Rod Opsin Research Articles

The Zpr-3 Antibody Recognizes the 320-354 Region of Rho and Labels Both Rods and Green Cones in Zebrafish.

Retinal markers with high quality and specificity are important for the observation of pathologic changes of retinal cells during retinal development, degeneration, and regeneration. The zpr-3 antibody is widely used to label rods in zebrafish, but the exact antigen is still unknown. In this study, we provided evidence to demonstrate that the antigen gene of zpr-3 is rho, which encodes the rod opsin, and the exact epitope of zpr-3 is the 320-354 region of Rho protein. More importantly, our immunofluorescence assays indicated that zpr-3 labels both the outer segments of rods and green cones on zebrafish retinal sections, probably due to the cross-reaction with the green-cone opsin. Our work is valuable for the scientific community to interpret the experimental data involving the zpr-3 antibody.

Modulating signalling lifetime to optimise a prototypical animal opsin for optogenetic applications

Animal opsins are light activated G-protein-coupled receptors, capable of optogenetic control of G-protein signalling for research or therapeutic applications. Animal opsins offer excellent photosensitivity, but their temporal resolution can be limited by long photoresponse duration when expressed outside their native cellular environment. Here, we explore methods for addressing this limitation for a prototypical animal opsin (human rod opsin) in HEK293T cells. We find that the application of the canonical rhodopsin kinase (GRK1)/visual arrestin signal termination mechanism to this problem is complicated by a generalised suppressive effect of GRK1 expression. This attenuation can be overcome using phosphorylation-independent mutants of arrestin, especially when these are tethered to the opsin protein. We further show that point mutations targeting the Schiff base stability of the opsin can also reduce signalling lifetime. Finally, we apply one such mutation (E122Q) to improve the temporal fidelity of restored visual responses following ectopic opsin expression in the inner retina of a mouse model of retinal degeneration (rd1). Our results reveal that these two strategies (targeting either arrestin binding or Schiff-base hydrolysis) can produce more time-delimited opsin signalling under heterologous expression and establish the potential of this approach to improve optogenetic performance.

Opsins as main regulators of skin biology

Opsins are light-sensitive proteins that are found across the animal kingdom. In mammals, opsins are classically associated with image-forming processes, a function exerted by cone and rod opsins. In early 2000, melanopsin was identified in the human retina as an important regulator of non-image forming events such as melatonin suppression, pupillary constriction, and circadian rhythm adjustment. The presence of different opsins and the biological processes that these proteins regulate in the skin are increasingly being described. Currently, opsins are considered light as well as thermosensors in the skin. However, additional regulatory functions, in a light and thermo-independent fashion, mostly likely via protein-protein interaction have set a new field of study. The goal of this review is to critically revise the literature on the role of opsins in skin physiology as well as in melanoma cancer.

One-stop assembly of adherent 3D retinal organoids from hiPSCs based on 3D-printed derived PDMS microwell platform

The three-dimensional (3D) retinal organoids (ROs) derived from human induced pluripotent stem cells (hiPSCs), mimicking the growth and development of the human retina, is a promising model for investigating inherited retinal diseases in vitro. However, the efficient generation of homogenous ROs remains a challenge. Here we introduce a novel polydimethylsiloxane (PDMS) microwell platform containing 62 V-bottom micro-cavities for the ROs differentiation from hiPSCs. The uniform adherent 3D ROs could spontaneously form using neural retina (NR) induction. Our results showed that the complex of NR (expressing VSX2), ciliary margin (CM) (expressing RDH10), and retinal pigment epithelium (RPE) (expressing ZO-1, MITF, and RPE65) developed in the PDMS microwell after the differentiation. It is important to note that ROs in PDMS microwell platforms not only enable one-stop assembly but also maintain homogeneity and mature differentiation over a period of more than 25 weeks without the use of BMP4 and Matrigel. Retinal ganglion cells (expressing BRN3a), amacrine cells (expressing AP2a), horizontal cells (expressing PROX1 and AP2α), photoreceptor cells for cone (expressing S-opsin and L/M-opsin) and rod (expressing Rod opsin), bipolar cells (expressing VSX2 and PKCα), and Müller glial cells (expressing GS and Sox9) gradually emerged. Furthermore, we replaced fetal bovine serum with human platelet lysate and established a xeno-free culture workflow that facilitates clinical application. Thus, our PDMS microwell platform for one-stop assembly and long-term culture of ROs using a xeno-free workflow is favorable for retinal disease modeling, drug screening, and manufacturing ROs for clinical translation.

