Light Trigger Research Articles

Catch and Release DNA Decoys: Capture and Photochemical Dissociation of NF-κB Transcription Factors.

Catch and release DNA decoys (CRDDs) are a new class of non-natural DNA probes that capture and dissociate from DNA-binding proteins using a light trigger. Photolytic cleavage of non-natural nucleobases in the CRDD yields abasic sites and truncation products that lower the affinity of the CRDD for its protein target. Herein, we demonstrate the ability of the first-generation CRDD to bind and release NF-κB proteins. This platform technology should be applicable to other DNA-binding proteins by modification of the target sequence.

A camera and image processing system for floc size distributions of suspended particles

The observation of floc size distribution (FSD) for quantitative description of its properties over a sufficient size range, from a few microns to a few millimeters, is still a challenge in most marine environments. In this study, an inexpensive image acquisition and processing system is developed for achieving this objective. Images are acquired by using a Sony Alpha NEX-5R camera body with a CMOS sensor, a Sony E-mount to Nikon F-mount adaptor, extension tubes, a Nikon macro lens, and a close-up lens that can identify flocs with a minimum size of 5μm. The light source and camera trigger are controlled by a micro-controller that was assembled for this project. These images are analyzed by using MATLAB Image Processing Toolbox. The processed floc size and their statistical distributions are confirmed with two available sample sets. The validated process is then applied to measure the steady state FSDs of kaolinite suspensions for different shear rates, suspended sediment concentrations, salinities, and a selected organic matter, guar gum. Although the presence of salt promotes flocculation of suspended kaolinite, only a small amount of salt, around 0.5ppt, is needed to reach the saturation status. Thus for the test salinities (0.5, 1, 2, 3, 5, and 9ppt), the measured FSDs show little difference among each other. On the other hand, guar gum affects kaolinite flocculation significantly and the maximum effect happens at a guar gum concentration around 15mg/L when the kaolinite concentration is around 0.52g/L. At this dosage the characteristic floc size is the largest.

Maximum likelihood positioning and energy correction for scintillation detectors

An algorithm for determining the crystal pixel and the gamma ray energy with scintillation detectors for PET is presented. The algorithm uses Likelihood Maximisation (ML) and therefore is inherently robust to missing data caused by defect or paralysed photo detector pixels. We tested the algorithm on a highly integrated MRI compatible small animal PET insert. The scintillation detector blocks of the PET gantry were built with the newly developed digital Silicon Photomultiplier (SiPM) technology from Philips Digital Photon Counting and LYSO pixel arrays with a pitch of 1 mm and length of 12 mm. Light sharing was used to readout the scintillation light from the scintillator pixel array with an SiPM array. For the performance evaluation of the proposed algorithm, we measured the scanner’s spatial resolution, energy resolution, singles and prompt count rate performance, and image noise. These values were compared to corresponding values obtained with Center of Gravity (CoG) based positioning methods for different scintillation light trigger thresholds and also for different energy windows. While all positioning algorithms showed similar spatial resolution, a clear advantage for the ML method was observed when comparing the PET scanner’s overall single and prompt detection efficiency, image noise, and energy resolution to the CoG based methods. Further, ML positioning reduces the dependence of image quality on scanner configuration parameters and was the only method that allowed achieving highest energy resolution, count rate performance and spatial resolution at the same time.

The countermeasures against the blinding attack in quantum key distribution

It has been shown that the single photon detectors (SPDs) based on the avalanche photodiode (APD) can be blinded and controlled by the bright light and short trigger pulses. Eavesdropper can get the full information without causing additional quantum bit error rate. Hence, in order to guarantee the security of the quantum key distribution (QKD) systems, some countermeasures, by changing the characteristic of the SPD or monitoring the parameters of the detector, are presented by some research groups. In this paper, we provide a new and effective countermeasure against the blinding attack based on improving the optical scheme of the decoding unit in the QKD system rather than only considering the characteristic of the SPD. In our proposal we use a coupler with asymmetric splitting ratio to distinguish the detection characteristic of the SPD with blinding attack from that without blinding attack. The detailed analysis shows that the proposed scheme is feasible to defense the blinding attack.

