Showing 151 - 175 of 1087 results
Synthesis of a Light-Controlled Phytochrome-Based Extracellular Matrix with Reversibly Adjustable Mechanical Properties.
Synthetic extracellular matrices with reversibly adjustable mechanical properties are essential for the investigation of how cells respond to dynamic mechanical cues as occurring in living organisms. One interesting approach to engineer dynamic biomaterials is the incorporation of photoreceptors from cyanobacteria or plants into polymer materials. Here, we give an overview of existing photoreceptor-based biomaterials and describe a detailed protocol for the synthesis of a phytochrome-based extracellular matrix (CyPhyGel). Using cell-compatible light in the red and far-red spectrum, the mechanical properties of this matrix can be adjusted in a fully reversible, wavelength-specific, and dose-dependent manner with high spatiotemporal control.
Light-Inducible CRISPR Labeling.
CRISPR labeling is a powerful technique to study the chromatin architecture in live cells. In CRISPR labeling, a catalytically dead CRISPR-Cas9 mutant is employed as programmable DNA-binding domain to recruit fluorescent proteins to selected genomic loci. The fluorescently labeled loci can then be identified as fluorescent spots and tracked over time by microscopy. A limitation of this approach is the lack of temporal control of the labeling process itself: Cas9 binds to the g(uide)RNA-complementary target loci as soon as it is expressed. The decoration of the genome with Cas9 molecules will, however, interfere with gene regulation and-possibly-affect the genome architecture itself. The ability to switch on and off Cas9 DNA binding in CRISPR labeling experiments would thus be important to enable more precise interrogations of the chromatin spatial organization and dynamics and could further be used to study Cas9 DNA binding kinetics directly in living human cells.Here, we describe a detailed protocol for light-inducible CRISPR labeling. Our method employs CASANOVA, an engineered, optogenetic anti-CRISPR protein, which efficiently traps the Streptococcus pyogenes (Spy)Cas9 in the dark, but permits Cas9 DNA targeting upon illumination with blue light. Using telomeres as exemplary target loci, we detail the experimental steps required for inducible CRISPR labeling with CASANOVA. We also provide instructions on how to analyze the resulting microscopy data in a fully automated fashion.
Optogenetic Control of Gene Expression Using Cryptochrome 2 and a Light-Activated Degron.
Optogenetic tools allow for use of light as an external input to control cellular processes. When applied to regulate the function of transcription factors, optogenetic approaches provide a tunable, reversible, and bidirectional method to control gene expression. Herein, we present a detailed method to induce gene expression in mammalian cells using the light dependent dimerization of cryptochrome 2 (CRY2) and CIB1 to complement a split transcription factor. We also describe a protocol to disrupt gene expression with light by fusing a dimeric transcription factor to CRY2. When combined with a light-induced degron attached to the gene product, this method allows for rapid modulation of target protein abundance.
Engineering a far-red light–activated split-Cas9 system for remote-controlled genome editing of internal organs and tumors.
It is widely understood that CRISPR-Cas9 technology is revolutionary, with well-recognized issues including the potential for off-target edits and the attendant need for spatiotemporal control of editing. Here, we describe a far-red light (FRL)–activated split-Cas9 (FAST) system that can robustly induce gene editing in both mammalian cells and mice. Through light-emitting diode–based FRL illumination, the FAST system can efficiently edit genes, including nonhomologous end joining and homology-directed repair, for multiple loci in human cells. Further, we show that FAST readily achieves FRL-induced editing of internal organs in tdTomato reporter mice. Finally, FAST was demonstrated to achieve FRL-triggered editing of the PLK1 oncogene in a mouse xenograft tumor model. Beyond extending the spectrum of light energies in optogenetic toolbox for CRISPR-Cas9 technologies, this study demonstrates how FAST system can be deployed for programmable deep tissue gene editing in both biological and biomedical contexts toward high precision and spatial specificity.
Optogenetic Rescue of a Patterning Mutant.