Pharmacochaperones as a novel approach to rescue misfolding rod opsin mutants associated with retinitis pigmentosa.

The correct trafficking of folded, functional rhodopsin (Rho) is critical to sustaining vision. Inherited destabilizing mutations in the rhodopsin (RHO) gene lead to a spectrum of blinding diseases called retinitis pigmentosa (RP) with currently no cure available. Therapeutic approaches to correct these impartments focus on the development of pharmacological chaperones that stabilize rod opsin. The native ligand, 11-cis-retinal, improves protein stability, folding, and trafficking of some mutated Rho variants. However, its chemical instability, toxicity, and poor pharmacokinetics limit its use as a therapeutic. In our laboratory, we focus our attention on finding chaperones with natural-like product scaffolds due to their broad chemical diversity. Furthermore, ∼50% of marketed small molecule drugs are derived from natural products scaffold, and some of them target GPCRs. Thus, we integrated computational, biochemical, biophysical, and in vivo analysis to evaluate non-retinoid ligands with diverse chemical scaffolds as potential chaperones of misfolding Rho variants. Our study led to the discovery of a novel chromenone-containing small molecule with favorable pharmacological properties that through direct binding to the orthosteric pocket enhanced rod opsin stability. This compound improved the membrane trafficking of multiple rod opsin mutants in vitro. Importantly, our studies unraveled the pharmacological potential of this new chromenone rod opsin ligand to slow down the progression of photoreceptor degeneration in the P23H Rho knock-in mice, a model of RP. Together, our studies encourage further search and evaluation of novel non-retinoid compounds that could mitigate the misfolding and mistrafficking of the Rho mutants to prolong the survival of photoreceptors in the retina, and thus delaying vision loss in RP.

Ontogenesis of the asymmetric parapineal organ in the zebrafish epithalamus.

The parapineal organ is a midline-derived epithalamic structure that in zebrafish adopts a left-sided position at embryonic stages to promote the development of left-right asymmetries in the habenular nuclei. Despite extensive knowledge about its embryonic and larval development, it is still unknown whether the parapineal organ and its profuse larval connectivity with the left habenula are present in the adult brain or whether, as assumed from historical conceptions, this organ degenerates during ontogeny. This paper addresses this question by performing an ontogenetic analysis using an integrative morphological, ultrastructural and neurochemical approach. We find that the parapineal organ is lost as a morphological entity during ontogeny, while parapineal cells are incorporated into the posterior wall of the adult left dorsal habenular nucleus as small clusters or as single cells. Despite this integration, parapineal cells retain their structural, neurochemical and connective features, establishing a reciprocal synaptic connection with the more dorsal habenular neuropil. Furthermore, we describe the ultrastructure of parapineal cells using transmission electron microscopy and report immunoreactivity in parapineal cells with antibodies against substance P, tachykinin, serotonin and the photoreceptor markers arrestin3a and rod opsin. Our findings suggest that parapineal cells form an integral part of a neural circuit associated with the left habenula, possibly acting as local modulators of the circuit. We argue that the incorporation of parapineal cells into the habenula may be part of an evolutionarily relevant developmental mechanism underlying the presence/absence of the parapineal organ in teleosts, and perhaps in a broader sense in vertebrates.

Retinal development and the expression profiles of opsin genes during larval development in Takifugu rubripes.

