Curated Optogenetic Publication Database

Abstract: CRISPR/Cas9 is a powerful tool for targeted genome editing experiments. Using CRISPR/Cas9, genes can be deleted or modified by inserting specific DNA sequences, encoding for fluorescent proteins, small peptide tags, or other modifications. Such experiments are essential for detailed gene and protein characterization. However, designing and cloning the corresponding constructs can be repetitive, time-consuming, and laborious. To assist users in CRISPR/Cas9-based genome engineering, we developed CrisprBuildr, an open-source, web-based application for designing modifications to their target genes. CrisprBuildr guides users through creating guide RNAs and repair template vectors to generate cloning maps. The application is designed for the Drosophila melanogaster genome but can serve as a template for other available genomes. We also created new tagging vectors using EGFP and mCherry combined with the small peptide SspB-Q73R for use in iLID-based optogenetic experiments.

Abstract: Microtubules are crucial regulators of plant development and are organized by a suite of microtubule-associated proteins (MAPs) that can rapidly remodel the array in response to various cues. This complexity has inspired countless studies into microtubule function from the subcellular to tissue scale, revealing an ever-increasing number of microtubule-dependent processes. Developing a comprehensive understanding of how local microtubule configuration, dynamicity, and remodeling drive developmental progression requires new approaches to capture and alter microtubule behavior. In this review, we will introduce the technological advancements we believe are poised to transform the study of microtubules in plant cells. In particular, we focus on (1) advanced imaging and analysis methods to quantify microtubule organization and behavior, and (2) novel tools to target specific microtubule populations in vivo. By showcasing innovative methodologies developed in non-plant systems, we hope to motivate their increased adoption and raise awareness of possible means of adapting them for studying microtubules in plants.

Abstract: The modification of key enzymes for chemical production plays a crucial role in enhancing the yield of targeted products. However, manipulating key nodes in specific signalling pathways remains constrained by traditional gene overexpression or knockout strategies. Discovering and designing optogenetic tools enable us to regulate enzymatic activity or gene expression at key nodes in a spatiotemporal manner, rather than relying solely on chemical induction throughout production processes. In this review, we discuss the recent applications of optogenetic tools in the regulation of microbial metabolites, plant sciences and disease therapies. We categorize optogenetic tools into five classes based on their distinct applications. First, light-induced gene expression schedules can balance the trade-off between chemical production and cell growth phases. Second, light-triggered liquid-liquid phase separation (LLPS) modules provide opportunities to co-localize and condense key enzymes for enhancing catalytic efficiency. Third, light-induced subcellular localized photoreceptors enable the relocation of protein of interest across various subcellular compartments, allowing for the investigation of their dynamic regulatory processes. Fourth, light-regulated enzymes can dynamically regulate production of cyclic nucleotides or investigate endogenous components similar with conditional depletion or recovery function of protein of interest. Fifth, light-gated ion channels and pumps can be utilized to investigate dynamic ion signalling cascades in both animals and plants, or to boost ATP accumulation for enhancing biomass or bioproduct yields in microorganisms. Overall, this review aims to provide a comprehensive overview of optogenetic strategies that have the potential to advance both basic research and bioindustry within the field of synthetic biology.

Abstract: Intracellular optogenetics represents a rapidly advancing biotechnology that enables precise, reversible control of protein activity, signaling dynamics, and cellular behaviours using genetically encoded, light-responsive systems. Originally pioneered in neuroscience through channelrhodopsins to manipulate neuronal excitability, the field has since expanded into diverse intracellular applications with broad implications for medicine, agriculture, and biomanufacturing. Key to these advances are photoreceptors such as cryptochrome 2 (CRY2), light-oxygen-voltage (LOV) domains, and phytochromes, which undergo conformational changes upon illumination to trigger conditional protein-protein interactions, localization shifts, or phase transitions. Recent engineering breakthroughs-including the creation of red-light responsive systems such as MagRed that exploit endogenous biliverdin-have enhanced tissue penetration, minimized phototoxicity, and expanded applicability to complex biological systems. This review provides an overarching synthesis of the molecular principles underlying intracellular optogenetic actuators, including the photophysical basis of light-induced conformational changes, oligomerization, and signaling control. We highlight strategies that employ domain fusions, rational mutagenesis, and synthetic circuits to extend their utility across biological and industrial contexts. We also critically assess current limitations, such as chromophore dependence, light delivery challenges, and safety considerations, so as to frame realistic paths towards translation. Looking ahead, future opportunities include multi-colour and multiplexed systems, integration with high-throughput omics and artificial intelligence, and development of non-invasive modalities suited for in vivo and industrial applications. Intracellular optogenetics is thus emerging as a versatile platform technology, with the potential to reshape how we interrogate biology and engineer cells for therapeutic, agricultural, and environmental solutions.