Animal embryos are patterned by a handful of highly conserved inductive signals. Yet, in most cases, it is unknown which pattern features (i.e., spatial gradients or temporal dynamics) are required to support normal development. An ideal experiment to address this question would be to "paint" arbitrary synthetic signaling patterns on "blank canvas" embryos to dissect their requirements. Here, we demonstrate exactly this capability by combining optogenetic control of Ras/extracellular signal-related kinase (ERK) signaling with the genetic loss of the receptor tyrosine-kinase-driven terminal signaling patterning in early Drosophila embryos. Blue-light illumination at the embryonic termini for 90 min was sufficient to rescue normal development, generating viable larvae and fertile adults from an otherwise lethal terminal signaling mutant. Optogenetic rescue was possible even using a simple, all-or-none light input that reduced the gradient of Erk activity and eliminated spatiotemporal differences in terminal gap gene expression. Systematically varying illumination parameters further revealed that at least three distinct developmental programs are triggered at different signaling thresholds and that the morphogenetic movements of gastrulation are robust to a 3-fold variation in the posterior pattern width. These results open the door to controlling tissue organization with simple optical stimuli, providing new tools to probe natural developmental processes, create synthetic tissues with defined organization, or directly correct the patterning errors that underlie developmental defects.
Bioluminescence-Triggered Photoswitchable Bacterial Adhesions Enable Higher Sensitivity and Dual-Readout Bacterial Biosensors for Mercury.
We present a new concept for whole-cell biosensors that couples the response to Hg2+ with bioluminescence and bacterial aggregation. This allows us to use the bacterial aggregation to preconcentrate the bioluminescent bacteria at the substrate surface and increase the sensitivity of Hg2+ detection. This whole-cell biosensor combines a Hg2+-sensitive bioluminescence reporter and light-responsive bacterial cell-cell adhesions. We demonstrate that the blue luminescence in response to Hg2+ is able to photoactivate bacterial aggregation, which provides a second readout for Hg2+ detection. In return, the Hg2+-triggered bacterial aggregation leads to faster sedimentation and more efficient formation of biofilms. At low Hg2+ concentrations, the enrichment of the bacteria in biofilms leads to an up to 10-fold increase in the signal. The activation of photoswitchable proteins with biological light is a new concept in optogenetics, and the presented bacterial biosensor design is transferable to other bioluminescent reporters with particular interest for environmental monitoring.
SynBio and the Boundaries between Functional and Pathogenic RepA-WH1 Bacterial Amyloids.
Amyloids are protein polymers that were initially linked to human diseases. Across the whole Tree of Life, many disease-unrelated proteins are now emerging for which amyloids represent distinct functional states. Most bacterial amyloids described are extracellular, contributing to biofilm formation. However, only a few have been found in the bacterial cytosol. This paper reviews from the perspective of synthetic biology (SynBio) our understanding of the subtle line that separates functional from pathogenic and transmissible amyloids (prions). In particular, it is focused on RepA-WH1, a functional albeit unconventional natural amyloidogenic protein domain that participates in controlling DNA replication of bacterial plasmids. SynBio approaches, including protein engineering and the design of allosteric effectors such as diverse ligands and an optogenetic module, have enabled the generation in RepA-WH1 of an intracellular cytotoxic prion-like agent in bacteria. The synthetic RepA-WH1 prion has the potential to develop into novel antimicrobials.
Structural and spectroscopic characterization of photoactive yellow protein and photoswitchable fluorescent protein constructs containing heavy atoms.
Photo-induced structural rearrangements of chromophore-containing proteins are essential for various light-dependent signaling pathways and optogenetic applications. Ultrafast structural and spectroscopic methods have offered insights into these structural rearrangements across many timescales. However, questions still remain about exact mechanistic details, especially regarding photoisomerization of the chromophore within these proteins femtoseconds to picoseconds after photoexcitation. Instrumentation advancements for time-resolved crystallography and ultrafast electron diffraction provide a promising opportunity to study these reactions, but achieving enough signal-to-noise is a constant challenge. Here we present four new photoactive yellow protein constructs and one new fluorescent protein construct that contain heavy atoms either within or around the chromophore and can be expressed with high yields. Structural characterization of these constructs, most at atomic resolution, show minimal perturbation caused by the heavy atoms compared to wild-type structures. Spectroscopic studies report the effects of the heavy atom identity and location on the chromophore's photophysical properties. None of the substitutions prevent photoisomerization, although certain rates within the photocycle may be affected. Overall, these new proteins containing heavy atoms are ideal samples for state-of-theart time-resolved crystallography and electron diffraction experiments to elucidate crucial mechanistic information of photoisomerization.