The light-sensitive capacity of fish larvae is determined by the structure of the retina and the opsins expressed in the retinal and nonretinal photoreceptors. In this study, the retinal structure and expression of opsin genes during the early developmental stage of Takifugu rubripes larvae were investigated. Histological examination showed that at 1 days after hatching (dah), seven layers were observed in the retina of T. rubripes larva, including the pigment epithelial layer [retinal pigment epithelium layer (RPE)], photoreceptor layer (PRos/is), outer nuclear layer (ONL), outer plexiform layer (OPL), inner nuclear layer (INL), inner plexiform layer (IPL) and ganglion cell layer (GCL). At 2dah, optic fibre layer (OFL) can be observed, and all eight layers were visible in the retina. By measuring the thickness of each layer, opposing developmental trends were found in the thickness of ONL, OPL, INL, IPL, GCL and OFL. The nuclear density of ONL, INL and GCL and the ratios of ONL/INL, ONL/GCL and INL/GCL were also measured and the ratio of ONL/GCL ranged from 1.9 at 2dah to 3.4 at 8dah and no significant difference was observed between the different developmental stages (P > 0.05). No significant difference was observed for the INL/GCL ratio between the different developmental stages, which ranged from 1.2 at 2dah to 2.0 at 18 dah (P > 0.05). The results of quantitative real-time polymerase chain reaction (PCR) showed that the expression of RH1, LWS, RH2-1, RH2-2, SWS2, rod opsin, opsin3 and opsin5 could be detected from 1dah. These results suggest that the well-developed retina and early expression of the opsins of T. rubripes during the period of transition from endogenous to mixed feeding might be critical for vision-based survival skills during the early life stages after hatching.

Early Proton Transfer Reaction in a Primate Blue-Sensitive Visual Pigment.

The proton transfer reaction belongs to one of the key triggers for the functional expression of membrane proteins. Rod and cone opsins are light-sensitive G-protein-coupled receptors (GPCRs) that undergo the cis-trans isomerization of the retinal chromophore in response to light. The isomerization event initiates a conformational change in the opsin protein moiety, which propagates the downstream effector signaling. The final step of receptor activation is the deprotonation of the retinal Schiff base, a proton transfer reaction which has been believed to be identical among the cone opsins. Here, we report an unexpected proton transfer reaction occurring in the early photoreaction process of primate blue-sensitive pigment (MB). By using low-temperature UV-visible spectroscopy, we found that the Lumi intermediate of MB formed in transition from the BL intermediate shows an absorption maximum in the UV region, indicating the deprotonation of the retinal Schiff base. Comparison of the light-induced difference FTIR spectra of Batho, BL, and Lumi showed significant α-helical backbone C=O stretching and protonated carboxylate C=O stretching vibrations only in the Lumi intermediate. The transition from BL to Lumi thus involves dramatic changes in protein environment with a proton transfer reaction between the Schiff base and the counterion resulting in an absorption maximum in the UV region.

Tulp1 deficiency causes early-onset retinal degeneration through affecting ciliogenesis and activating ferroptosis in zebrafish

Mutations in TUB-like protein 1 (TULP1) are associated with severe early-onset retinal degeneration in humans. However, the pathogenesis remains largely unknown. There are two homologous genes of TULP1 in zebrafish, namely tulp1a and tulp1b. Here, we generated the single knockout (tulp1a−/− and tulp1b−/−) and double knockout (tulp1-dKO) models in zebrafish. Knockout of tulp1a resulted in the mislocalization of UV cone opsins and the degeneration of UV cones specifically, while knockout of tulp1b resulted in mislocalization of rod opsins and rod-cone degeneration. In the tulp1-dKO zebrafish, mislocalization of opsins was present in all types of photoreceptors, and severe degeneration was observed at a very early age, mimicking the clinical manifestations of TULP1 patients. Photoreceptor cilium length was significantly reduced in the tulp1-dKO retinas. RNA-seq analysis showed that the expression of tektin2 (tekt2), a ciliary and flagellar microtubule structural component, was downregulated in the tulp1-dKO zebrafish. Dual-luciferase reporter assay suggested that Tulp1a and Tulp1b transcriptionally activate the promoter of tekt2. In addition, ferroptosis might be activated in the tulp1-dKO zebrafish, as suggested by the up-regulation of genes related to the ferroptosis pathway, the shrinkage of mitochondria, reduction or disappearance of mitochondria cristae, and the iron and lipid droplet deposition in the retina of tulp1-dKO zebrafish. In conclusion, our study establishes an appropriate zebrafish model for TULP1-associated retinal degeneration and proposes that loss of TULP1 causes defects in cilia structure and opsin trafficking through the downregulation of tekt2, which further increases the death of photoreceptors via ferroptosis. These findings offer insight into the pathogenesis and clinical treatment of early-onset retinal degeneration.

Developmental changes of opsin gene expression in ray-finned fishes (Actinopterygii).

