Opsin Gene Expression Research Articles

Adaptive variation in opsin expression of sticklebacks from different photic habitats

We studied phenotypic and genetic adaptation of the visual system of three-spined sticklebacks, Gasterosteus aculeatus, from North Uist, Scotland. We quantified differences in opsin gene expression of the four cone opsin genes among wild-caught fish from three lakes with clear and from three with tea-stained water and their offspring that were raised in clear water. In addition, visual sensitivity of wild-caught fish was modelled from opsin expression levels. Wild-caught fish from tea-stained waters had a lower SWS1 proportional expression than fish from clear waters, a difference that tended to be maintained in lab-bred fish. Compared to lab-bred fish, wild-caught fish had a higher SWS1 but lower SWS2 proportional expression independent of water clarity. For RH2 and LWS there were significant interactions between generation and water clarity. Reproductively mature fish had a higher LWS but lower proportional expression of RH2 than non-reproductive fish. Sex did not have a significant effect on expression. There was a significant positive association and, depending on chromophore ratio, a distinct match between the centre wavelengths, used as a proxy for spectral distribution, of ambient habitat light and spectral sensitivity indicating that the visual system of sticklebacks is tuned to their local light environment, suggesting adaptation.

Shining new light on naupliar eyes: A novel molecular phylogeny for Pleuromamma (Family: Metridinidae) and the characterization of luciferase and opsin expression

Pleuromamma (Giesbrecht, 1898) is a cosmopolitan genus of metridinid copepods, with species that perform remarkable diel vertical migrations (DVM) and emit a bioluminescent secretion when disturbed that varies both spectrally and kinetically. Copepod bioluminescence is autogenic and uses luciferase enzymes that catalyze a luciferin, coelenterazine, to produce light. Pleuromamma possess naupliar eyes, relatively simple photosensitive structures used for many visually-guided behaviors. Yet the fundamental molecular unit for vision, the opsin protein, has not been previously described for the family. The light producers and detectors are important to study because DVM is a behavior that mediates significant active elemental fluxes between the upper ocean and midwaters across vast stretches of oceanic habitat, and DVM is guided by visual behaviors, with animals tracking an isolume. Here we provide the first fully resolved molecular phylogeny for Pleuromamma (Family: Metridinidae) and describe the luciferase and opsin gene diversity and expression using de novo assembled transcriptomes. We successfully sequenced and assembled transcriptomes for 10 of 11 described species of Pleuromamma as well as two other metridinid species: Metridia longa and Gaussia princeps. In all species, we obtained coding sequences of one putative rhabdomeric middle wavelength sensitive visual opsin gene, as well as several non-visual opsins – a c-type pteropsin and a tetra-opsin type peropsin. Furthermore, Pleuromamma express luciferases from each of two main evolutionary clades (Luc1 and Luc2), and a single paralog (Luc2a) dominates expression throughout the group. The variation in luciferase number, sequence, and expression among species could lead to different spectral and kinetic properties of bioluminescence and aid in congener recognition.

Genome-Wide Association Study and transcriptome analysis reveals a complex gene network that regulates opsin gene expression and cell fate determination in Drosophila R7 photoreceptor cells.