Requirement of Irf6 and Esrp1/2 in frontonasal and palatal epithelium to regulate craniofacial and palate morphogenesis in mouse and zebrafish.
Orofacial clefts are among the most common human congenital malformations. Irf6 and Esrp1 are two key genes important for palate development, conserved across vertebrates. In the zebrafish, we found that irf6 regulates the expression of esrp1. Using RNAscope, we detailed overlapping Irf6 and Esrp1/2 gene expression in mouse and zebrafish embryonic oral epithelium and periderm. Genetic disruption of irf6 and esrp1/2 in the zebrafish resulted in cleft of the anterior neurocranium (ANC). In the esrp1/2 zebrafish mutant, cleft of the lip formed and appeared to tether into the ANC cleft. Lineage tracing of the anterior cranial neural crest cells revealed that cleft of the ANC resulted not from migration defect, but from impaired chondrogenesis. Molecular analysis of the aberrant cells interrupting ANC fusion revealed that this cell population espresses sox10 and irf6 and is adjacent to cells expressing epithelial krt4 and mesenchymal col1a1 genes. Detailed morphogenetic analysis of mouse Irf6 mutant revealed mesenchymal defects not observed in the Esrp1/2 mutant. Analysis of breeding compound Irf6;Esrp1;Esrp2 mutant suggests that these genes interact where the triple mutant is not observed. Taken together, these studies highlight the complementary analysis of Irf6 and Esrp1/2 in mouse and zebrafish models and captured an unique aberrant embryonic cell population that contributes to cleft pathogenesis. Future work characterizing this unqiue sox10+, irf6+ cell population will yield additional insight into cleft pathogenesis.
Molecular Mechanism of Light-Induced Conformational Switching of the LOV Domain in Aureochrome-1.
Light oxygen voltage-sensing (LOV) domains are widely found in photoreceptor proteins of plants, algae, fungi, and bacteria. Structural studies of LOV domains suggest that Phe and Gln residues located in the proximity of the chromophore undergo conformational changes upon illumination; however, the molecular mechanism associated with activation of the effector domain remains to be elucidated. Photozipper (PZ) protein is an N-terminally truncated aureochrome-1 comprising a LOV domain and a basic leucine zipper domain. Blue light (BL) induces PZ dimerization and subsequently increases its affinity for target DNA. In this study, we prepared PZ mutants with substitutions of F298 and Q317 and performed quantitative analyses in dark and light states. Substitutions of Q317 significantly reduced the light-induced changes in PZ affinity for the target DNA, especially in the case of the high affinities observed in the dark state. Upon illumination, all PZ mutants showed increased affinity for the target sequence, which demonstrated a clear correlation with the dimer fraction of each PZ mutant. These results suggest the existence of a conformational equilibrium and that its shift by a synergistic interaction between the chromophore and protein moiety probably enables BL-regulated switching of aureochrome-1.
Optogenetic control of gene expression in plants in the presence of ambient white light.
Optogenetics is the genetic approach for controlling cellular processes with light. It provides spatiotemporal, quantitative and reversible control over biological signaling and metabolic processes, overcoming limitations of chemically inducible systems. However, optogenetics lags in plant research because ambient light required for growth leads to undesired system activation. We solved this issue by developing plant usable light-switch elements (PULSE), an optogenetic tool for reversibly controlling gene expression in plants under ambient light. PULSE combines a blue-light-regulated repressor with a red-light-inducible switch. Gene expression is only activated under red light and remains inactive under white light or in darkness. Supported by a quantitative mathematical model, we characterized PULSE in protoplasts and achieved high induction rates, and we combined it with CRISPR-Cas9-based technologies to target synthetic signaling and developmental pathways. We applied PULSE to control immune responses in plant leaves and generated Arabidopsis transgenic plants. PULSE opens broad experimental avenues in plant research and biotechnology.
