Sensitivity Of Photoreceptors Research Articles

Optical influence of oil droplets on cone photoreceptor sensitivity.

ABSTRACTOil droplets are spherical organelles found in the cone photoreceptors of vertebrates. They are generally assumed to focus incident light into the outer segment, and thereby improve light catch because of the droplets' spherical lens-like shape. However, using full-wave optical simulations of physiologically realistic cone photoreceptors from birds, frogs and turtles, we find that pigmented oil droplets actually drastically reduce the transmission of light into the outer segment integrated across the full visible wavelength range of each species. Only transparent oil droplets improve light catch into the outer segments, and any enhancement is critically dependent on the refractive index, diameter of the oil droplet, and diameter and length of the outer segment. Furthermore, oil droplets are not the only optical elements found in cone inner segments. The ellipsoid, a dense aggregation of mitochondria situated immediately prior to the oil droplet, mitigates the loss of light at the oil droplet surface. We describe a framework for integrating these optical phenomena into simple models of receptor sensitivity, and the relevance of these observations to evolutionary appearance and loss of oil droplets is discussed.

Pluripotent stem cells and their utility in treating photoreceptor degenerations.

Age-related macular degeneration and inherited retinal degenerations represent the leading causes of blindness in industrialized countries. Despite different initiating causes, they share a common final pathophysiology, the loss of the light sensitive photoreceptors. Replacement by transplantation may offer a potential treatment strategy for both patient populations. The last decade has seen remarkable progress in our ability to generate retinal cell types, including photoreceptors, from a variety of murine and human pluripotent stem cell sources. Driven in large part by the requirement for renewable cell sources, stem cells have emerged not only as a promising source of replacement photoreceptors but also to provide in vitro systems with which to study retinal development and disease processes and to test therapeutic agents.

The unusual eyes of Xenos peckii (Strepsiptera: Xenidae) have green- and UV--sensitive photoreceptors.

The highly specialized evolution of Strepsiptera has produced one of the most unusual eyes among mature insects, perhaps in line with their extremely complex and challenging life cycle. This relatively rare insect order is one of the few for which it has been unclear what spectral classes of photoreceptors any of its members may possess, an even more apt question given the nocturnal evolution of the group. To address this question, we performed electroretinograms on adult male Xenos peckii: we measured spectral responses to equi-quantal monochromatic light flashes of different wavelengths, and established VlogI relationships to calculate spectral sensitivities. Based on opsin template fits, we found maximal spectral sensitivity (λmax) in the green domain at 539 nm. Application of a green light to 'bleach' green receptors revealed that a UV peak was contributed to by an independent UV opsin with a λmax of 346 nm. Transcriptomics and a phylogenetic analysis including 50 other opsin sequences further confirmed the presence of these two opsin classes. While these findings do not necessarily indicate that these unorthodox insects have color vision, they raise the possibility that UV vision plays an important role in the ability of X. peckii males to find the very cryptic strepsipteran females that are situated within their wasp hosts.

Bidirectional regulation of fragile X mental retardation protein phosphorylation controls rhodopsin homoeostasis.

Homoeostatic regulation of the light sensor, rhodopsin, is critical for the maintenance of light sensitivity and survival of photoreceptors. The major fly rhodopsin, Rh1, undergoes light-induced endocytosis and degradation, but its protein and mRNA levels remain constant during light/dark cycles. It is not clear how translation of Rh1 is regulated. Here, we show that adult photoreceptors maintain a constant, abundant quantity of ninaE mRNA, which encodes Rh1. We demonstrate that the Fmr1 protein associates with ninaE mRNA and represses its translation. Further, light exposure triggers a calcium-dependent dephosphorylation of Fmr1, which relieves suppression of Rh1 translation. We demonstrate that Mts, the catalytic subunit of protein phosphatase 2A (PP2A), mediates light-induced Fmr1 dephosphorylation in a regulatory B subunit of PP2A (CKa)-dependent manner. Finally, we show that blocking light-induced Rh1 translation results in reduced light sensitivity. Our results reveal the molecular mechanism of Rh1 homoeostasis and physiological consequence of Rh1 dysregulation.