Design of core–shell magnetic mesoporous silica hybrids for pH and UV light stimuli-responsive cargo release

The drug carrier system proposed here efficiently works under UV light and pH triggers for controlled release of model cargoes. The nanocarrier can be used in the targeted delivery of cargoes by the ‘ON’ and ‘OFF’ command by the UV light trigger.

Changes in hormone flux and signaling in white spruce (Picea glauca) seeds during the transition from dormancy to germination in response to temperature cues.

BackgroundSeeds use environmental cues such as temperature to coordinate the timing of their germination, allowing plants to synchronize their life history with the seasons. Winter chilling is of central importance to alleviate seed dormancy, but very little is known of how chilling responses are regulated in conifer seeds. White spruce (Picea glauca) is an important conifer species of boreal forests in the North American taiga. The recent sequencing and assembly of the white spruce genome allows for comparative gene expression studies toward elucidating the molecular mechanisms governing dormancy alleviation by moist chilling. Here we focused on hormone metabolite profiling and analyses of genes encoding components of hormone signal transduction pathways, to elucidate changes during dormancy alleviation and to help address how germination cues such as temperature and light trigger radicle emergence.ResultsABA, GA, and auxin underwent considerable changes as seeds underwent moist chilling and during subsequent germination; likewise, transcripts encoding hormone-signaling components (e.g. ABI3, ARF4 and Aux/IAA) were differentially regulated during these critical stages. During moist chilling, active IAA was maintained at constant levels, but IAA conjugates (IAA-Asp and IAA-Glu) were substantially accumulated. ABA concentrations decreased during germination of previously moist-chilled seeds, while the precursor of bioactive GA1 (GA53) accumulated. We contend that seed dormancy and germination may be partly mediated through the changing hormone concentrations and a modulation of interactions between central auxin-signaling pathway components (TIR1/AFB, Aux/IAA and ARF4). In response to germination cues, namely exposure to light and to increased temperature: the transfer of seeds from moist-chilling to 30 °C, significant changes in gene transcripts and protein expression occurred during the first six hours, substantiating a very swift reaction to germination-promoting conditions after seeds had received sufficient exposure to the chilling stimulus.ConclusionsThe dormancy to germination transition in white spruce seeds was correlated with changes in auxin conjugation, auxin signaling components, and potential interactions between auxin-ABA signaling cascades (e.g. the transcription factor ARF4 and ABI3). Auxin flux adds a new dimension to the ABA:GA balance mechanism that underlies both dormancy alleviation by chilling, and subsequent radicle emergence to complete germination by warm temperature and light stimuli.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-015-0638-7) contains supplementary material, which is available to authorized users.

A Method to Evaluate the Stimulation of a Real World Field of View by Means of a Spectroradiometric Analysis

Stimulation elicited by a real world field of view is related to the color, the intensity and the direction of the information reaching the eye: different spectral power distributions of light trigger different responses. An evaluation of the stimulation provided by the field of view can be performed by measuring the spectral radiance with a spectroradiometer and weighting this data with an efficiency curve. Different weights (physical, physiological and psychological) can lead to different analyses and consequently to different results. The proposed method allows an overall and simplified evaluation of the field of view based on spectral and luminance measures and a script that processes the luminous information. The final aim of this approach is to provide further information about the light stimulation reaching the retina and to supply a qualitative evaluation of the field of view, allowing to know how much stimulation is coming from a certain area within the visual field depending on the type of surface, basing on spectral and directional information. This approach can have practical implications, allowing technicians and designers to take into consideration the possible visual fields, in order to properly shape the features of stimulation throughout the day, hence following a field of view-based dynamic design.