Illuminating a Phytochrome Paradigm- a Light-Activated Phosphatase in Two-Component Signaling Uncovered.
Bacterial phytochrome photoreceptors usually belong to two-component signaling systems which transmit environmental stimuli to a response regulator through a histidine kinase domain. Phytochromes switch between red light-absorbing and far-red light-absorbing states. Despite exhibiting extensive structural responses during this transition, the model bacteriophytochrome from Deinococcus radiodurans (DrBphP) lacks detectable kinase activity. Here, we resolve this long-standing conundrum by comparatively analyzing the interactions and output activities of DrBphP and a bacteriophytochrome from Agrobacterium fabrum (AgP1). Whereas AgP1 acts as a conventional histidine kinase, we identify DrBphP as a light-sensitive phosphatase. While AgP1 binds its cognate response regulator only transiently, DrBphP does so strongly, which is rationalized at the structural level. Our data pinpoint two key residues affecting the balance between kinase and phosphatase activities, which immediately bears on photoreception and two-component signaling. The opposing output activities in two highly similar bacteriophytochromes inform the use of light-controllable histidine kinases and phosphatases for optogenetics.
Early But Not Delayed Optogenetic RAF Activation Promotes Astrocytogenesis in Mouse Neural Progenitors.
The RAS/RAF/MEK/ERK pathway promotes gliogenesis but the kinetic role of RAF1, a key RAF kinase, in the induction of astrocytogenesis remains to be elucidated. To address this challenge, we determine the temporal functional outcome of RAF1 during mouse neural progenitor cell differentiation using an optogenetic RAF1 system (OptoRAF1). OptoRAF1 allows for reversible activation of the RAF/MEK/ERK pathway via plasma membrane recruitment of RAF1 based on blue light-sensitive protein dimerizer CRY2/CIB1. We found that early light-induced OptoRAF1 activation in neural progenitor cells promotes cell proliferation and increased expression of glial markers and glia-enriched genes. However, delayed OptoRAF1 activation in differentiated neural progenitor had little effect on glia marker expression, suggesting that RAF1 is required to promote astrocytogenesis only within a short time window. In addition, activation of OptoRAF1 did not have a significant effect on neurogenesis, but was able to promote neuronal neurite growth.
βH-spectrin is required for ratcheting apical pulsatile constrictions during tissue invagination.
Actomyosin-mediated apical constriction drives a wide range of morphogenetic processes. Activation of myosin-II initiates pulsatile cycles of apical constrictions followed by either relaxation or stabilization (ratcheting) of the apical surface. While relaxation leads to dissipation of contractile forces, ratcheting is critical for the generation of tissue-level tension and changes in tissue shape. How ratcheting is controlled at the molecular level is unknown. Here, we show that the actin crosslinker βH-spectrin is upregulated at the apical surface of invaginating mesodermal cells during Drosophila gastrulation. βH-spectrin forms a network of filaments which co-localize with medio-apical actomyosin fibers, in a process that depends on the mesoderm-transcription factor Twist and activation of Rho signaling. βH-spectrin knockdown results in non-ratcheted apical constrictions and inhibition of mesoderm invagination, recapitulating twist mutant embryos. βH-spectrin is thus a key regulator of apical ratcheting during tissue invagination, suggesting that actin cross-linking plays a critical role in this process.
Biliverdin reductase-A deficiency brighten and sensitize biliverdin-binding chromoproteins.
