Curated Optogenetic Publication Database

Abstract: Oscillatory dynamics and their modulation are crucial for cellular decision-making; however, analysing these dynamics remains challenging. Here, we present a tool that combines the light-activated adenylate cyclase mPAC with the cAMP biosensor Pink Flamindo, enabling precise manipulation and real-time monitoring of cAMP oscillation frequencies in Dictyostelium. High-frequency modulation of cAMP oscillations induced cell aggregation and multicellular formation, even at low cell densities, such as a few dozen cells. At the population level, chemotactic aggregation is driven by modulated frequency signals. Additionally, modulation of cAMP frequency significantly reduced the amplitude of the shuttling behaviour of the transcription factor GtaC, demonstrating low-pass filter characteristics capable of converting subtle oscillation changes, such as from 6 min to 4 min, into gene expression. These findings enhance our understanding of frequency-selective cellular decoding and its role in cellular signalling and development.

Abstract: Cells contain thousands of different lipids. Their rapid and redundant metabolism, dynamic movement, and many interactions with other biomolecules have justly earned lipids a reputation as a vexing class of molecules to understand. Further, as the cell's hydrophobic metabolites, lipids assemble into supramolecular structures─most commonly bilayers, or membranes─from which they carry out myriad biological functions. Motivated by this daunting complexity, researchers across disciplines are bringing order to the seeming chaos of biological lipids and membranes. Here, we formalize these efforts as "synthetic lipid biology". Inspired by the idea, central to synthetic biology, that our abilities to understand and build biological systems are intimately connected, we organize studies and approaches across numerous fields to create, manipulate, and analyze lipids and biomembranes. These include construction of lipids and membranes from scratch using chemical and chemoenzymatic synthesis, editing of pre-existing membranes using optogenetics and protein engineering, detection of lipid metabolism and transport using bioorthogonal chemistry, and probing of lipid-protein interactions and membrane biophysical properties. What emerges is a portrait of an incipient field where chemists, biologists, physicists, and engineers work together in proximity─like lipids themselves─to build a clearer description of the properties, behaviors, and functions of lipids and membranes.

Abstract: Among all photosynthetic life forms, cyanobacteria exclusively possess a water-soluble, light-sensitive carotenoprotein complex known as orange carotenoid proteins (OCPs), crucial for their photoprotective mechanisms. These protein complexes exhibit both structural and functional modularity, with distinct C-terminal (CTD) and N-terminal domains (NTD) serving as light-responsive sensor and effector regions, respectively. The majority of cyanobacterial genomes contain genes for OCP homologs and related proteins, highlighting their essential role in survival of the organism over time. Cyanobacterial photoprotection primarily involves the translocation of carotenoid entity into the NTD, leading to remarkable conformational changes in both domains and formation of metastable OCPR. Subsequently, OCPR interacts with phycobiliprotein, inducing the quenching of excitation energy and a significant reduction in PS II fluorescence yield. In dark conditions, OCPR detaches from phycobilisomes and reverts to OCPO in the presence of fluorescent recovery proteins (FRP), sustaining a continuous cycle. Research suggests that the modular structure of the OCPs, coupled with its unique light-driven dissociation and re-association capability, opens avenues for exploiting its potential as light-controlled switches, offering various biotechnological applications.

Abstract: Komagataella phaffii, also known as Pichia pastoris, is a powerful host for recombinant protein production, in part due to its exceptionally strong and tightly controlled PAOX1 promoter. Most K. phaffii bioprocesses for recombinant protein production rely on PAOX1 to achieve dynamic control in two-phase processes. Cells are first grown under conditions that repress PAOX1 (growth phase), followed by methanol-induced recombinant protein expression (production phase). In this study, we propose a methanol-free approach for dynamic metabolic control in K. phaffii using optogenetics, which can help enhance input tunability and flexibility in process optimization and control. The light-responsive transcription factor EL222 from Erythrobacter litoralis is used to regulate protein production from the PC120 promoter in K. phaffii with blue light. We used two system designs to explore the advantages and disadvantages of coupling or decoupling EL222 integration with that of the gene of interest. We investigate the relationship between EL222 gene copy number and light dosage to improve production efficiency for intracellular and secreted proteins. Experiments in lab-scale bioreactors demonstrate the feasibility of the outlined optogenetic systems as potential alternatives to conventional methanol-inducible bioprocesses using K. phaffii.