An animal's ability to discriminate between differing wavelengths of light (i.e., color vision) is mediated, in part, by a subset of photoreceptor cells that express opsins with distinct absorption spectra. In Drosophila R7 photoreceptors, expression of the rhodopsin molecules, Rh3 or Rh4, is determined by a stochastic process mediated by the transcription factor spineless. The goal of this study was to identify additional factors that regulate R7 cell fate and opsin choice using a Genome Wide Association Study (GWAS) paired with transcriptome analysis via RNA-Seq. We examined Rh3 and Rh4 expression in a subset of fully-sequenced inbred strains from the Drosophila Genetic Reference Panel and performed a GWAS to identify 42 naturally-occurring polymorphisms-in proximity to 28 candidate genes-that significantly influence R7 opsin expression. Network analysis revealed multiple potential interactions between the associated candidate genes, spineless and its partners. GWAS candidates were further validated in a secondary RNAi screen which identified 12 lines that significantly reduce the proportion of Rh3 expressing R7 photoreceptors. Finally, using RNA-Seq, we demonstrated that all but four of the GWAS candidates are expressed in the pupal retina at a critical developmental time point and that five are among the 917 differentially expressed genes in sevenless mutants, which lack R7 cells. Collectively, these results suggest that the relatively simple, binary cell fate decision underlying R7 opsin expression is modulated by a larger, more complex network of regulatory factors. Of particular interest are a subset of candidate genes with previously characterized neuronal functions including neurogenesis, neurodegeneration, photoreceptor development, axon growth and guidance, synaptogenesis, and synaptic function.

Regulation of opsin and circadian clock genes on mate-finding behavior of the day-flying red moth, Phauda flammans (Walker)

ABSTRACT First, significantly higher mate-finding success was found under light condition than under constant darkness condition in Phauda flammans, a typical diurnal moth. We speculate that mate-finding behavior in P. flammans may be influenced by the light-sensitive opsin genes Long wavelength opsin (PfLW), Ultraviolet opsin (PfUV) and Blue opsin (PfBL), which are potentially regulated by both light-cues and endogenous circadian rhythms. Second, the circadian clock genes Period (PfPer), Timeless (PfTim), Cryptochrome1 (PfCry1), Cryptochrome2 (PfCRY2), Cryptochrome3 (PfCry-like), Clock (PfClk), Cycle (PfCyc), Vrille (PfVri), and Slimb (PfSli) were identified in P. flammans. Third, circadian rhythms in the relative expression levels of opsin and circadian clock genes were demonstrated via quantitative real-time PCR analysis, with peak expression coinciding with the mate-finding peak. Notably, the relative expression of PfLW in males P. flammans was significantly higher than that in females P. flammans at the mate-finding peaks Zeitgeber time (ZT) 8 and ZT 10 under light, while the expression of the opsin gene PfBL showed a similar pattern at ZT 10 under light. Additionally, the expression of the clock gene PfCry-like was significantly higher in males than in females at ZT 8 and ZT 10 under light, while PfPer, PfTim, PfClk and PfCyc exhibited similar male-biased expression patterns at ZT 10 under light. Conversely, PfCry1 and PfVri expression was significantly higher in females than in male at ZT 8 under light. In conclusion, sex differences were detected in the expression of opsin and circadian clock genes, which indicated that light-mediated regulation of these genes may contribute to the daytime mate-finding behavior of P. flammans.

Characteristics of pectens in diurnal and nocturnal birds and a new functional proposal relating to non-visual opsins.

The pecten is a fold-structured projection at the ocular fundus in bird eyes, showing morphological diversity between the diurnal and nocturnal species. However, its biological functions remain unclear. This study investigated the morphological and histological characteristics of pectens in wild birds. Additionally, the expression of non-visual opsin genes was studied in chicken pectens. These genes, identified in the chicken retina and brain, perceive light periodicity regardless of visual communication. Similar pleat numbers have been detected among bird taxa; however, pecten size ratios in the ocular fundus showed noticeable differences between diurnal and nocturnal birds. The pectens in nocturnal brown hawk owl show extremely poor vessel distribution and diameters compared with that of diurnal species. RT-PCR analysis confirmed the expression of Opn5L3, Opn4x, Rrh and Rgr genes. Insitu hybridization analysis revealed the distribution of Rgr-positive reactions in non-melanotic cells around the pecten vessels. This study suggests a novel hypothesis that pectens develop dominantly in diurnal birds as light acceptors and contribute to continuous visual function or the onset of periodic behaviour.

Differential Regulation of Opsin Gene Expression in Response to Internal and External Stimuli.

