Showing 1 - 25 of 55 results
Light-regulated voltage-gated potassium channels for acute interrogation of channel function in neurons and behavior.
Voltage-gated potassium (Kv) channels regulate the membrane potential and conductance of excitable cells to control the firing rate and waveform of action potentials. Even though Kv channels have been intensely studied for over 70 year, surprisingly little is known about how specific channels expressed in various neurons and their functional properties impact neuronal network activity and behavior in vivo. Although many in vivo genetic manipulations of ion channels have been tried, interpretation of these results is complicated by powerful homeostatic plasticity mechanisms that act to maintain function following perturbations in excitability. To better understand how Kv channels shape network function and behavior, we have developed a novel optogenetic technology to acutely regulate Kv channel expression with light by fusing the light-sensitive LOV domain of Vaucheria frigida Aureochrome 1 to the N-terminus of the Kv1 subunit protein to make an Opto-Kv1 channel. Recording of Opto-Kv1 channels expressed in Xenopus oocytes, mammalian cells, and neurons show that blue light strongly induces the current expression of Opto-Kv1 channels in all systems tested. We also find that an Opto-Kv1 construct containing a dominant-negative pore mutation (Opto-Kv1(V400D)) can be used to down-regulate Kv1 currents in a blue light-dependent manner. Finally, to determine whether Opto-Kv1 channels can elicit light-dependent behavioral effect in vivo, we targeted Opto-Kv1 (V400D) expression to Kv1.3-expressing mitral cells of the olfactory bulb in mice. Exposure of the bulb to blue light for 2-3 hours produced a significant increase in sensitivity to novel odors after initial habituation to a similar odor, comparable to behavioral changes seen in Kv1.3 knockout animals. In summary, we have developed novel photoactivatable Kv channels that provide new ways to interrogate neural circuits in vivo and to examine the roles of normal and disease-causing mutant Kv channels in brain function and behavior.
Optogenetic Tools for Manipulating Protein Subcellular Localization and Intracellular Signaling at Organelle Contact Sites.
Intracellular signaling processes are frequently based on direct interactions between proteins and organelles. A fundamental strategy to elucidate the physiological significance of such interactions is to utilize optical dimerization tools. These tools are based on the use of small proteins or domains that interact with each other upon light illumination. Optical dimerizers are particularly suitable for reproducing and interrogating a given protein-protein interaction and for investigating a protein's intracellular role in a spatially and temporally precise manner. Described in this article are genetic engineering strategies for the generation of modular light-activatable protein dimerization units and instructions for the preparation of optogenetic applications in mammalian cells. Detailed protocols are provided for the use of light-tunable switches to regulate protein recruitment to intracellular compartments, induce intracellular organellar membrane tethering, and reconstitute protein function using enhanced Magnets (eMags), a recently engineered optical dimerization system. © 2021 Wiley Periodicals LLC. Basic Protocol 1: Genetic engineering strategy for the generation of modular light-activated protein dimerization units Support Protocol 1: Molecular cloning Basic Protocol 2: Cell culture and transfection Support Protocol 2: Production of dark containers for optogenetic samples Basic Protocol 3: Confocal microscopy and light-dependent activation of the dimerization system Alternate Protocol 1: Protein recruitment to intracellular compartments Alternate Protocol 2: Induction of organelles' membrane tethering Alternate Protocol 3: Optogenetic reconstitution of protein function Basic Protocol 4: Image analysis Support Protocol 3: Analysis of apparent on- and off-kinetics Support Protocol 4: Analysis of changes in organelle overlap over time.
Optogenetic manipulation of cellular communication using engineered myosin motors.
Cells achieve highly efficient and accurate communication through cellular projections such as neurites and filopodia, yet there is a lack of genetically encoded tools that can selectively manipulate their composition and dynamics. Here, we present a versatile optogenetic toolbox of artificial multi-headed myosin motors that can move bidirectionally within long cellular extensions and allow for the selective transport of GFP-tagged cargo with light. Utilizing these engineered motors, we could transport bulky transmembrane receptors and organelles as well as actin remodellers to control the dynamics of both filopodia and neurites. Using an optimized in vivo imaging scheme, we further demonstrate that, upon limb amputation in axolotls, a complex array of filopodial extensions is formed. We selectively modulated these filopodial extensions and showed that they re-establish a Sonic Hedgehog signalling gradient during regeneration. Considering the ubiquitous existence of actin-based extensions, this toolbox shows the potential to manipulate cellular communication with unprecedented accuracy.