Tissue absorbance, light scattering, and autofluorescence are significantly lower in the near-infrared (NIR) range than in the visible range. Because of these advantages, NIR fluorescent proteins (FPs) are in high demand for in vivo imaging. Nevertheless, application of NIR FPs such as iRFP is still limited due to their dimness in mammalian cells. In contrast to GFP and its variants, iRFP requires biliverdin (BV) as a chromophore. The dimness of iRFP is at least partly due to rapid reduction of BV by biliverdin reductase A (BLVRA). Here, we established biliverdin reductase-a knockout (Blvra-/-) mice to increase the intracellular BV concentration and, thereby, to enhance iRFP fluorescence intensity. As anticipated, iRFP fluorescence intensity was significantly increased in all examined tissues of Blvra-/- mice. Similarly, the genetically encoded calcium indicator NIR-GECO1, which is engineered based on another NIR FP, mIFP, exhibited a marked increase in fluorescence intensity in mouse embryonic fibroblasts derived from Blvra-/- mice. We expanded this approach to an NIR light-sensing optogenetic tool, the BphP1-PpsR2 system, which also requires BV as a chromophore. Again, deletion of the Blvra gene markedly enhanced the light response in HeLa cells. These results indicate that the Blvra-/- mouse is a versatile tool for the in vivo application of NIR FPs and NIR light-sensing optogenetic tools. Key words: in vivo imaging, near-infrared fluorescent protein, biliverdin, biliverdin reductase, optogenetic tool.
Dual Function of PI(4,5)P2 in Insulin-Regulated Exocytic Trafficking of GLUT4 in Adipocytes.
Phosphoinositides are important signaling molecules involved in the regulation of vesicular trafficking. It has been implicated that phosphatidylinositol 4,5-bisphosphate [PI(4,5)P2] is involved in insulin-regulated GLUT4 translocation in adipocytes. However, it remains unclear where and how PI(4,5)P2 regulates discrete steps of GLUT4 vesicle translocation in adipocytes, especially on the exocytic arm of regulation. Here, we employed optogenetic tools to acutely control the PI(4,5)P2 metabolism in living cells. By combination of TIRFM imaging, we were able to monitor the temporal-spatial-dependent PI(4,5)P2 regulation on discrete steps of GLUT4 translocation in adipocytes. We found that the plasma membrane localized PI(4,5)P2 is crucial for proper insulin signaling propagation and for insulin-stimulated GLUT4 vesicle translocation in 3T3-L1 adipocytes. Global depletion of PI(4,5)P2 on the cell surface blunted insulin-stimulated Akt phosphorylation and abolished insulin effects in promotion of the docking and fusion of GLUT4 vesicle with the plasma membrane. Furthermore, by development of a novel optogenetic module to selectively modulate PI(4,5)P2 levels on the GLUT4 vesicle docking site, we identified an important regulatory role of PI(4,5)P2 in controlling of vesicle docking process. Local depletion of PI(4,5)P2 at the vesicle docking site promoted GLUT4 vesicle undocking, diminished insulin-stimulated GLUT4 vesicle docking and fusion, but without perturbation of insulin signaling propagation in adipocytes. Our results provide strong evidence that cell surface PI(4,5)P2 plays two distinct functions on regulation of the exocytic trafficking of GLUT4 in adipocytes. PI(4,5)P2 not only regulates the proper activation of insulin signaling in general but also controls GLUT4 vesicle docking process at the vesicle-membrane contact sites.
Photoactivatable RNA N6 -Methyladenosine Editing with CRISPR-Cas13.
RNA has important and diverse biological roles, but the molecular methods to manipulate it spatiotemporally are limited. Here, an engineered photoactivatable RNA N6 -methyladenosine (m6 A) editing system with CRISPR-Cas13 is designed to direct specific m6 A editing. Light-inducible heterodimerizing proteins CIBN and CRY2PHR are fused to catalytically inactive PguCas13 (dCas13) and m6 A effectors, respectively. This system, referred to as PAMEC, enables the spatiotemporal control of m6 A editing in response to blue light. Further optimization of this system to create a highly efficient version, known as PAMECR , allows the manipulation of multiple genes robustly and simultaneously. When coupled with an upconversion nanoparticle film, the optogenetic operation window is extended from the visible range to tissue-penetrable near-infrared wavelengths, which offers an appealing avenue to remotely control RNA editing. These results show that PAMEC is a promising optogenetic platform for flexible and efficient targeting of RNA, with broad applicability for epitranscriptome engineering, imaging, and future therapeutic development.
Nanobody-directed targeting of optogenetic tools to study signaling in the primary cilium.