Abstract: Small GTPases are critical regulators of cellular processes, such as cell migration, and comprise a family of over 167 proteins in the human genome. Importantly, the location-dependent regulation of small GTPase activity is integral to coordinating cellular signaling. Currently, there are no generalizable methods for directly controlling the activity of these signaling enzymes with subcellular precision. To address this issue, we introduce a modular, optogenetic platform for the spatial control of small GTPase activity within living cells, termed spLIT-small GTPases. This platform enabled spatially precise control of cytoskeletal dynamics such as filopodia formation (spLIT-Cdc42) and directed cell migration (spLIT-Rac1). Furthermore, a spLIT-RhoA system uncovered previously unreported long-range RhoA signaling in HeLa cells, resulting in bipolar membrane retraction. These results establish spLIT-small GTPases as a versatile platform for the direct, spatial control of small GTPase signaling and demonstrate the ability to uncover spatially defined aspects of small GTPase signaling.

Abstract: Phospholipase C-γ1 (PLC-γ1) signaling is required for mesenchymal chemotaxis, but is it sufficient to bias motility? PLC-γ1 enzyme activity is basally autoinhibited, and light-controlled membrane recruitment of wild-type (WT) PLC-γ1 (OptoPLC-γ1) in Plcg1-null fibroblasts does not trigger lipid hydrolysis, complicating efforts to isolate its contribution. Utilizing cancer-associated mutations to investigate the regulatory logic of PLC-γ1, we demonstrate that the canonical hallmark of enzyme activity, phosphorylated Tyr783 (pTyr783), is not a proxy for activity level, but is rather a marker of dysregulated autoinhibition. Accordingly, OptoPLC-γ1 with a deregulating mutation (P867R, S345F, or D1165H) exhibits elevated phosphorylation, and membrane localization of such is sufficient to activate substrate hydrolysis and concomitant motility responses. In particular, local recruitment of OptoPLC-γ1 S345F polarizes cell motility on demand. This response is spatially dose-sensitive and only partially reduced by blocking canonical PLC-γ1 signaling yet is lipase-dependent. Our findings reframe the interpretation of PLC-γ1 regulation and demonstrate that local activation of PLC-γ1 is sufficient to direct cell motility.

Abstract: Cellular immunotherapy has transformed cancer treatment by harnessing T cells to target malignant cells. However, its broader adoption is hindered by challenges such as efficacy loss, limited persistence, tumor heterogeneity, an immunosuppressive tumor microenvironment (TME), and safety concerns related to systemic adverse effects. Optogenetics, a technology that uses light-sensitive proteins to regulate cellular functions with high spatial and temporal accuracy, offers a potential solution to overcome these issues. By enabling targeted modulation of T cell receptor signaling, ion channels, transcriptional programming, and antigen recognition, optogenetics provides dynamic control over T cell activation, cytokine production, and cytotoxic responses. Moreover, optogenetic strategies can be applied to remodel the TME by selectively activating immune responses or inducing targeted immune cell depletion, thereby enhancing T cell infiltration and immune surveillance. However, practical hurdles such as limited tissue penetration of visible light and the need for cell- or tissue-specific gene delivery must be addressed for clinical translation. Emerging solutions, including upconversion nanoparticles, are being explored to improve light delivery to deeper tissues. Future integration of optogenetics with existing immunotherapies, such as checkpoint blockade and adoptive T cell therapies, could improve treatment specificity, minimize adverse effects, and provide real-time control over immune responses. By refining the precision and adaptability of immunotherapy, optogenetics promises to further enhance both the safety and efficacy of cancer immunotherapy.

Abstract: Over the past two decades, optogenetics has evolved from a conceptual framework into a powerful and versatile technology for controlling cellular processes with light. Rooted in the discovery and characterization of natural photoreceptors, the field has advanced through the development of genetically encoded, light-sensitive proteins that enable precise spatiotemporal control of ion flux, intracellular signaling, gene expression, and protein interactions. This review traces key milestones in the emergence of optogenetics and highlights the development of major optogenetic tools. From the perspective of genetic tool innovation, the focus is on how these tools have been engineered and optimized for novel or enhanced functions, altered spectral properties, improved light sensitivity, subcellular targeting, and beyond. Their broadening applications are also explored across neuroscience, cardiovascular biology, hematology, plant sciences, and other emerging fields. In addition, current trends such as all-optical approaches, multiplexed control, and clinical translation, particularly in vision restoration are discussed. Finally, ongoing challenges are addressed and outline future directions in optogenetic tool development and in vivo applications, positioning optogenetics as a transformative platform for basic research and therapeutic advancement.