A synthetic BRET-based optogenetic device for pulsatile transgene expression enabling glucose homeostasis in mice.
Pulsing cellular dynamics in genetic circuits have been shown to provide critical capabilities to cells in stress response, signaling and development. Despite the fascinating discoveries made in the past few years, the mechanisms and functional capabilities of most pulsing systems remain unclear, and one of the critical challenges is the lack of a technology that allows pulsatile regulation of transgene expression both in vitro and in vivo. Here, we describe the development of a synthetic BRET-based transgene expression (LuminON) system based on a luminescent transcription factor, termed luminGAVPO, by fusing NanoLuc luciferase to the light-switchable transcription factor GAVPO. luminGAVPO allows pulsatile and quantitative activation of transgene expression via both chemogenetic and optogenetic approaches in mammalian cells and mice. Both the pulse amplitude and duration of transgene expression are highly tunable via adjustment of the amount of furimazine. We further demonstrated LuminON-mediated blood-glucose homeostasis in type 1 diabetic mice. We believe that the BRET-based LuminON system with the pulsatile dynamics of transgene expression provides a highly sensitive tool for precise manipulation in biological systems that has strong potential for application in diverse basic biological studies and gene- and cell-based precision therapies in the future.
Optimized Vivid-derived Magnets photodimerizers for subcellular optogenetics in mammalian cells.
Light-inducible dimerization protein modules enable precise temporal and spatial control of biological processes in non-invasive fashion. Among them, Magnets are small modules engineered from the Neurospora crassa photoreceptor Vivid by orthogonalizing the homodimerization interface into complementary heterodimers. Both Magnets components, which are well-tolerated as protein fusion partners, are photoreceptors requiring simultaneous photoactivation to interact, enabling high spatiotemporal confinement of dimerization with a single-excitation wavelength. However, Magnets require concatemerization for efficient responses and cell preincubation at 28oC to be functional. Here we overcome these limitations by engineering an optimized Magnets pair requiring neither concatemerization nor low temperature preincubation. We validated these 'enhanced' Magnets (eMags) by using them to rapidly and reversibly recruit proteins to subcellular organelles, to induce organelle contacts, and to reconstitute OSBP-VAP ER-Golgi tethering implicated in phosphatidylinositol-4-phosphate transport and metabolism. eMags represent a very effective tool to optogenetically manipulate physiological processes over whole cells or in small subcellular volumes.
Light-inducible Deformation of Mitochondria in Live Cells.
Mitochondria, the powerhouse of the cell, are dynamic organelles that undergo constant morphological changes. Increasing evidence indicates that mitochondria morphologies and functions can be modulated by mechanical cues. However, the mechano-sensing and -responding properties of mitochondria and the correlation between mitochondrial morphologies and functions are unclear due to the lack of methods to precisely exert mechano-stimulation on and deform mitochondria inside live cells. Here we present an optogenetic approach that uses light to induce deformation of mitochondria by recruiting molecular motors to the outer mitochondrial membrane via light-activated protein-protein hetero-dimerization. Mechanical forces generated by motor proteins distort the outer membrane, during which the inner mitochondrial membrane can also be deformed. Moreover, this optical method can achieve subcellular spatial precision and be combined with other optical dimerizers and molecular motors. This method presents a novel mitochondria-specific mechano-stimulator for studying mitochondria mechanobiology and the interplay between mitochondria shapes and functions.
Clustering of the ζ-Chain Can Initiate T Cell Receptor Signaling.
T cell activation is initiated when ligand binding to the T cell receptor (TCR) triggers intracellular phosphorylation of the TCR-CD3 complex. However, it remains unknown how biophysical properties of TCR engagement result in biochemical phosphorylation events. Here, we constructed an optogenetic tool that induces spatial clustering of ζ-chain in a light controlled manner. We showed that spatial clustering of the ζ-chain intracellular tail alone was sufficient to initialize T cell triggering including phosphorylation of ζ-chain, Zap70, PLCγ, ERK and initiated Ca2+ flux. In reconstituted COS-7 cells, only Lck expression was required to initiate ζ-chain phosphorylation upon ζ-chain clustering, which leads to the recruitment of tandem SH2 domain of Zap70 from cell cytosol to the newly formed ζ-chain clusters at the plasma membrane. Taken together, our data demonstrated the biophysical relevance of receptor clustering in TCR signaling.