Determining how internal and external stimuli interact to determine developmental trajectories of traits is a challenge that requires the integration of different subfields of biology. Internal stimuli, such as hormones, control developmental patterns of phenotypic changes, which might be modified by external environmental cues (e.g. plasticity). Thyroid hormone (TH) modulates the timing of opsin gene expression in developing Midas cichlid fish (Amphilophus citrinellus). Moreover, fish reared in red light accelerate this developmental timing compared to fish reared in white light. Hence, we hypothesized that plasticity caused by variation in light conditions has coopted the TH signaling pathway to induce changes in opsin gene expression. We treated Midas cichlids with TH and crossed this treatment with two light conditions, white and red. We observed that not only opsin expression responded similarly to TH and red light but also that, at high TH levels, there is limited capacity for light-induced plasticity. Transcriptomic analysis of the eye showed that genes in the TH pathway were affected by TH, but not by light treatments. Coexpression network analyses further suggested that response to light was independent of the response to TH manipulations. Taken together, our results suggest independent mechanisms mediating development and plasticity during development of opsin gene expression, and that responses to environmental stimuli may vary depending on internal stimuli. This conditional developmental response to external factors depending on internal ones (e.g. hormones) might play a fundamental role in the patterns of phenotypic divergence observed in Midas cichlids and potentially other organisms.

The expression and function of opsin genes related to the phototactic behavior of Tuta absoluta

The expression and function of opsin genes related to the phototactic behavior of Tuta absoluta

A ubiquitous tire rubber additive induced serious eye injury in zebrafish (Danio rerio)

Previous studies have indicated that tire wear particles (TWPs) leachate exposure induced serious eye injury in fish through inhibiting the thyroid peroxidase (TPO) enzyme activity. However, the main TPO inhibitors in the leachate were still unknown. In this study, we identified 2-Mercaptobenzothiazole (MBT) as the potential TPO inhibitor in the TWPs leachate through references search, model prediction based on Danish QSAR and ToxCast database, molecular docking, and in vivo assay. We further explored the toxic mechanism of MBT under environmentally relevant concentrations. The decreased eye size of zebrafish larvae was mainly caused by the decreased lens diameter and cell density in the inner nuclear layer (INL) and outer nuclear layer (ONL) of the retina. Transcriptomics analysis demonstrated that the eye phototransduction function was significantly suppressed by inhibiting the photoreceptor cell proliferation process after MBT exposure. The altered opsin gene expression and decreased opsin protein levels were induced by weakening thyroid hormone signaling after MBT treatment. These results were comparable to those obtained from a known TPO inhibitor, methimazole. This study has identified MBT as the primary TPO inhibitor responsible for inducing eye impairment in zebrafish larvae exposed to TWPs leachate. It is crucial for reducing the toxicity of TWPs leachate in fish.

Identification, expression analysis, and functional verification of three opsin genes related to the phototactic behaviour of Ostrinia furnacalis.

Ostrinia furnacalis is a disreputable herbivorous pest that poses a serious threat to corn crops. Phototaxis in nocturnal moths plays a crucial role in pest prediction and control. Insect opsins are the main component of insect visual system. However, the inherent molecular relationship between phototactic behaviour and vision of insects remains a mystery. Herein, three opsin genes were identified and cloned from O. furnacalis (OfLW, OfBL, and OfUV). Bioinformatics analysis revealed that all opsin genes had visual pigment (opsin) retinal binding sites and seven transmembrane domains. Opsin genes were distributed across different developmental stages and tissues, with the highest expression in adults and compound eyes. The photoperiod-induced assay elucidated that the expression of three opsin genes in females were higher during daytime, while their expression in males tended to increase at night. Under the sustained darkness, the expression of opsin genes increased circularly, although the increasing amplitude in males was lower when compared with females. Furthermore, the expression of OfLW, OfBL, and OfUV was upregulated under green, blue, and ultraviolet light, respectively. The results of RNA interference showed that the knockout of opsin genes decreased the phototaxis efficiency of female and male moths to green, blue, and ultraviolet light. Our results reveal that opsin genes are involved in the phototactic behaviour of moths, providing a potential target gene for pest control and a basis for further investigation on the phototactic behaviour of Lepidoptera insects.