MECHANISMS OF INTERACTION BETWEEN THE CIRCADIAN SYSTEM, EEG RHYTHMS AND REGULATION OF VEGETATIVE PROCESSES

Aim - to investigate the dynamics of EEG rhythms and vegetative responses in human on a short-term exposure of the retina to the blue light in the spectrum of maximum sensitivity of circadian photoreceptors during daytime wake. Materials and methods. EEG parameters (BP-010302 BrainАmp Standart128), blood pressure and heart rate variability (HRV) were recorded at 22 volunteer students aged 18-20 years before, after and during the 2-5 minute stimulation of circadian retinal receptors by blue light with maximum wavelength of 480 nm. Results. The stimulation of the photoreceptors of the circadian system correlates with the dynamics of the following neurovegetative processes: desynchronization in beta2- and gamma EEG rhythms, synchronization in teta2- and alpha1-frequency bands; increase in the duration of RR interval and power of low-frequency component of HRV, decrease in the percentage of high-frequency oscillation spectrum of HRV and decrease in systolic blood pressure. Termination of the stimulation of circadian system photoreceptors causes the transformation of EEG rhythms response with predominance of synchronization in low (teta1, teta 2), medium (alpha 1, alpha 2, alfa 3) and high frequency (beta 2) bands. Conclusion. The paper shows the possibility of quick correction of human vegetative background by controlling the circadian system. The human circadian clock is likely to control functional brain activity involving beta 2- and gamma-quantization.

Octopamine cyclic release and its modulation of visual sensitivity in crayfish

The biogenic amine octopamine (OA) modulates invertebrate behavior by changing neuronal responses from sensory inputs to motor outputs. However, the OA modulation of visual sensitivity and its possible coupling to diurnal cycles remains unexplored. Here we studied the diurnal variations in the OA levels in the hemolymph of the crayfish Procambarus clarkii, its release from the structures in the eyestalk and its modulation of the retinal light sensitivity. The hemolymph concentration of OA and its amino acid precursor tyrosine was measured by high-resolution liquid chromatography; OA varied along the 24-hcycle. The peak value appeared about 2h before the light offset which preceded the peak locomotor activity. OA was found in every structure of the eyestalk but displayed higher levels in the retina–lamina ganglionaris. Moreover, OA was released from isolated eyestalks at a rate of 92nmol/eyestalk/min and a calcium-dependent release was evoked by incubation in a high potassium solution. OA injected into dark-adapted crayfish or applied to the isolated retina at concentrations of 1, 10 and 100μM produced a proportionally increasing reduction in the amplitude of the photoreceptor light responses. These OA concentrations did not affect the position of the visual accessory pigments. Our results suggest that OA release in the crayfish eyestalk is coupled to the 24-hcycle to regulate the diurnal reduction of the photoreceptor sensitivity and to favor the expression of exploratory locomotion during the dark phase of the circadian cycle.

Bioinspired Polarization Sensitive Photodetector System Using Orientation‐Tunable PDA Microfibers Arrays

Most insect eyes use microvillar photoreceptors, where the visual pigment rhodopsin is aligned within tubular microvilli, endowing the insects with amazing navigation ability through detecting the polarization of illuminating light in the sky. Herein, polydiacetylene‐polystyrene (PDA‐PS) hybrid microfibers are fabricated by electrospinning method and it is demonstrated that PDA‐PS hybrid microfibers exhibit interesting polarized waveguiding properties, which is found to be dependent on the ordered alignment of PDA chains, but not on the propagating distance or the wavelength of the excitation light. Moreover, three PDA‐PS microfibers with different polarized waveguiding behavior can be assembled together as polarization sensitive photoreceptors to mimic the natural rhabdome arrays in insect eyes, since the physical dimensions, structure, and function of single PDA‐PS microfiber are comparable to that of natural rhabdomere. image

Retinal, visual, and refractive development in retinopathy of prematurity.

The pivotal role of the neurosensory retina in retinopathy of prematurity (ROP) disease processes has been amply demonstrated in rat models. We have hypothesized that analogous cellular processes are operative in human ROP and have evaluated these presumptions in a series on non-invasive investigations of the photoreceptor and post-receptor peripheral and central retina in infants and children. Key results are slowed kinetics of phototransduction and deficits in photoreceptor sensitivity that persist years after ROP has completely resolved based on clinical criteria. On the other hand, deficits in post-receptor sensitivity are present in infancy regardless of the severity of the ROP but are not present in older children if the ROP was so mild that it never required treatment and resolved without a clinical trace. Accompanying the persistent deficits in photoreceptor sensitivity, there is increased receptive field size and thickening of the post-receptor retinal laminae in the peripheral retina of ROP subjects. In the late maturing central retina, which mediates visual acuity, attenuation of multifocal electroretinogram activity in the post-receptor retina led us to the discovery of a shallow foveal pit and significant thickening of the post-receptor retinal laminae in the macular region; this is most likely due to failure of the normal centrifugal movement of the post-receptor cells during foveal development. As for refractive development, myopia, at times high, is more common in ROP subjects than in control subjects, in accord with refractive findings in other populations of former preterms. This information about the neurosensory retina enhances understanding of vision in patients with a history of ROP, and taken as a whole, raises the possibility that the neurosensory retina is a target for therapeutic intervention.

