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Optogenetic approaches promise to revolutionize neuroscience by using light to manipulate neural activity in genetically or functionally defined neurons with millisecond precision. It is a neuromodulation technique facilitating monitoring and control of individual neurons in living organisms in real time. Harnessing the full potential of optogenetic tools, however, requires light to be targeted to the right neurons at the right time.

Physical delivery of virus to a given anatomical location can exploit or uncover circuit connectivity patterns either by making use of axonal projections or by using viruses that are able to cross one or more synapses. Cell types can be addressed if the cell type of interest has a known genetic identity. Directing the illumination source to a given set of cells or even individual neurons and processes is useful when the targets of interest are separated in space relative to the spatial resolution of the technique used.

As the study of neuroscience moves from dish to whole animal, new techniques are needed to study individual cellular responses within a broader functional context. Optogenetics is a technique that allows researchers to modulate the activity of target neurons using specific wavelengths of light. What makes the technique so useful is its ability to control neural activity so precisely even in free moving organisms. This is accomplished by coupling genetic expression of light-sensitive channel proteins within targeted cells to precision light exposure and measurement.

Optogenetic components

Although the concept of using light to control cellular behavior is well over 30 years old, obtaining the right optics, light source, photoactivatable protein, genetic construction tools was only accomplished first by the Karl Deisseroth laboratory in 2005.

Light sensitive proteins

The key reagents used in optogenetics are light-sensitive proteins. Several types of microbial opsins, are currently used to modulate neuronal function. Each type is sensitive to a different range of wavelengths and responds by altering different ion conductances. Blue light is commonly used to stimulate channelrhodopsin-2 (ChR2), a nonselective cation channel, resulting in potassium, sodium, and calcium flow which depolarizes the neuron to threshold. Other channelrhodopsin variants are now available that differ in depolarization and wavelength sensitivity characteristics yielding even finer control over neural modulation. The halorhodopsin (NpHR) class of chloride pumps, which respond to yellow light, are typically used to hyperpolarize neural membranes and induce inhibitory responses. 

Measuring the effects

The acceptance in the scientific community of optogenetics as an effective tool for modulating neural function or cellular signaling has come from careful verification of effects with traditional, well established tools. Electrodes are routinely used to record neural function during stimulation. So-called optogenetic sensors are also being used to measure calcium, chloride or membrane voltage shifts. Sequencing verifies the construct insertion. Protein presence and downstream protein-protein interactions and cell signaling are measured using antibodies and antibody-based technologies such as Western blotting and immunohistochemistry.

Below is a table showing the top published targets interrogated by optogenetics methods. Antibodies to these targets needed to verify protein presence/localization are also listed.