Abstract: Cells under high confinement form highly polarized hydrostatic pressure-driven, stable leader blebs that enable efficient migration in low adhesion, environments. Here we investigated the basis of the polarized bleb morphology of metastatic melanoma cells migrating in non-adhesive confinement. Using high-resolution time-lapse imaging and specific molecular perturbations, we found that EGF signaling via PI3K stabilizes and maintains a polarized leader bleb. Protein activity biosensors revealed a unique EGFR/PI3K activity gradient decreasing from rear-to-front, promoting PIP3 and Rac1-GTP accumulation at the bleb rear, with its antagonists PIP2 and RhoA-GTP concentrated at the bleb tip, opposite to the front-to-rear organization of these signaling modules in integrin-mediated mesenchymal migration. Optogenetic experiments showed that disrupting this gradient caused bleb retraction, underscoring the role of this signaling gradient in bleb stability. Mathematical modeling and experiments identified a mechanism where, as the bleb initiates, CD44 and ERM proteins restrict EGFR mobility in a membrane-apposed cortical actin meshwork in the bleb rear, establishing a rear-to-front EGFR-PI3K-Rac activity gradient. Thus, our study reveals the biophysical and molecular underpinnings of cell polarity in bleb-based migration of metastatic cells in non-adhesive confinement, and underscores how alternative spatial arrangements of migration signaling modules can mediate different migration modes according to the local microenvironment.

Abstract: Most bacteria lack membrane-enclosed organelles and rely on macromolecular scaffolds at different subcellular locations to recruit proteins for specific functions. Here, we demonstrate that the optogenetic CRY2-CIB1 system from Arabidopsis thaliana can be used to rapidly direct proteins to different subcellular locations with varying efficiencies in live Escherichia coli cells, including the nucleoid, the cell pole, the membrane, and the midcell division plane. Such light-induced re-localization can be used to rapidly inhibit cytokinesis in actively dividing E. coli cells. We further show that CRY2-CIBN binding kinetics can be modulated by green light, adding a new dimension of control to the system. Finally, we test this optogenetic system in three additional bacterial species, Bacillus subtilis, Caulobacter crescentus, and Streptococcus pneumoniae, providing important considerations for this system's applicability in bacterial cell biology.

Abstract: Collective cell migration and tissue morphogenesis play a variety of important roles in the development of many species. Tissue morphogenesis often generates mechanical forces that alter cell shapes and arrangements, resembling collective cell migration-like behaviors. Genetic methods have been widely used to study collective cell migration and its like behavior, advancing our understanding of these processes during development. However, a growing body of research shows that collective cell migration during development is not a simple behavior but is often combined with other cellular and tissue processes. In addition, different surrounding environments can also influence migrating cells, further complicating collective cell migration during development. Due to the complexity of developmental processes and tissues, traditional genetic approaches often encounter challenges and limitations. Thus, some methods with spatiotemporal control become urgent in dissecting collective cell migration and tissue morphogenesis during development. Optogenetics is a method that combines optics and genetics, providing a perfect strategy for spatiotemporally controlling corresponding protein activity in subcellular, cellular or tissue levels. In this review, we introduce the basic mechanisms underlying different optogenetic tools. Then, we demonstrate how optogenetic methods have been applied in vivo to dissect collective cell migration and tissue morphogenesis during development. Additionally, we describe some promising optogenetic approaches for advancing this field. Together, this review will guide and facilitate future studies of collective cell migration in vivo and tissue morphogenesis by optogenetics.

Abstract: This volume explores the latest advancements in the field of optogenetics and how it uses cellular light-sensing components and genetic engineering to control proteins and biological processes. The book chapters are organized into four parts. Part One focuses on intracellular optogenetic components for control of specific cell functions; Part Two looks at externally supplied light regulators that do not require genetic manipulation of target cells; Part Three highlights optogenetic control of organelles, and Part Four introduces technical tools required for light induction in optogenetic experiments, as well as a method for performing and analyzing optogenetic cell-cell adhesion. Written in the highly successful Methods in Molecular Biology series format, chapters include introductions to their respective topics, lists of the necessary materials and reagents, step-by-step, readily reproducible laboratory protocols, and tips on troubleshooting and avoiding known pitfalls. Cutting-edge and practical, Optogenetics: Methods and Protocols is a valuable resource to help researchers understand and apply the concepts of optogenetics and the underlying bioengineering principles, and establish the required technical light-illumination setups for administering light inputs and analysis of experimental outcomes.

