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To sense light, animals often utilize mechanisms that rely on visual pigments composed of opsin and retinal. The photon-induced isomerization of 11-cis-retinal to the all-trans configuration triggers phototransduction cascades, resulting in a change in the membrane potential of the photoreceptor. In mollusks, the most abundant opsin in the eye is Gq-coupled rhodopsin (Gq-rhodopsin). The Gq-rhodopsin-based visual pigment is bistable, with the regeneration of 11-cis-retinal occurring in a light-dependent manner without leaving the opsin moiety. 11-cis-retinal is also regenerated by the action of retinochrome in the cell bodies. Retinal binding protein (RALBP) mediates retinal transport between Gq-rhodopsin and retinochrome in the cytoplasm. However, recent studies have identified additional bistable opsins in mollusks, including Opn5 and xenopsin. It is unknown whether these bistable opsins require RALBP and retinochrome for the continuous regeneration of 11-cis-retinal. In the present study, we examined the expression of RALBP and retinochrome in the photoreceptors expressing Opn5 or Xenopsin in the heterobranch gastropods Limax and Peronia. Our findings revealed that retinochrome, but not RALBP, was present in some of the Opn5A-positive brain photosensory neurons of Limax. The ciliary cells in the dorsal eye of Peronia, which express Xenopsin2, lacked both retinochrome and RALBP. Therefore, bistable opsins do not necessarily depend on the RALBP-retinochrome system in a cell. We also examined the expression of other proteins that support visual function, such as β-arrestin, Gq, and Go, in all types of photoreceptors in these animals, and uncovered differences in the molecular composition among the photoreceptors. [ABSTRACT FROM AUTHOR]

Purpose: To evaluate the two‐year fundus examination outcomes of term infants undergoing eye screening. Methods: Retrospective review of our data of term infants at a tertiary care center (Ankara Bilkent City Hospital) from October 2021 to October 2023. All screened infants underwent red reflex test and dilated posterior segment examination. Abnormal ocular findings were documented using smartphone‐based imaging system. Results: A total of 5527 full‐term babies were enrolled to the study. Abnormal ocular findings were observed in 1031 newborns (18.6%), the most common of which were retinal white lesions in the peripheral retina (13%) (n = 720) and posterior segment hemorrhages (4.3%) (n = 243). Other findings included congenital hypertrophy of the retinal pigment epithelium (n = 14), choroidal nevus (n = 11), idiopathic peripheral retinal scar (n = 9), chorioretinal coloboma (n = 6), optic nerve coloboma (n = 4), familial exudative vitreoretinopathy (n = 4), optic nerve large cup (n = 2), optic nerve hypoplasia (n = 2), retinal calcification (n = 2), optic nerve pit (n = 2), morning glory disc anomaly (n = 1), vascular loop on the optic disc (n = 1), retinoblastoma (n = 1), X‐linked retinoschisis (n = 1), congenital toxoplasmosis (n = 1), thread‐shaped white lesion (n = 1), combined hamartoma of the retina and the retinal pigment epithelium (n = 1), foveal hypoplasia (n = 1), retinal dystrophy (n = 1), and astrocytic hamartoma (n = 1). Conclusions: Detailed eye examinations of term infants can reveal a range of ocular and/or systemic abnormalities that would not be caught through pupillary red reflex test. Smartphone‐based fundus imaging is a simple and effective method for documenting findings. [ABSTRACT FROM AUTHOR]

Retinal rods and cones underlie scotopic and photopic vision, respectively. Their pigments exhibit spontaneous isomerizations (quantal noise) in darkness due to intrinsic thermal energy. This quantal noise, albeit exceedingly low in rods, dictates the light threshold for scotopic vision. The same quantal noise in cones, however, is too low to explain the much higher diurnal light threshold. Separately, a dark continuous noise is present in rods, long accepted to originate from an intrinsic random activation of the cyclic guanosine monophosphate (cGMP)-phosphodiesterase enzyme mediating phototransduction downstream of the pigment. Here, we report the surprising finding that most of this rod dark continuous noise actually originates from rhodopsin itself. Importantly, we found the same continuous noise with a much higher magnitude from cone pigments. The rod and cone continuous noises are apparently both associated with a hitherto unrecognized "metastable" pigment conformational state physiologically resembling that in apo-opsin (opsin devoid of chromophore) and is intermittently active for very brief moments. The cone holopigment's high continuous noise is expected to act as an intrinsic equivalent light and adapt the cone dramatically, accounting for a major part of the light-sensitivity difference between rods and cones in darkness. [ABSTRACT FROM AUTHOR]

Purpose: Diving is an intense physical activity under hyperbaric and hyperoxic conditions. The aim of this study is to evaluate the long‐term effects of diving on the thicknesses of retinal layers and retinal anatomy in professional deep and scuba divers. Methods: The study included 52 eyes of deep divers who dive to depths of more than 130 feet (ft), 49 eyes of scuba divers who dive up to 130 ft, and 66 eyes of the control group, consisting of nondiving but regularly exercising males. Measurements of macular retinal layer thicknesses, peripapillary nerve fiber layer thickness, subfoveal choroidal thickness, and peripheral retinal examinations with scleral indentation were performed and statistically compared between the groups. Results: The mean diving duration was 455.00 ± 318.88 h in deep divers and 451.67 ± 281.10 h in scuba divers. The retinal pigment epithelium (RPE) was statistically significantly thicker in deep divers than in scuba divers and the control group on the 3 mm ring of the Early Treatment Diabetic Retinopathy Study grid. Subfoveal choroidal thickness was significantly thicker in deep divers than in scuba divers (p < 0.05). RPE abnormalities showed a significant increase in both the deep and scuba diver groups (p = 0.01). Conclusion: An increased thickening of the subfoveal choroid and RPE, resembling pachychoroid pigment epitheliopathy, was detected in deep divers over a long‐term duration. [ABSTRACT FROM AUTHOR]

When changing habitat during migration or ontogenesis, fish encounter changes of the visual environment, among which the most important is the spectral composition of light and turbidity. This leads to changes in the behavior, morphology, and physiology of the visual system, in particular, spectral sensitivity, which is determined by the properties of visual pigments. The masked greenling Hexagrammos octogrammus has an additional factor that shapes effective spectral sensitivity—the presence of densely bright orange cornea which reversibly changes its density depending on the state of light/dark adaptation. However, it is unknown to what extent the properties of visual pigments are matched to spectral properties of the developing cornea at the final stage of metamorphosis during migration of juveniles from pelagic to coastal environments. The findings of this microspectrophotometric study show that the range of the spectral sensitivity of rods and cones in juveniles is much wider than in adults, with a shift in the sensitivity of a significant part of the cells to shorter wavelengths. The reason for this is the large variation in the ratio of chromophores A1:A2 in the pigment mixture in each cell and possible expression of new opsins. This also indicates the asynchrony of pigment transformations in different types of photoreceptors and the incompleteness of these transformations on the eve of the transition to bottom life in shallow water. [ABSTRACT FROM AUTHOR]