An optimized toolbox for the optogenetic control of intracellular transport.
Cellular functioning relies on active transport of organelles by molecular motors. To explore how intracellular organelle distributions affect cellular functions, several optogenetic approaches enable organelle repositioning through light-inducible recruitment of motors to specific organelles. Nonetheless, robust application of these methods in cellular populations without side effects has remained challenging. Here, we introduce an improved toolbox for optogenetic control of intracellular transport that optimizes cellular responsiveness and limits adverse effects. To improve dynamic range, we employed improved optogenetic heterodimerization modules and engineered a photosensitive kinesin-3, which is activated upon blue light-sensitive homodimerization. This opto-kinesin prevented motor activation before experimental onset, limited dark-state activation, and improved responsiveness. In addition, we adopted moss kinesin-14 for efficient retrograde transport with minimal adverse effects on endogenous transport. Using this optimized toolbox, we demonstrate robust reversible repositioning of (endogenously tagged) organelles within cellular populations. More robust control over organelle motility will aid in dissecting spatial cell biology and transport-related diseases.
Light-inducible generation of membrane curvature in live cells with engineered BAR domain proteins.
Nanoscale membrane curvature is now understood to play an active role in essential cellular processes such as endocytosis, exocytosis and actin dynamics. Previous studies have shown that membrane curvature can directly affect protein function and intracellular signaling. However, few methods are able to precisely manipulate membrane curvature in live cells. Here, we report the development of a new method of generating nanoscale membrane curvature in live cells that is controllable, reversible, and capable of precise spatial and temporal manipulation. For this purpose, we make use of BAR domain proteins, a family of well-studied membrane-remodeling and membrane-sculpting proteins. Specifically, we engineered two optogenetic systems, opto-FBAR and opto-IBAR, that allow light-inducible formation of positive and negative membrane curvature, respectively. Using opto-FBAR, blue light activation results in the formation of tubular membrane invaginations (positive curvature), controllable down to the subcellular level. Using opto-IBAR, blue light illumination results in the formation of membrane protrusions or filopodia (negative curvature). These systems present a novel approach for light-inducible manipulation of nanoscale membrane curvature in live cells.
Optogenetic engineering to probe the molecular choreography of STIM1-mediated cell signaling.
Genetically encoded photoswitches have enabled spatial and temporal control of cellular events to achieve tailored functions in living cells, but their applications to probe the structure-function relations of signaling proteins are still underexplored. We illustrate herein the incorporation of various blue light-responsive photoreceptors into modular domains of the stromal interaction molecule 1 (STIM1) to manipulate protein activity and faithfully recapitulate STIM1-mediated signaling events. Capitalizing on these optogenetic tools, we identify the molecular determinants required to mediate protein oligomerization, intramolecular conformational switch, and protein-target interactions. In parallel, we have applied these synthetic devices to enable light-inducible gating of calcium channels, conformational switch, dynamic protein-microtubule interactions and assembly of membrane contact sites in a reversible manner. Our optogenetic engineering approach can be broadly applied to aid the mechanistic dissection of cell signaling, as well as non-invasive interrogation of physiological processes with high precision.
Minimally disruptive optical control of protein tyrosine phosphatase 1B.
Protein tyrosine phosphatases regulate a myriad of essential subcellular signaling events, yet they remain difficult to study in their native biophysical context. Here we develop a minimally disruptive optical approach to control protein tyrosine phosphatase 1B (PTP1B)-an important regulator of receptor tyrosine kinases and a therapeutic target for the treatment of diabetes, obesity, and cancer-and we use that approach to probe the intracellular function of this enzyme. Our conservative architecture for photocontrol, which consists of a protein-based light switch fused to an allosteric regulatory element, preserves the native structure, activity, and subcellular localization of PTP1B, affords changes in activity that match those elicited by post-translational modifications inside the cell, and permits experimental analyses of the molecular basis of optical modulation. Findings indicate, most strikingly, that small changes in the activity of PTP1B can cause large shifts in the phosphorylation states of its regulatory targets.
