Specific Photoreceptor Research Articles

Influence of Temperature and LED Light Spectra on Flavonoid Contents in Poa pratensis

Light and temperature are the driving forces in plant development and growth. Specific photoreceptors provide the ability to sense and interpret light and temperature to regulate growth. Under the limited light conditions in most sports stadiums, natural grasses suffer from light deficiency. Artificial light provided by light-emitting diodes (LEDs) is used to increase their growth and adjust their development. Flavonoids like flavonols and anthocyanins are influenced by light conditions and temperature. Increased blue light can elevate the content of these secondary metabolites. Remote measurements of internal parameters using non-destructive methods provided information on their content under different temperature conditions for quality monitoring. This experiment tested flavonoid contents in Kentucky bluegrass (Poa pratensis) for different blue-to-red light ratios (0.6 and 0.4) and three temperature courses (constant temperature of 4 °C, constant temperature of 12 °C, and temperature switching among 12–8–4–8–12 °C). The results show elevated levels of flavonoids under blue-dominant artificial light as well as increased content under low-temperature (4 °C) conditions. The lack of flavonoids at elevated temperatures (12 °C), especially under red-dominant light, suggests an increased requirement for artificial blue light at increased temperatures. Non-destructive flavonoid determination was suitable for this experiment and can therefore be used for practical sports turf quality monitoring.

Specific photoreceptor cell fate pathways are differentially altered in NR2E3-associated diseases

Mutations in NR2E3, a gene encoding an orphan nuclear transcription factor, cause two retinal dystrophies with a distinct phenotype, but the precise role of NR2E3 in rod and cone transcriptional networks remains unclear. To dissect NR2E3 function, we performed scRNA-seq in the retinas of wildtype and two different Nr2e3 mouse models that show phenotypes similar to patients carrying NR2E3 mutations. Our results reveal that rod and cone populations are not homogeneous and can be separated into different sub-classes. We identify a previously unreported cone pathway that generates hybrid cones co-expressing both cone- and rod-related genes. In mutant retinas, this hybrid cone subpopulation is more abundant and includes a subpopulation of rods transitioning towards a cone cell fate. Hybrid photoreceptors with high misexpression of cone- and rod-related genes are prone to regulated necrosis. Overall, our results shed light on the role of NR2E3 in modulating photoreceptor differentiation towards cone and rod fates and explain how different mutations in NR2E3 lead to distinct visual disorders in humans.

Chromatic pupillometry for evaluating melanopsin retinal ganglion cell function in Alzheimer's disease and other neurodegenerative disorders: a review.

The evaluation of pupillary light reflex (PLR) by chromatic pupillometry may provide a unique insight into specific photoreceptor functions. Chromatic pupillometry refers to evaluating PLR to different wavelengths and intensities of light in order to differentiate outer/inner retinal photoreceptor contributions to the PLR. Different protocols have been tested and are now established to assess in-vivo PLR contribution mediated by melanopsin retinal ganglion cells (mRGCs). These intrinsically photosensitive photoreceptors modulate the non-image-forming functions of the eye, which are mainly the circadian photoentrainment and PLR, via projections to the hypothalamic suprachiasmatic and olivary pretectal nucleus, respectively. In this context, chromatic pupillometry has been used as an alternative and non-invasive tool to evaluate the mRGC system in several clinical settings, including hereditary optic neuropathies, glaucoma, and neurodegenerative disorders such as Parkinson's disease (PD), idiopathic/isolated rapid eye movement sleep behavior disorder (iRBD), and Alzheimer's disease (AD). The purpose of this article is to review the key steps of chromatic pupillometry protocols for studying in-vivo mRGC-system functionality and provide the main findings of this technique in the research setting on neurodegeneration. mRGC-dependent pupillary responses are short-wavelength sensitive, have a higher threshold of activation, and are much slower and sustained compared with rod- and cone-mediated responses, driving the tonic component of the PLR during exposure to high-irradiance and continuous light stimulus. Thus, mRGCs contribute mainly to the tonic component of the post-illumination pupil response (PIPR) to bright blue light flash that persists after light stimulation is switched off. Given the role of mRGCs in circadian photoentrainment, the use of chromatic pupillometry to perform a functional evaluation of mRGcs may be proposed as an early biomarker of mRGC-dysfunction in neurodegenerative disorders characterized by circadian and/or sleep dysfunction such as AD, PD, and its prodromal phase iRBD. The evaluation by chromatic pupillometry of mRGC-system functionality may lay the groundwork for a new, easily accessible biomarker that can be exploited also as the starting point for future longitudinal cohort studies aimed at stratifying the risk of conversion in these disorders.

