Showing 151 - 175 of 528 results
Optogenetic control of the Dab1 signaling pathway.
The Reelin-Dab1 signaling pathway regulates development of the mammalian brain, including neuron migrations in various brain regions, as well as learning and memory in adults. Extracellular Reelin binds to cell surface receptors and activates phosphorylation of the intracellular Dab1 protein. Dab1 is required for most effects of Reelin, but Dab1-independent pathways may contribute. Here we developed a single-component, photoactivatable Dab1 (opto-Dab1) by using the blue light-sensitive dimerization/oligomerization property of A. thaliana Cryptochrome 2 (Cry2). Opto-Dab1 can activate downstream signals rapidly, locally, and reversibly upon blue light illumination. The high spatiotemporal resolution of the opto-Dab1 probe also allows us to control membrane protrusion, retraction and ruffling by local illumination in both COS7 cells and in primary neurons. This shows that Dab1 activation is sufficient to orient cell movement in the absence of other signals. Opto-Dab1 may be useful to study the biological functions of the Reelin-Dab1 signaling pathway both in vitro and in vivo.
Optogenetic manipulation of c-di-GMP levels reveals the role of c-di-GMP in regulating aerotaxis receptor activity in Azospirillum brasilense.
Bacterial chemotaxis receptors provide the sensory inputs that inform the direction of navigation in changing environments. Recently, we described the bacterial second messenger, c-di-GMP, as a novel regulator of a subclass of chemotaxis receptors. In Azospirillum brasilense, c-di-GMP binds to a chemotaxis receptor, Tlp1, and modulates its signaling function during aerotaxis. Here, we further characterize the role of c-di-GMP in aerotaxis using a novel dichromatic optogenetic system engineered for manipulating intracellular c-di-GMP levels in real time. This system comprises a red/near-infrared light-regulated diguanylate cyclase and a blue-light regulated c-di-GMP phosphodiesterase. It allows generation of transient changes in intracellular c-di-GMP concentrations within seconds of irradiation with appropriate light, which is compatible with the timescale of chemotaxis signaling. We provide experimental evidence that c-di-GMP binding to the Tlp1 receptor activates its signaling function during aerotaxis, which supports the role of transient changes in c-di-GMP levels as a means of adjusting the response of A. brasilense to oxygen gradients. We also show that intracellular c-di-GMP levels in A. brasilense changes with carbon metabolism. Our data support a model whereby c-di-GMP functions to imprint chemotaxis receptors with a record of recent metabolic experience, to adjust their contribution to the signaling output, thus allowing the cells to continually fine-tune chemotaxis sensory perception to their metabolic state.IMPORTANCE Motile bacteria use chemotaxis to change swimming direction in response to changes in environmental conditions. Chemotaxis receptors sense environmental signals and relay sensory information to the chemotaxis machinery, which ultimately controls the swimming pattern of cells. In bacteria studied to date, differential methylation has been known as a mechanism to control the activity of chemotaxis receptors and modulates their contribution to the overall chemotaxis response. Here, we used an optogenetic system to perturb intracellular concentrations of the bacterial second messenger, c-di-GMP, to show that in some chemotaxis receptors, c-di-GMP functions in a similar feedback loop to connect metabolic status of the cells to sensory activity of chemotaxis receptors.
Optogenetic methods in drug screening: technologies and applications.
The optogenetic revolution enabled spatially-precise and temporally-precise control over protein function, signaling pathway activation, and animal behavior with tremendous success in the dissection of signaling networks and neural circuits. Very recently, optogenetic methods have been paired with optical reporters in novel drug screening platforms. In these all-optical platforms, light remotely activated ion channels and kinases thereby obviating the use of electrophysiology or reagents. Consequences were remarkable operational simplicity, throughput, and cost-effectiveness that culminated in the identification of new drug candidates. These blueprints for all-optical assays also revealed potential pitfalls and inspire all-optical variants of other screens, such as those that aim at better understanding dynamic drug action or orphan protein function.
