doi.org/10.1101/2020.11.12.380089