Huntington's disease (HD) is a progressive neurodegenerative disorder characterized by motor dysfunction and cognitive decline. While retinal abnormalities have been documented in some HD patients and animal models, the nature of these abnormalities—specifically whether they originate in the inner or outer retina—remains unclear, particularly regarding their progression with age. This study investigates the retinal structure and function in HD transgenic mice (R6/1) compared to C57BL/6 J control mice at 2, 4, and 6 months of age, encompassing both pre-symptomatic and symptomatic stages of HD. Pathological assessments of the striatum and evaluations of motor function confirmed significant HD-related alterations in R6/1 mice at 6 months. Visual function was subsequently analyzed, accompanied by immunofluorescent staining of retinal and optic nerve tissues over time. Our findings revealed that R6/1 mice exhibited pronounced HD symptoms at 6 months, characterized by neuronal loss in the striatum and impaired locomotor abilities. Functionally, visual acuity declined at 6 months, while retinal light responses began to deteriorate by 4 months. Structurally, R6/1 mice demonstrated a global reduction in cone opsin expression as early as 2 months, with a decrease in rhodopsin levels at 4 months, alongside a thinner retinal structure compared to controls. Notably, rod bipolar cell populations were decreased at 6 months, exhibiting shorter dendritic branches and reduced synaptic connections with photoreceptors in the outer retina. Additionally, ganglion cell numbers in the inner retina decreased at 6 months, accompanied by aberrant neural fibers in the optic nerve. Microglial activation was evident at 4 months, while astrocytic activation was observed at 6 months. Aggregates of mutant huntingtin (mHTT) were first detected in the ganglion cell layer and optic nerve at 2 months, subsequently disseminating throughout all retinal layers with advancing age. These results indicate that retinal pathology in R6/1 mice manifests earlier in the outer retina than in the inner retina, which does not align with the progression of mHTT aggregation. Consequently, the R6/1 mouse retina may serve as a more effective model for elucidating the mechanisms underlying HD and evaluating potential therapeutic strategies, rather than functioning as an early diagnostic tool for the disease. [ABSTRACT FROM AUTHOR]

Fubai chrysanthemum is a kind of traditional Chinese medicine, which can be used as a common food, and is commonly used to improve and relieve visual fatigue. However, its pharmacodynamic material basis and action mechanisms in relieving visual fatigue have not been systematically studied. In this article, 11 absorbed ingredients from Fubai chrysanthemum were detected in rat plasma. Then, the target network pharmacology and KEGG pathway analysis were performed. It was found that Fubai chrysanthemum could inhibit various apoptotic cells and reduce oxidative damage of eyes by regulating the apoptosis pathway, thus alleviating visual fatigue. Further in vitro experiments showed that Fubai chrysanthemum could effectively protect against oxidation damage of adult retinal pigment epithelial cells (ARPE-19), retinal ganglion cells (RGC-5), and lens. The results of cell experiments showed that Fubai chrysanthemum could increase the cell activity, GSH content, and SOD content of ARPE-19 and RGC-5 after oxidative injury, while decreasing the IL-18 content. Similarly, in the study of lens transparency, we found that Fubai chrysanthemum could effectively alleviate the oxidative damage degree of the lens, and significantly increase the content of CAT, GSH, and SOD. The above results suggested that Fubai chrysanthemum could play an important role in alleviating visual fatigue through regulating cell apoptosis and antioxidative damage. [ABSTRACT FROM AUTHOR]

Background: This paper aimed to measure and characterize eleven monochromatic filters and twenty-two combinations used empirically to treat patients with visual dysfunctions to propose enhanced protocols based on solid evidence. Their wavelength, transmittance, and relative sensitivity were defined on the retinal cone cells. Methods: A double-beam UV-VIS-NIR spectrophotometer, VARIAN brand, Cary 5000 model, owned by the National Center of Metrology, with high precision and accuracy, was used to characterize all filters. Filters were purchased from Optomatters Corporation, Belgium. Results: When two or three filters are combined, their transmittance and relative sensitivity on the retinal cone cells decrease regardless of wavelength. As a result, the efficiency of combined filters may decrease during treatments. Additionally, most filters and combinations, regardless of the wavelength, transmit a considerable percentage of light from the red spectrum. A depressant is the best monochromatic filter, and Upsilon–Neurasthenic is the strongest combination to stimulate blue cone cells. In contrast, Stimulant and Delta–Theta are best for red and green cone cells. Mu–Delta and Mu–Theta can be interchangeable, as well as Alpha–Delta and Alpha–Theta. Conclusions: Results suggest that the current phototherapy treatment protocol must be deeply revised, and the number of filters and combinations should be reduced to reduce costs and time and boost efficiency. [ABSTRACT FROM AUTHOR]

The ultrafast photochemical reaction mechanism, transient spectra, and transition kinetics of the human blue cone visual pigment have been recorded at room temperature. Ultrafast time-resolved absorption spectroscopy revealed the progressive formation and decay of several metastable photo-intermediates, corresponding to the Batho to Meta-II photo-intermediates previously observed with bovine rhodopsin and human green cone opsin, on the picosecond to millisecond timescales following pulsed excitation. The experimental data reveal several interesting similarities and differences between the photobleaching sequences of bovine rhodopsin, human green cone opsin, and human blue cone opsin. While Meta-II formation kinetics are comparable between bovine rhodopsin and blue cone opsin, the transition kinetics of earlier photo-intermediates and qualitative characteristics of the Meta-I to Meta-II transition are more similar for blue cone opsin and green cone opsin. Additionally, the blue cone photo-intermediate spectra exhibit a high degree of overlap with uniquely small spectral shifts. The observed variation in Meta-II formation kinetics between rod and cone visual pigments is explained based on key structural differences. [ABSTRACT FROM AUTHOR]

Dichromatic color vision is mediated by two cone visual pigments in many eutherian mammals. After reentry into the sea, early cetaceans lost their violet-sensitive visual pigment (short wavelength-sensitive 1) independently in the baleen and toothed whale ancestors and thus obtained only monochromatic cone vision. Subsequently, losses of the middle/long wavelength-sensitive (M/LWS) pigment have also been reported in multiple whale lineages, leading to rhodopsin (RH1)-mediated rod monochromatic vision. To further elucidate the phenotypic evolution of whale visual pigments, we assessed the spectral tuning of both M/LWS and RH1 from representative cetacean taxa. Interestingly, although the coding sequences for M/LWS are intact in both the pygmy right whale and the Baird's beaked whale, no spectral sensitivity was detected in vitro. Pseudogenization of other cone vision-related genes is observed in the pygmy right whale, suggesting a loss of cone-mediated vision. After ancestral sequence reconstructions, ancient M/LWS pigments from cetacean ancestors were resurrected and functionally measured. Spectral tuning of M/LWS from the baleen whale ancestor shows that it is green sensitive, with a 40-nm shift in sensitivity to a shorter wavelength. For the ancestor of sperm whales, although no spectral sensitivity could be recorded for its M/LWS pigment, a substantial sensitivity shift (20 to 30 nm) to a shorter wavelength may have also occurred before its functional inactivation. The parallel phenotypic evolution of M/LWS to shorter wavelength sensitivity might be visual adaptations in whales allowing more frequent deep-sea activities, although additional ecological differentiations may have led to their subsequent losses. [ABSTRACT FROM AUTHOR]

Pseudoxanthoma elasticum (PXE) is a rare metabolic disease with autosomal recessive inheritance. The manifestation in PXE is represented by retinal complications, pseudoxanthomas of the skin folding areas, and arterial calcification. The retinal complications are caused by the calcification of Bruch's membrane beneath retinal pigment epithelial cells (RPE) that can lead to retinal macular degeneration. The exact mechanism for the retinal pathophysiology is not known, and patients have variable symptoms and findings. Two induced pluripotent stem cell (hiPSC) lines from a patient carrying the common homozygous mutation c.3421C > T, p.Arg1141X in the ATP‐binding cassette transporter gene (ABCC6; OMIM264800) were established and fully characterized. Then, RPE cells were differentiated, and molecular and functional characterization was conducted as a comparison to healthy controls. Data demonstrated that PXE‐specific high‐quality hiPSC lines can be established from a skin biopsy regardless of the skin‐related disease phenotype and disease‐specific RPE differentiation is feasible. The molecular and functional assessment of the PXE‐specific RPE indicated increased pigmentation and reduced epithelial barrier functions as well as phagocytosis activity as compared to healthy controls. Although preliminary data, this indicates possible RPE‐dependent factors that might explain the individual vulnerability of the retinas for macular degeneration in PXE. Future validation of the novel findings with additional PXE patients will be important. [ABSTRACT FROM AUTHOR]

