Curated Optogenetic Publication Database

Abstract: Optogenetic bacterial technology is a cutting-edge approach that combines optogenetics and microbiology, offering a transformative strategy for disease diagnosis and therapy. This synergistic merger transcends the limitations of traditional diagnostic and therapeutic methodologies in a highly controllable, accurate and non-invasive manner. In this review, we introduce the optogenetic systems developed for microbial engineering and summarize fundamental in vitro design principles underlying light-responsive signal transduction in bacteria, as well as the optogenetic regulation of bacterial behaviors. We address multidisciplinary solutions to the challenges in the in vivo applications of light-controlled bacteria, such as limited light excitation, suboptimal delivery and targeting, and difficulties in signal tracking and management. Furthermore, we comprehensively highlight the recent progress in photo-responsive bacteria for disease diagnosis and therapy, and discuss how to accelerate translational applications.

Abstract: The integrated stress response (ISR) is a conserved stress response that maintains homeostasis in eukaryotic cells. Modulating the ISR holds therapeutic potential for diseases including viral infection, cancer, and neurodegeneration, but few known compounds can do so without toxicity. Here, we present an optogenetic platform for the discovery of compounds that selectively modulate the ISR. Optogenetic clustering of PKR induces ISR-mediated cell death, enabling the high-throughput screening of 370,830 compounds. We identify compounds that potentiate cell death without cytotoxicity across diverse cell types and stressors. Mechanistic studies reveal that these compounds upregulate activating transcription factor 4 (ATF4), sensitizing cells to stress and apoptosis, and identify GCN2 as a molecular target. Additionally, these compounds exhibit antiviral activity, and one compound reduced viral titers in a mouse model of herpesvirus infection. Structure-activity and toxicology studies highlight opportunities to optimize therapeutic efficacy. This work demonstrates an optogenetic approach to drug discovery and introduces ISR potentiators with therapeutic potential.

Abstract: Teixeira et al. present UltraID-light-inducible protein aggregation (UltraID-LIPA), a technique that combines optogenetic induction of α-synuclein aggregation with proximity-based proteomics. This system enables high-resolution capture of early aggregation events in live cells and implicates known and novel endolysosomal proteins, offering a robust framework for dissecting early pathogenic mechanisms in synucleinopathies and guiding future innovations.

Abstract: Tau pathological aggregation in neurofibrillary tangles is a hallmark of several neurodegenerative diseases, including Alzheimer's disease. Phase separation is a thermodynamic process that plays an important role in biomolecular membrane-less condensate formation, while abnormal phase separation of tau leads to pathological aggregate formation. However, the detailed molecular mechanism underlying tau condensation remains not fully understood. Moreover, whether condensation-based pharmacological intervention will be helpful for the treatment of tau-associated neurodegenerative diseases remains elusive. Here, we used an optogenetic tool (optoDroplets) in combination with cell biology and pharmacology to explore the contribution of different domains for tau condensation in cells, and we found that proline-rich domain (PRD) phosphorylation, which is mainly regulated by glycogen synthase kinase 3 β (GSK3β), plays important roles for tau condensation. Moreover, phosphorylation of tau PRD regulates its mis-localization on nuclear speckle. Interestingly and importantly, we found that pharmacological inhibition of GSK3β can impede abnormal tau condensation to slow down the tau-associated pathological process.

Abstract: Neurodegenerative diseases involve toxic protein aggregation. Recent evidence suggests that biomolecular phase separation, a process in which proteins and nucleic acids form dynamic, liquid-like condensates, plays a key role in this aggregation. Optogenetics, originally developed to control neuronal activity with light, has emerged as a powerful tool to investigate phase separation in living systems. This is achieved by fusing disease-associated proteins to light-sensitive oligomerization domains, enabling researchers to induce or reverse condensate formation with precise spatial and temporal control. This review highlights how optogenetic systems such as OptoDroplet are being used to dissect the mechanisms of neurodegenerative disease. We examine how these tools have been applied in models of neurodegenerative diseases, such as amyotrophic lateral sclerosis, Alzheimer's, Parkinson's, and Huntington's disease. These studies implicate small oligomeric aggregates as key drivers of toxicity and highlight new opportunities for therapeutic screening. Finally, we discuss advances in light-controlled dissolution of condensates and future directions for applying optogenetics to combat neurodegeneration. By enabling precise, dynamic control of protein phase behavior in living systems, optogenetic approaches provide a powerful framework for elucidating disease mechanisms and informing the development of targeted therapies.

