Far-red fluorescent genetically encoded calcium ion indicators

Rochelin Dalangin; Bill Jia; Yitong Qi; Abhi Aggarwal; Kenryo Sakoi; Mikhail A. Drobizhev; Rosana S. Molina; Ronak H. Patel; Ahmed S. Abdelfattah; Jihong Zheng; Daniel Reep; Jeremy P. Hasseman; The GENIE Project Team; Getahun Tsegaye; Arthur Tsang; Glenn C Turner; Yufeng Zhao; Jiahui Wu; Kaspar Podgorski; Alison G. Tebo; Eric R. Schreiter; Thomas E. Hughes; Takuya Terai; Marie-Ève Paquet; Sean G. Megason; Adam E. Cohen; Yi Shen; Robert E. Campbell

doi:10.1038/s41467-025-58485-z

NeuroscienceNature CommunicationsApr 7, 2025

Peer-reviewed journal article

Far-red fluorescent genetically encoded calcium ion indicators

Rochelin Dalangin iD, Bill Jia iD, Yitong Qi, Abhi Aggarwal iD, Kenryo Sakoi, Mikhail A. Drobizhev iD, Rosana S. Molina iD, Ronak H. Patel iD, Ahmed S. Abdelfattah iD, Jihong Zheng iD, Daniel Reep iD, Jeremy P. Hasseman iD, The GENIE Project Team, Getahun Tsegaye, Arthur Tsang iD, Glenn C Turner iD, Yufeng Zhao iD, Jiahui Wu iD, Kaspar Podgorski iD, Alison G. Tebo iD, Eric R. Schreiter iD, Thomas E. Hughes iD, Takuya Terai iD, Marie-Ève Paquet iD, Sean G. Megason iD, , Robert E. Campbell iD

Abstract

Genetically encoded calcium ion (Ca2+) indicators (GECIs) are widely-used molecular tools for functional imaging of Ca2+ dynamics and neuronal activities on a single cell level. Here we report the design and development of two new far-red fluorescent GECIs, FR-GECO1a and FR-GECO1c, based on the monomeric far-red fluorescent protein mKelly. We characterized these far-red GECIs as purified proteins and assessed their performance when expressed in cultured neurons. FR-GECOs have excitation and emission maxima at ~ 596 nm and ~ 644 nm, respectively, display large responses to Ca2+ ({Delta}F/F0 = 6 for FR-GECO1a, 18 for FR-GECO1c), and are bright under both one-photon and two-photon illumination. FR-GECOs also have high affinities (apparent Kd = 29 nM for FR-GECO1a, 83 nM for FR-GECO1c) for Ca2+, and they enable sensitive and fast detection of single action potentials in neurons.

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