Purpose: The Beer–Lambert law suggests that visual pigment optical density (OD) should be linearly related to the length of photoreceptor outer segments (POSs). Mammalian studies indicate that visual pigment concentration increases with POS length, but the nature of this relationship may vary due to factors such as visual pigment packing density or retinal eccentricity, and may not necessarily be linearly related. The purpose of this study was to establish the relationship between OD and POS length in humans. Methods: Spectral domain optical coherence tomography (OCT) was used to image POS, and imaging retinal densitometry (IRD) was used to measure OD at corresponding locations in 19 healthy participants (age range 25–82 years). POS length and OD measurements were extracted from OCT and IRD images at 23 discrete locations spanning the central 9° of the retina. The averaged data from all participants were fitted with models based on the Beer–Lambert law to establish the relationship between OD and POS length. Results: Visual pigment OD increased monotonically with POS length, but the relationship was non‐linear, and a straight‐line fit, based on a simple interpretation of the Beer–Lambert law, provided a poor description. A model allowing for different rod and cone visual pigment concentrations provided a superior fit. Specifically, the data were well described by a model where the molar concentration of visual pigment in cones and rods were 3.8 × 10−3 mol/L and 1.8 × 10−3mol/L, respectively. Conclusions: In accordance with the Beer–Lambert law, the results indicate that OD increases monotonically with POS length in humans, but the precise relationship is dependent on photoreceptor type. These results suggest that visual pigment concentration in rods is only about 48% of that found in cones. This may be due to the ubiquitous nature of artificial light that works to reduce the concentration of rhodopsin in rod photoreceptors. [ABSTRACT FROM AUTHOR]

There are different types of treatment for eye diseases. Although the majority of eye diseases are curable with primary treatments and surgery, some of degenerative eye damages need regeneration that is not gained by conventional procedures. Stem cells, such as mesenchymal stem cells, human embryonic stem cell-derived retinal pigmented epithelium, and inducible pluripotent stem cells, are now considered one of the most important and safe methods for regeneration of various damaged tissues or organs. However, how will stem cell therapy contribute to regeneration and overcome degenerative eye diseases? This review discusses the regenerative mechanisms, clinical applications, and advantages of different types of stem cells for restoring degenerative eye diseases. [ABSTRACT FROM AUTHOR]

Vitreous cysts represent uncommon ophthalmological conditions. Most patients are asymptomatic, but a minority may experience symptoms such as floaters or blurred vision. Here, we report the case of a 2‐year‐old girl who was incidentally found to have a vitreous cyst in her left eye during a routine outpatient clinic visit. The cyst was observed to move with eye movements, was pigmented, lobulated, and measured 3 mm in diameter. Our patient exhibited several systemic manifestations. We recommended regular follow‐up through clinical examinations and monitoring of the cyst using B‐scan ultrasound. [ABSTRACT FROM AUTHOR]

The visual pigments known as opsins are the primary molecular basis for colour vision in animals. Insects are among the most diverse of animal groups and their visual systems reflect a variety of life histories. The study of insect opsins in the fruit fly Drosophila melanogaster has led to major advances in the fields of neuroscience, development and evolution. In the last 25 years, research in D. melanogaster has improved our understanding of opsin genotype-phenotype relationships while comparative work in other insects has expanded our understanding of the evolution of insect eyes via gene duplication, coexpression and homologue switching. Even so, until recently, technology and sampling have limited our understanding of the fundamental mechanisms that evolution uses to shape the diversity of insect eyes. With the advent of genome editing and in vitro expression assays, the study of insect opsins is poised to reveal new frontiers in evolutionary biology, visual neuroscience, and animal behaviour. This article is part of the theme issue 'Understanding colour vision: molecular, physiological, neuronal and behavioural studies in arthropods'.

Animal models of disease are paramount to understand retinal development, the pathophysiology of eye diseases, and to study neurodegeneration using optical coherence tomography (OCT) data. In this study, we present a comprehensive normative database of retinal thickness in C57BL6/129S mice using spectral-domain OCT data. The database covers a longitudinal period of 16 months, from 1 to 16 months of age, and provides valuable insights into retinal development and changes over time. Our findings reveal that total retinal thickness decreases with age, while the thickness of individual retinal layers and layer aggregates changes in different ways. For example, the outer plexiform layer (OPL), photoreceptor inner segments (ILS), and retinal pigment epithelium (RPE) thickened over time, whereas other retinal layers and layer aggregates became thinner. Additionally, we compare the retinal thickness of wild-type (WT) mice with an animal model of Alzheimer's disease (3 x Tg-AD) and show that the transgenic mice exhibit a decrease in total retinal thickness compared to age-matched WT mice, with statistically significant differences observed at all evaluated ages. This normative database of retinal thickness in mice will serve as a reference for future studies on retinal changes in neurodegenerative and eye diseases and will further our understanding of the pathophysiology of these conditions. [ABSTRACT FROM AUTHOR]

In nearly all animals, light‐sensing mediated by opsin visual pigments is important for survival and reproduction. Eyeless light‐sensing systems, though vital for many animals, have received relatively less attention than forms with charismatic or complex eyes. Despite no single light‐sensing organ, the sea anemone Nematostella vectensis has 29 opsin genes and multiple light‐mediated behaviors throughout development and reproduction, suggesting a deceptively complex light‐sensing system. To characterize one aspect of this light‐sensing system, we analyzed larval swimming behavior at high wavelength resolution across the ultraviolet and visual spectrum. N. vectensis larvae respond to light at least from 315 to 650 nm, which is a broad sensitivity range even compared to many animals with complex eyes. Planktonic swimming is induced by ultraviolet (UV) and violet wavelengths until 420 nm. Between 420 and 430 nm a behavioral switch occurs where at wavelengths longer than 430 nm, larvae respond to light by swimming down. Swimming down toward the substrate is distinct from light avoidance, as animals do not exhibit positive or negative phototaxis at any wavelength tested. At wavelengths longer than 575 nm, animals in the water column take increasingly longer to respond and this behavior is more variable until 650 nm where larval response is no different from the dark, suggesting these longer wavelengths lie outside of their sensitivity range. Larval swimming is the only motile stage in the life history of N. vectensis, and increased planktonic swimming could lead to greater dispersal range in potentially damaging shallow environments with short‐wavelength light exposure. Longer wavelength environments may indicate more suitable substrates for metamorphosis into the polyp stage, where the individual will remain for the rest of its life. Future work will test whether this robust behavior is mediated by multiple opsins. [ABSTRACT FROM AUTHOR]

Damselfishes (Pomacentridae) are one of the most behaviourally diverse, colourful and species‐rich reef fish families. One remarkable characteristic of damselfishes is their communication in ultraviolet (UV) light. Not only are they sensitive to UV, they are also prone to have UV‐reflective colours and patterns enabling social signalling. Using more than 50 species, we aimed to uncover the evolutionary history of UV colour and UV vision in damselfishes. All damselfishes had UV‐transmitting lenses, expressed the UV‐sensitive SWS1 opsin gene, and most displayed UV‐reflective patterns and colours. We find evidence for several tuning events across the radiation, and while SWS1 gene duplications are generally very rare among teleosts, our phylogenetic reconstructions uncovered two independent duplication events: one close to the base of the most species‐rich clade in the subfamily Pomacentrinae, and one in a single Chromis species. Using amino acid comparisons, we found that known spectral tuning sites were altered several times in parallel across the damselfish radiation (through sequence change and duplication followed by sequence change), causing repeated shifts in peak spectral absorbance of around 10 nm. Pomacentrinae damselfishes expressed either one or both copies of SWS1, likely to further finetune UV‐signal detection and differentiation. This highly advanced and modified UV vision among damselfishes, in particular the duplication of SWS1 among Pomacentrinae, might be seen as a key evolutionary innovation that facilitated the evolution of the exuberant variety of UV‐reflectance traits and the diversification of this coral reef fish lineage. [ABSTRACT FROM AUTHOR]