Different Starting Distances Affect 5-m Sprint Times.

The purpose of this study was to quantify the effect of different starting distances on 5-m sprint time and the accuracy of the initial timing gate. A single-beam timing gate system (1 m high) was used to measure 5-m sprint time in 13 male sports students. Each subject performed 3 valid trials for 3 starting distances: 0.3, 0.5, and 1.0 m from the initial timing lights, respectively. A high-speed video camera was used to track a reflective marker placed on the subjects' hip within a field of view around the initial timing gate. Accuracy of the initial timing gate was defined as the time between the initial timing light trigger and passing of the reflective marker by the initial timing gate. Sprint times were significantly faster for the 1.0-m starting distance (0.98 ± 0.06 seconds) than for the 0.5-m (1.05 ± 0.07 seconds) and the 0.3-m (1.09 ± 0.08 seconds) starting distances (p < 0.001). There were no differences in initial timing gate error between starting distances (p = 0.078). Hence, starting distance influenced sprint times but not the accuracy of the initial timing gate. Researchers and coaches should consider the effect of starting distance on 5-m sprint time and ensure consistent testing protocols. Based on the results of this study, we recommend a starting distance of 0.3 m that should be used for all sprint performance tests.

Lil3 Assembles with Proteins Regulating Chlorophyll Synthesis in Barley.

The light-harvesting-like (LIL) proteins are a family of membrane proteins that share a chlorophyll a/b-binding motif with the major light-harvesting antenna proteins of oxygenic photoautotrophs. LIL proteins have been associated with the regulation of tetrapyrrol biosynthesis, and plant responses to light-stress. Here, it was found in a native PAGE approach that chlorophyllide, and chlorophyllide plus geranylgeraniolpyrophosphate trigger assembly of Lil3 in three chlorine binding fluorescent protein bands, termed F1, F2, and F3. It is shown that light and chlorophyllide trigger accumulation of protochlorophyllide-oxidoreductase, and chlorophyll synthase in band F3. Chlorophyllide and chlorophyll esterified to geranylgeraniol were identified as basis of fluorescence recorded from band F3. A direct interaction between Lil3, CHS and POR was confirmed in a split ubiquitin assay. In the presence of light or chlorophyllide, geranylgeraniolpyrophosphate was shown to trigger a loss of the F3 band and accumulation of Lil3 and geranylgeranyl reductase in F1 and F2. No direct interaction between Lil3 and geranylgeraniolreductase was identified in a split ubiquitin assay; however, accumulation of chlorophyll esterified to phytol in F1 and F2 corroborated the enzymes assembly. Chlorophyll esterified to phytol and the reaction center protein psbD of photosystem II were identified to accumulate together with psb29, and APX in the fluorescent band F2. Data show that Lil3 assembles with proteins regulating chlorophyll synthesis in etioplasts from barley (Hordeum vulgare L.).

Photodegradable Gelatin-Based Hydrogels Prepared by Bioorthogonal Click Chemistry for Cell Encapsulation and Release.

In this study, we present a method for the fabrication of in situ forming gelatin and poly(ethylene glycol)-based hydrogels utilizing bioorthogonal, strain-promoted alkyne-azide cycloaddition as the cross-linking reaction. By incorporating nitrobenzyl moieties within the network structure, these hydrogels can be designed to be degradable upon irradiation with low intensity UV light, allowing precise photopatterning. Fibroblast cells encapsulated within these hydrogels were viable at 14 days and could be readily harvested using a light trigger. Potential applications of this new class of injectable hydrogel include its use as a 3D culturing platform that allows the capture and release of cells, as well as light-triggered cell delivery in regenerative medicine.