Abstract: The actin cytoskeleton forms a mesh-like network that drives cellular deformations. The network property is defined by the network density and the species of the actin-binding proteins. However, the relationship between the actin network density, the penetration ability of actin-binding proteins into the network, and resulting network dynamics remains elusive. Here, we report an in vitro optogenetic system, named OptoVCA, which induces Arp2/3-mediated actin network assembly on a lipid membrane. By changing the illumination power, duration, and pattern, the OptoVCA flexibly manipulates the density, thickness, and shape of the actin network. Taking these advantages, we examine the effects of the network density on the two representative actin-binding proteins, myosin and ADF/cofilin. We find that the penetration of myosin filaments into the network is strictly inhibited by only a several-fold increase in network density due to the steric hindrance. Furthermore, penetrated myosin filaments induce directional actin flow when the network has a density gradient. On the other hand, ADF/cofilin penetrates into the network regardless of network density, however, network disassembly is dramatically inhibited by only a several-fold increase in network density. Thus, the OptoVCA contributes to understanding cell mechanics through the examination of the network density-dependent effect on the actin-binding proteins.

Abstract: The CRISPR/Cas9 gene-editing technology, derived from the adaptive immune mechanisms of bacteria, has demonstrated remarkable advantages in fields such as gene function research and the treatment of genetic diseases due to its simplicity in design, precise targeting, and ease of use. Despite challenges such as off-target effects and cytotoxicity, effective spatiotemporal control strategies have been achieved for the CRISPR/Cas9 system through precise regulation of Cas9 protein activity as well as engineering of guide RNAs (gRNAs). This review provides a comprehensive analysis of the core components and functional mechanisms underlying the CRISPR/Cas9 system, highlights recent advancements in spatiotemporal control strategies, and discusses future directions for development.

Abstract: Development of neuronal connections is spatially and temporally controlled by extracellular cues which often activate their cognate cell surface receptors and elicit localized cellular responses. Here, we demonstrate the use of an optogenetic tool to activate receptor signaling locally to induce actin-mediated growth cone remodeling in neurons. Based on the light-induced interaction of light between Cryptochrome 2 (CRY2) and CIB1, we generated a bicistronic vector to co-expresses CRY2 fused to the intracellular domain of a guidance receptor and a membrane-anchored CIB1. When expressed in primary neurons, activation of the growth inhibitory PlexA4 receptor induced growth cone collapse, while activation of the growth stimulating TrkA receptor increased growth cone size. Moreover, local activation of either receptor not only elicited the predicted response in light-activated growth cones, but also an opposite response in neighboring no-light growth cones of the same neuron. Finally, this tool was used to reorient growth cones towards or away from light activation and to stimulate local actin polymerization for branch initiation along axonal shafts. These studies demonstrate the use of an optogenetic tool for precise spatial and temporal control of receptor signaling in neurons and support its future application in investigating cellular mechanisms of neuronal development and plasticity. [Media: see text] [Media: see text] [Media: see text] [Media: see text].

Abstract: Starvation, which is associated with inactivation of the growth-promoting TOR complex 1 (TORC1), is a strong environmental signal for cell differentiation. In the fission yeast Schizosaccharomyces pombe, nitrogen starvation has distinct physiological consequences depending on the presence of mating partners. In their absence, cells enter quiescence, and TORC1 inactivation prolongs their life. In presence of compatible mates, TORC1 inactivation is essential for sexual differentiation. Gametes engage in paracrine pheromone signaling, grow towards each other, fuse to form the diploid zygote, and form resistant, haploid spore progenies. To understand the signaling changes in the proteome and phospho-proteome during sexual reproduction, we developed cell synchronization strategies and present (phospho-)proteomic data sets that dissect pheromone from starvation signals over the sexual differentiation and cell-cell fusion processes. Unexpectedly, these data sets reveal phosphorylation of ribosomal protein S6 during sexual development, which we establish requires TORC1 activity. We demonstrate that TORC1 is re-activated by pheromone signaling, in a manner that does not require autophagy. Mutants with low TORC1 re-activation exhibit compromised mating and poorly viable spores. Thus, while inactivated to initiate the mating process, TORC1 is reactivated by pheromone signaling in starved cells to support sexual reproduction.

Abstract: As synthetic biology advances, the necessity for robust biocontainment strategies for genetically engineered organisms (GEOs) grows increasingly critical to mitigate biosafety risks related to their potential environmental release. This paper aims to evaluate environment signal-dependent biocontainment systems for engineered organisms, focusing specifically on leveraging triggered responses and combinatorial systems. There are different types of triggers-chemical, light, temperature, and pH-this review illustrates how these systems can be designed to respond to environmental signals, ensuring a higher safety profile. It also focuses on combinatorial biocontainment to avoid consequences of unintended GEO release into an external environment. Case studies are discussed to demonstrate the practical applications of these systems in real-world scenarios.

