301
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Bernstein JG, Boyden ES. Optogenetic tools for analyzing the neural circuits of behavior. Trends Cogn Sci 2011; 15:592-600. [PMID: 22055387 DOI: 10.1016/j.tics.2011.10.003] [Citation(s) in RCA: 166] [Impact Index Per Article: 12.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2011] [Revised: 10/11/2011] [Accepted: 10/11/2011] [Indexed: 01/04/2023]
Abstract
In order to understand how the brain generates behaviors, it is important to be able to determine how neural circuits work together to perform computations. Because neural circuits are made of a great diversity of cell types, it is critical to be able to analyze how these different kinds of cell work together. In recent years, a toolbox of fully genetically encoded molecules has emerged that, when expressed in specific neurons, enables the electrical activity of the targeted neurons to be controlled in a temporally precise fashion by pulses of light. We describe this optogenetic toolbox, how it can be used to analyze neural circuits in the brain and how optogenetics is impacting the study of cognition.
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Affiliation(s)
- Jacob G Bernstein
- MIT Media Lab and McGovern Institute, Departments of Brain and Cognitive Sciences, and Biological Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
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302
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Ground-state properties of the retinal molecule: from quantum mechanical to classical mechanical computations of retinal proteins. Theor Chem Acc 2011. [DOI: 10.1007/s00214-011-1054-1] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/15/2022]
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303
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Ellis-Davies GCR, Pugh EN. The 64th Symposium of the Society for General Physiologists: optogenetics and superresolution microscopy take center stage. ACTA ACUST UNITED AC 2011; 138:1-11. [PMID: 21708951 PMCID: PMC3135327 DOI: 10.1085/jgp.201110673] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
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304
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Venken KJ, Simpson JH, Bellen HJ. Genetic manipulation of genes and cells in the nervous system of the fruit fly. Neuron 2011; 72:202-30. [PMID: 22017985 PMCID: PMC3232021 DOI: 10.1016/j.neuron.2011.09.021] [Citation(s) in RCA: 306] [Impact Index Per Article: 23.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 09/26/2011] [Indexed: 12/26/2022]
Abstract
Research in the fruit fly Drosophila melanogaster has led to insights in neural development, axon guidance, ion channel function, synaptic transmission, learning and memory, diurnal rhythmicity, and neural disease that have had broad implications for neuroscience. Drosophila is currently the eukaryotic model organism that permits the most sophisticated in vivo manipulations to address the function of neurons and neuronally expressed genes. Here, we summarize many of the techniques that help assess the role of specific neurons by labeling, removing, or altering their activity. We also survey genetic manipulations to identify and characterize neural genes by mutation, overexpression, and protein labeling. Here, we attempt to acquaint the reader with available options and contexts to apply these methods.
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Affiliation(s)
- Koen J.T. Venken
- Department of Molecular and Human Genetics, Neurological Research Institute, Baylor College of Medicine, Houston, Texas, 77030
| | - Julie H. Simpson
- Janelia Farm Research Campus, Howard Hughes Medical Institute, Ashburn, Virginia, 20147
| | - Hugo J. Bellen
- Department of Molecular and Human Genetics, Neurological Research Institute, Baylor College of Medicine, Houston, Texas, 77030
- Program in Developmental Biology, Department of Neuroscience, Howard Hughes Medical Institute, Baylor College of Medicine, Houston, Texas, 77030
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305
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306
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Projection structure of channelrhodopsin-2 at 6 Å resolution by electron crystallography. J Mol Biol 2011; 414:86-95. [PMID: 22001017 DOI: 10.1016/j.jmb.2011.09.049] [Citation(s) in RCA: 55] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2011] [Revised: 09/27/2011] [Accepted: 09/29/2011] [Indexed: 01/10/2023]
Abstract
Channelrhodopsin-2 (ChR2) is the prototype of a new class of light-gated ion channels that is finding widespread applications in optogenetics and biomedical research. We present a 6-Å projection map of ChR2, obtained by cryo-electron microscopy of two-dimensional crystals grown from pure, heterologously expressed protein. The map shows that ChR2 is the same dimer with non-crystallographic 2-fold symmetry in three different membrane crystals. This is consistent with biochemical analysis, which shows a stable dimer in detergent solution. Comparison to the projection map to bacteriorhodopsin indicates a similar structure of seven transmembrane alpha helices. Based on the projection map and sequence alignments, we built a homology model of ChR2 that potentially accounts for light-induced channel gating. Although a monomeric channel is not ruled out, comparison to other membrane channels and transporters suggests that the ChR2 channel is located at the dimer interface on the 2-fold axis, lined by transmembrane helices 3 and 4.