Membrane dynamics induced by a PIP3 optogenetic tool.
Membrane dynamic structures such as filopodia, lamellipodia, and ruffles have important cellular functions in phagocytosis and cell motility, and in pathological states such as cancer metastasis. Phosphatidylinositol 3,4,5-trisphosphate (PIP3) is a crucial lipid that regulates PIP3 dynamics. Investigations of how PIP3 is involved in these functions have mainly relied on pharmacological interventions, and therefore have not generated detailed spatiotemporal information of membrane dynamics upon PIP3 production. In the present study, we applied an optogenetic approach using the CRY2–CIBN system. Using this system, we revealed that local PIP3 generation induced directional cell motility and membrane ruffles in COS7 cells. Furthermore, combined with structured illumination microscopy (SIM), membrane dynamics were investigated with high spatial resolution. We observed PIP3-induced apical ruffles and unique actin fiber behavior in that a single actin fiber protruded from the plasma membrane was taken up into the plasma membrane without depolymerization. This system has the potential to investigate other high-level cell motility and dynamic behaviors such as cancer cell invasion and wound healing with high spatiotemporal resolution, and could provide new insights of biological sciences for membrane dynamics.
A light-gated potassium channel for sustained neuronal inhibition.
Currently available inhibitory optogenetic tools provide short and transient silencing of neurons, but they cannot provide long-lasting inhibition because of the requirement for high light intensities. Here we present an optimized blue-light-sensitive synthetic potassium channel, BLINK2, which showed good expression in neurons in three species. The channel is activated by illumination with low doses of blue light, and in our experiments it remained active over (tens of) minutes in the dark after the illumination was stopped. This activation caused long periods of inhibition of neuronal firing in ex vivo recordings of mouse neurons and impaired motor neuron response in zebrafish in vivo. As a proof-of-concept application, we demonstrated that in a freely moving rat model of neuropathic pain, the activation of a small number of BLINK2 channels caused a long-lasting (>30 min) reduction in pain sensation.
Dual-controlled optogenetic system for the rapid down-regulation of protein levels in mammalian cells.
Optogenetic switches are emerging molecular tools for studying cellular processes as they offer higher spatiotemporal and quantitative precision than classical, chemical-based switches. Light-controllable gene expression systems designed to upregulate protein expression levels meanwhile show performances superior to their chemical-based counterparts. However, systems to reduce protein levels with similar efficiency are lagging behind. Here, we present a novel two-component, blue light-responsive optogenetic OFF switch (‘Blue-OFF’), which enables a rapid and quantitative down-regulation of a protein upon illumination. Blue-OFF combines the first light responsive repressor KRAB-EL222 with the protein degradation module B-LID (blue light-inducible degradation domain) to simultaneously control gene expression and protein stability with a single wavelength. Blue-OFF thus outperforms current optogenetic systems for controlling protein levels. The system is described by a mathematical model which aids in the choice of experimental conditions such as light intensity and illumination regime to obtain the desired outcome. This approach represents an advancement of dual-controlled optogenetic systems in which multiple photosensory modules operate synergistically. As exemplified here for the control of apoptosis in mammalian cell culture, the approach opens up novel perspectives in fundamental research and applications such as tissue engineering.
A green light-responsive system for the control of transgene expression in mammalian and plant cells.
The ever-increasing complexity of synthetic gene networks and applications of synthetic biology requires precise and orthogonal gene expression systems. Of particular interest are systems responsive to light as they enable the control of gene expression dynamics with unprecedented resolution in space and time. While broadly used in mammalian backgrounds, however, optogenetic approaches in plant cells are still limited due to interference of the activating light with endogenous photoreceptors. Here, we describe the development of the first synthetic light-responsive system for the targeted control of gene expression in mammalian and plant cells that responds to the green range of the light spectrum in which plant photoreceptors have minimal activity. We first engineered a system based on the light-sensitive bacterial transcription factor CarH6 and its cognate DNA operator sequence CarO from Thermus thermophilus to control gene expression in mammalian cells. The system was functional in various mammalian cell lines, showing high induction (up to 350-fold) along with low leakiness, as well as high reversibility. We quantitatively described the systems characteristics by the development and experimental validation of a mathematical model. Finally, we transferred the system into A. thaliana protoplasts and demonstrated gene expression in response to green light. We expect that this system will provide new opportunities in applications based on synthetic gene networks and will open up perspectives for optogenetic studies in mammalian and plant cells.