Abstract: The actin cytoskeleton forms a meshwork that drives cellular deformation. Network properties, determined by density and actin-binding proteins, are crucial, yet how density governs protein penetration and dynamics remains unclear. Here, we report an in vitro optogenetic system, named OptoVCA, enabling Arp2/3 complex-mediated actin assembly on lipid membranes. By tuning illumination power, duration, and pattern, OptoVCA flexibly manipulates the density, thickness, and shape of the actin network. Taking these advantages, we examine how network density affects two actin-binding proteins: myosin and ADF/cofilin. We find that even modest increases in density strictly inhibit myosin filament penetration by steric hindrance. Penetrated myosin filaments generate directional actin flow in networks with density gradients. In contrast, ADF/cofilin accesses networks regardless of density, yet network disassembly is markedly reduced by increased density. Thus, OptoVCA reveals that network density differentially regulates actin-binding protein penetration and activity. These findings advance understanding of cell mechanics through precise, light-based manipulation of cytoskeletal structure.

Abstract: During development, epithelia function as malleable sheets that undergo extensive remodeling to shape developing embryos. Optogenetic control of Rho signaling provides an avenue to investigate mechanisms of epithelial morphogenesis, but transgenic optogenetic tools can be limited by variability in expression levels and deleterious effects of transgenic overexpression on development. Here, we use CRISPR/Cas9 to tag Drosophila RhoGEF2 and Cysts/Dp114RhoGEF with components of the iLID/SspB optogenetic heterodimer, permitting light-dependent control over endogenous protein activities. Using quantitative optogenetic perturbations, we uncover a dose-dependence of tissue furrow depth and bending behavior on RhoGEF recruitment, revealing mechanisms by which developing embryos can shape tissues into particular morphologies. We show that at the onset of gastrulation, furrows formed by cell lateral contraction are oriented and size-constrained by basal actomyosin. Our findings demonstrate the use of quantitative, 3D-patterned perturbations of cell contractility to precisely shape tissue structures and interrogate developmental mechanics.

Abstract: Oncolytic virus (OVs) therapy has emerged as a promising modality in cancer immunotherapy, attracting growing attention for its multifaceted mechanisms of tumor elimination. However, its efficacy as a monotherapy remains constrained by physiological barriers, limited delivery routes, and suboptimal immune activation. Phototherapy, an innovative and rapidly advancing cancer treatment technology, can mitigate these limitations when used in conjunction with OVs, enhancing viral delivery, amplifying tumor destruction, and boosting antitumor immune responses. This review provides the first comprehensive analysis of synergistic integration of OVs with both photodynamic therapy (PDT) and photothermal therapy (PTT). It also explores their applications in optical imaging-guided diagnosis and optogenetically controlled delivery. Furthermore, it discusses emerging strategies involving biomimetic virus or viroid-based vectors in conjunction with phototherapy, and delves into the immunomodulatory mechanisms of this combinatorial approach. While promising in preclinical models, these combined strategies are still largely in early-stage research. Challenges such as limited light penetration, delivery efficiency, and safety concerns remain to be addressed for clinical translation. Consequently, the integration of OV therapy and phototherapy represents a compelling strategy in cancer treatment, offering significant promise for advancing precision oncology and next-generation immunotherapies.

Abstract: Optogenetically regulated enzymes offer unprecedented spatiotemporal control over protein activity, intermolecular interactions, and intracellular signaling. Many design strategies have been developed for their fabrication based on the principles of intrinsic allostery, oligomerization or 'split' status, intracellular compartmentalization, and steric hindrance. In addition to employing photosensory domains as part of the traditional optogenetic toolset, the specificity of effector domains has also been leveraged for endogenous applications. Here, we discuss the dynamics of light activation while providing a bird's eye view of the crafting approaches, targets, and impact of optogenetic enzymes in orchestrating cellular functions, as well as the bottlenecks and an outlook into the future.

Abstract: Intermediate filaments (IFs) are a key component of the cytoskeleton, essential for regulating cell mechanics, maintaining nuclear integrity, organelle positioning, and modulating cell signaling. Current insights into IF function primarily come from studies using long-term perturbations, such as protein depletion or mutation. Here, we present tools that allow rapid manipulation of vimentin IFs in the whole cytoplasm or within specific subcellular regions by inducibly coupling them to microtubule motors, either pharmacologically or using light. Rapid perinuclear clustering of vimentin had no major immediate effects on the actin or microtubule organization, cell spreading, or focal adhesion number, but it reduced cell stiffness. Mitochondria and endoplasmic reticulum (ER) sheets were reorganized due to vimentin clustering, whereas lysosomes were only briefly displaced and rapidly regained their normal distribution. Keratin moved along with vimentin in some cell lines but remained intact in others. Our tools help to study the immediate and local effects of vimentin perturbation and identify direct links of vimentin to other cellular structures.