Assembly Domain-Based Optogenetic System for the Efficient Control of Cellular Signaling.
We previously developed the Magnet system, which consists of two distinct Vivid protein variants, one positively and one negatively charged, designated the positive Magnet (pMag) and negative Magnet (nMag), respectively. These two proteins bind to each other through electrostatic interactions, preventing unwanted homodimerization and providing selective light-induced heterodimerization. The Magnet system enables the manipulation of cellular functions such as protein-protein interactions and genome editing, although the system could be improved further. To enhance the ability of pMagFast2 (a pMag variant with fast kinetics) to bind nMag, we introduced several pMagFast2 modules in tandem into a single construct, pMagFast2(3×). However, the expression level of this construct decreased drastically with increasing number of pMagFast2 molecules integrated into a single construct. In the present study, we applied a new approach to improve the Magnet system based on an assembly domain (AD). Among several ADs, the Ca(2+)/calmodulin-dependent protein kinase IIα association domain (CAD) most enhanced the Magnet system. The present CAD-Magnet system overcame a trade-off issue between the expression level and binding affinity. The CAD-converged 12 pMag photoswitches exhibited a stronger interaction with nMag after blue light irradiation compared with monomeric pMag. Additionally, the CAD played a key role in converging effector proteins as well in a single complex. Owing to these substantial improvements, the CAD-Magnet system combined with Tiam1 allowed us to robustly induce localized formation of vertical ruffles on the apical plasma membrane. The CAD-Magnet system combined with 4D imaging was instrumental in revealing the dynamics of ruffle formation.
Optical control of cell signaling by single-chain photoswitchable kinases.
Protein kinases transduce signals to regulate a wide array of cellular functions in eukaryotes. A generalizable method for optical control of kinases would enable fine spatiotemporal interrogation or manipulation of these various functions. We report the design and application of single-chain cofactor-free kinases with photoswitchable activity. We engineered a dimeric protein, pdDronpa, that dissociates in cyan light and reassociates in violet light. Attaching two pdDronpa domains at rationally selected locations in the kinase domain, we created the photoswitchable kinases psRaf1, psMEK1, psMEK2, and psCDK5. Using these photoswitchable kinases, we established an all-optical cell-based assay for screening inhibitors, uncovered a direct and rapid inhibitory feedback loop from ERK to MEK1, and mediated developmental changes and synaptic vesicle transport in vivo using light.
Optogenetic switches for light-controlled gene expression in yeast.
Light is increasingly recognized as an efficient means of controlling diverse biological processes with high spatiotemporal resolution. Optogenetic switches are molecular devices for regulating light-controlled gene expression, protein localization, signal transduction and protein-protein interactions. Such molecular components have been mainly developed through the use of photoreceptors, which upon light stimulation undergo conformational changes passing to an active state. The current repertoires of optogenetic switches include red, blue and UV-B light photoreceptors and have been implemented in a broad spectrum of biological platforms. In this review, we revisit different optogenetic switches that have been used in diverse biological platforms, with emphasis on those used for light-controlled gene expression in the budding yeast Saccharomyces cerevisiae. The implementation of these switches overcomes the use of traditional chemical inducers, allowing precise control of gene expression at lower costs, without leaving chemical traces, and positively impacting the production of high-value metabolites and heterologous proteins. Additionally, we highlight the potential of utilizing this technology beyond laboratory strains, by optimizing it for use in yeasts tamed for industrial processes. Finally, we discuss how fungal photoreceptors could serve as a source of biological parts for the development of novel optogenetic switches with improved characteristics. Although optogenetic tools have had a strong impact on basic research, their use in applied sciences is still undervalued. Therefore, the invitation for the future is to utilize this technology in biotechnological and industrial settings.
Investigations of human myosin VI targeting using optogenetically controlled cargo loading.