Where visual fields coming from? ‐ A short introduction from neurophysiology point of view

Visual fields refer to the area of vision that can be seen by each eye when it is fixed in a certain position. The visual fields are created by the combination of the images received by each eye, which are then processed by the brain to create a single, unified image. The visual fields are divided into four quadrants: superior, inferior, nasal, and temporal. Each eye sees a slightly different portion of the visual field, and the brain combines these two images to create a three‐dimensional perception of the world.The visual fields are outcome of the interaction of the ocular structures, optic nerve, and brain centres. The eye captures images of the visual field through the cornea and lens, which focus the light onto the retina. The retina contains specialized photoreceptors, which convert the light into electrical signals that are transmitted through the optic nerve to the brain. The images are first integrated and processed within lateral geniculate nuclei of the thalamus. In this important structure visual stimuli are first filtered, to eliminate irrelevant or unnecessary information, allowing only important visual signals to pass on to the visual cortex, then integrated from both eyes, allowing for depth perception and 3D vision, processed, based on features such as colour, contrast, and movement, which are then relayed to the visual cortex and synchronized with other sensory information in the brain, allowing for a coherent perception of the environment. The visual cortex in the brain then processes these integrated signals to create the perception of the visual field. This complex process allows us to see and interpret the world around us, including objects, people, and scenery, and to respond to them in a meaningful way.

Contributed Session II: Binocular combination of the pupil response depends on photoreceptor pathway.

The pupillary light response is driven by three classes of retinal photoreceptor. Cones and rods are involved in the initial constriction of the pupil, whereas melanopsin-containing intrinsically photosensitive Retinal Ganglion Cells (ipRGCs) maintain constriction over longer timescales. Previous work has characterized the contributions of photoreceptor signals to pupil control, but relatively little is known about binocular combination of these signals when simultaneously stimulating the retina in both eyes. We measured changes in pupil size in 48 participants using a binocular eye-tracker, targeting specific photoreceptor classes with a binocular 10-primary light engine and the silent substitution method. We stimulated the periphery of the retina using light flickering at 0.4 and 0.5 Hz. Participants viewed a disc of either achromatic flickering light, or contrast modulations that targeted the ipRGCs, or the opponent colour pathways L-M or S-(L+M). Using a modified virtual reality headset, we presented the stimuli at a range of modulation amplitudes in three different ocular configurations: monocular, binocular, and dichoptic. We obtained clear pupil responses at both the first and the second harmonic frequencies. Suppression levels differed across conditions with the strongest suppression measured for the L-M condition. We account for the results in a single modelling framework where the weight of interocular suppression determines the binocular combination properties.

PDE6D Mediates Trafficking of Prenylated Proteins NIM1K and UBL3 to Primary Cilia.

Mutations in PDE6D impair the function of its cognate protein, phosphodiesterase 6D (PDE6D), in prenylated protein trafficking towards the ciliary membrane, causing the human ciliopathy Joubert Syndrome (JBTS22) and retinal degeneration in mice. In this study, we purified the prenylated cargo of PDE6D by affinity proteomics to gain insight into PDE6D-associated disease mechanisms. By this approach, we have identified a specific set of PDE6D-interacting proteins that are involved in photoreceptor integrity, GTPase activity, nuclear import, or ubiquitination. Among these interacting proteins, we identified novel ciliary cargo proteins of PDE6D, including FAM219A, serine/threonine-protein kinase NIM1 (NIM1K), and ubiquitin-like protein 3 (UBL3). We show that NIM1K and UBL3 localize inside the cilium in a prenylation-dependent manner. Furthermore, UBL3 also localizes in vesicle-like structures around the base of the cilium. Through affinity proteomics of UBL3, we confirmed its strong interaction with PDE6D and its association with proteins that regulate small extracellular vesicles (sEVs) and ciliogenesis. Moreover, we show that UBL3 localizes in specific photoreceptor cilium compartments in a prenylation-dependent manner. Therefore, we propose that UBL3 may play a role in the sorting of proteins towards the photoreceptor outer segment, further explaining the development of PDE6D-associated retinal degeneration.