Light signaling in photosynthetic eukaryotes with ‘green’ and ‘red’ chloroplasts

Light drives one of the most important processes on earth–photosynthesis. Besides providing the energy for carbon reduction, it is also an important signaling source, which largely influences the acclimation and adaptation behavior of algae and plants. Two different ways of light perception can be differentiated: direct and indirect light signaling. Direct light signaling is based on the action of photoreceptors. Indirect light signaling originates from the photosynthetic light reaction and is either based on the redox state of the photosynthetic electron transport chain or on reactive oxygen species. Especially the indirect signaling raises a specific challenge for plants and algae: while the signal perception occurs in the chloroplast, the largest part of the target genes is located in the nucleus, i.e. the triggering signal needs to cross several membranes. Green algae and plants (the ‘greens’) achieved to establish mechanisms which transfer the so called ‘retrograde’ signal from the chloroplast into the nucleus. Besides identifying the primary light triggers and regulated target genes, researchers discovered a bunch of secondary messengers, which may connect the light trigger with the target genes in a signaling network. Still, the exact signaling cascades are basically unknown so far.The knowledge about direct light signaling in organisms with ‘red’ plastids (red algae and those with secondary red plastids, such as stramenopiles, hacrobians and dinoflagellates) is comparatively little compared to the ‘greens’. However, it is clearly advancing and interesting novelties were found in recent years, e.g. the discovery of the aureochrome photoreceptor class. In contrast, the knowledge about indirect light signaling in these organisms is still in its infancy. Given their ecological importance in the aquatic environment and for global net primary production, this lack of information needs to be removed in future research. This review aims at providing a comparatively short summary about light signaling in the ‘greens’, while gathering most of the information available for the ‘reds’, which may attract researchers to start studying light signaling in this largely neglected group.

Photodamage of lipid bilayers by irradiation of a fluorescently labeled cell-penetrating peptide

BackgroundFluorescently labeled cell-penetrating peptides can translocate into cells by endocytosis and upon light irradiation, lyse the endocytic vesicles. This photo-inducible endosomolytic activity of Fl–CPPs can be used to efficiently deliver macromolecules such as proteins and nucleic acids and other small organic molecules into the cytosol of live cells. The requirement of a light trigger to induce photolysis provides a more spatial and temporal control to the intracellular delivery process. MethodsIn this report, we examine the molecular level mechanisms by which cell-penetrating peptides such as TAT when labeled with small organic fluorophore molecules acquire a photo-induced lytic activity using a simplified model of lipid vesicles. ResultsThe peptide TAT labeled with 5(6)-carboxytetramethylrhodamine binds to negatively charged phospholipids, thereby bringing the fluorophore in close proximity to the membrane of liposomes. Upon light irradiation, the excited fluorophore produces reactive oxygen species at the lipid bilayer and oxidation of the membrane is achieved. In addition, the fluorescent peptide causes aggregation of photo-oxidized lipids, an activity that requires the presence of arginine residues in the peptide sequence. ConclusionsThese results suggest that the cell-penetrating peptide plays a dual role. On one hand, TAT targets a conjugated fluorophore to membranes. On the other hand, TAT participates directly in the destabilization of photosensitized membranes. Peptide and fluorophore therefore appear to act in synergy to destroy membranes efficiently. General significanceUnderstanding the mechanism behind Fl–CPP mediated membrane photodamage will help to design optimally photo-endosomolytic compounds.

Light-responsive helical polypeptides capable of reducing toxicity and unpacking DNA: toward nonviral gene delivery.

Gene delivery vehicles: Helical, cationic polypeptides with light-responsive domains showed potent membrane activity and promoted efficient cellular internalization of DNA (see picture). After transfection, a light trigger induces protecting-group removal to expose anionic carboxylate groups. The reduced cationic charge and helix distortion of the polypeptides result in enhanced DNA unpacking and reduced material toxicity because of the eliminated membrane activity.