Myosins play countless critical roles in the cell, each requiring it to be activated at a specific location and time. To control myosin VI with this specificity, we created an optogenetic tool for activating myosin VI by fusing the light-sensitive Avena sativa phototropin1 LOV2 domain to a peptide from Dab2 (LOVDab), a myosin VI cargo protein. Our approach harnesses the native targeting and activation mechanism of myosin VI, allowing direct inferences on myosin VI function. LOVDab robustly recruits human full-length myosin VI to various organelles in vivo and hinders peroxisome motion in a light-controllable manner. LOVDab also activates myosin VI in an in vitro gliding filament assay. Our data suggest that protein and lipid cargoes cooperate to activate myosin VI, allowing myosin VI to integrate Ca(2+), lipid, and protein cargo signals in the cell to deploy in a site-specific manner.
Optogenetic control of cellular forces and mechanotransduction.
Contractile forces are the end effectors of cell migration, division, morphogenesis, wound healing and cancer invasion. Here we report optogenetic tools to upregulate and downregulate such forces with high spatiotemporal accuracy. The technology relies on controlling the subcellular activation of RhoA using the CRY2/CIBN light-gated dimerizer system. We fused the catalytic domain (DHPH domain) of the RhoA activator ARHGEF11 to CRY2-mCherry (optoGEF-RhoA) and engineered its binding partner CIBN to bind either to the plasma membrane or to the mitochondrial membrane. Translocation of optoGEF-RhoA to the plasma membrane causes a rapid and local increase in cellular traction, intercellular tension and tissue compaction. By contrast, translocation of optoGEF-RhoA to mitochondria results in opposite changes in these physical properties. Cellular changes in contractility are paralleled by modifications in the nuclear localization of the transcriptional regulator YAP, thus showing the ability of our approach to control mechanotransductory signalling pathways in time and space.
Epigenetic Editing of Ascl1 Gene in Neural Stem Cells by Optogenetics.
Enzymes involved in epigenetic processes such as methyltransferases or demethylases are becoming highly utilized for their persistent DNA or histone modifying efficacy. Herein, we have developed an optogenetic toolbox fused to the catalytic domain (CD) of DNA-methyltransferase3A (DNMT3A-CD) or Ten-Eleven Dioxygenase-1 (TET1-CD) for loci-specific alteration of the methylation state at the promoter of Ascl1 (Mash1), a candidate proneuron gene. Optogenetical protein pairs, CRY2 linked to DNMT3A-CD or TET1-CD and CIB1 fused to a Transcription Activator-Like Element (TALE) locating an Ascl1 promoter region, were designed for site specific epigenetic editing. A differentially methylated region at the Ascl1 promoter, isolated from murine dorsal root ganglion (hypermethylated) and striated cells (hypomethylated), was targeted with these optogenetic-epigenetic constructs. Optimized blue-light illumination triggered the co-localization of TALE constructs with DNMT3A-CD or TET1-CD fusion proteins at the targeted site of the Ascl1 promoter. We found that this spatiotemporal association of the fusion proteins selectively alters the methylation state and also regulates gene activity. This proof of concept developed herein holds immense promise for the ability to regulate gene activity via epigenetic modulation with spatiotemporal precision.
Fast cAMP Modulation of Neurotransmission via Neuropeptide Signals and Vesicle Loading.
Cyclic AMP (cAMP) signaling augments synaptic transmission, but because many targets of cAMP and protein kinase A (PKA) may be involved, mechanisms underlying this pathway remain unclear. To probe this mechanism, we used optogenetic stimulation of cAMP signaling by Beggiatoa-photoactivated adenylyl cyclase (bPAC) in Caenorhabditis elegans motor neurons. Behavioral, electron microscopy (EM), and electrophysiology analyses revealed cAMP effects on both the rate and on quantal size of transmitter release and led to the identification of a neuropeptidergic pathway affecting quantal size. cAMP enhanced synaptic vesicle (SV) fusion by increasing mobilization and docking/priming. cAMP further evoked dense core vesicle (DCV) release of neuropeptides, in contrast to channelrhodopsin (ChR2) stimulation. cAMP-evoked DCV release required UNC-31/Ca(2+)-dependent activator protein for secretion (CAPS). Thus, DCVs accumulated in unc-31 mutant synapses. bPAC-induced neuropeptide signaling acts presynaptically to enhance vAChT-dependent SV loading with acetylcholine, thus causing increased miniature postsynaptic current amplitudes (mPSCs) and significantly enlarged SVs.