Vision plays a vital biological role in organisms, which depends on the visual pigment molecules (opsin plus chromophore). The expansion or reduction of spectral channels in the organisms is determined by distinct opsin classes and copy numbers resulting from duplication or loss. Within Coleoptera, the superfamily Elateroidea exhibits a great diversity of morphological and physiological characteristics, such as bioluminescence, making this group an important model for opsin studies. While molecular and physiological studies have been conducted in Lampyridae and Elateridae, other families remain unexplored. Here, we reused transcriptome datasets from Elateroidea species, including members of Elateridae, Lampyridae, Phengodidae, Rhagophthalmidae, Cantharidae, and Lycidae, to detect the diversity of putative opsin genes in this superfamily. In addition, we tested the signature of sites under positive selection in both ultraviolet (UV)‐ and long‐wavelength (LW)‐opsin classes. Although the visual system in Elateroidea is considered simple, we observed events of duplication in LW‐ and UV‐opsin, as well as the absence of UV‐opsin in distinct families, such as larval Phengodidae individuals. We detected different copies of LW‐opsins that were highly expressed in the eyes of distinct tribes of fireflies, indicating the possible selection of each copy during the evolution of the sexual mating to avoid spectrum overlapping. In Elateridae, we found that the bioluminescent species had a distinct LW‐opsin copy compared with the non‐bioluminescent species, suggesting events of duplication and loss. The signature of positive selection showed only one residue associated with the chromophore binding site in the Elateroidea, which may produce a bathochromic shift in the wavelength absorption spectra in this family. Overall, this study brings important content and fills gaps regarding opsin evolution in Elateroidea. [ABSTRACT FROM AUTHOR]

Visual systems adapt to different light environments through several avenues including optical changes to the eye and neurological changes in how light signals are processed and interpreted. Spectral sensitivity can evolve via changes to visual pigments housed in the retinal photoreceptors through gene duplication and loss, differential and coexpression, and sequence evolution. Frogs provide an excellent, yet understudied, system for visual evolution research due to their diversity of ecologies (including biphasic aquatic-terrestrial life cycles) that we hypothesize imposed different selective pressures leading to adaptive evolution of the visual system, notably the opsins that encode the protein component of the visual pigments responsible for the first step in visual perception. Here, we analyze the diversity and evolution of visual opsin genes from 93 new eye transcriptomes plus published data for a combined dataset spanning 122 frog species and 34 families. We find that most species express the four visual opsins previously identified in frogs but show evidence for gene loss in two lineages. Further, we present evidence of positive selection in three opsins and shifts in selective pressures associated with differences in habitat and life history, but not activity pattern. We identify substantial novel variation in the visual opsins and, using microspectrophotometry, find highly variable spectral sensitivities, expanding known ranges for all frog visual pigments. Mutations at spectral-tuning sites only partially account for this variation, suggesting that frogs have used tuning pathways that are unique among vertebrates. These results support the hypothesis of adaptive evolution in photoreceptor physiology across the frog tree of life in response to varying environmental and ecological factors and further our growing understanding of vertebrate visual evolution. [ABSTRACT FROM AUTHOR]

Colour polymorphisms have long served as model systems in evolutionary studies and continue to inform about processes involved in the origin and dynamics of biodiversity. Modern sequencing tools allow for evaluating whether phenotypic differences between morphs reflect genetic differentiation rather than developmental plasticity, and for investigating whether polymorphisms represent intermediate stages of diversification towards speciation. We investigated phenotypic and genetic differentiation between two colour morphs of the butterfly Fabriciana adippe using a combination of ddRAD‐sequencing and comparisons of body size, colour patterns and optical properties of bright wing spots. The silvery‐spotted adippe form had larger and darker wings and reflected UV light, while the yellow cleodoxa form displayed more green scales and reflected very little UV, showcasing that they constitute distinct and alternative integrated phenotypes. Genomic analyses revealed genetic structuring according to source population, and to colour morph, suggesting that the phenotypic differentiation reflects evolutionary modifications. We report 17 outlier loci associated with colour morph, including ultraviolet‐sensitive visual pigment (UVRh1), which is associated with intraspecific communication and mate choice in butterflies. Together with the demonstration that the wings of the adippe (but essentially not the cleodoxa) morph reflect UV light, that UV reflectance is higher in females than males and that morphs differ in wing size, this suggests that these colour morphs might represent genetically integrated phenotypes, possibly adapted to different microhabitats. We propose that non‐random mating might contribute to the differentiation and maintenance of the polymorphism. [ABSTRACT FROM AUTHOR]

A delicate balance between photon absorption for vision and the protection of photoreceptors from light damage is pivotal for ocular health. This equilibrium is governed by the lightabsorbing 11-cis-retinylidene chromophore of visual pigments, which, upon bleaching, transforms into all-trans-retinal and undergoes regeneration through an enzymatic pathway, named the visual cycle. Chemical side reactions of retinaldehyde during the recycling process can generate by-products that may result in a depletion of retinoids. In our study, we have clarified the crucial roles played by melanin pigmentation and the retinoid transporter STRA6 in preventing this loss and preserving the integrity of the visual cycle. Our experiments initially confirmed that consecutive green and blue light bleaching of isolated bovine rhodopsin produced 9-cis and 13-cis retinal. The same unusual retinoids were found in the retinas of mice exposed to intense light, with elevated concentrations observed in albino mice. Examining the metabolic fate of these visual cycle byproducts revealed that 9-cis-retinal, but not 13-cis-retinal, was recycled back to all-trans-retinal through an intermediate called isorhodopsin. However, investigations in Stra6 knockout mice unveiled that the generation of these visual cycle byproducts correlated with a light-induced loss of ocular retinoids and visual impairment. Collectively, our findings uncover important novel aspects of visual cycle dynamics, with implications for ocular health and photoreceptor integrity. [ABSTRACT FROM AUTHOR]

Intraspecific functional variation is critical for adaptation to rapidly changing environments. For visual opsins, functional variation can be characterized in vitro and often reflects a species' ecological niche but is rarely considered in the context of intraspecific variation or the impact of recent environmental changes on species of cultural or commercial significance. Investigation of adaptation in postglacial lakes can provide key insight into how rapid environmental changes impact functional evolution. Here, we report evidence for molecular adaptation in vision in 2 lineages of Nearctic fishes that are deep lake specialists: ciscoes and deepwater sculpin. We found depth-related variation in the dim-light visual pigment rhodopsin that evolved convergently in these 2 lineages. In vitro characterization of spectral sensitivity of the convergent deepwater rhodopsin alleles revealed blue-shifts compared with other more widely distributed alleles. These blue-shifted rhodopsin alleles were only observed in deep clear postglacial lakes with underwater visual environments enriched in blue light. This provides evidence of remarkably rapid and convergent visual adaptation and intraspecific functional variation in rhodopsin. Intraspecific functional variation has important implications for conservation, and these fishes are of conservation concern and great cultural, commercial, and nutritional importance to Indigenous communities. We collaborated with the Saugeen Ojibway Nation to develop and test a metabarcoding approach that we show is efficient and accurate in recovering the ecological distribution of functionally relevant variation in rhodopsin. Our approach bridges experimental analyses of protein function and genetics-based tools used in large-scale surveys to better understand the ecological extent of adaptive functional variation. [ABSTRACT FROM AUTHOR]

Photoreceptor cells in the vertebrate retina have a highly compartmentalized morphology for efficient phototransduction and vision. Rhodopsin, the visual pigment in rod photoreceptors, is densely packaged into the rod outer segment sensory cilium and continuously renewed through essential synthesis and trafficking pathways housed in the rod inner segment. Despite the importance of this region for rod health and maintenance, the subcellular organization of rhodopsin and its trafficking regulators in the mammalian rod inner segment remain undefined. We used super-resolution fluorescence microscopy with optimized retinal immunolabeling techniques to perform a single molecule localization analysis of rhodopsin in the inner segments of mouse rods. We found that a significant fraction of rhodopsin molecules was localized at the plasma membrane, at the surface, in an even distribution along the entire length of the inner segment, where markers of transport vesicles also colocalized. Thus, our results collectively establish a model of rhodopsin trafficking through the inner segment plasma membrane as an essential subcellular pathway in mouse rod photoreceptors. Photoreceptor cells of the retina are maintained through a complex protein trafficking network. This study uses quantitative super-resolution microscopy to reveal the trafficking of the essential visual pigment rhodopsin in the inner segment region of rod photoreceptors. [ABSTRACT FROM AUTHOR]