Fish often change their habitat and trophic preferences during development. Dramatic functional differences between embryos, larvae, juveniles and adults also concern sensory systems, including vision. Here, we focus on the photoreceptors (rod and cone cells) in the retina and their gene expression profiles during development. Using comparative transcriptomics on 63 species, belonging to 23 actinopterygian orders, we report general developmental patterns of opsin expression, mostly suggesting an increased importance of the rod opsin (RH1) gene and the long-wavelength-sensitive cone opsin, and a decreasing importance of the shorter wavelength-sensitive cone opsin throughout development. Furthermore, we investigate in detail ontogenetic changes in 14 selected species (from Polypteriformes, Acipenseriformes, Cypriniformes, Aulopiformes and Cichliformes), and we report examples of expanded cone opsin repertoires, cone opsin switches (mostly within RH2) and increasing rod : cone ratio as evidenced by the opsin and phototransduction cascade genes. Our findings provide molecular support for developmental stage-specific visual palettes of ray-finned fishes and shifts between, which most likely arose in response to ecological, behavioural and physiological factors.

Development of dim-light vision in the nocturnal reef fish family Holocentridae. I: Retinal gene expression.

ABSTRACTDevelopmental changes to the visual systems of animals are often associated with ecological shifts. Reef fishes experience a change in habitat between larval life in the shallow open ocean to juvenile and adult life on the reef. Some species also change their lifestyle over this period and become nocturnal. While these ecological transitions are well documented, little is known about the ontogeny of nocturnal reef fish vision. Here, we used transcriptomics to investigate visual development in 12 representative species from both subfamilies, Holocentrinae (squirrelfishes) and Myripristinae (soldierfishes), in the nocturnal coral reef fish family, Holocentridae. Results revealed that the visual systems of holocentrids are initially well adapted to photopic conditions with pre-settlement larvae having high levels of cone opsin gene expression and a broad cone opsin gene repertoire (8 genes). At reef settlement, holocentrids started to invest more in their scotopic visual system, and compared with adults, showed upregulation of genes involved in cell differentiation/proliferation. By adulthood, holocentrids had well developed scotopic vision with high levels of rod opsin gene expression, reduced cone opsin gene expression and repertoire (1–4 genes) and upregulated phototransduction genes. Finally, although the two subfamilies shared similar ecologies across development, their visual systems diverged after settlement, with Myripristinae investing more in scotopic vision than Holocentrinae. Hence, both ecology and phylogeny are likely to determine the development of the holocentrid visual system.

An EvoDevo Study of Salmonid Visual Opsin Dynamics and Photopigment Spectral Sensitivity.

Salmonids are ideal models as many species follow a distinct developmental program from demersal eggs and a large yolk sac to hatching at an advanced developmental stage. Further, these economically important teleosts inhabit both marine- and freshwaters and experience diverse light environments during their life histories. At a genome level, salmonids have undergone a salmonid-specific fourth whole genome duplication event (Ss4R) compared to other teleosts that are already more genetically diverse compared to many non-teleost vertebrates. Thus, salmonids display phenotypically plastic visual systems that appear to be closely related to their anadromous migration patterns. This is most likely due to a complex interplay between their larger, more gene-rich genomes and broad spectrally enriched habitats; however, the molecular basis and functional consequences for such diversity is not fully understood. This study used advances in genome sequencing to identify the repertoire and genome organization of visual opsin genes (those primarily expressed in retinal photoreceptors) from six different salmonids [Atlantic salmon (Salmo salar), brown trout (Salmo trutta), Chinook salmon (Oncorhynchus tshawytcha), coho salmon (Oncorhynchus kisutch), rainbow trout (Oncorhynchus mykiss), and sockeye salmon (Oncorhynchus nerka)] compared to the northern pike (Esox lucius), a closely related non-salmonid species. Results identified multiple orthologues for all five visual opsin classes, except for presence of a single short-wavelength-sensitive-2 opsin gene. Several visual opsin genes were not retained after the Ss4R duplication event, which is consistent with the concept of salmonid rediploidization. Developmentally, transcriptomic analyzes of Atlantic salmon revealed differential expression within each opsin class, with two of the long-wavelength-sensitive opsins not being expressed before first feeding. Also, early opsin expression in the retina was located centrally, expanding dorsally and ventrally as eye development progressed, with rod opsin being the dominant visual opsin post-hatching. Modeling by spectral tuning analysis and atomistic molecular simulation, predicted the greatest variation in the spectral peak of absorbance to be within the Rh2 class, with a ∼40 nm difference in λmax values between the four medium-wavelength-sensitive photopigments. Overall, it appears that opsin duplication and expression, and their respective spectral tuning profiles, evolved to maximize specialist color vision throughout an anadromous lifecycle, with some visual opsin genes being lost to tailor marine-based vision.

