Rational Engineering of XCaMPs, a Multicolor GECI Suite for In Vivo Imaging of Complex Brain Circuit Dynamics

Abstract

To decipher dynamic brain information processing, current genetically encoded calcium indicators (GECIs) are limited in single action potential (AP) detection speed, combinatorial spectral compatibility, and two-photon imaging depth. To address this, here, we rationally engineered a next-generation quadricolor GECI suite, XCaMPs. Single AP detection was achieved within 3-10 ms of spike onset, enabling measurements of fast-spike trains in parvalbumin (PV)-positive interneurons in the barrel cortex in vivo and recording three distinct (two inhibitory and one excitatory) ensembles during pre-motion activity in freely moving mice. In vivo paired recording of preand postsynaptic firing revealed spatiotemporal constraints of dendritic inhibition in layer 1 in vivo, between axons of somatostatin (SST)-positive interneurons and apical tufts dendrites of excitatory pyramidal neurons. Finally, non-invasive, subcortical imaging using red XCaMP-R uncovered somatosensationevoked persistent activity in hippocampal CA1 neurons. Thus, the XCaMPs offer a critical enhancement of solution space in studies of complex neuronal circuit dynamics.

jYCaMP: An optimized calcium indicator for two-photon imaging at fiber laser wavelengths

“…Significantly-correlated sites showed apposed structures and highly-coordinated dynamics (Fig 2fg). These results demonstrate that jYCaMP's improved coexcitation with RFPs enables previously-challenging two-color experiments, which previously required high excitation powers 16,18,19 that can damage neurites 20 .…”

“…2b). Simultaneous 1030 nm excitation of jYCaMP1s and jRGECO1a enabled recording of distinct Ca 2+ dynamics in spatially-overlapping axonal and dendritic compartments, which has been used to identify putative synapses 16,18,19 . We compared jGCaMP7s to jYCaMP1s for such detection of coactive axons and dendrites, based on trial-to-trial correlations to dendritic jRGECO responses at putative boutons.…”

Correction of β3 integrin haplo-insufficiency by CRISPRa normalizes cortical network activity

“…While MEAs provided information mainly in the temporal domain, jRCaMP1b fluorescence transients exhibited high variability in amplitude also within the same recordings (Figs 1A and 4A), suggesting variability in the underlying firing activity (Inoue et al, 2019). Although the average amplitude of the fluorescence signals was not different across conditions (Fig 4C), their variability allowed us to gain a better insight into the level of synchrony of the networks.…”

“…We next asked whether these differences affected cortical network activity. To this end, we used a red-shifted genetically encoded Ca 2+ indicator, jRCaMP1b (Dana et al, 2016), to monitor spontaneous fluorescence signals in neurons (Fig 1), which can be interpreted as correlates of neuronal activity (Inoue et al, 2019). Somatic jRCaMP1b transients had a favorable signal-to-noise ratio (Fig 1A, B).…”

Simultaneous electrophysiological recording and fiber photometry in freely behaving mice

“…Genetically encoded indicators offer complementary advantages over in vivo electrophysiological approaches Deo and Lavis, 2018;Wang et al, 2019). Over the last two decades, genetically encoded calcium indicators (GECIs) have been widely used to interrogate not only neuronal ensemble dynamics, but also activity of non-neuronal cells, such as astrocytes in vivo (Nakai et al, 2001;Chen et al, 2013;Stobart et al, 2018;Dana et al, 2019;Inoue et al, 2019;Stringer et al, 2019). For example, GECIs enable to target specific cell-types and allow for the long-term monitoring of neuronal activity in vivo.…”