Abstract: Controlling CRISPR/Cas9 gene editing at the spatiotemporal resolution level, especially for in vivo applications, remains a great challenge. Here, we developed a near-infrared (NIR) light-activated nanophotonic system (UCPP) for controlled CRISPR-Cas9 gene editing and synergistic photodynamic therapy (PDT). Lanthanide-doped upconversion nanoparticles are not only employed as carriers for intracellular plasmid delivery but also serve as the nanotransducers to convert NIR light (980 nm) into visible light with emission at 460 and 650 nm, which could result in simultaneous activation of gene editing and PDT processes, respectively. Such unique design not only achieves light-controlled precise gene editing of hypoxia-inducible factor 1α with minimal off-target effect, which effectively ameliorates the hypoxic state at tumor sites, but also facilitates the deep-seated PDT process with synergistic antitumor effect. This optogenetically activatable CRISPR-Cas9 nanosystem holds great potential for spatially controlled in vivo gene editing and targeted cancer therapy.

Abstract: Background Optogenetic systems use light-responsive proteins to control gene expression with the “flip of a switch”. One such tool is the light activated CRISPR effector (LACE) system. Its ability to regulate gene expression in a tunable, reversible, and spatially resolved manner makes it attractive for many applications. However, LACE relies on delivery of four separate components on individual plasmids, which can limit its use. Here, we optimize LACE to reduce the number of plasmids needed to deliver all four components. Results The two-plasmid LACE (2pLACE) system combines the four components of the original LACE system into two plasmids. Following construction, the behavior of 2pLACE was rigorously tested using optogenetic control of enhanced green fluorescent protein (eGFP) expression as a reporter. We optimized the ratio of the two plasmids, measured activation as a function of light intensity, and determined the frequency of the light to activate the maximum fluorescence. Overall, the 2pLACE system showed a similar dynamic range, tunability, and activation kinetics as the original four plasmid LACE (4pLACE) system. Interestingly, 2pLACE also had less variability in activation signal compared to 4pLACE. Conclusions This simplified system for optogenetics will be more amenable to biotechnology applications where variability needs to be minimized. By optimizing the LACE system to use fewer plasmids, 2pLACE becomes a flexible tool in multiple research applications.

Abstract: Aberrant aggregation of the prion-like, RNA-binding protein TDP-43 underlies several debilitating neurodegenerative proteinopathies, including amyotrophic lateral sclerosis (ALS). Here, we define how short, specific RNAs antagonize TDP-43 aggregation. Short, specific RNAs engage and stabilize the TDP-43 RNA-recognition motifs, which allosterically destabilizes a conserved helical region in the prion-like domain, thereby promoting aggregationresistant conformers. By mining sequence space, we uncover short RNAs with enhanced activity against TDP-43 and diverse disease-linked variants. The solubilizing activity of enhanced short RNA chaperones corrects aberrant TDP-43 phenotypes in optogenetic models and ALS patientderived neurons. Remarkably, an enhanced short RNA chaperone mitigates TDP-43 proteinopathy and neurodegeneration in mice. Our studies reveal mechanisms of short RNA chaperones and pave the way for the development of short RNA therapeutics for fatal TDP-43 proteinopathies.

Abstract: Light as an environmental signal can effectively regulate various biological processes in microbial systems. Optical and optogenetic tools are able to utilize light for precise control methods with minimal interference. Recently, research on these tools has extended to the field of microbiology. Distinguishing from existing reviews, this review narrows the scope of application into food sector, focusing on advances in optical and optogenetic tools for microbial control, including optical tools targeting pathogenic or probiotic bacteria for non-thermal sterilization, antimicrobial photodynamic therapy, or photobiomodulation, combined with nanomaterials as photosensors for food analysis. As well as using optogenetic tools for more convenient and precise control in food production processes, covering reversible induction, metabolic flux regulation, biofilm formation, and inhibition. These tools offer new solutions to goals that cannot be achieved by traditional methods, and they are still maturing to explore other uses in the food field.