Glutamine Amide Flip Elicits Long Distance Allosteric Responses in the LOV Protein Vivid.
Light-oxygen-voltage (LOV) domains sense blue light through the photochemical formation of a cysteinyl-flavin covalent adduct. Concurrent protonation at the flavin N5 position alters the hydrogen bonding interactions of an invariant Gln residue that has been proposed to flip its amide side chain as a critical step in the propagation of conformational change. Traditional molecular dynamics (MD) and replica-exchange MD (REMD) simulations of the well-characterized LOV protein Vivid (VVD) demonstrate that the Gln182 amide indeed reorients by ∼180° in response to either adduct formation or reduction of the isoalloxazine ring to the neutral semiquinone, both of which involve N5 protonation. Free energy simulations reveal that the relative free energies of the flipped Gln conformation and the flipping barrier are significantly lower in the light-adapted state. The Gln182 flip stabilizes an important hinge-bβ region between the PAS β-sheet and the N-terminal cap helix that in turn destabilizes an N-terminal latch region against the PAS core. Release of the latch, observed both experimentally and in the simulations, is known to mediate light-induced VVD dimerization. This computational study of a LOV protein, unprecedented in its agreement with experiment, provides an atomistic view of long-range allosteric coupling in a photoreceptor.
Optogenetic Control of Synaptic Composition and Function.
The molecular composition of the postsynaptic membrane is sculpted by synaptic activity. During synaptic plasticity at excitatory synapses, numerous structural, signaling, and receptor molecules concentrate at the postsynaptic density (PSD) to regulate synaptic strength. We developed an approach that uses light to tune the abundance of specific molecules in the PSD. We used this approach to investigate the relationship between the number of AMPA-type glutamate receptors in the PSD and synaptic strength. Surprisingly, adding more AMPA receptors to excitatory contacts had little effect on synaptic strength. Instead, we observed increased excitatory input through the apparent addition of new functional sites. Our data support a model where adding AMPA receptors is sufficient to activate synapses that had few receptors to begin with, but that additional remodeling events are required to strengthen established synapses. More broadly, this approach introduces the precise spatiotemporal control of optogenetics to the molecular control of synaptic function.
Femtosecond to Millisecond Dynamics of Light Induced Allostery in the Avena sativa LOV Domain.
The rational engineering of photosensor proteins underpins the field of optogenetics, in which light is used for spatiotemporal control of cell signaling. Optogenetic elements function by converting electronic excitation of an embedded chromophore into structural changes on the microseconds to seconds time scale, which then modulate the activity of output domains responsible for biological signaling. Using time-resolved vibrational spectroscopy coupled with isotope labeling, we have mapped the structural evolution of the LOV2 domain of the flavin binding phototropin Avena sativa (AsLOV2) over 10 decades of time, reporting structural dynamics between 100 fs and 1 ms after optical excitation. The transient vibrational spectra contain contributions from both the flavin chromophore and the surrounding protein matrix. These contributions are resolved and assigned through the study of four different isotopically labeled samples. High signal-to-noise data permit the detailed analysis of kinetics associated with the light activated structural evolution. A pathway for the photocycle consistent with the data is proposed. The earliest events occur in the flavin binding pocket, where a subpicosecond perturbation of the protein matrix occurs. In this perturbed environment, the previously characterized reaction between triplet state isoalloxazine and an adjacent cysteine leads to formation of the adduct state; this step is shown to exhibit dispersive kinetics. This reaction promotes coupling of the optical excitation to successive time-dependent structural changes, initially in the β-sheet and then α-helix regions of the AsLOV2 domain, which ultimately gives rise to Jα-helix unfolding, yielding the signaling state. This model is tested through point mutagenesis, elucidating in particular the key mediating role played by Q513.