Abstract: Mitochondrial fission is controlled by dynamin-like proteins, the dysregulation of which is correlated with diverse diseases. Fission dynamin-like proteins are GTP hydrolysis-driven mechanoenzymes that self-oligomerize into helical structures that constrict membranes to achieve fission while also remodeling membranes by inducing negative Gaussian curvature, which is essential for the completion of fission. Despite advances in optical and electron imaging technologies, the underlying mechanics of mitochondrial fission remain unclear due to the multiple times involved in the dynamics of mechanoenzyme activity, oligomer disassembly, and membrane remodeling. Here, we examine how multiscale phenomena in dynamin Drp1 synergistically influence membrane fission using a mechanical model calibrated with small-angle X-ray scattering structural data and informed by a machine learning analysis of the Drp1 sequence, and tested the concept using optogenetic mechanostimulation of mitochondria in live cells. We find that free dynamin-like proteins can trigger a "snap-through instability" that enforces a shape transition from an oligomer-confined cylindrical membrane to a drastically narrower catenoid-shaped neck within the spontaneous hemi-fission regime, in a manner that depends critically on the length of the confined tube. These results indicate how the combination of assembly and paradoxically disassembly of dynamin-like proteins can lead to diverse pathways to scission.

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: 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: Cortical positioning of the meiotic spindle within an oocyte is required to expel chromosomes into polar bodies to generate a zygote with the correct number of chromosomes. In C. elegans, yolk granules and mitochondria are packed inward, away from the cortex, while the spindle moves outward, both in a kinesin-dependent manner. The kinesin-dependent inward packing of yolk granules suggests the existence of microtubules with minus ends at the cortex and plus ends extending inward, making it unclear how kinesin moves the spindle outward. We hypothesize that the inward packing of organelles might indirectly force the spindle outward by volume exclusion. To test this hypothesis, we generate a strain in which the only kinesin consists of motor domains with no cargo-binding tail optogenetically attached to mitochondria. This mitochondria-only kinesin packs mitochondria into a tight ball and efficiently moves the meiotic spindle to the cortex, supporting the volume exclusion hypothesis.

Abstract: Lipids are a major class of biological molecules, the primary components of cellular membranes, and critical signaling molecules that regulate cell biology and physiology. Due to their dynamic behavior within membranes, rapid transport between organelles, and complex and often redundant metabolic pathways, lipids have traditionally been considered among the most challenging biological molecules to study. In recent years, a plethora of tools bridging the chemistry-biology interface has emerged for studying different aspects of lipid biology. Here, we provide an overview of these approaches. We discuss methods for lipid detection, including genetically encoded biosensors, synthetic lipid analogs, and metabolic labeling probes. For targeted manipulation of lipids, we describe pharmacological agents and controllable enzymes, termed membrane editors, that harness optogenetics and chemogenetics. To conclude, we survey techniques for elucidating lipid-protein interactions, including photoaffinity labeling and proximity labeling. Collectively, these strategies are revealing new insights into the regulation, dynamics, and functions of lipids in cell biology.

Abstract: The binding of photoswitchable molecules to partners forms the basis of many naturally occurring light-dependent signaling pathways and various photopharmacological and optogenetic tools. A critical parameter affecting the function of these molecules is the thermal half-life of the light state. Reports in the literature indicate that, in some cases, a binding partner can significantly influence the thermal half-life, while in other cases it has no effect. Here, we present a unifying framework for quantitatively analyzing the effects of binding partners on thermal reversion rates. We focus on photoswitchable protein/binder interactions involving LOV domains, photoactive yellow protein, and CBCR GAF domains with partners that bind either the light or the dark state of the photoswitchable domain. We show that the effect of a binding partner depends on the extent to which the transition state for reversion resembles the dark state or the light state. We quantify this resemblance with a ϕswitching value, where ϕswitching = 1 if the conformation of the part of the photoswitchable molecule that interacts with the binding partner closely resembles its dark state conformation and ϕswitching = 0 if it resembles its light state. In addition to providing information on the transition state for switching, this analysis can guide the design of photoswitchable systems that retain useful thermal half-lives in practice. The analysis also provides a basis for the use of simple kinetic measurements to determine effective changes in affinity even in complex milieu.