Abstract: Corynebacterium glutamicum is a key industrial workhorse for producing amino acids and high-value chemicals. Balancing metabolic flow between cell growth and product synthesis is crucial for enhancing production efficiency. Developing dynamic, broadly applicable, and minimally toxic gene regulation tools for C. glutamicum remains challenging, as optogenetic tools ideal for dynamic regulatory strategies have not yet been developed. This study introduces an advanced light-controlled gene expression system using light-controlled RNA-binding proteins (RBP), a first for Corynebacterium glutamicum. We established a gene expression regulation system, 'LightOnC.glu', utilizing the light-controlled RBP to construct light-controlled transcription factors in C. glutamicum. Simultaneously, we developed a high-performance light-controlled gene interference system using CRISPR/Cpf1 tools. The metabolic flow in the synthesis network was designed to enable the production of chitin oligosaccharides (CHOSs) and chondroitin sulphate oligosaccharides A (CSA) for the first time in C. glutamicum. Additionally, a light-controlled bioreactor was constructed, achieving a CHOSs production concentration of 6.2 g/L, the highest titer recorded for CHOSs biosynthesis to date. Herein, we have established a programmable light-responsive genetic circuit in C. glutamicum, advancing the theory of dynamic regulation based on light signaling. This breakthrough has potential applications in optimizing metabolic modules in other chassis cells and synthesizing other compounds.

Abstract: The endoplasmic reticulum (ER) links to multiple organelles through membrane contact sites (MCS), which play critical roles in signal transduction, cell homeostasis and stress response. However, studying the behaviour and functions of MCS in plants is still challenging, partially due to the lack of site-specific markers. Here, we used an optogenetic reporter, LiMETER (Light-inducible Membrane-Tethered cortical ER), to study the structure and dynamics of ER-PM contact sites (EPCS) in plants. Upon blue light activation, LiMETER is recruited to the EPCS rapidly, while this process is reversible when blue light is turned off. Compared with other EPCS reporters, LiMETER specifically and reversibly labels the contact sites, causing little side-effects on the ER structure and plant development. With its help, we re-examined the formation of ER-PM connections induced by cell-intrinsic factors or extracellular stimuli. We found that EPCSs are preferably localised at ER tubules and the edge of ER cisternae, and their number increased significantly under abiotic stress conditions. The abundance of ER and PM interaction is also developmental dependent, suggesting a direct link between ER-PM interaction, ER function and cell homeostasis. Taken together, we showed that LiMETER is an improved marker for functional and microscopical studies of ER-PM interaction, demonstrating the effectiveness of optogenetic tools in future research.

Abstract: Abstract Tauopathy is a spectrum of diseases characterized by fibrillary tau aggregate formation in neurons and glial cells in the brain. Tau aggregation originates in the brainstem and entorhinal cortex and then spreads throughout the brain in Alzheimer’s disease (AD), which is the most prevalent type of tauopathy. Understanding the mechanism by which locally developed tau pathology propagates throughout the brain is crucial for comprehending AD pathogenesis. Therefore, a novel model of tau pathology that artificially induces tau aggregation in targeted cells at specific times is essential. This study describes a novel optogenetic module, OptoTau, which is a human tau with the P301L mutation fused with a photosensitive protein CRY2olig, inducing various forms of tau according to the temporal pattern of blue light illumination pattern. Continuous blue light illumination for 12 h to Neuro2a cells that stably express OptoTau (OptoTauKI cells) formed clusters along microtubules, many of which eventually accumulated in aggresomes. Conversely, methanol-resistant tau aggregation was formed when alternating light exposure and darkness in 30-min cycles for 8 sets per day were repeated over 8 days. Methanol-resistant tau was induced more rapidly by repeating 5-min illumination followed by 25-min darkness over 24 h. These results indicate that OptoTau induced various tau aggregation stages based on the temporal pattern of blue light exposure. Thus, this technique exhibits potential as a novel approach to developing specific tau aggregation in targeted cells at desired time points.

Abstract: Research for biopharmaceutical production processes with mammalian cells steadily aims to enhance the cell-specific productivity as a means for optimizing total productivities of bioreactors. Whereas current technologies such as pH, temperature, and osmolality shift require modifications of the cultivation medium, the use of optogenetic switches in recombinant producer cells might be a promising contact-free alternative. However, the proper application of optogenetically engineered cells requires a detailed understanding of basic cellular responses of cells that do not yet contain the optogenetic switches. The knowhow of ideal light exposure to enable the optimum use of related approaches is missing so far. Consequently, the current study set out to find optimum conditions for IgG1 producing Chinese hamster ovary (CHO) cells which were exposed to blue LED light. Growth characteristics, cell-specific productivity using enzyme-linked immunosorbent assay, as well as cell cycle distribution using flow cytometry were analyzed. Whereas too harsh light exposure causes detrimental growth effects that could be compensated with antioxidants, a surprising boost of cell-specific productivity by 57% occurred at optimum high light doses. The increase coincided with an increased number of cells in the G1 phase of the cell cycle after 72 h of illumination. The results present a promising new approach to boost biopharmaceutical productivity of mammalian cells simply by proper light exposure without any further optogenetic engineering. KEY POINTS: • Blue LED light hinders growth in CHO DP-12 cells • Antioxidants protect to a certain degree from blue light effects • Illumination with blue LED light raises cell-specific productivity.