Diurnal and circadian regulation of opsin-like transcripts in the eyeless cnidarian Hydra.

Opsins play a key role in the ability to sense light both in image-forming vision and in non-visual photoreception (NVP). These modalities, in most animal phyla, share the photoreceptor protein: an opsin-based protein binding a light-sensitive chromophore by a lysine (Lys) residue. So far, visual and non-visual opsins have been discovered throughout the Metazoa phyla, including the photoresponsive Hydra, an eyeless cnidarian considered the evolutionary sister species to bilaterians. To verify whether light influences and modulates opsin gene expression in Hydra, we utilized four expression sequence tags, similar to two classic opsins (SW rhodopsin and SW blue-sensitive opsin) and two non-visual opsins (melanopsin and peropsin), in investigating the expression patterns during both diurnal and circadian time, by means of a quantitative RT-PCR. The expression levels of all four genes fluctuated along the light hours of diurnal cycle with respect to the darkness one and, in constant dark condition of the circadian cycle, they increased. The monophasic behavior in the L12:D12 cycle turned into a triphasic expression profile during the continuous darkness condition. Consequently, while the diurnal opsin-like expression revealed a close dependence on light hours, the highest transcript levels were found in darkness, leading us to novel hypothesis that in Hydra, an "internal" biological rhythm autonomously supplies the opsins expression during the circadian time. In conclusion, in Hydra, both diurnal and circadian rhythms apparently regulate the expression of the so-called visual and non-visual opsins, as already demonstrated in higher invertebrate and vertebrate species. Our data confirm that Hydra is a suitable model for studying ancestral precursor of both visual and NVP, providing useful hints on the evolution of visual and photosensory systems.

Opsin expression varies across larval development and taxa in pteriomorphian bivalves.

Many marine organisms have a biphasic life cycle that transitions between a swimming larva with a more sedentary adult form. At the end of the first phase, larvae must identify suitable sites to settle and undergo a dramatic morphological change. Environmental factors, including photic and chemical cues, appear to influence settlement, but the sensory receptors involved are largely unknown. We targeted the protein receptor, opsin, which belongs to large superfamily of transmembrane receptors that detects environmental stimuli, hormones, and neurotransmitters. While opsins are well-known for light-sensing, including vision, a growing number of studies have demonstrated light-independent functions. We therefore examined opsin expression in the Pteriomorphia, a large, diverse clade of marine bivalves, that includes commercially important species, such as oysters, mussels, and scallops. Genomic annotations combined with phylogenetic analysis show great variation of opsin abundance among pteriomorphian bivalves, including surprisingly high genomic abundance in many species that are eyeless as adults, such as mussels. Therefore, we investigated the diversity of opsin expression from the perspective of larval development. We collected opsin gene expression in four families of Pteriomorphia, across three distinct larval stages, i.e., trochophore, veliger, and pediveliger, and compared those to adult tissues. We found larvae express all opsin types in these bivalves, but opsin expression patterns are largely species-specific across development. Few opsins are expressed in the adult mantle, but many are highly expressed in adult eyes. Intriguingly, opsin genes such as retinochrome, xenopsins, and Go-opsins have higher levels of expression in the later larval stages when substrates for settlement are being tested, such as the pediveliger. Investigating opsin gene expression during larval development provides crucial insights into their intricate interactions with the surroundings, which may shed light on how opsin receptors of these organisms respond to various environmental cues that play a pivotal role in their settlement process.

Functional opsin patterning for Drosophila color vision is established through signaling pathways in adjacent object-detection neurons.