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307
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Abstract
Both observational and perturbational technologies are essential for advancing the understanding of brain function and dysfunction. But while observational techniques have greatly advanced in the last century, techniques for perturbation that are matched to the speed and heterogeneity of neural systems have lagged behind. The technology of optogenetics represents a step toward addressing this disparity. Reliable and targetable single-component tools (which encompass both light sensation and effector function within a single protein) have enabled versatile new classes of investigation in the study of neural systems. Here we provide a primer on the application of optogenetics in neuroscience, focusing on the single-component tools and highlighting important problems, challenges, and technical considerations.
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Affiliation(s)
- Ofer Yizhar
- Department of Bioengineering, Stanford University, Stanford, CA 94305, USA
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308
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309
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Abstract
The absorption of light by bound or diffusible chromophores causes conformational rearrangements in natural and artificial photoreceptor proteins. These rearrangements are coupled to the opening or closing of ion transport pathways, the association or dissociation of binding partners, the enhancement or suppression of catalytic activity, or the transcription or repression of genetic information. Illumination of cells, tissues, or organisms engineered genetically to express photoreceptor proteins can thus be used to perturb biochemical and electrical signaling with exquisite cellular and molecular specificity. First demonstrated in 2002, this principle of optogenetic control has had a profound impact on neuroscience, where it provides a direct and stringent means of probing the organization of neural circuits and of identifying the neural substrates of behavior. The impact of optogenetic control is also beginning to be felt in other areas of cell and organismal biology.
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Affiliation(s)
- Gero Miesenböck
- Centre for Neural Circuits and Behaviour, Department of Physiology, Anatomy, and Genetics, University of Oxford, Oxford OX1 3TA, United Kingdom.
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310
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Busskamp V, Roska B. Optogenetic approaches to restoring visual function in retinitis pigmentosa. Curr Opin Neurobiol 2011; 21:942-6. [PMID: 21708457 DOI: 10.1016/j.conb.2011.06.001] [Citation(s) in RCA: 74] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2011] [Accepted: 06/03/2011] [Indexed: 12/15/2022]
Abstract
Retinitis pigmentosa is a hereditary eye disease that affects photoreceptors and leads to blindness. The discovery of a microbial light-gated channel and the subsequent development of similar 'optogenetic' sensors have opened the door to creating artificial photoreceptors in the remaining retinal circuits of retinitis pigmentosa retinas via gene therapy. Here we review recent studies in animal models of retinitis pigmentosa that have combined knowledge of retinal cell types, circuits and computations with the ability to equip cell types with optogenetic sensors in order to restore visual activity. We also discuss the translational potential of this therapy.
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Affiliation(s)
- Volker Busskamp
- Neural Circuit Laboratories, Friedrich Miescher Institute for Biomedical Research, Basel, Switzerland
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311
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Abstract
Light control of motility behavior (phototaxis and photophobic responses) in green flagellate algae is mediated by sensory rhodopsins homologous to phototaxis receptors and light-driven ion transporters in prokaryotic organisms. In the phototaxis process, excitation of the algal sensory rhodopsins leads to generation of transmembrane photoreceptor currents. When expressed in animal cells, the algal phototaxis receptors function as light-gated cation channels, which has earned them the name "channelrhodopsins." Channelrhodopsins have become useful molecular tools for light control of cellular activity. Only four channelrhodopsins, identified in Chlamydomonas reinhardtii and Volvox carteri, have been reported so far. By screening light-induced currents among algal species, we identified that the phylogenetically distant flagellate Mesostigma viride showed photoelectrical responses in vivo with properties suggesting a channelrhodopsin especially promising for optogenetic use. We cloned an M. viride channelrhodopsin, MChR1, and studied its channel activity upon heterologous expression. Action spectra in HEK293 cells match those of the photocurrents observed in M. viride cells. Comparison of the more divergent MChR1 sequence to the previously studied phylogenetically clustered homologs and study of several MChR1 mutants refine our understanding of the sequence determinants of channelrhodopsin function. We found that MChR1 has the most red-shifted and pH-independent spectral sensitivity so far reported, matches or surpasses known channelrhodopsins' channel kinetics features, and undergoes minimal inactivation upon sustained illumination. This combination of properties makes MChR1 a promising candidate for optogenetic applications.