In many organisms, sensory abilities develop and evolve according to the changing demands of navigating, foraging, and communication across different environments and life stages. Teleost fish inhabit heterogeneous light environments and exhibit a large diversity in visual system properties among species. Cichlids are a classic example of this diversity; visual system variation is generated by different tuning mechanisms that involve both genetic factors and phenotypic plasticity. Here, we document the developmental progression of visual pigment gene expression in Lake Victoria cichlids and test if these patterns are influenced by variation in light conditions. We reared two sister species of Pundamilia to adulthood in two distinct visual conditions that resemble the light environments that they naturally inhabit in Lake Victoria. We also included interspecific first‐generation hybrids. We focused on the four opsins that are expressed in Pundamilia adults (using real‐time quantitative polymerase chain reaction (RT‐qPCR)) (SWS2B, SWS2A, RH2A, and LWS) at 17 time points. We find that opsin expression profiles progress from shorter‐wavelength sensitive opsins to longer‐wavelength sensitive opsins with increasing age, in both species and their hybrids. The developmental trajectories of opsin expression also responded plastically to the visual conditions. Developmental and environmental plasticity in opsin expression may provide an important stepping stone in the evolution of cichlid visual system diversity. Research highlights: In Lake Victoria cichlid fish, expression levels of opsin genes (encoding visual pigments) differ between developmental stages and between experimental light treatments. This plasticity may contribute to the evolution of cichlid visual system diversity. [ABSTRACT FROM AUTHOR]

Driven by the energy of a photon, the visual pigments in rod and cone photoreceptor cells isomerize 11-cis-retinal to the all-trans configuration. This photochemical reaction initiates the signal transduction pathway that eventually leads to the transmission of a visual signal to the brain and leaves the opsins insensitive to further light stimulation. For the eye to restore light sensitivity, opsins require recharging with 11-cis-retinal. This trans-cis back conversion is achieved through a series of enzymatic reactions composing the retinoid (visual) cycle. Although it is evident that the classical retinoid cycle is critical for vision, the existence of an adjunct pathway for 11-cis-retinal regeneration has been debated for many years. Retinal pigment epithelium (RPE)-retinal G protein-coupled receptor (RGR) has been identified previously as a mammalian retinaldehyde photoisomerase homologous to retinochrome found in invertebrates. Using pharmacological, genetic, and biochemical approaches, researchers have now established the physiological relevance of the RGR in 11-cis-retinal regeneration. The photoisomerase activity of RGR in the RPE and Müller glia explains how the eye can remain responsive in daylight. In this review, we will focus on retinoid metabolism in the eye and visual chromophore regeneration mediated by RGR.

Background. Anti-vascular endothelial growth factor (anti-VEGF) therapy via intravitreal injection is an effective treatment for patients with abnormal ocular neovascularization, such as age-related macular degeneration (AMD) and diabetic macular edema (DME). However, prolonged and frequent anti-VEGF treatment is associated with a risk of local and systemic adverse events, including geographic atrophy, cerebrovascular disease, and death. Furthermore, some patients do not adequately respond to anti-VEGF therapy. Hypoxia-inducible factor (HIF) is a transcription factor that controls the expression of hypoxia-responsive genes involved in angiogenesis, inflammation, and metabolism. The HIF/VEGF pathway plays an important role in neovascularization, and the inhibition of HIF activation could be an effective biomolecular target for neovascular diseases. The demand for disease prevention or treatment using functional foods such as superfoods has increased in recent years. Few reports to date have focused on the antineovascular effects of superfoods in the retinal pigment epithelium (RPE). In light of the growing demand for functional foods, we aimed to find novel HIF inhibitors from superfoods worked in RPE cells, which could be an adjuvant for anti-VEGF therapy. Methods. Seven superfoods were examined to identify novel HIF inhibitor candidates using luciferase assay screening. We used the human RPE cell line ARPE-19 and fetal human RPE (fhRPE) to investigate the biomolecular actions of novel HIF inhibitors using quantitative PCR and western blotting. Results. Under CoCl2-induced pseudohypoxic condition and 1% oxygen hypoxic incubation, camu-camu (Myrciaria dubia) showed HIF inhibitory effects determined by luciferase assays. Camu-camu downregulated HIF-1α and VEGFA mRNA expressions in a concentration-dependent manner. Camu-camu also inhibited HIF-1α protein expressions, and its inhibitory effect was greater than that of vitamin C, which is present at high levels in camu-camu. Conclusion. The camu-camu extract suppressed the activation of HIF and VEGF in RPE cells. This could assist anti-VEGF therapy in patients with abnormal ocular neovascularization. [ABSTRACT FROM AUTHOR]

Background and Aims: Ophthalmological abnormalities have been reported in hereditary transthyretin‐related amyloidosis (ATTRv, v for variant) but not in wild‐type transthyretin‐related amyloidosis (ATTRwt). Methods: Patients with ATTRwt, ATTRv, and light chain amyloidosis (AL) and healthy subjects (controls) underwent complete eye examination, including optical coherence tomography (OCT), OCT angiography (OCTA), and in vivo corneal confocal microscopy (CCM). Results: Seventeen ATTRwt, nine ATTRv, two ATTRv carriers, and seven AL patients were enrolled. Compared with other groups, ATTRwt patients had 10 letters lower visual acuity and a higher prevalence of glaucoma, cataract, and retinal pigment epithelium alterations. In the whole group of patients, especially in ATTRwt, we observed (1) a reduced corneal nerve fiber length and more tortuous stromal nerves at CCM, (2) a reduced macular volume and peripapillary nerve fiber layer thickness at OCT, and (3) impairment of peripapillary and macular vascularization at OCTA. Interpretation: Ophthalmological abnormalities are common in ATTRwt, significantly impairing visual acuity. Noninvasive imaging modalities allow for the identification of small nerve fibers and small vessel damage, which may represent further warning signs for early diagnosis of ATTRwt. [ABSTRACT FROM AUTHOR]

Investigations of the molecular mechanisms behind detection of short, and particularly ultraviolet, wavelengths in arthropods have relied heavily on studies from insects due to the relative ease of heterologous expression of modified opsin proteins in model organisms like Drosophila. However, species outside of the Insecta can provide information on mechanisms for spectral tuning as well as the evolutionary history of pancrustacean visual pigments. Here we investigate the basis of spectral tuning in malacostracan short wavelength sensitive (SWS) opsins using phylogenetic comparative methods. Tuning sites that may be responsible for the difference between ultraviolet (UV) and violet visual pigment absorbance in the Malacostraca are identified, and the idea that an amino acid polymorphism at a single site is responsible for this shift is shown to be unlikely. Instead, we suggest that this change in absorbance is accomplished through multiple amino acid substitutions. On the basis of our findings, we conducted further surveys to identify spectral tuning mechanisms in the order Stomatopoda where duplication of UV opsins has occurred. Ancestral state reconstructions of stomatopod opsins from two main clades provide insight into the amino acid changes that lead to differing absorption by the visual pigments they form, and likely contribute the basis for the wide array of UV spectral sensitivities found in this order. [ABSTRACT FROM AUTHOR]