Near-infrared light-controlled gene expression and protein targeting in neurons and non-neuronal cells.
Near-infrared (NIR) light-inducible binding of bacterial phytochrome BphP1 to its engineered partner QPAS1 is used for optical protein regulation in mammalian cells. However, there are no data on the application of the BphP1-QPAS1 pair in cells derived from various mammalian tissues. Here, we tested functionality of two BphP1-QPAS1-based optogenetic tools, such as an NIR and blue light-sensing system for control of protein localization (iRIS) and an NIR light-sensing system for transcription activation (TA), in several cell types including cortical neurons. We found that the performance of these optogenetic tools often rely on physiological properties of a specific cell type, such as nuclear transport, which may limit applicability of blue light-sensitive component of iRIS. In contrast, the NIR-light-sensing part of iRIS performed well in all tested cell types. The TA system showed the best performance in HeLa, U-2 OS and HEK-293 cells. Small size of the QPAS1 component allows designing AAV viral particles, which were applied to deliver the TA system to neurons.
Light-activated protein interaction with high spatial subcellular confinement.
Methods to acutely manipulate protein interactions at the subcellular level are powerful tools in cell biology. Several blue-light-dependent optical dimerization tools have been developed. In these systems one protein component of the dimer (the bait) is directed to a specific subcellular location, while the other component (the prey) is fused to the protein of interest. Upon illumination, binding of the prey to the bait results in its subcellular redistribution. Here, we compared and quantified the extent of light-dependent dimer occurrence in small, subcellular volumes controlled by three such tools: Cry2/CIB1, iLID, and Magnets. We show that both the location of the photoreceptor protein(s) in the dimer pair and its (their) switch-off kinetics determine the subcellular volume where dimer formation occurs and the amount of protein recruited in the illuminated volume. Efficient spatial confinement of dimer to the area of illumination is achieved when the photosensitive component of the dimerization pair is tethered to the membrane of intracellular compartments and when on and off kinetics are extremely fast, as achieved with iLID or Magnets. Magnets and the iLID variants with the fastest switch-off kinetics induce and maintain protein dimerization in the smallest volume, although this comes at the expense of the total amount of dimer. These findings highlight the distinct features of different optical dimerization systems and will be useful guides in the choice of tools for specific applications.
Optogenetic activation of EphB2 receptor in dendrites induced actin polymerization by activating Arg kinase.
Erythropoietin-producing hepatocellular (Eph) receptors regulate a wide array of developmental processes by responding to cell-cell contacts. EphB2 is well-expressed in brain and known to be important for dendritic spine development, as well as for the maintenance of the synapses, although the mechanisms of these functions have not been fully understood. Here we studied EphB2's functions in hippocampal neurons with an optogenetic approach, which allows us to specify spatial regions of signal activation and monitor in real-time the consequences of signal activation. We designed and constructed OptoEphB2, a genetically encoded photoactivatable EphB2. Photoactivation of OptoEphB2 in fibroblast cells induced receptor phosphorylation and resulted in cell rounding - a well-known cellular response to EphB2 activation. In contrast, local activation of OptoEphb2 in dendrites of hippocampal neurons induces rapid actin polymerization, resulting dynamic dendritic filopodial growth. Inhibition of Rac1 and CDC42 did not abolish OptoEphB2-induced actin polymerization. Instead, we identified Abelson Tyrosine-Protein Kinase 2 (Abl2/Arg) as a necessary effector in OptoEphB2-induced filopodia growth in dendrites. These findings provided new mechanistic insight into EphB2's role in neural development and demonstrated the advantage of OptoEphB as a new tool for studying EphB signaling.
Gradients of Rac1 Nanoclusters Support Spatial Patterns of Rac1 Signaling.