Chromenone derivatives as novel pharmacological chaperones for retinitis pigmentosa-linked rod opsin mutants.

The correct expression of folded, functional rhodopsin (Rho) is critical for visual perception. However, this seven-transmembrane helical G protein-coupled receptor is prone to mutations with pathological consequences of retinal degeneration in retinitis pigmentosa (RP) due to Rho misfolding. Pharmacological chaperones that stabilize the inherited Rho variants by assisting their folding and membrane targeting could slow the progression of RP. In this study, we employed virtual screening of synthetic compounds with a natural product scaffold in conjunction with in vitro and in vivo evaluations to discover a novel chromenone-containing small molecule with favorable pharmacological properties that stabilize rod opsin. This compound reversibly binds to unliganded bovine rod opsin with an EC50 value comparable to the 9-cis-retinal chromophore analog and partially rescued membrane trafficking of multiple RP-related rod opsin variants in vitro. Importantly, this novel ligand of rod opsin was effective in vivo in murine models, protecting photoreceptors from deterioration caused by either bright light or genetic insult. Together, our current study suggests potential broad therapeutic implications of the new chromenone-containing non-retinoid small molecule against retinal diseases associated with photoreceptor degeneration.

Genome-wide identification and expression patterns of opsin genes during larval development in Chinese perch (Siniperca chuatsi)

Vision is important for fish to forage food and fishes express opsin genes to receive visual signals. Chinese perch (Siniperca chuatsi) larvae prey on other fish species larvae at firstfeeding but donoteat any zooplankton, the expression of opsin genes in S. chuatsilarvae is unknown. In this study, we conducted a whole-genome analysis and demonstrated that S. chuatsihave5cone opsin genes (sws1, sws2Aα, sws2Aβ, rh2and lws)and 2 rod opsin genes (rh1and rh1-exorh). The syntenicanalysisshowedthe flanking genes ofall opsin genes were conserved during fish evolution, but the ancestorof S. chuatsimightlost some opsin gene copies duringtheevolution.The phylogeneticanalysisshowed sws1of S. chuatsiwas closest to those of Lates calcariferwhich had a truncated sws1gene; the sws2Aα, sws2Aβ,lws,rh2,rh1 andrh1-exorh of S. chuatsihad a closer relationship with those of Percomorpha fishes.Importantly, results of in situhybridization showed the sws1 opsingene,which is related to forage zooplankton,had extremely low levelexpression in retinaat early stages.Surprisingly, the rh2 opsin gene had a high level expression at firstfeeding stage. The sws2Aα, sws2Aβand lwshad a little expression at early stages but the lwsshowed a increasing trend with larval development, rh1 opsin gene expression appeared at15 dph. In thisstudy, we found a specialpattern of visual opsin genes expression in S. chuatsi, it might influence the larval first feeding and feeding habit.

Seeing Picasso: an investigation into the visual system of the triggerfish Rhinecanthus aculeatus.

ABSTRACTVision is used by animals to find food and mates, avoid predators, defend resources and navigate through complex habitats. Behavioural experiments are essential for understanding animals' perception but are often challenging and time-consuming; therefore, using species that can be trained easily for complex tasks is advantageous. Picasso triggerfish, Rhinecanthus aculeatus, have been used in many behavioural studies investigating vision and navigation. However, little is known about the molecular and anatomical basis of their visual system. We addressed this knowledge gap here and behaviourally tested achromatic and chromatic acuity. In terms of visual opsins, R. aculeatus possessed one rod opsin gene (RH1) and at least nine cone opsins: one violet-sensitive SWS2B gene, seven duplicates of the blue–green-sensitive RH2 gene (RH2A, RH2B, RH2C1-5) and one red-sensitive LWS gene. However, only five cone opsins were expressed: SWS2B expression was consistent, while RH2A, RH2C-1 and RH2C-2 expression varied depending on whether fish were sampled from the field or aquaria. Levels of LWS expression were very low. Using fluorescence in situ hybridisation, we found SWS2B was expressed exclusively in single cones, whereas RH2A and RH2Cs were expressed in opposite double cone members. Anatomical resolution estimated from ganglion cell densities was 6.8 cycles per degree (cpd), which was significantly higher than values obtained from behavioural testing for black-and-white achromatic stimuli (3.9 cpd) and chromatic stimuli (1.7–1.8 cpd). These measures were twice as high as previously reported. This detailed information on their visual system will help inform future studies with this emerging focal species.

