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Molecular optogenetics is a highly dynamic research field. In the past two years, the field was characterized by the development of new allosteric switches as well as the forward integration of optogenetics research towards application. Further, two areas of research have significantly gathered momentum, the use of optogenetics to control liquid-liquid phase separation as well as the application of optogenetic tools in the extracellular space. Here, we review these areas and discuss future directions., Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships that may be considered as potential competing interests: Wilfried Weber has patent pending to University of Freiburg. The OptoAAV technology reviewed in this article is covered by a patent application by the University of Freiburg, Germany, of which WW is an inventor., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

Receptor tyrosine kinases (RTKs) play crucial roles in human health, and their misregulation is implicated in disorders ranging from neurodegenerative diseases to cancers. The highly conserved mechanism of activation of RTKs makes them especially appealing candidates for control via optogenetic dimerization methods. This work offers a strategy for using the improved light-induced dimer (iLID) system with a constructed tandem dimer of its binding partner nano (tdnano) to build light-activatable versions of RTKs. In the absence of light, the iLID-RTK is cytosolic, monomeric, and inactive. Under blue light, the iLID + tdnano system recruits two copies of iLID-RTK to tdnano, dimerizing, and activating the RTK. We demonstrate that iLID opto-iTrkA and opto-iTrkB are capable of reproducing downstream ERK and Akt signaling only in the presence of tdnano. We further show with our opto-iTrkA that the system is compatible with multi-day and population-level activation of TrkA in PC12 cells. By leveraging genetic targeting of tdnano, we achieve RTK activation at a specific subcellular location even with whole-cell illumination, allowing us to confidently probe the impact of context on signaling outcome., (Copyright © 2020. Published by Elsevier Ltd.)

Cells rely on a complex network of spatiotemporally regulated signaling activities to effectively transduce information from extracellular cues to intracellular machinery. To probe this activity architecture, researchers have developed an extensive molecular tool kit of fluorescent biosensors and optogenetic actuators capable of monitoring and manipulating various signaling activities with high spatiotemporal precision. The goal of this review is to provide readers with an overview of basic concepts and recent advances in the development and application of genetically encodable biosensors and optogenetic tools for understanding signaling activity., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

The interactions between the brain and the immune system are bidirectional. Nevertheless, we have far greater understanding of how the immune system affects the brain than how the brain affects immunity. New technological developments such as optogenetics and chemogenetics (using DREADDs; Designer Receptors Exclusively Activated by Designer Drugs) can bridge this gap in our understanding, as they enable an unprecedented mechanistic and systemic analysis of the communication between the brain and the immune system. In this review, we discuss new experimental approaches for revealing neuronal circuits that can participate in regulation of immunity. In addition, we discuss methods, specifically optogenetics and chemogenetics, that enable targeted neuronal manipulation to reveal how different brain regions affect immunity. We describe how these techniques can be used as an experimental platform to address fundamental questions in psychoneuroimmunology and to understand how neuronal circuits associate with different psychological states can affect physiology., (Copyright © 2016 Elsevier Inc. All rights reserved.)

In recent years, the development and extensive use of optogenetics resulted in impressive findings on the neurobiology of anxiety and depression in animals. Indeed, it permitted to depict precisely the role of specific cell populations in various brain areas, including the amygdala nuclei, the auditory cortex, the anterior cingulate, the hypothalamus, the hippocampus and the bed nucleus of stria terminalis in specific aspects of fear and anxiety behaviors. Moreover, these findings emphasized the involvement of projections from the ventral tegmental area to the nucleus accumbens and the medial prefrontal cortex in eliciting depressive-like behaviors in stress-resilient mice or in inhibiting the expression of such behaviors in stress-vulnerable mice. Here we describe the optogenetic toolbox, including recent developments, and then review how the use of this technique contributed to dissect further the circuit underlying anxiety- and depression-like behaviors. We then point to some drawbacks of the current studies, particularly a) the sharp contrast between the sophistication of the optogenetic tools and the rudimentary aspect of the behavioral assays used, b) the fact that the studies were generally undertaken using normal rodents, that is animals that have not been subjected to experimental manipulations shifting them to a state relevant for pathologies and c) that the opportunity to explore the potential of these techniques to develop innovative therapeutics has been fully ignored yet. Finally, we discuss the point that these findings frequently ignore the complexity of the circuitry, as they focus only on a particular subpart of it. We conclude that users of this cutting edge technology could benefit from dialog between behavioral neuroscientists, psychiatrists and pharmacologists to further improve the impact of the findings., (Copyright © 2014 Elsevier Inc. All rights reserved.)