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312
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Azeredo da Silveira R, Roska B. Cell types, circuits, computation. Curr Opin Neurobiol 2011; 21:664-71. [PMID: 21641794 DOI: 10.1016/j.conb.2011.05.007] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2011] [Revised: 05/10/2011] [Accepted: 05/10/2011] [Indexed: 12/25/2022]
Abstract
How does the connectivity of a neuronal circuit, together with the individual properties of the cell types that take part in it, result in a given computation? We examine this question in the context of retinal circuits. We suggest that the retina can be viewed as a parallel assemblage of many small computational devices, highly stereotypical and task-specific circuits afferent to a given ganglion cell type, and we discuss some rules that govern computation in these devices. Multi-device processing in retina poses conceptual problems when it is contrasted with cortical processing. We lay out open questions both on processing in retinal circuits and on implications for cortical processing of retinal inputs.
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Affiliation(s)
- Rava Azeredo da Silveira
- Department of Physics and Department of Cognitive Studies, École Normale Supérieure, Paris, France.
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313
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Abstract
Inherited retinal degeneration results from many different mutations in either photoreceptor-specific or nonphotoreceptor-specific genes. However, nearly all mutations lead to a common blinding phenotype that initiates with rod cell death, followed by loss of cones. In most retinal degenerations, other retinal neuron cell types survive for long periods after blindness from photoreceptor loss. One strategy to restore light responsiveness to a retina rendered blind by photoreceptor degeneration is to express light-regulated ion channels or transporters in surviving retinal neurons. Recent experiments in rodents have restored light-sensitivity by expressing melanopsin or microbial opsins either broadly throughout the retina or selectively in the inner segments of surviving cones or in bipolar cells. Here, we present an approach whereby a genetically and chemically engineered light-gated ionotropic glutamate receptor (LiGluR) is expressed selectively in retinal ganglion cells (RGCs), the longest-surviving cells in retinal blinding diseases. When expressed in the RGCs of a well-established model of retinal degeneration, the rd1 mouse, LiGluR restores light sensitivity to the RGCs, reinstates light responsiveness to the primary visual cortex, and restores both the pupillary reflex and a natural light-avoidance behavior.
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314
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Boyden ES. A history of optogenetics: the development of tools for controlling brain circuits with light. F1000 BIOLOGY REPORTS 2011; 3:11. [PMID: 21876722 PMCID: PMC3155186 DOI: 10.3410/b3-11] [Citation(s) in RCA: 124] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 12/03/2022]
Abstract
Understanding how different kinds of neuron in the brain work together to implement sensations, feelings, thoughts, and movements, and how deficits in specific kinds of neuron result in brain diseases, has long been a priority in basic and clinical neuroscience. “Optogenetic” tools are genetically encoded molecules that, when targeted to specific neurons in the brain, enable their activity to be driven or silenced by light. These molecules are microbial opsins, seven-transmembrane proteins adapted from organisms found throughout the world, which react to light by transporting ions across the lipid membranes of cells in which they are genetically expressed. These tools are enabling the causal assessment of the roles that different sets of neurons play within neural circuits, and are accordingly being used to reveal how different sets of neurons contribute to the emergent computational and behavioral functions of the brain. These tools are also being explored as components of prototype neural control prosthetics capable of correcting neural circuit computations that have gone awry in brain disorders. This review gives an account of the birth of optogenetics and discusses the technology and its applications.
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Affiliation(s)
- Edward S Boyden
- Media Lab, McGovern Institute, Department of Brain and Cognitive Sciences and Department of Biological Engineering MIT, 77 Massachusetts Avenue, Cambridge, MA 02139 USA
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315
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Boyden ES. A history of optogenetics: the development of tools for controlling brain circuits with light. F1000 BIOLOGY REPORTS 2011; 3:11. [PMID: 21876722 DOI: 10.3410/b] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
Understanding how different kinds of neuron in the brain work together to implement sensations, feelings, thoughts, and movements, and how deficits in specific kinds of neuron result in brain diseases, has long been a priority in basic and clinical neuroscience. "Optogenetic" tools are genetically encoded molecules that, when targeted to specific neurons in the brain, enable their activity to be driven or silenced by light. These molecules are microbial opsins, seven-transmembrane proteins adapted from organisms found throughout the world, which react to light by transporting ions across the lipid membranes of cells in which they are genetically expressed. These tools are enabling the causal assessment of the roles that different sets of neurons play within neural circuits, and are accordingly being used to reveal how different sets of neurons contribute to the emergent computational and behavioral functions of the brain. These tools are also being explored as components of prototype neural control prosthetics capable of correcting neural circuit computations that have gone awry in brain disorders. This review gives an account of the birth of optogenetics and discusses the technology and its applications.
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Affiliation(s)
- Edward S Boyden
- Media Lab, McGovern Institute, Department of Brain and Cognitive Sciences and Department of Biological Engineering MIT, 77 Massachusetts Avenue, Cambridge, MA 02139 USA
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