Vision is mainly based on two different tasks, object detection and color discrimination, carried out by photoreceptor (PR) cells. The Drosophila compound eye consists of ∼800 ommatidia. Every ommatidium contains eight PR cells, six outer cells (R1-R6) and two inner cells (R7 and R8), by which object detection and color vision are achieved, respectively. Expression of opsin genes in R7 and R8 is highly coordinated through the instructive signal from R7 to R8, and two major ommatidial subtypes are distributed stochastically; pale type expresses Rh3/Rh5 and yellow type expresses Rh4/Rh6 in R7/R8. The homeodomain protein Defective proventriculus (Dve) is expressed in yellow-type R7 and in six outer PRs, and it is involved in Rh3 repression to specify the yellow-type R7. dve mutant eyes exhibited atypical coupling, Rh3/Rh6 and Rh4/Rh5, indicating that Dve activity is required for proper opsin coupling. Surprisingly, Dve activity in R1 is required for the instructive signal, whereas activity in R6 and R7 blocks the signal. Our results indicate that functional coupling of two different neurons is established through signaling pathways from adjacent neurons that are functionally different.

Repeated Divergence in Opsin Gene Expression Mirrors Photic Habitat Changes in Rapidly Evolving Crater Lake Cichlid Fishes.

AbstractSelection pressures differ along environmental gradients, and traits tightly linked to fitness (e.g., the visual system) are expected to track such variation. Along gradients, adaptation to local conditions might be due to heritable and nonheritable environmentally induced variation. Disentangling these sources of phenotypic variation requires studying closely related populations in nature and in the laboratory. The Nicaraguan lakes represent an environmental gradient in photic conditions from clear crater lakes to very turbid great lakes. From two old, turbid great lakes, Midas cichlid fish (Amphilophus cf. citrinellus) independently colonized seven isolated crater lakes of varying light conditions, resulting in a small adaptive radiation. We estimated variation in visual sensitivities along this photic gradient by measuring cone opsin gene expression among lake populations. Visual sensitivities observed in all seven derived crater lake populations shifted predictably in direction and magnitude, repeatedly mirroring changes in photic conditions. Comparing wild-caught and laboratory-reared fish revealed that 48% of this phenotypic variation is genetically determined and evolved rapidly. Decreasing intrapopulation variation as environments become spectrally narrower suggests that different selective landscapes operate along the gradient. We conclude that the power to predict phenotypic evolution along gradients depends on both the magnitude of environmental change and the selective landscape shape.

Unstable environmental conditions constrain the fine-tune between opsin sensitivity and underwater light in an Amazon forest stream fish.

Visual adaptations can stem from variations in amino acid composition, chromophore utilization, and differential opsin gene expression levels, enabling individuals to adjust their light sensitivity to environmental lighting conditions. In stable environments, adaptations often involve amino acid substitutions, whereas in unstable conditions, differential gene expression may be a more relevant mechanism. Amazon forest streams present diverse underwater lighting conditions and experience short-term water colour fluctuations. In these environments, it is less likely for genetic and amino acid sequences to undergo modifications that tailor opsin proteins to the prevailing lighting conditions, particularly in species having several copies of the same gene. The sailfin tetra, Crenuchus spilurus, inhabits black and clear water Amazon forest streams. The long-wavelength sensitivity (LWS) is an important component for foraging and courtship. Here, we investigated LWS opsin genes in the sailfin tetra. Three copies of LWS1 and two copies of LWS2 genes were found. The maximum absorbance wavelength (λmax) estimated from the amino acid sequences of LWS1 genes exhibited variation among the different copies. In contrast, the copies of LWS2 genes showed identical expected λmax values. Although the amino acid positions affecting λmax varied among LWS genes, they remained consistent among populations living in different water colours. The relative expression levels of LWS genes differed between gene copies. While not formally tested, our results suggest that in fluctuating environments, visual adaptations may primarily stem from alterations in gene expression profiles and/or chromophore usage rather than precise genetic tuning of protein light sensitivity to environmental lighting conditions.

Developmental and environmental plasticity in opsin gene expression in Lake Victoria cichlid fish.