Rac1 is a small RhoGTPase switch that orchestrates actin branching in space and time and protrusion/retraction cycles of the lamellipodia at the cell front during mesenchymal migration. Biosensor imaging has revealed a graded concentration of active GTP-loaded Rac1 in protruding regions of the cell. Here, using single-molecule imaging and super-resolution microscopy, we show an additional supramolecular organization of Rac1. We find that Rac1 partitions and is immobilized into nanoclusters of 50-100 molecules each. These nanoclusters assemble because of the interaction of the polybasic tail of Rac1 with the phosphoinositide lipids PIP2 and PIP3. The additional interactions with GEFs and possibly GAPs, downstream effectors, and other partners are responsible for an enrichment of Rac1 nanoclusters in protruding regions of the cell. Our results show that subcellular patterns of Rac1 activity are supported by gradients of signaling nanodomains of heterogeneous molecular composition, which presumably act as discrete signaling platforms.
Intracellular production of hydrogels and synthetic RNA granules by multivalent molecular interactions.
Some protein components of intracellular non-membrane-bound entities, such as RNA granules, are known to form hydrogels in vitro. The physico-chemical properties and functional role of these intracellular hydrogels are difficult to study, primarily due to technical challenges in probing these materials in situ. Here, we present iPOLYMER, a strategy for a rapid induction of protein-based hydrogels inside living cells that explores the chemically inducible dimerization paradigm. Biochemical and biophysical characterizations aided by computational modelling show that the polymer network formed in the cytosol resembles a physiological hydrogel-like entity that acts as a size-dependent molecular sieve. We functionalize these polymers with RNA-binding motifs that sequester polyadenine-containing nucleotides to synthetically mimic RNA granules. These results show that iPOLYMER can be used to synthetically reconstitute the nucleation of biologically functional entities, including RNA granules in intact cells.
Understanding CRY2 interactions for optical control of intracellular signaling.
Arabidopsis cryptochrome 2 (CRY2) can simultaneously undergo light-dependent CRY2-CRY2 homo-oligomerization and CRY2-CIB1 hetero-dimerization, both of which have been widely used to optically control intracellular processes. Applications using CRY2-CIB1 interaction desire minimal CRY2 homo-oligomerization to avoid unintended complications, while those utilizing CRY2-CRY2 interaction prefer robust homo-oligomerization. However, selecting the type of CRY2 interaction has not been possible as the molecular mechanisms underlying CRY2 interactions are unknown. Here we report CRY2-CIB1 and CRY2-CRY2 interactions are governed by well-separated protein interfaces at the two termini of CRY2. N-terminal charges are critical for CRY2-CIB1 interaction. Moreover, two C-terminal charges impact CRY2 homo-oligomerization, with positive charges facilitating oligomerization and negative charges inhibiting it. By engineering C-terminal charges, we develop CRY2high and CRY2low with elevated or suppressed oligomerization respectively, which we use to tune the levels of Raf/MEK/ERK signaling. These results contribute to our understanding of the mechanisms underlying light-induced CRY2 interactions and enhance the controllability of CRY2-based optogenetic systems.Cryptochrome 2 (CRY2) can form light-regulated CRY2-CRY2 homo-oligomers or CRY2-CIB1 hetero-dimers, but modulating these interactions is difficult owing to the lack of interaction mechanism. Here the authors identify the interactions facilitating homo-oligomers and introduce mutations to create low and high oligomerization versions.
Discovery of long-range inhibitory signaling to ensure single axon formation.
A long-standing question in neurodevelopment is how neurons develop a single axon and multiple dendrites from common immature neurites. Long-range inhibitory signaling from the growing axon is hypothesized to prevent outgrowth of other immature neurites and to differentiate them into dendrites, but the existence and nature of this inhibitory signaling remains unknown. Here, we demonstrate that axonal growth triggered by neurotrophin-3 remotely inhibits neurite outgrowth through long-range Ca2+ waves, which are delivered from the growing axon to the cell body. These Ca2+ waves increase RhoA activity in the cell body through calcium/calmodulin-dependent protein kinase I. Optogenetic control of Rho-kinase combined with computational modeling reveals that active Rho-kinase diffuses to growing other immature neurites and inhibits their outgrowth. Mechanistically, calmodulin-dependent protein kinase I phosphorylates a RhoA-specific GEF, GEF-H1, whose phosphorylation enhances its GEF activity. Thus, our results reveal that long-range inhibitory signaling mediated by Ca2+ wave is responsible for neuronal polarization.Emerging evidence suggests that gut microbiota influences immune function in the brain and may play a role in neurological diseases. Here, the authors offer in vivo evidence from a Drosophila model that supports a role for gut microbiota in modulating the progression of Alzheimer's disease.