Recent advances in low-level laser therapy on depression

Photobiomodulation (PBM), as a form of light therapy, has been applied broadly in the medical practice. The biological photoreceptors use small-molecule cofactors called chromophores to detect light and convert a physical signal into a biochemical signal transmission cascade. Visible light (380–780 nm) can activate specialized photoreceptors to stimulate vision and regulate circadian rhythm. Compared with visible light, near-infrared (NIR) light (780–1,100 nm) has better tissue penetration depths, enabling us to carry out non-invasive low-level laser therapy (LLLT) for different tissues. Mitochondrial cytochrome c oxidase is the main NIR photoreceptor. The basic effect is to promote the generation of ATP through the respiratory chain. LLLT can enhance blood circulation, alleviate inflammation, promote muscle damage repair, stem cell proliferation and so on. The neuroprotective effect of LLLT on central nervous system (CNS) diseases has been preliminarily verified in animal models, which is expected to improve the cognitive function of Alzheimer’s patients, motor symptoms of Parkinson’s patients and mental disorders of patients with depression, thus improving the quality of life of patients. Understanding its protective effect and mechanisms will contribute to better therapeutic application in the future. In this review, we will discuss the antidepressant effect of LLLT, its possible mechanisms, and existing problems with its applications.

Flashes of UV-C light are perceived by UVR8, the photoreceptor of UV-B light

Light is an important regulator of plant morphogenesis and plant-pathogen interactions via specific photoreceptors and signaling pathways. Besides visible light, other electromagnetic radiations may play roles, notably ultraviolet (UV) light. The UV part of the electromagnetic spectrum includes UV-A (315 nm - 400 nm), UV-B (280 nm - 315 nm) and UV-C radiations (200 nm - 280 nm). UV-B and UV-C have been reported to increase plant resistance to plant pathogens after the UV perception and signaling stages. The perception of UV-B radiation is achieved by the dimer protein UVR8 (UV RESISTANCE LOCUS 8). Even though the action spectrum of this photoreceptor overlaps in the UV-C domain, it has never been formally demonstrated that UVR8 could also act as a photoreceptor of UV-C light. We provide here original observations showing that UVR8 can indeed perceive UV-C light provided that the latter is in the form of flashes (1s) and not continuous illuminations (the 60s). Our observations also show that the response of UVR8 to flashes of UV-C light is dose-dependent. They could explain why flashes of UV-C light are more effective for stimulating plant defenses than continuous illuminations for the same amount of energy delivered to plants (J/m2). Eventually, our observations support ongoing trials that aim at using UV-C light as an environmental-friendly plant resistance inducer in field conditions.

Light receptors in the avian brain and seasonal reproduction.

Detection and transduction of photic cues by nonvisual photoreceptors, located in the deep brain, is a critical component of timing seasonal reproduction in birds. However, the precise identity of the photoreceptors responsible for detection of salient photic cues remains uncertain and debated. Here I review of the existing evidence for each of the three candidate photoreceptive opsins: Vertebrate Ancient Opsin, Melanopsin, and Neuropsin, including localization, action spectrum, and data from experimental manipulation of opsin expression. These findings are compared to an updated list of key criteria established in the literature as a litmus for classifying an opsin as the "breeding photoreceptor." Integrating evidence for each of the candidate photoreceptors with respect to these criteria reveals support for all three opsins in regulation of seasonal reproduction. Taken together these findings strongly suggest that transduction of seasonal photoperiodic information involves the activity of multiple photoreceptor types and populations functioning in concert. This review also highlights the need to shift attention from simply identifying "the breeding photoreceptor" to a more integrative approach aiming to parse the contribution of specific photoreceptor populations within the brain.

Photoreceptors' gene expression of Arabidopsis thaliana grown with biophilic LED-sourced lighting systems.