The Spatiotemporal Limits of Developmental Erk Signaling.
Animal development is characterized by signaling events that occur at precise locations and times within the embryo, but determining when and where such precision is needed for proper embryogenesis has been a long-standing challenge. Here we address this question for extracellular signal regulated kinase (Erk) signaling, a key developmental patterning cue. We describe an optogenetic system for activating Erk with high spatiotemporal precision in vivo. Implementing this system in Drosophila, we find that embryogenesis is remarkably robust to ectopic Erk signaling, except from 1 to 4 hr post-fertilization, when perturbing the spatial extent of Erk pathway activation leads to dramatic disruptions of patterning and morphogenesis. Later in development, the effects of ectopic signaling are buffered, at least in part, by combinatorial mechanisms. Our approach can be used to systematically probe the differential contributions of the Ras/Erk pathway and concurrent signals, leading to a more quantitative understanding of developmental signaling.
Transcription activator-like effector-mediated regulation of gene expression based on the inducible packaging and delivery via designed extracellular vesicles.
Transcription activator-like effector (TALE) proteins present a powerful tool for genome editing and engineering, enabling introduction of site-specific mutations, gene knockouts or regulation of the transcription levels of selected genes. TALE nucleases or TALE-based transcription regulators are introduced into mammalian cells mainly via delivery of the coding genes. Here we report an extracellular vesicle-mediated delivery of TALE transcription regulators and their ability to upregulate the reporter gene in target cells. Designed transcriptional activator TALE-VP16 fused to the appropriate dimerization domain was enriched as a cargo protein within extracellular vesicles produced by mammalian HEK293 cells stimulated by Ca-ionophore and using blue light- or rapamycin-inducible dimerization systems. Blue light illumination or rapamycin increased the amount of the TALE-VP16 activator in extracellular vesicles and their addition to the target cells resulted in an increased expression of the reporter gene upon addition of extracellular vesicles to the target cells. This technology therefore represents an efficient delivery for the TALE-based transcriptional regulators.
Optogenetic toolkit for precise control of calcium signaling.
Calcium acts as a second messenger to regulate a myriad of cell functions, ranging from short-term muscle contraction and cell motility to long-term changes in gene expression and metabolism. To study the impact of Ca2+-modulated 'ON' and 'OFF' reactions in mammalian cells, pharmacological tools and 'caged' compounds are commonly used under various experimental conditions. The use of these reagents for precise control of Ca2+ signals, nonetheless, is impeded by lack of reversibility and specificity. The recently developed optogenetic tools, particularly those built upon engineered Ca2+ release-activated Ca2+ (CRAC) channels, provide exciting opportunities to remotely and non-invasively modulate Ca2+ signaling due to their superior spatiotemporal resolution and rapid reversibility. In this review, we briefly summarize the latest advances in the development of optogenetic tools (collectively termed as 'genetically encoded Ca2+ actuators', or GECAs) that are tailored for the interrogation of Ca2+ signaling, as well as their applications in remote neuromodulation and optogenetic immunomodulation. Our goal is to provide a general guide to choosing appropriate GECAs for optical control of Ca2+ signaling in cellulo, and in parallel, to stimulate further thoughts on evolving non-opsin-based optogenetics into a fully fledged technology for the study of Ca2+-dependent activities in vivo.
Precision Optogenetic Tool for Selective Single- and Multiple-Cell Ablation in a Live Animal Model System.
