Optimized ratiometric calcium sensors for functional in vivo imaging of neurons and T lymphocytes

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Thestrup, Thomas
Litzlbauer, Julia
Bartholomaus, Ingo
Mues, Marsilius
Russo, Luigi
Dana, Hod
Kovalchuk, Yuri
Liang, Yajie
Kalamakis, Georgios
Lauka, Yvonne
Becker, Stefan
Witte, Gregor
Geiger, Anselm
Allen, Taylor
Rome, Lawrence C.
Chen, Tsai-Wen
Kim, Douglas S.
Garaschuk, Olga
Griesinger, Christian
Griesbeck, Oliver
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The quality of genetically encoded calcium indicators (GECIs) has improved dramatically in recent years, but high-performing ratiometric indicators are still rare. Here we describe a series of fluorescence resonance energy transfer (FRET)-based calcium biosensors with a reduced number of calcium binding sites per sensor. These ‘Twitch’ sensors are based on the C-terminal domain of Opsanus troponin C. Their FRET responses were optimized by a large-scale functional screen in bacterial colonies, refined by a secondary screen in rat hippocampal neuron cultures. We tested the in vivo performance of the most sensitive variants in the brain and lymph nodes of mice. The sensitivity of the “Twitch” sensors matched that of synthetic calcium dyes and allowed visualization of tonic action potential firing in neurons and high resolution functional tracking of T lymphocytes. Given their ratiometric readout, their brightness, large dynamic range and linear response properties, Twitch sensors represent versatile tools for neuroscience and immunology.
Author Posting. © The Author(s), 2013. This is the author's version of the work. It is posted here by permission of Nature Publishing Group for personal use, not for redistribution. The definitive version was published in Nature Methods 11 (2014): 175-182, doi:10.1038/nmeth.2773.
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