Gene NameCat no.DescriptionKey ApplicationsSpecies Reactivity
LARGE In Testing Anti-LARGE Rabbit Polyclonal Antibody WB, IHC
CHAT AB143 Anti-ChAT Rabbit polyclonal Antibody WB, IHC, IH(P), IP Mk, H, R, M, Bat, Fe
CHAT AB144 Anti-ChAT Goat polyclonal Antibody WB, IHC R, Gp, M
CHAT AB144P Anti-ChAT Goat polyclonal Antibody WB, IHC Op, Av, Gp, H, M, Mk, R
CHAT AB1582 Anti-ChAT Sheep polyclonal Antibody WB, IHC Rb, Gp, R
CHAT AB5042 Anti-ChAT Rabbit polyclonal Antibody IHC R, Av, GP
CHAT AB5042P Anti-ChAT Rabbit polyclonal Antibody IHC, ELISA R
CHAT AB15468 Anti-ChAT Chicken polyclonal Antibody IHC, ICC M
CHAT MAB5270-100UG Anti-ChAT Mouse Monoclonal Antibody WB, ELISA, IHC, IH(P) R, H, Po
CHAT MAB305 Anti-ChAT Mouse Monoclonal Antibody IHC R, H, Mk
CHAT MAB5350 Anti-ChAT Mouse Monoclonal Antibody IHC, WB, ELISA R, Gp, H, Mk
CHAT MAB5422 Anti-ChAT Mouse Monoclonal Antibody WB, ELISA H
ACHE MAB303 Anti-Acetylcholinesterase Mouse Monoclonal Antibody IP, ELISA, IHC Mk, B, Ca, Ch, Gp, H
REST 07-579 Anti-REST Rabbit Polyclonal Antibody WB R, H, Mk
REST 09-019 Anti-REST Rabbit Polyclonal Antibody WB R, H, M
PARK2 AB5112 Anti-PARK2(Parkin) Rabbit Polyclonal Antibody IHC, ELISA, WB R, H
PARK2 05-882 Anti-PARK2(Parkin) Mouse Monoclonal Antibody IHC, IP, WB, ICC M, H
PARK2 MAB5512 Anti-PARK2(Parkin) Mouse Monoclonal Antibody IHC, IP, WB M, H
THY1 CBL415 Anti-Thy-1 Mouse Monoclonal Antibody FC, IP, IH H
THY1 CBL1500F Anti-Thy-1 Mouse Monoclonal Antibody-FITC ICC, FC M
THY1 MABF34 Anti-Thy-1 Rat Monoclonal Antibody FUNC, WB M
AGRP AB3402P Anti-Aouti Related Protein Rabbit Polyclonal Antibody WB, ELISA M
POMC AB5087 Anti-Melanocyte Stimulating Hormone α (POMC) Sheep Polyclonal Antibody RIA, IHC H, M, R
SLC17A6 MAB5504 Anti-Vesicular Glutamate Transporter 2 Mouse Monoclonal Antibody IHC, WB H, M, R
SLC17A6 MAB55054A4 Anti-Vesicular Glutamate Transporter 2 Mouse Monoclonal Antibody-Alexa488 IHC H, M, R
CRY2 AB15056 Anti-Cryptochrome 2 Rabbit Polyclonal Antibody WB M
HCRT PC362 Anti-HCRT/Orexin Rabbit Polyclonal Antibody EIA, IHC, IF H, M, R
HCRT PC345 Anti-HCRT/Orexin Rabbit Polyclonal Antibody EIA, IHC, IF H, M, R
HCRT AB3096 Anti-HCRT/Orexin Rabbit Polyclonal Antibody EIA, IHC, WB H, M, R
HCRT AB3098 Anti-HCRT/Orexin Rabbit Polyclonal Antibody EIA,WB Fe, H, M, R
HCRT AB3704 Anti-HCRT/Orexin Rabbit Polyclonal Antibody IHC R
HCRT AB15690 Anti-HCRT/Orexin Chicken Polyclonal Antibody EIA H, M, R
KITLG AP1154 Anti-KITLG Mouse Monoclonal Antibody EIA H
RAC1 05-389 Anti-Rac1 Mouse Monoclonal Antibody WB, IHC, IP R, H, M
RAC1 07-1464 Anti-Rac1 Rabbit Polyclonal Antibody WB R, H, M

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Optogenetics and Cell Signaling

The narrow targeting of specific cell types conferred by Optogenetics may have extensive value in interrogating protein-protein interactions in signaling pathways. Traditional cell signaling research techniques are often limited in spatial or temporal resolution and plagued by off-target effects. The precision offered by optogenetics allows easier delivery, activation, and recovery of cellular function. In using this new approach, nicely reviewed by (Zhang and Cui, Trends Biotechnol. 2015), signaling could be manipulated by either light-induced protein translocation or light-induced protein uncaging. In the first case, light controlled target protein binding could be used to study DNA transcription, protein splicing, catalytic activity, protein inactivation or even protein trafficking and secretion. In the second case, light controlled uncaging could release steric inhibition of signaling members resulting in modulation of downstream pathways. In combination with recently developed genome editing techniques, optogenetic modulation of intracellular signaling could be a valuable tool in tightly controlling genetic manipulation in gene therapy.

Zhang, K. and Cui, B. (2015) Optogenetic control of intracellular signaling pathways. Trends Biotechnol. 33:92-100.