Using specific photoreceptors, plants can sense light signals fundamental to their growth and development under changing light conditions. Phytochromes sense red and far-red light, cryptochromes and phototropins sense UV-A and blue light, while the UVR8 gene senses UV-B signals. The study of the molecular mechanisms used by plants to respond to artificial biophilic lighting is of pivotal importance for the implementation of biophilic approaches in indoor environments. CoeLux® is a new lighting system that reproduces the effect of natural sunlight entering through an opening in the ceiling, with a realistic sun perceived at an infinite distance surrounded by a clear blue sky. We used the model plant Arabidopsis thaliana to assess the gene expression of the main plant photoreceptors at different light intensities and at different times after exposure to the CoeLux® light type, using high-pressure sodium (HPS) lamps as control light type. Genes belonging to different families of photoreceptors showed a similar expression pattern, suggesting the existence of a common upstream regulation of mRNA transcription. In particular, PHYA, PHYC, PHYD, CRY1, CRY2, PHOT1, and UVR8, showed a common expression pattern with marked differences between the two light types applied; under the HPS light type, the expression levels are raising with the decrease of light intensity, while under the CoeLux® light type, the expression levels remain nearly constant at a high fold. Moreover, we showed that under biophilic illumination the light spectrum plays a crucial role in the response of plants to light intensity, both at the molecular and morphological levels.

Transcriptional regulation of photoprotection in dark-to-light transition-More than just a matter of excess light energy.

In nature, photosynthetic organisms are exposed to different light spectra and intensities depending on the time of day and atmospheric and environmental conditions. When photosynthetic cells absorb excess light, they induce nonphotochemical quenching to avoid photodamage and trigger expression of “photoprotective” genes. In this work, we used the green alga Chlamydomonas reinhardtii to assess the impact of light intensity, light quality, photosynthetic electron transport, and carbon dioxide on induction of the photoprotective genes (LHCSR1, LHCSR3, and PSBS) during dark-to-light transitions. Induction (mRNA accumulation) occurred at very low light intensity and was independently modulated by blue and ultraviolet B radiation through specific photoreceptors; only LHCSR3 was strongly controlled by carbon dioxide levels through a putative enhancer function of CIA5, a transcription factor that controls genes of the carbon concentrating mechanism. We propose a model that integrates inputs of independent signaling pathways and how they may help the cells anticipate diel conditions and survive in a dynamic light environment.

Somatostatin signalling promotes the differentiation of rod photoreceptors in human pluripotent stem cell-derived retinal organoid.

ObjectivesStem cell‐derived photoreceptor replacement therapy is a promising strategy for the treatment of retinal degenerative disease. The development of 3D retinal organoids has permitted the production of photoreceptors. However, there is no strategy to enrich a specific photoreceptor subtype due to inadequate knowledge of the molecular mechanism underlying the photoreceptor fate determination. Hence, our aim is to explore the uncharacterized function of somatostatin signalling in human pluripotent stem cell‐derived photoreceptor differentiation.Materials and Methods3D retinal organoids were achieved from human embryonic stem cell. The published single‐cell RNA‐sequencing datasets of human retinal development were utilized to further investigate the transcriptional regulation of photoreceptor differentiation. The assays of immunofluorescence staining, lentivirus transfection, real‐time quantitative polymerase chain reaction and western blotting were performed.ResultsWe identified that the somatostatin receptor 2 (SSTR2)‐mediated signalling was essential for rod photoreceptor differentiation at the precursor stage. The addition of the cognate ligand somatostatin in human 3D retinal organoids promoted rod photoreceptor differentiation and inhibited cone photoreceptor production. Furthermore, we found that the genesis of rod photoreceptors was modulated by endogenous somatostatin specifically secreted by developing retinal ganglion cells.ConclusionsOur study identified SSTR2 signalling as a novel extrinsic regulator for rod photoreceptor fate determination in photoreceptor precursors, which expands the repertoire of functional signalling pathways in photoreceptor development and sheds light on the optimization of the photoreceptor enrichment strategy.

Articles of Significant Interest in This Issue

Cyanobacteria thrive in hot springs as part of thick, laminated biofilms (microbial mats). Bunbury et al. (e00196-22) describe distinct phototactic responses of cyanobacterial residents that allow the cells to move spatially in the biofilms for optimal light absorption. Specific photoreceptors and signal transduction pathways control the photoresponses and finely tune the positioning of the cells in the complex community.