Optogenetics is a technology using light-sensitive proteins to control signaling pathways and physiological processes in cells and organs and has been applied in neuroscience, cardiovascular sciences, and many other research fields. Most commonly used optogenetic actuators are sensitive to blue and green light, but red-light activation would allow better tissue penetration and less phototoxicity. Cyp27c1 is a recently deorphanized cytochrome P450 enzyme that converts vitamin A1 to vitamin A2, thereby red-shifting the spectral sensitivity of visual pigments and enabling near-infrared vision in some aquatic species. Here, we investigated the ability of Cyp27c1-generated vitamin A2 to induce a shift in spectral sensitivity of the light-gated ion channel Channelrhodopsin-2 (ChR2) and its red-shifted homolog ReaChR. We used patch clamp to measure photocurrents at specific wavelengths in HEK 293 cells expressing ChR2 or ReaChR. Vitamin A2 incubation red-shifted the wavelength for half-maximal currents (λ50%) by 6.8 nm for ChR2 and 12.4 nm for ReaChR. Overexpression of Cyp27c1 in HEK 293 cells showed mitochondrial localization, and HPLC analysis showed conversion of vitamin A1 to vitamin A2. Notably, the λ50% of ChR2 photocurrents was red-shifted by 10.5 nm, and normalized photocurrents at 550 nm were about twofold larger with Cyp27c1 expression. Similarly, Cyp27c1 shifted the λ50% of ReaChR photocurrents by 14.3 nm and increased normalized photocurrents at 650 nm almost threefold. Since vitamin A2 incubation is not a realistic option for in vivo applications and expression of Cyp27c1 leads to a greater red-shift in spectral sensitivity, we propose co-expression of this enzyme as a novel strategy for red-shifted optogenetics. [ABSTRACT FROM AUTHOR]

Background: Dopamine has been suggested to be a stop signal for eye growth and affects the development of myopia. Acupuncture is known to increase dopamine secretion and is widely used to treat myopia clinically. Objective: The aim of this study was to determine if acupuncture inhibits myopia progression in form deprived Syrian hamsters by inducing rises in dopamine content that in turn suppress inflammasome activation. Methods: Acupuncture was applied at LI4 and Taiyang every other day for 21 days. The levels of molecules associated with the dopamine signaling pathway, inflammatory signaling pathway and inflammasome activation were determined. A dopamine agonist (apomorphine) was used to evaluate if activation of the dopaminergic signaling pathway suppresses myopia progression by inhibiting inflammasome activation in primary retinal pigment epithelial (RPE) cells. A dopamine receptor 1 (D1R) inhibitor (SCH39166) was also administered to the hamsters. Results: Acupuncture inhibited myopia development by increasing dopamine levels and activating the D1R signaling pathway. Furthermore, we also demonstrated that nucleotide-binding oligomerization domain (NOD)-, leucine-rich repeat (LRR)- and pyrin domain-containing protein 3 (NLR) family pyrin domain-containing 3 (NLRP3) inflammasome activation was inhibited by activation of the D1R signaling pathway. Conclusion: Our findings suggest that acupuncture inhibits myopia development by suppressing inflammation, which is initiated by activation of the dopamine—D1R signaling pathway. [ABSTRACT FROM AUTHOR]

Enhancers function with a basal promoter to control the transcription of target genes. Enhancer regulatory activity is often studied using reporter-based transgene assays. However, unmatched results have been reported when selected enhancers are silenced in situ. In this study, using genomic deletion analysis in mice, we investigated the roles of two previously identified enhancers and the promoter of the Rho gene that codes for the visual pigment rhodopsin. The Rho gene is robustly expressed by rod photoreceptors of the retina, and essential for the subcellular structure and visual function of rod photoreceptors. Mutations in RHO cause severe vision loss in humans. We found that each Rho regulatory region can independently mediate local epigenomic changes, but only the promoter is absolutely required for establishing active Rho chromatin configuration and transcription and maintaining the cell integrity and function of rod photoreceptors. To our surprise, two Rho enhancers that enable strong promoter activation in reporter assays are largely dispensable for Rho expression in vivo. Only small and age-dependent impact is detectable when both enhancers are deleted. Our results demonstrate context-dependent roles of enhancers and highlight the importance of studying functions of cis-regulatory regions in the native genomic context. [ABSTRACT FROM AUTHOR]

This study aimed to investigate the prevalence of color vision deficiencies (CVDs) and determine whether carriers could be detected by analyzing the visual pigment genes. Materials and Methods: The data of students who underwent routine CVD screening using the Ishihara color test in Kaohsiung, Southern Taiwan were analyzed. Furthermore, the DNA samples of 80 randomly selected females and four obligate carriers were analyzed. The most upstream genes, downstream genes, and the most downstream genes in the red/green pigment gene arrays were amplified separately using polymerase chain reaction (PCR), and exon 5 of each gene was analyzed. The prevalence of congenital red–green CVD in this study was 3.46% in males and 0.14% in females. The PCR analysis of the first gene, downstream gene, and last gene revealed normal patterns in 73 normal cases. Seven unusual patterns were detected in two proton carriers and five deutan carriers. Among the randomly selected females, 8.8% (7/80) were CVD carriers. The prevalence of CVD among male Taiwanese students in this study was 3.46%. Female carriers of congenital CVD can be identified by molecular analysis of the visual pigment genes. The proportion of CVD carriers among the randomly selected females was 8.8%, which was slightly higher than expected and further studies are warranted. [ABSTRACT FROM AUTHOR]

Background: Anthropometry facilitates the evaluation of risks associated with reduced macular pigment optical density (MPOD). Objectives: To investigate the predictors and anthropometric indices associated with MPOD in healthy adult in Arab population. Design: This is a cross-sectional study. Methods: The MPOD was measured at 0.5° from fovea using a heterochromatic flicker photometer. Healthy participants aged between 20 and 40 years were recruited. The study evaluated the following data of the participants: height, weight, body mass index, body fat percentage, basal metabolic rate, visceral fat level, muscle mass, bone mineral content, and percentage of protein and body water. The correlation between MPOD with anthropometrics and demographic data was evaluated using Spearman's correlation test. The differences among genders were investigated using the Mann–Whitney U test. The smoking effect on MPOD was analyzed using the Friedman test. Results: In all, 143 participants were recruited. The median ± interquartile range was calculated for age (23 ± 4 years), visual acuity (0.00 ± 0.00 logMAR), and MPOD (0.41 ± 0.18). The average MPOD was higher in males than in females but it was not statistically significant (p > 0.05); on the other hand, they were statistically significantly different in most of the anthropometric data. A significant relationship was found between MPOD and percentage of body fat, protein, and body water (r = 0.30, p < 0.05). The observed median MPOD value was higher in this study than that found in previous studies in white populations, but lower than that found in studies investigating Asian populations. Conclusion: One of the most important risk factors of age-related macular degeneration is associated with a relative absence of macular pigment. This study brought into focus percentage of protein and body water for further studies as well as the well-established links with body fat and obesity. Unknown predictors of MPOD remain uncovered. The study also provided first report on normative values of MPOD for Arab population and confirmed the differences from other ethnicities. [ABSTRACT FROM AUTHOR]

Rods and cones are the photoreceptor cells containing the visual pigment proteins that initiate visual phototransduction following the absorption of a photon. Photon absorption induces the photochemical transformation of a visual pigment, which results in the sequential formation of distinct photo-intermediate species on the femtosecond to millisecond timescales, whereupon a visual electrical signal is generated and transmitted to the brain. Time-resolved spectroscopic studies of the rod and cone photo-intermediaries enable the detailed understanding of initial events in vision, namely the key differences that underlie the functionally distinct scotopic (rod) and photopic (cone) visual systems. In this paper, we review our recent ultrafast (picoseconds to milliseconds) transient absorption studies of rod and cone visual pigments with a detailed comparison of the transient molecular spectra and kinetics of their respective photo-intermediaries. Key results include the characterization of the porphyropsin (carp fish rhodopsin) and human green-cone opsin photobleaching sequences, which show significant spectral and kinetic differences when compared against that of bovine rhodopsin. These results altogether reveal a rather strong interplay between the visual pigment structure and its corresponding photobleaching sequence, and relevant outstanding questions that will be further investigated through a forthcoming study of the human blue-cone visual pigment are discussed. [ABSTRACT FROM AUTHOR]

