A sensitive orange fluorescent calcium ion indicator for imaging neural activity

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bioRxiv. 2025 Jul 31;. doi: 10.1101/2025.07.28.667269

A sensitive orange fluorescent calcium ion indicator for imaging neural activity Turner LabTuraga LabTool Translation Team (T3)

Aggarwal A, Baker HA, Dürst CD, Chen I, de Chambrier P, Gonzales JM, Marvin JS, Vandal M, Lundberg T, Sakoi K, Patel R, Wang C, Visser F, Fouad Y, Sunil S, Wiens M, Terai T, Takahashi-Yamashiro K, Thompson RJ, Brown TA, Nasu Y, Nguyen MD, Gordon GR, McFarlane S, Podgorski K, Holtmaat A, Campbell RE, Lohman AW

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Abstract

Genetically encoded calcium indicators (GECIs) are vital tools for fluorescence-based visualization of neuronal activity with high spatial and temporal resolution. However, current highest-performance GECIs are predominantly green or red fluorescent, limiting multiplexing options and efficient excitation with fixed-wavelength femtosecond lasers operating at 1030 nm. Here, we introduce OCaMP (also known as O-GECO2), an orange fluorescent GECI engineered from O-GECO1 through targeted substitutions to improve calcium affinity while retaining the favorable photophysical properties of mOrange2. OCaMP exhibits improved two-photon cross-section, responsiveness, photostability, and calcium affinity relative to O-GECO1. In cultured neurons, zebrafish, and mouse cortex, OCaMP outperforms the red GECIs jRCaMP1a and jRGECO1a in sensitivity, kinetics, and signal-to-noise ratio. These properties establish OCaMP as a robust tool for high-fidelity neural imaging optimized for 1030 nm excitation and a compromise-free option within the spectral gap between existing green and red GECIs.

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A sensitive orange fluorescent calcium ion indicator for imaging neural activity

Abstract

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