Abstract: Mitochondria contain double membranes that enclose their contents. Within their interior, the mitochondrial genome and its RNA products are condensed into ∼100 nm sized (ribo)nucleoprotein complexes. How these endogenous condensates maintain their roughly uniform size and spatial distributions within membranous mitochondria remains unclear. Here, we engineered an optogenetic tool (mt-optoIDR) that allowed for controlled formation of synthetic condensates upon light activation in live mitochondria. Using live cell super-resolution microscopy, we visualized the nucleation of small, yet elongated condensates (mt-opto-condensates), which recapitulated the morphologies of endogenous mitochondrial condensates. We decoupled the contribution of the double membranes from the environment within the matrix by overexpressing the dominant negative mutant of a membrane fusion protein (Drp1K38A). The resulting bulbous mitochondria had significantly more dynamic condensates that coarsened into a single, prominent droplet. These observations inform how mitochondrial membranes can limit the growth and dynamics of the condensates they enclose, without the need of additional regulatory mechanisms.

Abstract: Alpha-synuclein (α-syn) aggregation is a defining feature of Parkinson's disease (PD) and related synucleinopathies. Despite significant research efforts focused on understanding α-syn aggregation mechanisms, the early stages of this process remain elusive, largely due to limitations in experimental tools that lack the temporal resolution to capture these dynamic events. Here, we introduce UltraID-LIPA, an innovative platform that combines the light-inducible protein aggregation (LIPA) system with the UltraID proximity-dependent biotinylation assay to identify α-syn-interacting proteins and uncover key mechanisms driving its oligomerization. UltraID-LIPA successfully identified 38 α-syn-interacting proteins, including both established and previously unreported candidates, highlighting the accuracy and robustness of the approach. Notably, a strong interaction with endolysosomal and membrane-associated proteins was observed, supporting the hypothesis that interactions with membrane-bound organelles are pivotal in the early stages of α-syn aggregation. This powerful platform provides new insights into dynamic protein aggregation events, enhancing our understanding of synucleinopathies and other proteinopathies.

Abstract: The microtubule-associated protein tau aggregates into oligomeric complexes that highly correlate with Alzheimer’s disease (AD) progression. Increasing evidence suggests that nuclear membrane disruption occurs in AD and related tauopathies, but whether this is a cause or consequence of neurodegeneration remains unclear. Using the optogenetically inducible 4R1N Tau::mCherry::Cry2Olig (optoTau) system in iPSC-derived neurons, we demonstrate that tau oligomerization triggers nuclear rupture and nuclear membrane invagination. Pathological tau accumulates at sites of invagination, inducing structural abnormalities in the nuclear envelope and piercing into the nuclear space. These findings were confirmed in the humanized P301S tau (PS19) transgenic mouse model, where nuclear envelope disruption appeared as an early-onset event preceding neurodegeneration. Further validation in post-mortem AD brain tissues revealed nuclear lamina disruption correlating with pathological tau emergence in early-stage patients. Notably, electron microscopy shows that tau-induced nuclear invagination triggers global chromatin reorganization, potentially driving aberrant gene expression and protein translation associated with AD. These findings suggest that nuclear membrane disruption is an early and possibly causative event in tau-mediated neurodegeneration, establishing a mechanistic link between tau oligomerization and nuclear stress. Further investigation into nuclear destabilization could inform clinical strategies for mitigating AD pathogenesis.