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.

Imidacloprid affects the visual behavior of adult zebrafish (Danio rerio) by mediating the expression of opsin and phototransduction genes and altering the metabolism of neurotransmitters

Imidacloprid poses a significant threat to aquatic ecosystems. In this study, we investigated the visual toxicity of imidacloprid and the underlying molecular mechanisms in adult zebrafish. After exposure to imidacloprid at environmental relevant concentrations (10 and 100μg/L) for 21 days, the detectable contents of imidacloprid were 23.0 ± 0.80 and 121 ± 1.56 ng/mg in eyes of adult zebrafish, respectively. The visual behavior of adult zebrafish was impaired including a reduced ability to track smoothly visual stimuli and visually guided self-motion. The immunofluorescence experiment showed that the content of Rhodopsin (Rho) in the retina of zebrafish was changed significantly. The expression rhythm of genes played key roles in capturing photons in dim (rho) and bright (opn1mw3, opn1lw2 and opn1sw2) light, and in phototransduction (gnb3b, arr3a and rpe65a), was disrupted significantly throughout a 24-h period in adult zebrafish. Targeted metabolomics analysis showed that the content of 16 metabolites associated with neurotransmitter function changed significantly, and were enriched in top three metabolism pathways including Arginine biosynthesis, Alanine, aspartate and glutamate metabolism, and Tryptophan metabolism. These results indicated that imidacloprid exposure at environmentally relevant concentrations could cause optical toxicity through disturbing the expression of opsins and affecting the phototransduction in the retina of zebrafish adults.

SAT013 Characterization Of CRISPR/Cas9 Induced RXR Isotype Mutants In Xenopus Laevis

Abstract Disclosure: J.D. Furlow: None. S. Saini: None. B.J. Mengeling: None. M.E. Horb: None. Retinoid-X receptors (RXRs) occupy a unique position in the nuclear receptor (NR) superfamily. While some actions of the highly conserved RXRs may be independent, RXRs most often are heterodimer partners for several NRs that regulate development, reproduction and metabolism. As such, environmental chemicals interfering with the activity of RXRs and their partners may have significant deleterious effects on human health, often in developmental window, cell-type, and gene selective ways. The frog Xenopus has long served as an excellent model for studying vertebrate development including thyroid hormone action, and recent advances in genome editing have greatly enhanced its utility for investigating basic cell and organismal biology as well as human disease processes. To determine isotype specific roles in response to natural and synthetic ligands as well as candidate environmental chemicals interacting with RXRs in vivo, we created targeted germline mutations in the Xenopus tropicalis RXRα (rxra), RXRβ (rxrb), and RXRγ (rxrg) genes. For CRISPR/Cas9 mediated genome editing, guide RNAs were designed to target sequences just prior to or within the first RXR DNA binding domains. We raised all three RXR homozygous null mutants up to and through metamorphosis. The rxrb and rxrg homozygous null mutants completed metamorphosis and allowed us to establish adult null lines, but the rxra homozygous null mutants die at metamorphic climax, reminiscent of the thyroid hormone receptor (thra/thrb) double mutants. Some rxra mutant froglets also lack forearms or have forelimb defects, implying a role for rxra in RA mediated forelimb specification. The X. tropicalis rxrg homozygous null mutants show a trend toward an increased rate of metamorphosis versus matched wild-type controls, with significantly elevated tshb gene expression as newly metamorphosed froglets suggesting impaired negative feedback by TH. Significantly altered opsin gene expression in the froglet eye was also observed in rxrg mutant retinas: elevated short wave opsins opn1sw1 and opn1sw2 and sharply reduced long wave opsin opn1lw. This elevated tshb and opn1sw1 expression is highly similar to what is found in mouse rxrg null mutants; thus RXRγ action in the eye and pituitary appears to be highly conserved between mammals and amphibians. The establishment of these new RXR isotype mutant specific lines will support the expanded use of Xenopus to study basic biology and environmental toxicology involving TR-RXR and other NR-RXR partnerships. Presentation: Saturday, June 17, 2023