Croc eyes fine-tuned to lurk at water surface

Crocodiles and alligators have perched at the water's edge waiting for the perfect dining opportunity to pass for millions of years. Explaining how the animals also spend much of their time immersed in water with only their eyes and nostrils protruding above the surface, Nicolas Nagloo from The University of Western Australia adds that this posture provides them with a unique perspective on the world. ‘The water surface makes up the majority of the bottom of the visual field and the visual horizon occurs along the riverbanks where the crocodile sees best’, he says. However, while the visual worlds of saltwater and freshwater crocodiles are essentially identical above the water's surface, the light conditions are significantly different when the animals are submerged: ‘In freshwater habitats, there is an abundance of long wavelength [red] light… In contrast, saltwater habitats transmit a broader range of wavelengths, providing a greater amount of short wavelength [blue] light’, Nagloo explains. Knowing that crocodiles cannot see clearly when submerged but they have a fantastic assortment of adaptations that help them to see and hunt in dim conditions, Nagloo and his colleagues Shaun Collin, Jan Hemmi and Nathan Hart decided to gaze into the eyes of two Australian crocodile species to find out more about their colour vision and visual clarity.Investigating the structure of the retina at the back of the eyes of juvenile saltwater crocodiles (Crocodylus porosus) and freshwater crocodiles (Crocodylus johnstoni), Nagloo discovered that instead of having a compact fovea (a depression in the retina where there is a high density of photoreceptors that provide a high-resolution view of the world), the foveae of saltwater and freshwater crocodiles are stretched across the back of the eye in line with the horizon. Describing the elongated structure as a foveal streak, Nagloo says, ‘[it] gives greater visual clarity’, adding that the elongated shape of the structure allows both species to keep a close eye on events on the riverbank without moving their heads.However, when Nagloo investigated the sensitivity of the different photoreceptors in both species’ eyes, he was surprised to find that the crocodiles have relatively sophisticated colour vision, provided by three colour-sensitive cones that are tuned to violet, green and red wavelengths. Also, the sensitivity of the saltwater crocodiles' colour photoreceptors was slightly shifted to shorter (bluer) wavelengths compared with that of the photoreceptors of the freshwater crocodiles, even though neither species can focus underwater, suggesting that they may use their vision underwater more than had been thought.Considering the subtle differences between the visual systems of the two Australian species, Nagloo says that the crocodiles have finely tuned visual systems that give each species an advantage while in their own environments. And he is now keen to find out how the vision of both species adapts as they grow. ‘We know that eye size has a big effect on visual clarity and we also know that saltwater crocodiles reach much greater maximum body sizes than freshwater crocodiles, so it would be interesting to find out whether the eye of saltwater crocodiles also gets much bigger than the freshwaters’ and what impact that would have on visual clarity,’ he says.

Correlated Evolution of Short Wavelength Sensitive Photoreceptor Sensitivity and Color Pattern in Lake Malawi Cichlids

For evolutionary ecologists, the “holy grail” of visual ecology is to establish an unambiguous link between photoreceptor sensitivity, the spectral environment, and the perception of specific visual stimuli (e.g., mates, food, predators, etc.). Due to the bright nuptial colors of the males, and the role female mate choice plays in their evolution, the haplochromine cichlid fishes of the African great lakes are favorite research subjects for such investigations. Despite this attention, current evidence is equivocal; while distinct correlations among photoreceptor sensitivity, photic environment, and male coloration exist in Lake Victorian haplochromines, attempts to find such correlations in Lake Malawian cichlids have failed. Lake Malawi haplochromines have a wide variability in their short-wavelength-sensitive photoreceptors, especially compared to their mid- and long-wavelength-sensitive photoreceptors; these cichlids also vary in the degree to which they express one of three basic color patterns (vertical bars, horizontal stripes, and solid patches of colors), each of which is likely used in a different form of communication. Thus, we hypothesize that, in these fishes, spectral sensitivity and color pattern have evolved in a correlated fashion to maximize visual communication; specifically, ultraviolet sensitivity should be found in vertically-barred species to promote ‘private’ communication, while striped species should be less likely to have ultraviolet sensitivity, since their color pattern carries ‘public’ information. Using phylogenetic independent contrasts, we found that barred species had strong sensitivity to ultraviolet wavelengths, but that striped species typically lacked sensitivity to ultraviolet light. Further, the only variable, even when environmental variables were simultaneously considered, that could predict ultraviolet sensitivity was color pattern. We also found that, using models of correlated evolution, color pattern and ultraviolet sensitivity are correlated in Lake Malawi cichlid evolution, with the likely ancestor being a vertically-barred, ultraviolet-sensitive species, the descendants of which lost both ultraviolet sensitivity and a barred color pattern. These results, indicating that communication of ‘public’ and ‘private’ signals is mediated via differing perceptions of color patterns, suggest a functional connection between visual sensitivity and colour pattern, a novel finding in Lake Malawi cichlids.