Abstract: Light is a critical environmental factor that governs the growth and development of plants. Plants have specialised photoreceptor proteins, which allow them to sense both quality and quantity of light and drive a wide range of responses critical for optimising growth, resource use and adaptation to changes in environment. Understanding the role of these photoreceptors in plant biology has opened up potential avenues for engineering crops with enhanced productivity by engineering photoreceptor activity and/or action. The ability to manipulate plant genomes through genetic engineering and synthetic biology approaches offers the potential to unlock new agricultural innovations by fine-tuning photoreceptors or photoreceptor pathways that control plant traits of agronomic significance. Additionally, optogenetic tools which allow for precise, light-triggered control of plant responses are emerging as powerful technologies for real-time manipulation of plant cellular responses. As these technologies continue to develop, the integration of photoreceptor engineering and optogenetics into crop breeding programs could potentially revolutionise how plant researchers tackle challenges of plant productivity. Here we provide an overview on the roles of key photoreceptors in regulating agronomically important traits, the current state of plant photoreceptor engineering, the emerging use of optogenetics and synthetic biology, and the practical considerations of applying these approaches to crop improvement. This review seeks to highlight both opportunities and challenges in harnessing photoreceptor engineering approaches for enhancing plant productivity. In this review, we provide an overview on the roles of key photoreceptors in regulating agronomically important traits, the current state of plant photoreceptor engineering, the emerging use of optogenetics and synthetic biology, and the practical considerations of applying these approaches to crop improvement.

Abstract: Background Cytoplasmic aggregation of TAR DNA binding protein 43 (TDP-43) in neurons is one of the hallmarks of TDP-43 proteinopathy. Amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD) are closely associated with TDP-43 proteinopathy; however, it remains uncertain whether TDP-43 aggregation initiates the pathology or is a consequence of it. Methods To demonstrate the pathology of TDP-43 aggregation, we applied the optoDroplet technique in Caenorhabditis elegans (C. elegans), which allows spatiotemporal modulation of TDP-43 phase separation and assembly. Results We demonstrate that optogenetically induced TDP-43 aggregates exhibited insolubility similar to that observed in TDP-43 proteinopathy. These aggregates increased the severity of neurodegeneration, particularly in GABAergic motor neurons, and exacerbated sensorimotor dysfunction in C. elegans. Conclusions We present an optogenetic C. elegans model of TDP-43 proteinopathy that provides insight into the neuropathological mechanisms of TDP-43 aggregates. Our model serves as a promising tool for identifying therapeutic targets for TDP-43 proteinopathy.

Abstract: Transcription factors relay information from the external environment to gene regulatory networks that control cell physiology. To confer signalling specificity, robustness and coordination, these signalling networks use temporal communication codes, such as the amplitude, duration or frequency of signals. Although much is known about how temporal information is encoded, a mechanistic understanding of how gene regulatory networks decode signalling dynamics is lacking. Recent advances in our understanding of phase separation of transcriptional condensates provide new biophysical frameworks for both temporal encoding and decoding mechanisms. In this Perspective, we summarize the mechanisms by which transcriptional condensates could enable temporal decoding through signal adaptation, memory and persistence. We further outline methods to probe and manipulate dynamic communication codes of transcription factors and condensates to rationally control gene activation.

Abstract: Precise regulation of protein abundance is critical for cellular homeostasis, whose dysfunction may directly lead to human diseases. Optogenetics allows rapid and reversible control of precisely defined cellular processes, which has the potential to be utilized for regulation of protein dynamics at various scales. Here, we developed a novel optogenetics-based protein degradation system, namely Peptide-mediated OptoTrim-Away (POT) which employs expressed small peptides to effectively target endogenous and unmodified proteins. By engineering the light-induced oligomerization of the E3 ligase TRIM21, POT can rapidly trigger protein degradation via the proteasomal pathway. Our results showed that the developed POT-PI3K and POT-GPX4 modules, which used the iSH2 and FUNDC1 domains to specifically target phosphoinositide 3-kinase (PI3K) and glutathione peroxidase 4 (GPX4) respectively, were able to potently induce the degradation of these endogenous proteins by light. Both live-cell imaging and biochemical experiments validated the potency of these tools in downregulating cancer cell migration, proliferation, and even promotion of cell apoptosis. Therefore, we believe the POT offers an alternative and practical solution for rapid manipulation of endogenous protein levels, and it could potentially be employed to dissect complex signaling pathways in cell and for targeted cellular therapies.