Cell ablation is a strategy to study cell lineage and function during development. Optogenetic methods are an important cell-ablation approach, and we have previously developed a mini singlet oxygen generator (miniSOG) tool that works in the living Caenorhabditis elegans. Here, we use directed evolution to generate miniSOG2, an improved tool for cell ablation via photogenerated reactive oxygen species. We apply miniSOG2 to a far more complex model animal system, Drosophila melanogaster, and demonstrate that it can be used to kill a single neuron in a Drosophila larva. In addition, miniSOG2 is able to photoablate a small group of cells in one of the larval wing imaginal discs, resulting in an adult with one incomplete and one normal wing. We expect miniSOG2 to be a useful optogenetic tool for precision cell ablation at a desired developmental time point in live animals, thus opening a new window into cell origin, fate and function, tissue regeneration, and developmental biology.
Spatiotemporal Control of Intracellular Phase Transitions Using Light-Activated optoDroplets.
Phase transitions driven by intrinsically disordered protein regions (IDRs) have emerged as a ubiquitous mechanism for assembling liquid-like RNA/protein (RNP) bodies and other membrane-less organelles. However, a lack of tools to control intracellular phase transitions limits our ability to understand their role in cell physiology and disease. Here, we introduce an optogenetic platform that uses light to activate IDR-mediated phase transitions in living cells. We use this "optoDroplet" system to study condensed phases driven by the IDRs of various RNP body proteins, including FUS, DDX4, and HNRNPA1. Above a concentration threshold, these constructs undergo light-activated phase separation, forming spatiotemporally definable liquid optoDroplets. FUS optoDroplet assembly is fully reversible even after multiple activation cycles. However, cells driven deep within the phase boundary form solid-like gels that undergo aging into irreversible aggregates. This system can thus elucidate not only physiological phase transitions but also their link to pathological aggregates.
A Photoactivatable Innate Immune Receptor for Optogenetic Inflammation.
Although spatial and temporal elements of immune activation mediate the intensity of the immune response, few tools exist to directly examine these effects. To elucidate the spatiotemporal aspects of innate immune responses, we designed an optogenetic pattern recognition receptor that activates in response to blue light. We demonstrate direct receptor activation, leading to spatial and temporal control of downstream signaling pathways in a variety of relevant cell types. We combined our platform with Bi-molecular Fluorescence Complementation (BiFC), resulting in selective fluorescent labeling of cells in which receptor activation has occurred.
TAEL: a zebrafish-optimized optogenetic gene expression system with fine spatial and temporal control.
Here, we describe an optogenetic gene expression system optimized for use in zebrafish. This system overcomes the limitations of current inducible expression systems by enabling robust spatial and temporal regulation of gene expression in living organisms. Because existing optogenetic systems show toxicity in zebrafish, we re-engineered the blue-light-activated EL222 system for minimal toxicity while exhibiting a large range of induction, fine spatial precision and rapid kinetics. We validate several strategies to spatially restrict illumination and thus gene induction with our new TAEL (TA4-EL222) system. As a functional example, we show that TAEL is able to induce ectopic endodermal cells in the presumptive ectoderm via targeted sox32 induction. We also demonstrate that TAEL can be used to resolve multiple roles of Nodal signaling at different stages of embryonic development. Finally, we show how inducible gene editing can be achieved by combining the TAEL and CRISPR/Cas9 systems. This toolkit should be a broadly useful resource for the fish community.
Engineering extrinsic disorder to control protein activity in living cells.
Optogenetic and chemogenetic control of proteins has revealed otherwise inaccessible facets of signaling dynamics. Here, we use light- or ligand-sensitive domains to modulate the structural disorder of diverse proteins, thereby generating robust allosteric switches. Sensory domains were inserted into nonconserved, surface-exposed loops that were tight and identified computationally as allosterically coupled to active sites. Allosteric switches introduced into motility signaling proteins (kinases, guanosine triphosphatases, and guanine exchange factors) controlled conversion between conformations closely resembling natural active and inactive states, as well as modulated the morphodynamics of living cells. Our results illustrate a broadly applicable approach to design physiological protein switches.