Signalling beyond photon absorption: extracellular retinoids and growth factors modulate rod photoreceptor sensitivity.

We propose that the end product of chromophore bleaching in rod photoreceptors, all-trans retinol, is part of a feedback loop that increases the sensitivity of the phototransduction cascade in rods. A previously described light-induced hypersensitivity in rods, termed adaptive potentiation, is reduced by exogenously applied all-trans retinol but not all-trans retinal. This potentiation is produced by insulin-like growth factor-1, whose binding proteins are located in the extracellular matrix, even in our isolated retina preparation after removal of the retinal pigmented epithelium. Simple modelling suggests that the light stimuli used in the present study will produce sufficient all-trans retinol within the interphotoreceptor matrix to explain the potentiation effect. Photoreceptors translate the absorption of photons into electrical signals for propagation through the visual system. Mammalian photoreceptor signalling has largely been studied in isolated cells, and such studies have necessarily avoided the complex environment of supportive proteins that surround the photoreceptors. The interphotoreceptor matrix (IPM) contains an array of proteins that aid in both structural maintenance and cellular homeostasis, including chromophore turnover. In signalling photon absorption, the chromophore 11-cis retinal is first isomerized to all-trans retinal, followed by conversion to all-trans retinol (ROL) for removal from the photoreceptor. Interphotoreceptor retinoid-binding protein (IRBP) is the most abundant protein in the IPM, and it promotes the removal of bleached chromophores and recycling in the nearby retinal pigment epithelium. By studying the light responses of isolated mouse retinas, we demonstrate that ROL can act as a feedback signal onto photoreceptors that influences the sensitivity of phototransduction. In addition to IRBP, the IPM also contains insulin-like growth factor-1 (IGF-1) and its associated binding proteins, although their functions have not yet been described. We demonstrate that extracellular application of physiological concentrations of IGF-1 can increase rod photoreceptor sensitivity in mammalian retinas. We also determine that chromophores and growth factors can limit the range of a newly described form of photoreceptor light adaptation. Finally, fluorescent antibodies demonstrate the presence of IRBP and IGFBP-3 in isolated retinas. A simple model of the formation and release of ROL into the extracellular space quantitatively describes this novel feedback loop.

Vision on the high seas: spatial resolution and optical sensitivity in two procellariiform seabirds with different foraging strategies.

Procellariiform or 'tubenosed' seabirds are challenged to find prey and orient over seemingly featureless oceans. Previous studies have found that life-history strategy (burrow versus surface nesting) was correlated to foraging strategy. Burrow nesters tended to track prey using dimethyl sulphide (DMS), a compound associated with phytoplankton, whereas surface-nesting species did not. Burrow nesters also tended to be smaller and more cryptic, whereas surface nesters were larger with contrasting plumage coloration. Together these results suggested that differences in life-history strategy might also be linked to differences in visual adaptations. Here, we used Leach's storm petrel, a DMS-responder, and northern fulmar, a non-responder, as model species to test this hypothesis on their sensory ecology. From the retinal ganglion cell density and photoreceptor dimensions, we determined that Leach's storm petrels have six times lower spatial resolution than the northern fulmars. However, the optical sensitivity of rod photoreceptors is similar between species. These results suggest that under similar atmospheric conditions, northern fulmars have six times the detection range for similarly sized objects. Both species have extended visual streaks with a central area of highest spatial resolution, but only the northern fulmar has a central fovea. The prediction that burrow-nesting DMS-responding procellariiforms should differ from non-responding species nesting in the open holds true for spatial resolution, but not for optical sensitivity. This result may reflect the fact that both species rely on olfaction for their nocturnal foraging activity, but northern fulmars might use vision more during daytime.

