A genetically targeted optical sensor to monitor calcium signals in astrocyte processes

Shigetomi, Eiji; Kracun, Sebastian; Sofroniew, Michael V.; Khakh, Baljit S.

doi:10.1038/nn.2557

Cited by 225 publications

(268 citation statements)

References 51 publications

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“…We first verified that BAPTA-AM applied through bulk loading specifically localizes in astrocytes as suggested by others [32]. Ca 2+ events of BAPTA-AM-loaded slices were monitored in astrocytes using Fluo-4 and in pyramidal neurons using Lck-GCamp3 [33] (Figure S3; Movie S3). The chelation of intracellular calcium (Ca 2+ i ) by BAPTA-AM prevented ATP-mediated calcium transients in astrocytes ( Figure S3A), but it did not affect carbachol-induced calcium spiking in neurons ( Figure S3B).…”

Section: Synaptic Activity Regulates Pap Motility Through Mglurs and supporting

confidence: 74%

Activity-Dependent Structural Plasticity of Perisynaptic Astrocytic Domains Promotes Excitatory Synapse Stability

et al. 2014

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SummaryBackground: Excitatory synapses in the CNS are highly dynamic structures that can show activity-dependent remodeling and stabilization in response to learning and memory. Synapses are enveloped with intricate processes of astrocytes known as perisynaptic astrocytic processes (PAPs). PAPs are motile structures displaying rapid actin-dependent movements and are characterized by Ca 2+ elevations in response to neuronal activity. Despite a debated implication in synaptic plasticity, the role of both Ca 2+ events in astrocytes and PAP morphological dynamics remain unclear. Results: In the hippocampus, we found that PAPs show extensive structural plasticity that is regulated by synaptic activity through astrocytic metabotropic glutamate receptors and intracellular calcium signaling. Synaptic activation that induces long-term potentiation caused a transient PAP motility increase leading to an enhanced astrocytic coverage of the synapse. Selective activation of calcium signals in individual PAPs using exogenous metabotropic receptor expression and two-photon uncaging reproduced these effects and enhanced spine stability. In vivo imaging in the somatosensory cortex of adult mice revealed that increased neuronal activity through whisker stimulation similarly elevates PAP movement. This in vivo PAP motility correlated with spine coverage and was predictive of spine stability. Conclusions: This study identifies a novel bidirectional interaction between synapses and astrocytes, in which synaptic activity and synaptic potentiation regulate PAP structural plasticity, which in turn determines the fate of the synapse. This mechanism may represent an important contribution of astrocytes to learning and memory processes.

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Section: Synaptic Activity Regulates Pap Motility Through Mglurs and supporting

confidence: 74%

Activity-Dependent Structural Plasticity of Perisynaptic Astrocytic Domains Promotes Excitatory Synapse Stability

et al. 2014

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“…Autocrine effects cannot be strictly excluded, such as glutamate-induced astrocytic release of, for example, growth factors, cytokines, or small-molecule gliotransmitters (e.g., ATP). However, it appears unlikely that glial release of ATP or other substances would lead to effective medium concentrations (39,40) in our model, in which astrocytes are deliberately cultured at high interindividual distance with 0.05 μL diffusion volume per cell.…”

Section: Discussionmentioning

confidence: 99%

Structural plasticity of perisynaptic astrocyte processes involves ezrin and metabotropic glutamate receptors

Lavialle

Aumann

Anlauf

et al. 2011

Proc. Natl. Acad. Sci. U.S.A.