UV and Visible Spectrum LED Lighting as Abiotic Elicitors of Bioactive Compounds in Sprouts, Microgreens, and Baby Leaves-A Comprehensive Review including Their Mode of Action.

Background: According to social demands, the agri-food industry must elaborate convenient safe and healthy foods rich in phytochemicals while minimising processing inputs like energy consumption. Young plants in their first stages of development represent great potential. Objective: This review summarises the latest scientific findings concerning the use of UV and visible spectrum LED lighting as green, sustainable, and low-cost technologies to improve the quality of sprouts, microgreens, and baby leaves to enhance their health-promoting compounds, focusing on their mode of action while reducing costs and energy. Results: These technologies applied during growing and/or after harvesting were able to improve physiological and morphological development of sprouted seeds while increasing their bioactive compound content without compromising safety and other quality attributes. The novelty is to summarise the main findings published in a comprehensive review, including the mode of action, and remarking on the possibility of its postharvest application where the literature is still scarce. Conclusions: Illumination with UV and/or different regions of the visible spectrum during growing and shelf life are good abiotic elicitors of the production of phytochemicals in young plants, mainly through the activation of specific photoreceptors and ROS production. However, we still need to understand the mechanistic responses and their dependence on the illumination conditions.

Slow vision: Measuring melanopsin-mediated light effects in animal models.

Mammalian retinas contain three specialized photoreceptors: the rods and cones in the outer retina, whose primary function is to support visual perception in dim and bright environments, respectively, and a small subset of retinal ganglion cells ("intrinsically photosensitive" retinal ganglion cells; ipRGCs), which are directly light-responsive owing to their expression of the photopigment melanopsin. Melanopsin photoreception is optimized to encode low-frequency changes in the light environment and, as a result, extends the temporal and spatial range over which light is detected by the retina. ipRGCs innervate many brain areas, and this allows melanopsin light responses to be used for diverse purposes, ranging from the synchronization of the circadian clock with the solar day to light's regulation of mood, alertness, and neuroendocrine and cognitive functions. In this review, we discuss the methods and findings that have contributed to our understanding of melanopsin across biology. We particularly focus on the approaches that allow melanopsin to be studied at a systems/whole animal level and how these methods have illuminated the role of melanopsin in diverse physiological outputs.

Synaptic targets of photoreceptors specialized to detect color and skylight polarization in Drosophila.

Color and polarization provide complementary information about the world and are detected by specialized photoreceptors. However, the downstream neural circuits that process these distinct modalities are incompletely understood in any animal. Using electron microscopy, we have systematically reconstructed the synaptic targets of the photoreceptors specialized to detect color and skylight polarization in Drosophila, and we have used light microscopy to confirm many of our findings. We identified known and novel downstream targets that are selective for different wavelengths or polarized light, and followed their projections to other areas in the optic lobes and the central brain. Our results revealed many synapses along the photoreceptor axons between brain regions, new pathways in the optic lobes, and spatially segregated projections to central brain regions. Strikingly, photoreceptors in the polarization-sensitive dorsal rim area target fewer cell types, and lack strong connections to the lobula, a neuropil involved in color processing. Our reconstruction identifies shared wiring and modality-specific specializations for color and polarization vision, and provides a comprehensive view of the first steps of the pathways processing color and polarized light inputs.

Effects of visible light on mechanisms of skin photoaging.

Human skin is not only affected by ultraviolet radiation but also by visible light wavelengths emitted by sunlight, electronic devices, and light emitting diodes. Similar to the ultraviolet radiation, visible light has been implicated in photoaging. In this review, the effects of blue light, yellow light, red light, and broad visible light are discussed in relation with photoaging. Different visible light wavelengths likely contribute beneficial and deleterious effects on photoaging by way of interaction with specific photoreceptors, ROS production, and other photon-mediated reactions. Further in vivo studies are needed to determine the mechanism and action spectrum of photoaging in humans, as well as optimal photoprotection with coverage against visible light wavelengths.

A combinatorial cis-regulatory logic restricts color-sensing Rhodopsins to specific photoreceptor subsets in Drosophila.