PERSISTENT RETINAL CHANGES AFTER INTRAVITREAL OCRIPLASMIN

Postmarket analysis helps identify potentially important side effects not discovered during clinical trials. Ocriplasmin is a recently approved medication administered by intravitreal injection for the treatment of symptomatic vitreomacular adhesion and macular hole. Overall, clinical trials of ocriplasmin have shown a relatively high safety profile. However, recently, a series of case reports have highlighted acute vision loss associated with abnormal findings on spectral domain optical coherence tomography and electroretinography. A 70-year-old man developed multiple discrete pockets of macular subretinal fluid 10 weeks after intravitreal ocriplasmin injection, with minimal resolution of fluid over 11 months. Electroretinographic findings demonstrated persistent rod photoreceptor sensitivity loss at 14 months after injection. This is the first report of persistent electroretinographic and optical coherence tomographic abnormalities after ocriplasmin injection. Electroretinography abnormalities were noted in a small percentage of patients during ocriplasmin clinical trials and in a recent series of case reports and postmarket survey analysis. The authors propose that cleavage of fibronectin and laminin causes disruption of the interphotoreceptor matrix, leading to the ellipsoid layer attenuation and resultant electroretinographic sensitivity loss and subretinal fluid described on spectral domain optical coherence tomography. Persistent changes over 14 months in this patient indicate that ocriplasmin may have the potential to cause permanent retinal damage.

Wavelength discrimination in the hummingbird hawkmoth Macroglossum stellatarum

Despite the strong relationship between insect vision and the spectral properties of flowers, the visual system has been studied in detail in only a few insect pollinator species. For instance, wavelength discrimination thresholds have been determined in two species only: the honeybee (Apis mellifera) and the butterfly Papilio xuthus. Here, we present the wavelength discrimination thresholds (Δλ) for the hawkmoth Macroglossum stellatarum. We compared the data with those found for the honeybee, the butterfly P. xuthus and the predictions of a colour discrimination model. After training moths to feed from a rewarded disc illuminated with a monochromatic light, we tested them in a dual-choice situation, in which they had to choose between light of the training wavelength and a novel unrewarded wavelength. To characterise the Δλ function, we decreased the difference between wavelengths in subsequent tests. We also varied the light intensity to test its effect on the discrimination capacity. In agreement with the predictions of the model, we found two expected minima of discrimination where photoreceptor sensitivities overlap, as well as a third, minor, unpredicted minimum around the peak of the blue photoreceptor. Macroglossum stellatarum is capable of discriminating between lights with a wavelength difference of 1-2 nm. These discrimination minima are similar to those found for the tetrachromatic P. xuthus, and are better than those of the honeybee. The moth is also capable of using achromatic information to discriminate between lights of long wavelengths.

Algal Photobiology: A Rich Source of Unusual Light Sensitive Proteins for Synthetic Biology and Optogenetics.

The light absorption system in eukaryotic (micro)algae includes highly sensitive photoreceptors, which change their conformation in response to different light qualities on a subsecond time scale and induce physiological and behavioral responses. Some of the light sensitive modules are already in use to engineer and design photoswitchable tools for control of cellular and physiological activities in living organisms with various degrees of complexity. Thus, identification of new light sensitive modules will not only extend the source material for the generation of optogenetic tools but also foster the development of new light-based strategies in cell signaling research. Apart from searching for new proteins with suitable light-sensitive modules, smaller variants of existing light-sensitive modules would be helpful to simplify the construction of hybrid genes and facilitate the generation of mutated and chimerized modules. Advances in genome and transcriptome sequencing as well as functional analysis of photoreceptors and their interaction partners will help to discover new light sensitive modules.