Plasma Membrane Association but Not Midzone Recruitment of RhoGEF ECT2 Is Essential for Cytokinesis.
Cytokinesis, the final step of cell division, begins with the formation of a cleavage furrow. How the mitotic spindle specifies the furrow at the equator in animal cells remains unknown. Current models propose that the concentration of the RhoGEF ECT2 at the spindle midzone and the equatorial plasma membrane directs furrow formation. Using chemical genetic and optogenetic tools, we demonstrate that the association of ECT2 with the plasma membrane during anaphase is required and sufficient for cytokinesis. Local membrane targeting of ECT2 leads to unilateral furrowing, highlighting the importance of local ECT2 activity. ECT2 mutations that prevent centralspindlin binding compromise concentration of ECT2 at the midzone and equatorial membrane but sustain cytokinesis. While the association of ECT2 with the plasma membrane is essential for cytokinesis, our data suggest that ECT2 recruitment to the spindle midzone is insufficient to account for equatorial furrowing and may act redundantly with yet-uncharacterized signals.
LOVTRAP: A Versatile Method to Control Protein Function with Light.
We describe a detailed procedure for the use of LOVTRAP, an approach to reversibly sequester and release proteins from cellular membranes using light. In the application described here, proteins that act at the plasma membrane are held at mitochondria in the dark, and reversibly released by irradiation. The technique relies on binding of an engineered Zdk domain to a LOV2 domain, with affinity <30 nM in the dark and >500 nM upon irradiation between 400 and 500 nm. LOVTRAP can be applied to diverse proteins, as it requires attaching only one member of the Zdk/LOV2 pair to the target protein, and the other to the membrane where the target protein is to be sequestered. Light-induced protein release occurs in less than a second, and the half-life of return can be adjusted using LOV point mutations (∼2 to 500 sec). © 2016 by John Wiley & Sons, Inc.
Optogenetic clustering of CNK1 reveals mechanistic insights in RAF and AKT signalling controlling cell fate decisions.
Scaffold proteins such as the multidomain protein CNK1 orchestrate the signalling network by integrating and controlling the underlying pathways. Using an optogenetic approach to stimulate CNK1 uncoupled from upstream effectors, we identified selective clusters of CNK1 that either stimulate RAF-MEK-ERK or AKT signalling depending on the light intensity applied. OptoCNK1 implemented in MCF7 cells induces differentiation at low light intensity stimulating ERK activity whereas stimulation of AKT signalling by higher light intensity promotes cell proliferation. CNK1 clustering in response to increasing EGF concentrations revealed that CNK1 binds to RAF correlating with ERK activation at low EGF dose. At higher EGF dose active AKT binds to CNK1 and phosphorylates and inhibits RAF. Knockdown of CNK1 protects CNK1 from this AKT/RAF crosstalk. In C2 skeletal muscle cells CNK1 expression is induced with the onset of differentiation. Hence, AKT-bound CNK1 counteracts ERK stimulation in differentiated but not in proliferating cells. Ectopically expressed CNK1 facilitates C2 cell differentiation and knockdown of CNK1 impaired the transcriptional network underlying C2 cell differentiation. Thus, CNK1 expression, CNK1 clustering and the thereto related differential signalling processes decide on proliferation and differentiation in a cell type- and cell stage-dependent manner by orchestrating AKT and RAF signalling.
Strategies for the photo-control of endogenous protein activity.
Photo-controlled or 'optogenetic' effectors interfacing with endogenous protein machinery allow the roles of endogenous proteins to be probed. There are two main approaches being used to develop optogenetic effectors: (i) caging strategies using photo-controlled conformational changes, and (ii) protein relocalization strategies using photo-controlled protein-protein interactions. Numerous specific examples of these approaches have been reported and efforts to develop general methods for photo-control of endogenous proteins are a current focus. The development of improved screening and selection methods for photo-switchable proteins would advance the field.