From Embryo to Adult Life: Differential Expression of Visual Opsins in the Flatfish Solea senegalensis Under Different Light Spectra and Photoperiods

Visual photoreceptors in fish are usually adjusted to the light environment to ensure the highest efficiency and best adaptation. In the Senegalese sole, metamorphosis determines migration from pelagic to benthic habitats, with marked differences in both light intensity and spectrum. Here, we analysed the ontogeny of six visual photopigments, namely, rod opsin (rh1), short wavelength-sensitive (sws1 and sws2), medium wavelength-sensitive (rh2.3 and rh2.4), and long wavelength-sensitive (lws) cone opsins, in sole specimens maintained in light-dark cycles of white (LDW), blue (LDB), red (LDR), and continuous white (LL) lights by using RT-qPCR and in situ hybridisation. Most of the opsins displayed a similar developmental expression pattern under all tested conditions. However, lower transcripts were detected under LDR and LL compared to LDW and LDB. A significant increase in gene expression was detected before and after metamorphosis, reaching minimum transcript levels at hatching and during metamorphosis. Interestingly, green opsins (rh2.3 and rh2.4) displayed a significant increase only before metamorphosis, with their expression remaining low during and after metamorphosis. The rod opsin and short-, medium-, and long-wavelength sensitive cone opsins were detected in retinal photoreceptors of the sole from pre-metamorphic to adult stages by in situ hybridisation. In adults, the short-wavelength cone opsins (sws1 and sws2) were found in single cones, whereas the medium- (rh2.4) and long-wavelength (lws) cone opsins were present in double cones. The results obtained by in situ hybridisation in the retina of developing sole, in terms of number of positive cells and/or intensity of labelling, were consistent with the ontogenetic transcript patterns found by RT-qPCR, suggesting that most of the visual opsin expressions detected in the whole specimens could correspond to retinal expression. Taken together, our results pointed out that the ontogeny of the Senegalese sole is accompanied by remodelling in opsin gene expression, with the green-cone opsins being the most abundant photopigments in pre-metamorphosis and rod opsin the dominant visual photopigment from the completion of metamorphosis onwards. These results enlarge our knowledge of flatfish metamorphosis and ecology and provide useful information to develop light protocols adapted to different ontogenetic stages that could improve welfare and production in sole aquaculture.

Evolutionary analyses of visual opsin genes in frogs and toads: Diversity, duplication, and positive selection.

Among major vertebrate groups, anurans (frogs and toads) are understudied with regard to their visual systems, and little is known about variation among species that differ in ecology. We sampled North American anurans representing diverse evolutionary and life histories that likely possess visual systems adapted to meet different ecological needs. Using standard molecular techniques, visual opsin genes, which encode the protein component of visual pigments, were obtained from anuran retinas. Additionally, we extracted the visual opsins from publicly available genome and transcriptome assemblies, further increasing the phylogenetic and ecological diversity of our dataset to 33 species in total. We found that anurans consistently express four visual opsin genes (RH1, LWS, SWS1, and SWS2, but not RH2) even though reported photoreceptor complements vary widely among species. The proteins encoded by these genes showed considerable sequence variation among species, including at sites known to shift the spectral sensitivity of visual pigments in other vertebrates and had conserved substitutions that may be related to dim‐light adaptation. Using molecular evolutionary analyses of selection (dN/dS) we found significant evidence for positive selection at a subset of sites in the dim‐light rod opsin gene RH1 and the long wavelength sensitive cone opsin LWS. The function of sites inferred to be under positive selection are largely unknown, but a few are likely to affect spectral sensitivity and other visual pigment functions based on proximity to previously identified sites in other vertebrates. We also found the first evidence of visual opsin duplication in an amphibian with the duplication of the LWS gene in the African bullfrog, which had distinct LWS copies on the sex chromosomes suggesting the possibility of sex‐specific visual adaptation. Taken together, our results indicate that ecological factors, such as habitat and life history, as well as behavior, may be driving changes to anuran visual systems.