Abstract: In the field of tissue engineering, achieving precise spatiotemporal control over engineered cells is critical for sculpting functional 2D cell cultures into intricate morphological shapes. In this study, we engineer light-responsive mammalian cells and target them with dynamic light patterns to realize 2D cell culture patterning control. To achieve this, we developed μPatternScope (μPS), a modular framework for software-controlled projection of high-resolution light patterns onto microscope samples. μPS comprises hardware and software suite governing pattern projection and microscope maneuvers. Together with a 2D culture of the engineered cells, we utilize μPS for controlled spatiotemporal induction of apoptosis to generate desired 2D shapes. Furthermore, we introduce interactive closed-loop patterning, enabling a dynamic feedback mechanism between the measured cell culture patterns and the light illumination profiles to achieve the desired target patterning trends. Our work offers innovative tools for advanced tissue engineering applications through seamless fusion of optogenetics, optical engineering, and cybernetics.

Abstract: Microtubule acetylation is implicated in regulating cell motility, yet its physiological role in directional migration and the underlying molecular mechanisms have remained unclear. This knowledge gap has persisted primarily due to a lack of tools capable of rapidly manipulating microtubule acetylation in actively migrating cells. To overcome this limitation and elucidate the causal relationship between microtubule acetylation and cell migration, we developed a novel optogenetic actuator, optoTAT, which enables precise and rapid induction of microtubule acetylation within minutes in live cells. Using optoTAT, we observed striking and rapid responses at both molecular and cellular level. First, microtubule acetylation triggers release of the RhoA activator GEF-H1 from sequestration on microtubules. This release subsequently enhances actomyosin contractility and drives focal adhesion maturation. These subcellular processes collectively promote sustained directional cell migration. Our findings position GEF-H1 as a critical molecular responder to microtubule acetylation in the regulation of directed cell migration, revealing a dynamic crosstalk between the actin and microtubule cytoskeletal networks.

Abstract: Recent advances in tissue engineering have been remarkable, yet the precise control of cellular behavior in 2D and 3D cultures remains challenging. One approach to address this limitation is to genomically engineer optogenetic control of cellular processes into tissues using gene switches that can operate with only a few genomic copies. Here, we implement blue and red light-responsive gene switches to engineer genomically stable two- and three-dimensional mammalian tissue models. Notably, we achieve precise control of cell death and morphogen-directed patterning in 2D and 3D tissues by optogenetically regulating cell necroptosis and synthetic WNT3A signaling at high spatiotemporal resolution. This is accomplished using custom-built patterned LED systems, including digital mirrors and photomasks, as well as laser techniques. These advancements demonstrate the capability of precise spatiotemporal modulation in tissue engineering and open up new avenues for developing programmable 3D tissue and organ models, with significant implications for biomedical research and therapeutic applications.

Abstract: The use of optogenetic tools offers an excellent method for spatially and temporally regulated gene and protein expression in cell therapeutic approaches. This could be useful as a concomitant therapeutic measure, especially in small body compartments such as the inner ear, for example, during cochlea implantation, to enhance neuronal cell survival and function. Here, we used the blue light activatable CRY2/CIB system to induce transcription of brain-derived neurotrophic factor (BDNF) in human cells. Transfection with three plasmids, encoding for the optogenetic system and the target, as well as illumination protocols were optimized with luciferase as a reporter to achieve the highest protein expression in human embryonic kidney cells 293. Illumination was performed either with a light-emitting diode or with a scanning laser setup. The optimized protocols were applied for the production of BDNF. We could demonstrate a 64.7-fold increase of BNDF expression upon light induction compared to the basal level. Light-induced BDNF was biologically active and enhanced survival and neurite growth of spiral ganglion neurons. The optogenetic approach can be transferred to autologous cell systems, such as bone marrow-derived mesenchymal stem cells, and thus represents the first optogenetic neurotrophic therapy for the inner ear.