Color vision in Drosophila melanogaster is based on the expression of five different color-sensing Rhodopsin proteins in distinct subtypes of photoreceptor neurons. Promoter regions of less than 300 base pairs are sufficient to reproduce the unique, photoreceptor subtype-specific rhodopsin expression patterns. The underlying cis-regulatory logic remains poorly understood, but it has been proposed that the rhodopsin promoters have a bipartite structure: the distal promoter region directs the highly restricted expression in a specific photoreceptor subtype, while the proximal core promoter region provides general activation in all photoreceptors. Here, we investigate whether the rhodopsin promoters exhibit a strict specialization of their distal (subtype specificity) and proximal (general activation) promoter regions, or if both promoter regions contribute to generating the photoreceptor subtype-specific expression pattern. To distinguish between these two models, we analyze the expression patterns of a set of hybrid promoters that combine the distal promoter region of one rhodopsin with the proximal core promoter region of another rhodopsin. We find that the function of the proximal core promoter regions extends beyond providing general activation: these regions play a previously underappreciated role in generating the non-overlapping expression patterns of the different rhodopsins. Therefore, cis-regulatory motifs in both the distal and the proximal core promoter regions recruit transcription factors that generate the unique rhodopsin patterns in a combinatorial manner. We compare this combinatorial regulatory logic to the regulatory logic of olfactory receptor genes and discuss potential implications for the evolution of rhodopsins.

Modulations in irradiance directed at melanopsin, but not cone photoreceptors, reliably alter electrophysiological activity in the suprachiasmatic nucleus and circadian behaviour in mice.

Intrinsically photosensitive retinal ganglion cells convey intrinsic, melanopsin-based, photoreceptive signals alongside those produced by rods and cones to the suprachiasmatic nucleus (SCN) circadian clock. To date, experimental data suggest that melanopsin plays a more significant role in measuring ambient light intensity than cone photoreception. Such studies have overwhelmingly used diffuse light stimuli, whereas light intensity in the world around us varies across space and time. Here, we investigated the extent to which melanopsin or cone signals support circadian irradiance measurements in the presence of naturalistic spatiotemporal variations in light intensity. To address this, we first presented high- and low-contrast movies to anaesthetised mice whilst recording extracellular electrophysiological activity from the SCN. Using a mouse line with altered cone sensitivity (Opn1mwR mice) and multispectral light sources we then selectively varied irradiance of the movies for specific photoreceptor classes. We found that steps in melanopic irradiance largely account for the light induced-changes in SCN activity over a range of starting light intensities and in the presence of spatiotemporal modulation. By contrast, cone-directed changes in irradiance only influenced SCN activity when spatiotemporal contrast was low. Consistent with these findings, under housing conditions where we could independently adjust irradiance for melanopsin versus cones, the period lengthening effects of constant light on circadian rhythms in behaviour were reliably determined by melanopic irradiance, regardless of irradiance for cones. These data add to the growing evidence that modulating effective irradiance for melanopsin is an effective strategy for controlling the circadian impact of light.

Change of transcription level of photoreceptor-specific CRX gene in the peripheral blood of the participants of an arctic world oceanic international flight

To reveal the dynamics of CRX expression level in humans after a prolonged temporary exposure to polar day conditions. The study included 6 pilots (males from 39 to 69 y.o.) who participated in the Arctic World Oceanic International Flight Sever Vash (West to East, from 62°N 74°E to 72°N 114°E). Samples of peripheral blood for RNA isolation were collected at the start and at the end of the flight. The level of mRNA in the samples was evaluated based on the data of quantitative real-time PCR of the CRX gene, as well as the b2M and TBP housekeeping genes (reference). Expression of the CRX gene in the studied group (p<0.01) was revealed; the total average level of mRNA was about 3 times higher prior to, and approximately 7 times higher after normalization to the b2M gene. Five pilots had increased expression of the CRX gene within the range of -1.53 to -3.07 (Z-score of <0 before the flight and >0 after the flight). In one pilot, the level of CRX expression was higher at the start, but it reduced by the end of the circumnavigation flight. The results confirm the hypothesis that the CRX gene is expressed after a prolonged temporary exposure to polar day conditions. It was also revealed that during rapid adaptation, equal changes in the illumination of retinal photoreceptors lead to different individual dynamics of CRX expression.