Preparation and Characterization of Light-Switchable Polymer Networks Attached to Solid Substrates

Surface-attached polymer networks that carry light-responsive nitrospiropyran groups in a hydrophilic PDMAA matrix were prepared on planar silicon and glass surfaces and were characterized with respect to their switching behavior under the influence of an external light trigger. Functional polymers bearing light-responsive units as well as photo-cross-linkable benzophenone groups were first synthesized using free radical copolymerization. The number of spiropyran groups in the copolymer was controlled by adjusting the concentration of the respective monomer in the copolymerization feed. The polymer films were prepared by spin-coating the functional polymers from solution and by ultraviolet light (UV)-induced cross-linking utilizing benzophenone photochemistry. On substrates with immobilized benzophenone groups, the complete polymer network is linked to the surface. The dry thickness of the films can be controlled over a wide range from a few nanometers up to more than 1 μm. The integration of such light-switchable organic moieties into a surface-attached polymer network allows one to increase the overall number of light-responsive groups per surface area by adjusting the amount of surface-attached polymer networks. The spiropyran's function in dry (solvent-free) and swollen polymer films can be reversibly switched by UV and visible irradiation. In addition, the switching in water is faster than in the dry state. Therefore, implementing light-responsive spiropyran functions in polymer films linked to solid surfaces could allow for switching of the chemical and optical surface properties in a fast and spatially controlled fashion.

Tissue penetration of photodynamic therapy

Photodynamic therapy typically uses visible light to locally activate a therapeutic agent, but the tissue-depth penetration of visible light is weak. As a solution, Idris et al. prepared a nanoparticle that contained a component able to convert a near-infrared (NIR) light trigger into visible light, in addition to two photosensitizers that generate cytotoxic oxygen radicals in response to visible light. The resultant laser NIR-activated nanoparticles reduced the viability of mouse melanoma cells in vitro; furthermore, injection and activation of this agent in melanoma-bearing mice slowed tumour growth in vivo.

Photo-controlled metal-ion (Zn2+ and Cd2+) release in aqueous Tween-20 micelle solution

Photo-controlled metal-ion (Zn(2+) and Cd(2+)) release in aqueous micelle solution (tris-HCl, pH = 7.4) has been described using 2-((2-mercaptophenylimino)methyl) phenol as ligand. It is found that both the ligand-Zn complex (1) and the ligand-Cd complex (2) are stable in micelle solution, and Zn(2+) (Cd(2+)) can be released from the complex with 365 nm light trigger. Accompanying the metal-ion release, the ligand is photo-converted to 2-(benzothiazol-2-yl) phenol (3) as product, and the turn-on fluorescence is detected. The fluorescence intensity increases with the photo-triggered release until Zn(2+) (Cd(2+)) is completely released, which is beneficial for monitoring the process of photo-controlled metal ion release. Control experiments demonstrate that no binding occurs between 3 and Zn(2+) (Cd(2+)) in micelle solution and there is no binding between cations and micelle, either.

Functional Profiling Identifies Genes Involved in Organ-Specific Branches of the PIF3 Regulatory Network in Arabidopsis

The phytochrome (phy)-interacting basic helix-loop-helix transcription factors (PIFs) constitutively sustain the etiolated state of dark-germinated seedlings by actively repressing deetiolation in darkness. This action is rapidly reversed upon light exposure by phy-induced proteolytic degradation of the PIFs. Here, we combined a microarray-based approach with a functional profiling strategy and identified four PIF3-regulated genes misexpressed in the dark (MIDAs) that are novel regulators of seedling deetiolation. We provide evidence that each one of these four MIDA genes regulates a specific facet of etiolation (hook maintenance, cotyledon appression, or hypocotyl elongation), indicating that there is branching in the signaling that PIF3 relays. Furthermore, combining inferred MIDA gene function from mutant analyses with their expression profiles in response to light-induced degradation of PIF3 provides evidence consistent with a model where the action of the PIF3/MIDA regulatory network enables an initial fast response to the light and subsequently prevents an overresponse to the initial light trigger, thus optimizing the seedling deetiolation process. Collectively, the data suggest that at least part of the phy/PIF system acts through these four MIDAs to initiate and optimize seedling deetiolation, and that this mechanism might allow the implementation of spatial (i.e., organ-specific) and temporal responses during the photomorphogenic program.