Lutein delays photoreceptor degeneration in a mouse model of retinitis pigmentosa.

Retinitis pigmentosa is a retinal disease characterized by photoreceptor degeneration. There is currently no effective treatment for retinitis pigmentosa. Although a mixture of lutein and other antioxidant agents has shown promising effects in protecting the retina from degeneration, the role of lutein alone remains unclear. In this study, we administered intragastric lutein to Pde6brd10 model mice, which display degeneration of retinal photoreceptors, on postnatal days 17 (P17) to P25, when rod apoptosis reaches peak. Lutein at the optimal protective dose of 200 mg/kg promoted the survival of photoreceptors compared with vehicle control. Lutein increased rhodopsin expression in rod cells and opsin expression in cone cells, in line with an increased survival rate of photoreceptors. Functionally, lutein improved visual behavior, visual acuity, and retinal electroretinogram responses in Pde6brd10 mice. Mechanistically, lutein reduced the expression of glial fibrillary acidic protein in Müller glial cells. The results of this study confirm the ability of lutein to postpone photoreceptor degeneration by reducing reactive gliosis of Müller cells in the retina and exerting anti-inflammatory effects. This study was approved by the Laboratory Animal Ethics Committee of Jinan University (approval No. LACUC-20181217-02) on December 17, 2018.

Viral Transduction of Human Rod Opsin or Channelrhodopsin Variants to Mouse ON Bipolar Cells Does Not Impact Retinal Anatomy or Cause Measurable Death in the Targeted Cells.

The viral gene delivery of optogenetic actuators to the surviving inner retina has been proposed as a strategy for restoring vision in advanced retinal degeneration. We investigated the safety of ectopic expression of human rod opsin (hRHO), and two channelrhodopsins (enhanced sensitivity CoChR-3M and red-shifted ReaChR) by viral gene delivery in ON bipolar cells of the mouse retina. Adult Grm6Cre mice were bred to be retinally degenerate or non-retinally degenerate (homozygous and heterozygous for the rd1Pde6b mutation, respectively) and intravitreally injected with recombinant adeno-associated virus AAV2/2(quad Y-F) serotype containing a double-floxed inverted transgene comprising one of the opsins of interest under a CMV promoter. None of the opsins investigated caused changes in retinal thickness; induced apoptosis in the retina or in transgene expressing cells; or reduced expression of PKCα (a specific bipolar cell marker). No increase in retinal inflammation at the level of gene expression (IBA1/AIF1) was found within the treated mice compared to controls. The expression of hRHO, CoChR or ReaChR under a strong constitutive promoter in retinal ON bipolar cells following intravitreal delivery via AAV2 does not cause either gross changes in retinal health, or have a measurable impact on the survival of targeted cells.

Toxic effects of triclocarban on larval zebrafish: A focus on visual dysfunction.

Triclocarban (TCC) is considered an endocrine disruptor and shows antagonist activity on thyroid receptors. In view of the report that thyroid hormone signaling mediates retinal cone photoreceptor specification, we hypothesize that TCC could impair visual function, which is vital to wildlife. In order to verify our hypothesis, we assessed alteration in the retinal structure (retinal layer thickness and cell density), visually-mediated behavior, cone and rod opsin gene expression, and photoreceptor immunostaining in zebrafish larvae exposed to TCC at environmentally realistic concentrations (0.16±0.005µg/L, L-group) and one-fifth of the median lethal concentrations (25.4±1.02µg/L, H-group). Significant decrease in eye size, ganglion cell density, optokinetic response, and phototactic response can be observed in the L-group, while the thickness of outer nuclear layer, where the cell bodies of cone and rod cells are located, was significantly reduced with the down-regulation of critical opsin gene (opn1sw2, opn1mw1, opn1mw3, opn1lw1, opn1lw2, and rho) expression and rhodopsin immunofluorescence in the H-group. It should be noted that TCC could affect the sensitivity of zebrafish larvae to red and green light according to the results of behavioral and opsin gene expression analysis. These findings provide the first evidence to support our hypothesis that the visual system, a novel toxicological target, is affected by TCC. Consequently, we urgently call for a more in-depth exploration of TCC-induced ocular toxicity to aquatic organisms and even to humans.