233

264

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The peripheral astrocyte process (PAP) preferentially associates with the synapse. The PAP, which is not found around every synapse, extends to or withdraws from it in an activity-dependent manner. Although the pre-and postsynaptic elements have been described in great molecular detail, relatively little is known about the PAP because of its difficult access for electrophysiology or light microscopy, as they are smaller than microscopic resolution. We investigated possible stimuli and mechanisms of PAP plasticity. Immunocytochemistry on rat brain sections demonstrates that the actin-binding protein ezrin and the metabotropic glutamate receptors (mGluRs) 3 and 5 are compartmentalized to the PAP but not to the GFAP-containing stem process. Further experiments applying ezrin siRNA or dominant-negative ezrin in primary astrocytes indicate that filopodia formation and motility require ezrin in the membrane/cytoskeleton bound (i.e., T567-phosphorylated) form. Glial processes around synapses in situ consistently display this ezrin form. Possible motility stimuli of perisynaptic glial processes were studied in culture, based on their similarity with filopodia. Glutamate and glutamate analogues reveal that rapid (5 min), glutamate-induced filopodia motility is mediated by mGluRs 3 and 5. Ultrastructurally, these mGluR subtypes were also localized in astrocytes in the rat hippocampus, preferentially in their fine PAPs. In vivo, changes in glutamatergic circadian activity in the hamster suprachiasmatic nucleus are accompanied by changes of ezrin immunoreactivity in the suprachiasmatic nucleus, in line with transmitter-induced perisynaptic glial motility. The data suggest that (i) ezrin is required for the structural plasticity of PAPs and (ii) mGluRs can stimulate PAP plasticity.A strocytes act as a third partner in synaptic signal processing by responding to neurotransmitters and by releasing "gliotransmitters" (1, 2). Structurally, the astrocyte functions mainly through its peripheral processes, which constitute approximately 80% of the cell's membrane (3). These peripheral astrocyte processes (PAPs) are frequently extremely fine (<50 nm) and display an extreme surface-to-volume ratio. They are rarely studied in live tissue, as they are not directly accessible to electrophysiology, cannot be isolated for biochemistry, and are smaller than microscopic resolution. However, they also wrap synapses, but most studies on glia-synaptic interaction can only indiscriminately refer to them as the astrocyte. At the ultrastructural level, the PAPs, although abundant in the neuropil, specifically prefer contacting synapses and dendrites versus axons (4). The synaptic wrapping is highly dynamic (5-9) and also activity-dependent even in the context of physiological functions, such as motor learning, daily fluctuations of the circadian clock, lactation, parturition, or dehydration (10-15). Here, we asked two questions about the structural basis of glia-synaptic interaction: What is the stimulus for PAP plasticity, and what are the intra...

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“…This suggests that Ca 2þ signals in the subplasmamembranous regions can be separately regulated from those in the cytosol. Therefore, the subplasmamembranous domains have been one of the major targets of GECIs, and several types of GECIs have been localized to the plasma membrane by fusion with plasma membrane-anchoring motifs, such as myristoylation, palmitoylation, or farnesylation tags (18,61), or with plasma membrane-localized transporters (62,63). GEGIs fused with synaptic proteins, such as synaptosome-associated protein of 25 kDa (SNAP25), synaptophysin, and synaptobrevin, have been also used to detect microdomain Ca 2þ signals in the synapse (18,64).…”

Section: Subplasmamembranementioning

confidence: 99%

Genetically Encoded Fluorescent Indicators for Organellar Calcium Imaging

Suzuki

Kanemaru

Iino

2016

Biophysical Journal

115

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Optical Ca 2þ indicators are powerful tools for investigating intracellular Ca 2þ signals in living cells. Although a variety of Ca 2þ indicators have been developed, deciphering the physiological functions and spatiotemporal dynamics of Ca 2þ in intracellular organelles remains challenging. Genetically encoded Ca 2þ indicators (GECIs) using fluorescent proteins are promising tools for organellar Ca 2þ imaging, and much effort has been devoted to their development. In this review, we first discuss the key points of organellar Ca 2þ imaging and summarize the requirements for optimal organellar Ca 2þ indicators. Then, we highlight some of the recent advances in the engineering of fluorescent GECIs targeted to specific organelles. Finally, we discuss the limitations of currently available GECIs and the requirements for advancing the research on intraorganellar Ca 2þ signaling.

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A genetically targeted optical sensor to monitor calcium signals in astrocyte processes

Cited by 225 publications

References 51 publications

Activity-Dependent Structural Plasticity of Perisynaptic Astrocytic Domains Promotes Excitatory Synapse Stability

Activity-Dependent Structural Plasticity of Perisynaptic Astrocytic Domains Promotes Excitatory Synapse Stability

Structural plasticity of perisynaptic astrocyte processes involves ezrin and metabotropic glutamate receptors

Genetically Encoded Fluorescent Indicators for Organellar Calcium Imaging

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