Compartmentalization of cellular signaling forms the molecular basis of cellular behavior. The primary cilium constitutes a subcellular compartment that orchestrates signal transduction independent from the cell body. Ciliary dysfunction causes severe diseases, termed ciliopathies. Analyzing ciliary signaling has been challenging due to the lack of tools investigate ciliary signaling. Here, we describe a nanobody-based targeting approach for optogenetic tools in mammalian cells and in vivo in zebrafish to specifically analyze ciliary signaling and function. Thereby, we overcome the loss of protein function observed after fusion to ciliary targeting sequences. We functionally localized modifiers of cAMP signaling, the photo-activated adenylate cyclase bPAC and the light-activated phosphodiesterase LAPD, and the cAMP biosensor mlCNBD-FRET to the cilium. Using this approach, we studied the contribution of spatial cAMP signaling in controlling cilia length. Combining optogenetics with nanobody-based targeting will pave the way to the molecular understanding of ciliary function in health and disease.
PhotoGal4: A Versatile Light-Dependent Switch for Spatiotemporal Control of Gene Expression in Drosophila Explants.
We present here PhotoGal4, a phytochrome B-based optogenetic switch for fine-tuned spatiotemporal control of gene expression in Drosophila explants. This switch integrates the light-dependent interaction between phytochrome B and PIF6 from plants with regulatory elements from the yeast Gal4/UAS system. We found that PhotoGal4 efficiently activates and deactivates gene expression upon red- or far-red-light irradiation, respectively. In addition, this optogenetic tool reacts to different illumination conditions, allowing for fine modulation of the light-dependent response. Importantly, by simply focusing a laser beam, PhotoGal4 induces intricate patterns of expression in a customized manner. For instance, we successfully sketched personalized patterns of GFP fluorescence such as emoji-like shapes or letterform logos in Drosophila explants, which illustrates the exquisite precision and versatility of this tool. Hence, we anticipate that PhotoGal4 will expand the powerful Drosophila toolbox and will provide a new avenue to investigate intricate and complex problems in biomedical research.
Development of optogenetic tools to manipulate cell cycle checkpoints.
In order to understand the systematic regulation of the cell cycle, we need more precise tools for cell-cycle perturbation. Optogenetics is a powerful technique for precisely controlling cellular signaling at higher spatial and temporal resolution. Here, we report optogenetic tools for the rapid and reversible control of cell-cycle checkpoints with a red/far-red light photoreceptor, phytochrome B (PhyB). We established fission yeast cells producing phycocyanobilin as a chromophore of PhyB, and demonstrated light-dependent protein recruitment to the plasma membrane, nucleus, and kinetochore. Using this system, we developed optogenetic manipulation of the cell cycle in two ways: the Opto-G2/M checkpoint triggered G2/M cell cycle arrest in response to red light, and Opto-SAC induced a spindle assembly checkpoint (SAC) in response to red light and then quickly released the SAC by far-red light.
Genetically-encoded biosensors for analyzing and controlling cellular process in yeast.
Yeast has been a robust platform to manufacture a broad range of biofuels, commodity chemicals, natural products and pharmaceuticals. The membrane-bound organelles in yeast provide us the means to access the specialized metabolism for various biosynthetic applications. The separation and compartmentalization of genetic and metabolic events presents us the opportunity to precisely control and program gene expression for higher order biological functions. To further advance yeast synthetic biology platform, genetically encoded biosensors and actuators haven been engineered for in vivo monitoring and controlling cellular processes with spatiotemporal resolutions. The dynamic response, sensitivity and operational range of these genetically encoded sensors are determined by the regulatory architecture, dynamic assemly and interactions of the related proteins and genetic elements. This review provides an update of the basic design principles underlying the allosteric transcription factors, GPCR and optogenetics-based sensors, aiming to precisely analyze and control yeast cellular processes for various biotechnological applications.
Collective ERK/Akt activity waves orchestrate epithelial homeostasis by driving apoptosis-induced survival.