Cave-adapted animals provide a unique opportunity to study the evolutionary mechanisms underlying phenotypic, metabolic, behavioral, and genetic evolution in response to cave environments. The Mexican tetra (Astyanax mexicanus) is considered a unique model system as it shows both surface and cave-dwelling morphs. To date, at least 33 different cave populations have been identified, with phylogenetic studies suggesting an origin from at least two independent surface lineages, thereby providing a unique opportunity to study parallel evolution. In the present study, we carried out the most exhaustive phylogeographic study of A. mexicanus to date, including cave and surface localities, using two mitochondrial markers (cytochrome b (cyt b) and cytochrome c oxidase subunit I (COI)) and nuclear rhodopsin visual pigment (rho). Additionally, we inferred the molecular evolution of rho within the two contrasting environments (cave and surface) and across three geographic regions (Sierra de El Abra, Sierra de Guatemala, and Micos). In total, 267 individuals were sequenced for the two mitochondrial fragments and 268 individuals were sequenced for the rho visual pigment from 22 cave and 46 surface populations. Phylogeographic results based on the mitochondrial data supported the two-lineage hypothesis, except for the Pachón and Chica caves, whose introgression has been largely documented. The Sierra de El Abra region depicted the largest genetic diversity, followed by the Sierra de Guatemala region. Regarding the phylogeographic patterns of rho, we recovered exclusive haplogroups for the Sierra de El Abra (Haplogroup I) and Sierra de Guatemala regions (Haplogroup IV). Moreover, a 544 bp deletion in the rho gene was observed in the Escondido cave population from Sierra de Guatemala, reducing the protein from seven to three intramembrane domains. This change may produce a loss-of-function (LOF) but requires further investigation. Regarding nonsynonymous (dN) and synonymous (dS) substitution rates (omega values ω), our results revealed the prevailing influence of purifying selection upon the rho pigment for both cave and surface populations (ω<1), but relaxation at the El Abra region. Notably, in contrast to the other two regions, we observed an increase in the number of dN mutations for Sierra de El Abra. However, given that a LOF was exclusively identified in the Sierra de Guatemala region, we cannot dismiss the possibility of a pleiotropic effect on the Rho protein. [ABSTRACT FROM AUTHOR]

The article "Tribute to Dr. William L. Pak" published in the Journal of Neurogenetics reflects on Dr. Pak's pioneering work in neurogenetics, particularly in the field of phototransduction. Dr. Pak's transition from particle physics to biology, and his groundbreaking use of genetics to study phototransduction in Drosophila, laid the foundation for the emerging field of neurogenetics. Despite initial skepticism, Dr. Pak's research ultimately revealed the involvement of a signaling cascade of proteins in photoreceptor transduction in both vertebrate and invertebrate species. The article highlights Dr. Pak's enthusiasm, energy, and commitment to unraveling the mysteries of nature through genetics. [Extracted from the article]

Animal opsins, light-sensitive G protein-coupled receptors, have been used for optogenetic tools to control G protein-dependent signaling pathways. Upon G protein activation, the Gα and Gβγ subunits drive different intracellular signaling pathways, leading to complex cellular responses. For some purposes, Gα- and Gβγ-dependent signaling needs to be separately modulated, but these responses are simultaneously evoked due to the 1:1 stoichiometry of Gα and Gβγ Nevertheless, we show temporal activation of G protein using a self-inactivating invertebrate opsin, Platynereis c-opsin1, drives biased signaling for Gβγ-dependent GIRK channel activation in a light-dependent manner by utilizing the kinetic difference between Gβγ-dependent and Gα-dependent responses. The opsin-induced transient Gi/o activation preferentially causes activation of the kinetically fast Gβγ-dependent GIRK channels rather than slower Gi/oα-dependent adenylyl cyclase inhibition. Although similar Gβγ-biased signaling properties were observed in a self-inactivating vertebrate visual pigment, Platynereis c-opsin1 requires fewer retinal molecules to evoke cellular responses. Furthermore, the Gβγ-biased signaling properties of Platynereis c-opsin1 are enhanced by genetically fusing with RGS8 protein, which accelerates G protein inactivation. The self-inactivating invertebrate opsin and its RGS8-fusion protein can function as optical control tools biased for Gβγ-dependent ion channel modulation. [ABSTRACT FROM AUTHOR]

Vertebrate rods and cones operate over a wide range of ambient illumination, which is provided by light adaptation mechanisms regulating the sensitivity and speed of the phototransduction cascade. Three calcium-sensitive feedback loops are well established in both rods and cones: acceleration of the quenching of a lightactivated visual pigment and cGMP synthesis by guanylate cyclase, and increased affinity of ion channels for cGMP. Accumulating evidence suggests that the molecular mechanisms of light adaptation are more complex. While investigating these putative mechanisms, we discovered a novel phenomenon, observing that the recovery of light sensitivity in rods after turning off non-saturating adaptive light can take tens of seconds. Moreover, after a formal return of the membrane current to the dark level, cell sensitivity to the stimuli remains decreased for a further 1–2 min. We termed this phenomenon of prolonged photoreceptor desensitization ‘adaptation memory’ (of previous illumination) and the current study is focused on its detailed investigation in rods and an attempt to find the same phenomenon in cones. In rods, we have explored the dependencies of this phenomenon on adapting conditions, specifically, the intensity and duration of adapting illumination. Additionally, we report that fish and frog red-sensitive cones possess similar features of adaptation memory, such as a drop in sensitivity just after the steps of bright light and slow sensitivity recovery. However, we have found that the rate of this process and its nature are not the same as in rods. Our results indicate that the nature of the temporary drop in the sensitivity in rods and cones after adapting steps of light is different. In the rods, adaptation memory could be attributed to the existence of long-lasting modifications of the components of the phototransduction cascade after adapting illumination. In cones, the observed form of the adaptation memory seems to be due to the sensitivity drop caused by a decrease in the availability of the visual pigment, that is, by bleaching. [ABSTRACT FROM AUTHOR]

Background: Diabetic retinopathy (DR) is a common complication of diabetes with nocuous effects on patients' eye health, typically accompanies by excessive inflammation and oxidative stress. Insulin‐like growth factor‐2 messenger RNA‐binding protein 3 (IGF2BP3) was engaged with inflammation, whereas its precise role in the DR process was unclear. And enhanced lncRNA metastasis‐associated lung adenocarcinoma transcript 1 (MALAT1) and decreased ascorbic acid (AA) were also found in DR. This study was to explore the regulatory role and mechanism of IGF2BP3, MALAT1 and AA in the high glucose (HG)‐induced retinal pigment epithelial (RPE) cell injury. Methods: ARPE‐19 cells were treated with HG to establish the in vitro RPE cell injury model. The mRNA and protein levels of the gene were evaluated by qRT‐PCR or Western blot. Immunofluorescence detected the translocation condition of the p65 protein. Inflammatory factor levels were detected by ELISA assays. Apoptosis was detected by flow cytometry. The binding interaction of IGF2BP3 and MALAT1 was validated by RIP‐qPCR assays. Results: In HG‐induced RPE cell injury, IGF2BP3 expression, inflammatory response and apoptosis were enhanced. Next, the IGF2BP3 activated the NF‐κB signalling to promote the RPE cell injury development. MALAT1 could directly bind with IGF2BP3 and up‐regulate its expression. In addition, AA ameliorated the HG‐induced RPE cell injury through the regulation of MALAT1. Conclusion: Ascorbic acid ameliorated HG‐induced RPE cell injury by repressing the NF‐κB signalling pathway via modulating the MALAT1/IGF2BP3 axis. [ABSTRACT FROM AUTHOR]

The visual ecology of early mammals remains poorly resolved. Studies of ancestral photopigments suggest an ancient transition from nocturnal to more crepuscular conditions. By contrast, the phenotypic shifts following the split of monotremes and therians—which lost their SWS1 and SWS2 opsins, respectively—are less clear. To address this, we obtained new phenotypic data on the photopigments of extant and ancestral monotremes. We then generated functional data for another vertebrate group that shares the same photopigment repertoire as monotremes: the crocodilians. By characterizing resurrected ancient pigments, we show that the ancestral monotreme underwent a dramatic acceleration in its rhodopsin retinal release rate. Moreover, this change was likely mediated by three residue replacements, two of which also arose on the ancestral branch of crocodilians, which exhibit similarly accelerated retinal release. Despite this parallelism in retinal release, we detected minimal to moderate changes in the spectral tuning of cone visual pigments in these groups. Our results imply that ancestral forms of monotremes and crocodilians independently underwent niche expansion to encompass quickly changing light conditions. This scenario—which accords with reported crepuscular activity in extant monotremes—may help account for their loss of the ultraviolet-sensitive SWS1 pigment but retention of the blue-sensitive SWS2. [ABSTRACT FROM AUTHOR]