Optogenetic activation of Plexin-B1 reveals contact repulsion between osteoclasts and osteoblasts.
During bone remodelling, osteoclasts induce chemotaxis of osteoblasts and yet maintain spatial segregation. We show that osteoclasts express the repulsive guidance factor Semaphorin 4D and induce contact inhibition of locomotion (CIL) in osteoblasts through its receptor Plexin-B1. To examine causality and elucidate how localized Plexin-B1 stimulation may spatiotemporally coordinate its downstream targets in guiding cell migration, we develop an optogenetic tool for Plexin-B1 designated optoPlexin. Precise optoPlexin activation at the leading edge of migrating osteoblasts readily induces local retraction and, unexpectedly, distal protrusions to steer cells away. These morphological changes are accompanied by reorganization of Myosin II, PIP3, adhesion and active Cdc42. We attribute the resultant repolarization to RhoA/ROCK-mediated redistribution of β-Pix, which activates Cdc42 and promotes protrusion. Thus, our data demonstrate a causal role of Plexin-B1 for CIL in osteoblasts and reveals a previously unknown effect of Semaphorin signalling on spatial distribution of an activator of cell migration.
Optical control of membrane tethering and interorganellar communication at nanoscales.
Endoplasmic reticulum (ER) forms an extensive intracellular membranous network in eukaryotes that dynamically connects and communicates with diverse subcellular compartments such as plasma membrane (PM) through membrane contact sites (MCSs), with the inter-membrane gaps separated by a distance of 10-40 nm. Phosphoinositides (PI) constitute an important class of cell membrane phospholipids shared by many MCSs to regulate a myriad of cellular events, including membrane trafficking, calcium homeostasis and lipid metabolism. By installing photosensitivity into a series of engineered PI-binding domains with minimal sizes, we have created an optogenetic toolkit (designated as 'OptoPB') to enable rapid and reversible control of protein translocation and inter-membrane tethering at MCSs. These genetically-encoded, single-component tools can be used as scaffolds for grafting lipid-binding domains to dissect molecular determinants that govern protein-lipid interactions in living cells. Furthermore, we have demonstrated the use of OptoPB as a versatile fusion tag to photomanipulate protein translocation toward PM for reprogramming of PI metabolism. When tethered to the ER membrane with the insertion of flexible spacers, OptoPB can be applied to reversibly photo-tune the gap distances at nanometer scales between the two organellar membranes at MCSs, and to gauge the distance requirement for the free diffusion of protein complexes into MCSs. Our modular optical tools will find broad applications in non-invasive and remote control of protein subcellular localization and interorganellar contact sites that are critical for cell signaling.
A simple optogenetic MAPK inhibitor design reveals resonance between transcription-regulating circuitry and temporally-encoded inputs.
Engineering light-sensitive protein regulators has been a tremendous multidisciplinary challenge. Optogenetic regulators of MAPKs, central nodes of cellular regulation, have not previously been described. Here we present OptoJNKi, a light-regulated JNK inhibitor based on the AsLOV2 light-sensor domain using the ubiquitous FMN chromophore. OptoJNKi gene-transfer allows optogenetic applications, whereas protein delivery allows optopharmacology. Development of OptoJNKi suggests a design principle for other optically regulated inhibitors. From this, we generate Optop38i, which inhibits p38MAPK in intact illuminated cells. Neurons are known for interpreting temporally-encoded inputs via interplay between ion channels, membrane potential and intracellular calcium. However, the consequences of temporal variation of JNK-regulating trophic inputs, potentially resulting from synaptic activity and reversible cellular protrusions, on downstream targets are unknown. Using OptoJNKi, we reveal maximal regulation of c-Jun transactivation can occur at unexpectedly slow periodicities of inhibition depending on the inhibitor's subcellular location. This provides evidence for resonance in metazoan JNK-signalling circuits.