Abstract: Receptor tyrosine kinases (RTKs) play key roles in coordinating cell movement at both single-cell and tissue scales. The recent development of optogenetic tools for controlling RTKs and their downstream signaling pathways suggests that these responses may be amenable to engineering-based control for sculpting tissue shape and function. Here, we report that a light-controlled epidermal growth factor (EGF) receptor (OptoEGFR) can be deployed in epithelial cells for precise, programmable control of long-range tissue movements. We show that in OptoEGFR-expressing tissues, light can drive millimeter-scale cell rearrangements to densify interior regions or produce rapid outgrowth at tissue edges. Light-controlled tissue movements are driven primarily by phosphoinositide 3-kinase (PI3K) signaling, rather than diffusible ligands, tissue contractility, or ERK kinase signaling as seen in other RTK-driven migration contexts. Our study suggests that synthetic, light-controlled RTKs could serve as a powerful platform for controlling cell positions and densities for diverse applications, including wound healing and tissue morphogenesis.

Abstract: Proteins phase-separate to form condensates that partition and concentrate biomolecules into membraneless compartments. These condensates can exhibit dichotomous behaviors in biology by supporting cellular physiology or instigating pathological protein aggregation1–3. Tau and α- synuclein (αSyn) are neuronal proteins that form heterotypic (Tau:αSyn) condensates associated with both physiological and pathological processes. Tau and αSyn functionally regulate microtubules8–12, but are also known to misfold and co-deposit in aggregates linked to various neurodegenerative diseases4,5,6,7, which highlights the paradoxically ambivalent effect of Tau:αSyn condensation in health and disease. Here, we show that tubulin modulates Tau:αSyn condensates by promoting microtubule interactions, competitively inhibiting the formation of homotypic and heterotypic pathological oligomers. In the absence of tubulin, Tau-driven protein condensation accelerates the formation of toxic Tau:αSyn heterodimers and amyloid fibrils. However, tubulin partitioning into Tau:αSyn condensates modulates protein interactions, promotes microtubule polymerization, and prevents Tau and αSyn oligomerization and aggregation. We distinguished distinct Tau and αSyn structural states adopted in tubulin-absent (pathological) and tubulin-rich (physiological) condensates, correlating compact conformations with aggregation and extended conformations with function. Furthermore, using various neuronal cell models, we showed that loss of stable microtubules, which occurs in Alzheimer’s disease and Parkinsons disease patients13,14, results in pathological oligomer formation and loss of neurites, and that functional condensation using an inducible optogenetic Tau construct resulted in microtubule stablization. Our results identify that tubulin is a critical modulator in switching Tau:αSyn pathological condensates to physiological, mechanistically relating the loss of stable microtubules with disease progression. Tubulin restoration strategies and Tau-mediated microtubule stabilization can be potential therapies targeting both Tau-specific and Tau/αSyn mixed pathologies.

Abstract: Optogenetics is an empowering technology that uses light-responsive proteins to control biological processes. Because of its genetic tractability, abundance of genetic tools, and robust culturing conditions, Saccharomyces cerevisiae has served for many years as an ideal platform in which to study, develop, and apply a wide range of optogenetic systems. In many instances, yeast has been used as a steppingstone in which to characterize and optimize optogenetic tools to later be deployed in higher eukaryotes. More recently, however, optogenetic tools have been developed and deployed in yeast specifically for biotechnological applications, including in nonconventional yeasts. In this review, we summarize various optogenetic systems responding to different wavelengths of light that have been demonstrated in diverse yeast species. We then describe various applications of these optogenetic tools in yeast, particularly in metabolic engineering and recombinant protein production. Finally, we discuss emerging applications in yeast cybergenetics-the interfacing of yeast and computers for closed-loop controls of yeast bioprocesses-and the potential impact of optogenetics in other future biotechnological applications.

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: Hsp70 prevents protein aggregation and is cytoprotective, but sustained Hsp70 overexpression is problematic. Therefore, we characterized small molecule agonists that augment Hsp70 activity. Because cumbersome assays were required to assay agonists, we developed cell-based and in vivo assays in which disease-associated consequences of Hsp70 activation can be quantified. One assay uses an optogenetic system in which the formation of TDP-43 inclusions can be controlled, and the second assay employs a zebrafish model for acute kidney injury (AKI). These complementary assays will facilitate future work to identify new Hsp70 agonists as well as optimized agonist derivatives.