Plasticity of cone photoreceptors in adult zebrafish revealed by thyroid hormone exposure

Vertebrate color vision is predominantly mediated by the presence of multiple cone photoreceptor subtypes that are each maximally sensitive to different wavelengths of light. Thyroid hormone (TH) has been shown to be essential in the spatiotemporal patterning of cone subtypes in many species, including cone subtypes that express opsins that are encoded by tandemly replicated genes. TH has been shown to differentially regulate the tandemly replicated lws opsin genes in zebrafish, and exogenous treatments alter the expression levels of these genes in larvae and juveniles. In this study, we sought to determine whether gene expression in cone photoreceptors remains plastic to TH treatment in adults. We used a transgenic lws reporter line, multiplexed fluorescence hybridization chain reaction in situ hybridization, and qPCR to examine the extent to which cone gene expression can be altered by TH in adults. Our studies revealed that opsin gene expression, and the expression of other photoreceptor genes, remains plastic to TH treatment in adult zebrafish. In addition to retinal plasticity, exogenous TH treatment alters skin pigmentation patterns in adult zebrafish after 5 days. Taken together, our results show a remarkable level of TH-sensitive plasticity in the adult zebrafish.

Visual opsin gene expression evolution in the adaptive radiation of cichlid fishes of Lake Tanganyika.

Tuning the visual sensory system to the ambient light is essential for survival in many animal species. This is often achieved through duplication, functional diversification, and/or differential expression of visual opsin genes. Here, we examined 753 new retinal transcriptomes from 112 species of cichlid fishes from Lake Tanganyika to unravel adaptive changes in gene expression at the macro-evolutionary and ecosystem level of one of the largest vertebrate adaptive radiations. We found that, across the radiation, all seven cone opsins-but not the rhodopsin-rank among the most differentially expressed genes in the retina, together with other vision-, circadian rhythm-, and hemoglobin-related genes. We propose two visual palettes characteristic of very shallow- and deep-water living species, respectively, and show that visual system adaptations along two major ecological axes, macro-habitat and diet, occur primarily via gene expression variation in a subset of cone opsin genes.

Expression and function of opsin genes associated with phototaxis in Zeugodacus cucurbitae Coquillett (Diptera: Tephritidae).

Zeugodacus cucuribitae is a major agricultural pest that causes significant damage to varieties of plants. Vision plays a critical role in phototactic behavior of herbivorous insects. However, the effect of opsin on the phototactic behavior in Z.cucuribitae remain unknown. The aim of the research is to explore the key opsin genes that associate with phototaxis behavior of Z. cucurbitae. We identified five opsin genes and analyzed their expression patterns. The relative expression levels of ZcRh1, ZcRh4 and ZcRh6 were highest in 4-day-old larvae, ZcRh2 and ZcRh3 were highest in 3rd-instar larvae and 5-day-old pupae, respectively. Furthermore, five opsin genes had the highest expression levels in compound eyes, followed by the antennae and head, whereas the lower occurred in other tissues. The expression of the long-wavelength-sensitive (LW) opsins first decreased and then increased under green light exposure. In contrast, the expression of ultraviolet-sensitive (UV) opsins first increased and then decreased with the duration of UV exposure. Silencing of LW opsin (dsZcRh1, dsZcRh2, and dsZcRh6) and UV opsin (dsZcRh3 and dsZcRh4) reduced the phototactic efficiency of Z. cucurbitae to green light by 52.27%, 60.72%, and 67.89%, and to UV light by 68.59% and 61.73%, respectively. The study found that RNAi inhibited the expression of opsin, thereby inhibiting the phototaxis of Z. cucurbitae. This result provides theoretical support for the physical control of Z. cucurbitae and lays the foundation for further exploration of the mechanism of insect phototaxis. This article is protected by copyright. All rights reserved.