Abstract: Light-based immunotherapy uses specific wavelengths of light to activate or modulate immune responses. It primarily employs two mechanisms: direct activation of immune cells and indirect modulation of the tumor microenvironment (TME). Several light-based technologies are under investigation or clinical use in immunotherapy, including photodynamic immunotherapy (PDIT) and photothermal therapy (PTT). Optogenetic tools have the potential to precisely control T-cell receptor activation, cytokine release, or the activity of other immune effector cells. Light-based technologies present innovative opportunities within the realm of immunotherapy. The ability to precisely regulate immune cell activation via optogenetics, alongside the improved targeting of cancer cells through photoimmunotherapy, signifies a transformative shift in our strategies for immune modulation. Although many of these technologies remain in the experimental stage for various applications, initial findings are encouraging, especially concerning cancer treatment and immune modulation. Continued research and clinical trials are essential to fully harness the capabilities of light technology in the context of immune cell therapy.

Abstract: Optogenetics has substantially enhanced our understanding of biological processes by enabling high-precision tracking and manipulation of individual cells. It relies on photosensitive proteins to monitor and control cellular activities, thereby paving the way for significant advancements in complex system research. Photosensitive proteins play a vital role in the development of optogenetics, facilitating the establishment of cutting-edge methods. Recent breakthroughs in protein design have opened up opportunities to develop protein-based tools that can precisely manipulate and monitor cellular activities. These advancements will significantly accelerate the development and application of optogenetic tools. This article emphasizes the pivotal role of protein design in the development of optogenetic tools, offering insights into potential future directions. We begin by providing an introduction to the historical development and fundamental principles of optogenetics, followed by an exploration of the operational mechanisms of key photosensitive domains, which includes clarifying the conformational changes they undergo in response to light, such as allosteric modulation and dimerization processes. Building on this foundation, we reveal the development of protein design tools that will enable the creation of even more sophisticated optogenetic techniques.

Abstract: Ras has traditionally been regarded as a positive regulator and therapeutic target due to its role in cell proliferation, but recent findings indicate a more nuanced role in cell migration, where suppressed Ras activity can unexpectedly promote migration. To clarify this complexity, we systematically modulate Ras activity using various RasGEF and RasGAP proteins and assess their effects on migration dynamics. Leveraging optogenetics, we assess the immediate, non-transcriptional effects of Ras signaling on migration. Local RasGEF recruitment to the plasma membrane induces protrusions and new fronts to effectively guide migration, even in the absence of GPCR/G-protein signaling whereas global recruitment causes immediate cell spreading halting cell migration. Local RasGAP recruitment suppresses protrusions, generates new backs, and repels cells whereas global relocation either eliminates all protrusions to inhibit migration or preserves a single protrusion to maintain polarity. Consistent local and global increases or decreases in signal transduction and cytoskeletal activities accompany these morphological changes. Additionally, we performed cortical tension measurements and found that RasGEFs generally increase cortical tension while RasGAPs decrease it. Our results reveal a biphasic relationship between Ras activity and cellular dynamics, reinforcing our previous findings that optimal Ras activity and cortical tension are critical for efficient migration.

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: 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: Live imaging techniques have revolutionized our understanding of paracrine signaling, a crucial form of cell-to-cell communication in biological processes. This review examines recent advances in visualizing and tracking paracrine factors through four key stages: secretion from producing cells, diffusion through extracellular space, binding to target cells, and activation of intracellular signaling within target cells. Paracrine factor secretion can be directly visualized by fluorescent protein tagging to ligand, or indirectly by visualizing the cleavage of the transmembrane pro-ligands or plasma membrane fusion of endosomes comprising the paracrine factors. Diffusion of paracrine factors has been studied using techniques such as fluorescence correlation spectroscopy (FCS), fluorescence recovery after photobleaching (FRAP), fluorescence decay after photoactivation (FDAP), and single-molecule tracking. Binding of paracrine factors to target cells has been visualized through various biosensors, including GPCR-activation-based (GRAB) sensors and Förster resonance energy transfer (FRET) probes for receptor tyrosine kinases. Finally, activation of intracellular signaling is monitored within the target cells by biosensors for second messengers, transcription factors, and so on. In addition to the imaging tools, the review also highlights emerging optogenetic and chemogenetic tools for triggering the release of paracrine factors, which is essential for associating the paracrine factor secretion to biological outcomes during the bioimaging of paracrine factor signaling.Key words: paracrine signaling, live imaging, biosensors, optogenetics, chemogenetics.