Abstract: Biomolecular condensates (BMCs), play significant roles in organizing cellular functions in the absence of membranes through phase separation events involving RNA, proteins, and RNA-protein complexes. These membrane-less organelles form dynamic multivalent weak interactions, often involving intrinsically disordered proteins or regions (IDPs/IDRs). However, the nature of these crucial interactions, how most of these organelles are organized and are functional, remains unknown. Aberrant condensates have been implicated in neurodegenerative diseases and various cancers, presenting novel therapeutic opportunities for small molecule condensate modulators. Recent advancements in optogenetic technologies, particularly Corelet, enable precise manipulation of BMC dynamics within living cells, facilitating high-throughput screening for small molecules that target these complex structures. By elucidating the molecular mechanisms governing BMC formation and function, this innovative approach holds promise to unlock therapeutic strategies against previously "undruggable" protein targets, paving the way for effective interventions in disease.

Abstract: Biomolecular condensates appear throughout cell physiology and pathology, but the specific role of condensation or its dynamics is often difficult to determine. Optogenetics offers an expanding toolset to address these challenges, providing tools to directly control condensation of arbitrary proteins with precision over their formation, dissolution, and patterning in space and time. In this review, we describe the current state of the field for optogenetic control of condensation. We survey the proteins and their derivatives that form the foundation of this toolset, and we discuss the factors that distinguish them to enable appropriate selection for a given application. We also describe recent examples of the ways in which optogenetic condensation has been used in both basic and applied studies. Finally, we discuss important design considerations when engineering new proteins for optogenetic condensation, and we preview future innovations that will further empower this toolset in the coming years.

Abstract: Synucleinopathies, including Parkinson's disease, dementia with Lewy bodies, and multiple system atrophy, are triggered by α-synuclein aggregation, triggering progressive neurodegeneration. However, the intracellular α-synuclein aggregation mechanism remains unclear. Herein, we demonstrate that RNA G-quadruplex assembly forms scaffolds for α-synuclein aggregation, contributing to neurodegeneration. Purified α-synuclein binds RNA G-quadruplexes directly through the N terminus. RNA G-quadruplexes undergo Ca2+-induced phase separation and assembly, accelerating α-synuclein sol-gel phase transition. In α-synuclein preformed fibril-treated neurons, RNA G-quadruplex assembly comprising synaptic mRNAs co-aggregates with α-synuclein upon excess cytoplasmic Ca2+ influx, eliciting synaptic dysfunction. Forced RNA G-quadruplex assembly using an optogenetic approach evokes α-synuclein aggregation, causing neuronal dysfunction and neurodegeneration. The administration of 5-aminolevulinic acid, a protoporphyrin IX prodrug, prevents RNA G-quadruplex phase separation, thereby attenuating α-synuclein aggregation, neurodegeneration, and progressive motor deficits in α-synuclein preformed fibril-injected synucleinopathic mice. Therefore, Ca2+ influx-induced RNA G-quadruplex assembly accelerates α-synuclein phase transition and aggregation, potentially contributing to synucleinopathies.

Abstract: RNA molecules play a vital role in linking genetic information with various cellular processes. In recent years, a variety of optogenetic tools have been engineered for regulating cellular RNA metabolism and functions. These highly desirable tools can offer non-intrusive control with spatial precision, remote operation, and biocompatibility. Here, we would like to review these currently available approaches that can regulate RNAs with light: from non-genetically encodable chemically modified oligonucleotides to genetically encoded RNA aptamers that recognize photosensitive small-molecule or protein ligands. Some key applications of these optogenetic tools will also be highlighted to illustrate how they have been used for regulating all aspects of the RNA life cycle: from RNA synthesis, maturation, modification, and translation to their degradation, localization, and phase separation control. Some current challenges and potential practical utilizations of these RNA optogenetic tools will also be discussed.