Extreme environments, such as Antarctic habitats, present major challenges for many biological processes. Antarctic icefishes (Crynotothenioidea) represent a compelling system to investigate the molecular basis of adaptation to cold temperatures. Here, we explore how the sub-zero habitats of Antarctic icefishes have impacted rhodopsin (RH1) function, the temperature-sensitive dim-light visual pigment found in rod photoreceptors. Using likelihood models and ancestral reconstruction, we find that accelerated evolutionary rates in icefish RH1 underlie unique amino acid mutations absent from other deep-dwelling fishes, introduced before (S160A) and during (V259M) the onset of modern polar conditions. Functional assays reveal that these mutations red-shift rhodopsin spectral absorbance, consistent with spectral irradiance under sea ice. These mutations also lower the activation energy associated with retinal release of the light-activated RH1, and accelerate its return to the dark state, likely compensating for a cold-induced decrease in kinetic rates. These are adaptations in key properties of rhodopsin that mediate rod sensitivity and visual performance in the cold dark seas of the Antarctic. [ABSTRACT FROM AUTHOR]

Photic niche shifts of mammals are associated with changing visual capabilities, primarily mediated by three visual pigments, two (SWS1 and M/LWS) of them for color vision and rhodopsin (RH1) for dim-light vision. To further elucidate molecular mechanisms of mammalian visual adaptations to different light environments, a systematic study incorporating evolutionary analyses across diverse groups and in vitro assays have been carried out. Here, we collected gene sequences for the three opsins from 220 species covering all major mammalian clades. After screening for cone opsin gene losses, we estimated selective pressures on each of the three genes and compared the levels of selection experienced by species living in bright- and dim-light environments. SWS1 pigment is shown to experience accelerated evolution in species living in bright-light environments as has RH1 in aquatic cetaceans, indicating potential shifts for ecological adaptations. To further elucidate the functional mechanisms for these two pigments, we then carried out site-directed mutagenesis in representative taxa. For SWS1, violet and ultraviolet sensitivities in the pika and mouse are mainly affected by substitutions at the critical sites 86 and 93, which have strong epistatic interaction. For RH1, the phenotypic difference between the sperm whale and bovine sequences is largely contributed by a substitution at site 195, which could be critical for dim-light sensation for deep-diving species. Different evolutionary patterns for the visual pigments have been identified in mammals, which correspond to photic niches, although additional phenotypic assays are still required to fully explain the functional mechanisms. [ABSTRACT FROM AUTHOR]

Kochiae Fructus, the ripe fruit of Kochia scoparia , is a traditional Chinese medicine commonly used to treat eye discomforts and vision problems. Although Kochiae Fructus is mentioned in many classical Chinese medical texts, its protective effects and the roles of its active phytochemicals in eye treatment still lack scientific exploration. This study aimed to clarify the protective effects and identify the active fractions and compounds of Kochiae Fructus against oxidative stress-induced retinal pigment epithelium (RPE) cell death. Liquid-liquid partitioning was employed to prepare active fractions. Silica gel, RP-18, and Sephadex™ LH-20 gels were used as stationary phases to purify the compounds through column chromatography. Cell models were established by treating ARPE-19 (RPE cell line) with hydrogen peroxide (H₂O₂) and tert-butyl hydroperoxide (TBHP), respectively. The methanol aqueous fraction from ethyl acetate-soluble extract (KSEM) alleviated oxidant-induced RPE cell death in a dose-dependent manner and activated the Nrf2/HO-1 pathway, a critical defense mechanism against oxidative damage. The isolated flavonols in fraction KSEM, hyperoside, quercetin, and kaempferol, reduced oxidant-induced cell mortality, with quercetin showing the strongest effect. Moreover, combination treatment revealed that hyperoside and kaempferol synergistically enhanced the protective effects of quercetin, making the combined treatment more efficient than quercetin alone. The protective effects of Kochiae Fructus against oxidative damage in RPE cell was validated with the KSEM fraction. The compound quercetin was identified as the important contributor. However, the synergistic effect of the hyperoside, quercetin, and kaempferol mixture may play a dominant role in the protective action of Kochiae Fructus. Overall, these findings highlight the potential of Kochiae Fructus and its flavonol mixture as a basis for developing treatments targeting ocular diseases associated with oxidative damage in retina. [Display omitted] • Kochiae Fructus active fraction attenuates oxidative stress-induced RPE cell death by activating the Nrf2/HO-1 pathway. • Key compounds identified: quercetin, hyperoside, and kaempferol. • Synergistic effects of flavonols enhance protective action. [ABSTRACT FROM AUTHOR]

Spectral tuning of visual pigments often facilitates adaptation to new environments, and it is intriguing to study the visual ecology of pelagic sharks with secondarily expanded habitats. The whale shark, which dives into the deep sea of nearly 2,000 meters besides near-surface filter feeding, was previously shown to possess the ‘blueshifted’ rhodopsin (RHO), which is a signature of deep-sea adaptation. In this study, our spectroscopy of recombinant whale shark RHO mutants revealed that this blue shift is caused dominantly by an unprecedented spectral tuning site 94. In humans, the mutation at the site causes congenital stationary night blindness (CSNB) by reducing the thermal stability of RHO. Similarly, the RHO of deep-diving whale shark has reduced thermal stability, which was experimentally shown to be achieved by site 178 and 94. RHOs having the natural substitution at site 94 are also found in some Antarctic fishes, suggesting that the blue shift by the substitution at the CSNB site associated with the reduction in thermal stability might be allowed in cold-water deep-sea habitats. [ABSTRACT FROM AUTHOR]

Background. Age-related macular degeneration (AMD) is the leading cause of serious vision loss in the elderly. Regulating microRNA (miRNA) gene expression offers exciting new avenues for treating AMD. This study aimed to investigate whether miRNAs and their target genes play an antiapoptotic role during oxidative stress-induced apoptosis of retinal pigment epithelial (RPE) cells via mini-αA. Methods. ARPE-19 cells were treated with 3.5 mM NaIO3 for 48 h to establish a retinal degeneration model. Cells were treated with mini-αA (10, 15, and 20 μM) for 4 h. miR-155-5p was knocked down and overexpressed. Cell viability and apoptosis were measured using the Cell Counting Kit-8 assay and flow cytometry, respectively. The reactive oxygen species level was detected by flow cytometry. miR-155-5p target genes were predicted via bioinformatics. Gene Ontology and Kyoto Encyclopedia of Genes and Genomes analyses were performed for miR-155-5p target genes. A quantitative real-time polymerase chain reaction was performed to detect miRNAs and cell cycle-related target genes. Western blotting was performed to measure the levels of apoptotic pathway genes encoding Bcl-2, Bax, cleaved caspase-3, and cyclin-dependent kinase 2 (CDK2). Dual-luciferase reporter gene assay was performed to verify the targeted binding relationship between miR-155-5p and CDK2. Results. NaIO3 can induce oxidative damage and promote apoptosis. Conversely, mini-αA had inhibitory effects and could reverse the oxidative damage and apoptosis triggered by NaIO3 in the retinal degeneration model. The expression of miR-155-5p was upregulated in cells treated with NaIO3 and was downregulated after mini-αA treatment. Furthermore, miR-155-5p can target the following cell cycle-related and proliferation-related genes: CDK2, CDK4, CCND1, and CCND2. Moreover, our study indicated that miR-155-5p was involved in the antioxidative damage and antiapoptotic effects of mini-αA via CDK2 regulation. Conclusions. miR-155-5p promotes the antioxidative damage and antiapoptotic effects of mini-αA during oxidative stress-induced apoptosis of RPE cells via CDK2 regulation. This study provides a new therapeutic target for AMD. [ABSTRACT FROM AUTHOR]