Optogenenetics refers to a family of techniques which allow modulation of biological processes using light. Over the past 12 years, optogenetics has revolutionized neuroscience and is now expanding to impact many fields of biology. There are now genetic tools which can be used for photo-control of signal transduction, gene expression, apoptosis, histone modification, cytoskeletal dynamics, and many more processes.
The incredible power of optogenetics comes from the very high spatial and temporal resolution possible using light, as opposed to chemical or genetic effects. Optogenetics can also be combined with other genetic or chemical approaches to further increase the level of experimental control. For example, optogenetic constructs can be targeted to specific cell types or subcellular locations, or can be engineered to require specific chemical cofactors, further limiting when and where light-induced effects will occur.
The key component of an optogenetics experiment are light-sensitive proteins or protein domains. Membrane-bound rhodopsin family-members were the first proteins to be used as optogenetic actuators in neuroscience. Rhodopsins can be either type I, which are generally channels or pumps, and can be used to modulate voltage and ion gradients across membranes, or type II, which are GPCR family members, and allow broad effects on cellular signaling pathways1-3. Newer, engineered optogenetic tools consist of diverse photo-sensor domains linked to protein domains which mediate a biological function specified by the researcher. Here are a few examples of how some photo-sensor domains have been used in optogenetic experiments.
The light-oxygen-voltage sensor (LOV) family domains are used to engineer chimeric proteins in which photoexcitation controls dimerization and conformational changes. Some notable examples include using the AsLOV2 domain to optogenetically inhibit REST, a master regulator of neural genes4, using the VVD domain linked to caspase-9 to optically control apoptosis5, use of the LOV2 domain to introduce allosteric switches into diverse motility signaling proteins6, and using AsLOV2 to regulate the binding of tetracycline to the Tet repressor7. Blue-light sensor (BLUF) domains induce more limited structural changes in response to light, and have been used to regulate transcription factor activity8, and to control nucleotidyl cyclases9. Cryptochrome (CRY) domains have been used for light-dependent control of the Raf/MEK/ERK pathway10, have been combined with the transcription activator-like effector (TALE) DNA-binding domains to allow optogenetic control of gene expression and epigenetic modifications11, and have been combined with the CRISPR/Cas9 system to achieve light-controlled genome editing12.
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