A Light Trigger for DNA Nanotechnology

DNA minicircles with light-activated ‘caged’ interaction modules—based either on sticky ends or G-quadruplex interactions—do not form dimers until they are irradiated with near-UV light (not harmful for DNA). This technology offers a level of spatiotemporal (hybridization) control for functional nanoarchitectures.

Control of neural synchrony with light activated opsins

Synchronous neural activity occurs throughout the normal brain and has been associated with many important brain functions. Abnormal patterns of neural synchrony have been implicated in several neurological and psychiatric disorders such as epilepsy, autism, schizophrenia, and Parkinson’s disease. Several attempts have been made over the last decade to suppress pathological neural synchrony through the use of pharmacological agents or electrical stimulation. However, these therapeutic techniques present significant technical challenges. For example, problems with pharmacological interventions include slow onset and offset, low target specificity and peripheral side effects. Problems with electrical stimulation include the lack of mechanistic understanding of the effect of the electrical stimulation on brain dynamics, trial and error methodology to determine effective stimulation parameters, limited battery life resulting in repeated invasive surgeries, and difficulty in producing purely inhibitory stimulus. Recent developments in the field of molecular and genetic biology now offer the opportunity to use optical techniques to modulate neuronal activity in vivo by making neurons light sensitive through the use of light activated opsins. Optical stimulation has potentially very significant advantages over previous techniques both in terms of temporal and spatial resolution. In addition, it allows for cell specific selective targeting to modulate neuronal activity. Here, we investigate, in the setting of a computational simulation, a control strategy to modulate neural synchrony in a network of genetically engineered neurons that are sensitive to light stimulation. Our principle aim is to use the mean field signal generated by the network in the regime of stable network synchrony to generate an appropriate optical stimulation feedback signal u(t) to suppress the network synchrony. The feedback signal is designed so as to achieve neural desynchrony with minimum variance between the intrinsic frequency of the individual neuron in a given network and the resulting frequency of the neuron oscillator in the desynchronized state of the network. The schematic diagram of the control architecture explored in this study is demonstrated in Figure ​Figure1A.1A. Figure ​Figure1B1B represents the stable synchronous state of the genetically modified parvalbumin positive inhibitory neuronal network (all to all coupled) in absence of any feedback control. Figures ​Figures1B1B-​-1C1C provides examples of successful control of neural synchrony using two distinctly different forms of control signals. Figure 1 A) Schematic of the control architecture. The controller generates the feedback signal u(t) that triggers an optical signal, which is feedback onto the genetically modified network. The light trigger activates Channelrhodopsin (ChR2) protein embedded ...

Imiquimod 5% cream for isolated lichen planus of the lip

Lichen planus (LP) of the lips is a rare condition that is generally associated with other parts of the oral mucosa. Lip localization has an increased risk, since external trauma, smoking and ultraviolet light trigger malignant transformation. Only a few cases of isolated LP of the lips have been reported up to now, but results of larger series on oral LP suggest that it might be underestimated. Treatment of oral LP is usually difficult and lesions are generally resistant or recur, so that novel therapy alternatives are necessary. Here we report four cases of isolated LP of the lip successfully treated with imiquimod 5% cream. It was applied twice daily, 5 days a week, for 2 weeks. Two weeks after therapy, complete clinical and histopathological resolution was observed. No recurrence was observed during the 5, 10 and 18 months' follow-up period in cases 4, 3 and 1, respectively. Clinical and histopathological cure was also observed in case 2, but the patient showed clinical activation after 6 months. We suggest that imiquimod 5% cream is a safe and effective therapeutic treatment for oral LP.