Abstract: Proteinaceous inclusions formed by C9orf72-derived dipeptide-repeat (DPR) proteins are a histopathological hallmark in ∼50% of familial amyotrophic lateral sclerosis/frontotemporal dementia (ALS/FTD) cases. However, DPR aggregation/inclusion formation could not be efficiently recapitulated in cell models for four out of five DPRs. In this study, using optogenetics, we achieved chemical-free poly-PR condensation/aggregation in cultured cells including human motor neurons, with spatial and temporal control. Strikingly, nuclear poly-PR condensates had anisotropic, hollow-center appearance, resembling TDP-43 anisosomes, and their growth was limited by RNA. These condensates induced abnormal TDP-43 granulation in the nucleus without stress response activation. Cytoplasmic poly-PR aggregates forming under prolonged opto-stimulation were more persistent than its nuclear condensates, selectively sequestered TDP-43 in a demixed state and surrounded spontaneous stress granules. Thus, poly-PR condensation accompanied by nuclear TDP-43 dysfunction may constitute an early pathological event in C9-ALS/FTD. Anisosome-type condensates of disease-linked proteins may represent a common molecular species in neurodegenerative disease.

Abstract: During animal development, the spatiotemporal properties of molecular events largely determine the biological outcomes. Conventional gene analysis methods lack the spatiotemporal resolution for precise dissection of developmental mechanisms. Although optogenetic tools exist for manipulating designer proteins in cultured cells, few have been successfully applied to endogenous proteins in live animals. Here, we report OptoTrap, a light-inducible clustering system for manipulating endogenous proteins of diverse sizes, subcellular locations, and functions in Drosophila. This system turns on fast, is reversible in minutes or hours, and contains variants optimized for neurons and epithelial cells. By using OptoTrap to disrupt microtubules and inhibit kinesin-1 in neurons, we show that microtubules support the growth of highly dynamic dendrites and that kinesin-1 is required for patterning of low- and high-order dendritic branches in differential spatiotemporal domains. OptoTrap allows for precise manipulation of endogenous proteins in a spatiotemporal manner and thus holds promise for studying developmental mechanisms in a wide range of cell types and developmental stages.

Abstract: Macrophages measure the "eat-me" signal immunoglobulin G (IgG) to identify targets for phagocytosis. We tested whether prior encounters with IgG influence macrophage appetite. IgG is recognized by the Fc receptor. To temporally control Fc receptor activation, we engineered an Fc receptor that is activated by the light-induced oligomerization of Cry2, triggering phagocytosis. Using this tool, we demonstrate that subthreshold Fc receptor activation primes mouse bone-marrow-derived macrophages to be more sensitive to IgG in future encounters. Macrophages that have previously experienced subthreshold Fc receptor activation eat more IgG-bound human cancer cells. Increased phagocytosis occurs by two discrete mechanisms-a short- and long-term priming. Long-term priming requires new protein synthesis and Erk activity. Short-term priming does not require new protein synthesis and correlates with an increase in Fc receptor mobility. Our work demonstrates that IgG primes macrophages for increased phagocytosis, suggesting that therapeutic antibodies may become more effective after initial priming doses.

Abstract: Intracellular tau aggregation requires a local protein concentration increase, referred to as "droplets". However, the cellular mechanism for droplet formation is poorly understood. Here, we expressed OptoTau, a P301L mutant tau fused with CRY2olig, a light-sensitive protein that can form homo-oligomers. Under blue light exposure, OptoTau increased tau phosphorylation and was sequestered in aggresomes. Suppressing aggresome formation by nocodazole formed tau granular clusters in the cytoplasm. The granular clusters disappeared by discontinuing blue light exposure or 1,6-hexanediol treatment suggesting that intracellular tau droplet formation requires microtubule collapse. Expressing OptoTau-ΔN, a species of N-terminal cleaved tau observed in the Alzheimer's disease brain, formed 1,6-hexanediol and detergent-resistant tau clusters in the cytoplasm with blue light stimulation. These intracellular stable tau clusters acted as a seed for tau fibrils in vitro. These results suggest that tau droplet formation and N-terminal cleavage are necessary for neurofibrillary tangles formation in neurodegenerative diseases.