Circularly Polarized Light as a Communication Signal in Mantis Shrimps

Animals that communicate using conspicuous body patterns face a trade-off between desired detection by intended receivers and undesired detection from eavesdropping predators, prey, rivals, or parasites. In some cases, this trade-off favors the evolution of signals that are both hidden from predators and visible to conspecifics. Animals may produce covert signals using a property of light that is invisible to those that they wish to evade, allowing them to hide in plain sight (e.g., dragonfish can see their own, otherwise rare, red bioluminescence). The use of the polarization of light is a good example of a potentially covert communication channel, as very few vertebrates are known to use polarization for object-based vision. However, even these patterns are vulnerable to eavesdroppers, as sensitivity to the linearly polarized component of light is widespread among invertebrates due to their intrinsically polarization sensitive photoreceptors. Stomatopod crustaceans appear to have gone one step further in this arms race and have evolved a sensitivity to the circular polarization of light, along with body patterns producing it. However, to date we have no direct evidence that any of these marine crustaceans use this modality to communicate with conspecifics. We therefore investigated circular polarization vision of the mantis shrimp Gonodactylaceus falcatus and demonstrate that (1) the species produces strongly circularly polarized body patterns, (2) they discriminate the circular polarization of light, and (3) that they use circular polarization information to avoid occupied burrows when seeking a refuge.

Cyp27c1 Red-Shifts the Spectral Sensitivity of Photoreceptors by Converting Vitamin A1 into A2

Some vertebrate species have evolved means of extending their visual sensitivity beyond the range of human vision. One mechanism of enhancing sensitivity to long-wavelength light is to replace the 11-cis retinal chromophore in photopigments with 11-cis 3,4-didehydroretinal. Despite over a century of research on this topic, the enzymatic basis of this perceptual switch remains unknown. Here, we show that a cytochrome P450 family member, Cyp27c1, mediates this switch by converting vitamin A1 (the precursor of 11-cis retinal) into vitamin A2 (the precursor of 11-cis 3,4-didehydroretinal). Knockout of cyp27c1 in zebrafish abrogates production of vitamin A2, eliminating the animal's ability to red-shift its photoreceptor spectral sensitivity and reducing its ability to see and respond to near-infrared light. Thus, the expression of a single enzyme mediates dynamic spectral tuning of the entire visual system by controlling the balance of vitamin A1 and A2 in the eye.

Optics of cone photoreceptors in the chicken (Gallus gallus domesticus).

Vision is the primary sensory modality of birds, and its importance is evident in the sophistication of their visual systems. Coloured oil droplets in the cone photoreceptors represent an adaptation in the avian retina, acting as long-pass colour filters. However, we currently lack understanding of how the optical properties and morphology of component structures (e.g. oil droplet, mitochondrial ellipsoid and outer segment) of the cone photoreceptor influence the transmission of light into the outer segment and the ultimate effect they have on receptor sensitivity. In this study, we use data from microspectrophotometry, digital holographic microscopy and electron microscopy to inform electromagnetic models of avian cone photoreceptors to quantitatively investigate the integrated optical function of the cell. We find that pigmented oil droplets primarily function as spectral filters, not light collection devices, although the mitochondrial ellipsoid improves optical coupling between the inner segment and oil droplet. In contrast, unpigmented droplets found in violet-sensitive cones double sensitivity at its peak relative to other cone types. Oil droplets and ellipsoids both narrow the angular sensitivity of single cone photoreceptors, but not as strongly as those in human cones.

A colour to birds and to humans: why is it so different?

The avian visual model has become nowadays a standard for quantifying colours of birds. Here, I review the biological bases of the importance of visual modelling to most ornithologists, focusing on the causes of the difference in colours to birds and to humans, both proximately and ultimately. Not only the sensitivity of retinal photoreceptors and performances of ocular media, but also the number of photoreceptor types are all attributed to the bird–human difference proximately. As the ultimate cause, the evolutionary history of birds and humans should divide the colours perceived by them: birds would retain their colour vision from the ancient ancestry, while primates such as humans would have reacquired the colour vision relatively recently. Finally, I review how to process and to analyze data produced by the visual model.

Function and evolutionary origin of unicellular camera-type eye structure.

The ocelloid is an extraordinary eyespot organelle found only in the dinoflagellate family Warnowiaceae. It contains retina- and lens-like structures called the retinal body and the hyalosome. The ocelloid has been an evolutionary enigma because of its remarkable resemblance to the multicellular camera-type eye. To determine if the ocelloid is functionally photoreceptive, we investigated the warnowiid dinoflagellate Erythropsidinium. Here, we show that the morphology of the retinal body changed depending on different illumination conditions and the hyalosome manifests the refractile nature. Identifying a rhodopsin gene fragment in Erythropsidinium ESTs that is expressed in the retinal body by in situ hybridization, we also show that ocelloids are actually light sensitive photoreceptors. The rhodopsin gene identified is most closely related to bacterial rhodopsins. Taken together, we suggest that the ocelloid is an intracellular camera-type eye, which might be originated from endosymbiotic origin.