Cell death events continuously challenge epithelial barrier function, yet are crucial to eliminate old or critically damaged cells. How such apoptotic events are spatio-temporally organized to maintain epithelial homeostasis remains unclear. We observe waves of Extracellular Signal-Regulated Kinase (ERK) and AKT serine/threonine kinase (Akt) activity pulses that originate from apoptotic cells and propagate radially to healthy surrounding cells. Such a propagation requires Epidermal Growth Factor Receptor (EGFR) and matrix metalloproteinase (MMP) signaling. At the single-cell level, ERK/Akt waves act as spatial survival signals that locally protect cells in the vicinity of the epithelial injury from apoptosis for a period of 3-4 hours. At the cell population level, ERK/Akt waves maintain epithelial homeostasis (EH) in response to mild or intense insults. Disruption of this spatial signaling system results in the inability of a model epithelial tissue to ensure barrier function in response to cellular stress.
The Association Kinetics Encode the Light Dependence of Arabidopsis Phytochrome B Interactions.
Plant phytochromes enable vital adaptations to red and far-red light. At the molecular level, these responses are mediated by light-regulated interactions between phytochromes and partner proteins, foremost the phytochrome-interacting factors (PIF). Although known for decades, quantitative analyses of these interactions have long been sparse. To address this deficit, we here studied by an integrated fluorescence-spectroscopic approach the equilibrium and kinetics of Arabidopsis thaliana phytochrome B (AtPhyB) binding to a tetramerized PIF6 variant. Several readouts consistently showed the stringently light-regulated interaction to be little affected by PIF tetramerization. Analysis of the binding kinetics allowed the determination of bimolecular association and unimolecular dissociation rate constants as a function of light. Unexpectedly, the stronger affinity of AtPhyB under red light relative to far-red light is entirely due to accelerated association rather than decelerated dissociation. The association reaction under red light is highly efficient and only threefold slower than the diffusion limit. The present findings pertain equally to the analysis of signal transduction in plants and to the biotechnological application of phytochromes.
Engineered Illumination Devices for Optogenetic Control of Cellular Signaling Dynamics.
Spatially and temporally varying patterns of morphogen signals during development drive cell fate specification at the proper location and time. However, current in vitro methods typically do not allow for precise, dynamic spatiotemporal control of morphogen signaling and are thus insufficient to readily study how morphogen dynamics affect cell behavior. Here, we show that optogenetic Wnt/β-catenin pathway activation can be controlled at user-defined intensities, temporal sequences, and spatial patterns using engineered illumination devices for optogenetic photostimulation and light activation at variable amplitudes (LAVA). By patterning human embryonic stem cell (hESC) cultures with varying light intensities, LAVA devices enabled dose-responsive control of optoWnt activation and Brachyury expression. Furthermore, time-varying and spatially localized patterns of light revealed tissue patterning that models the embryonic presentation of Wnt signals in vitro. LAVA devices thus provide a low-cost, user-friendly method for high-throughput and spatiotemporal optogenetic control of cell signaling for applications in developmental and cell biology.
An optogenetic method for interrogating YAP1 and TAZ nuclear-cytoplasmic shuttling.
The shuttling of transcription factors and transcriptional regulators in and out of the nucleus is central to the regulation of many biological processes. Here we describe a new method for studying the rates of nuclear entry and exit of transcriptional regulators. A photo-responsive AsLOV (Avena sativa Light Oxygen Voltage) domain is used to sequester the transcriptional regulators, YAP1 and TAZ/WWTR1, on the surface of mitochondria. Illumination with blue light is used to release fluorophore-tagged YAP1 and TAZ from mitochondria and their entry into the nucleus can be observed. Cessation of blue light illumination leads to re-sequestration on the surface of mitochondria. This method generates three distinct curves that are then used to fit ordinary differential equations for the rates of nuclear entry and exit. Using this method, we demonstrate that phosphorylation of YAP1 on sites of canonical regulation by LATS1/2 enhances its rate of nuclear export. Moreover, we provide evidences that YAP1 import and export rates, despite high intercellular variability, are correlated within the same cell. Interestingly, the ratio of import and export rates correlated with nuclear-cytoplasmic (NC) distribution of YAP1 and TAZ proteins at steady state.