Constancy of synaptic ribbon numbers in the retina of the arctic chary,Salvelinus alpinus

Synopsis At high latitudes, such as in Iceland, the daily photoperiod varies from almost continuous darkness in winter to virtually constant light in summer. Previous studies of detailed retinal structure in vertebrates have shown significant daily and annual effects of photoperiod. We sampled arctic charr in Iceland during the summer, including fish that were both light- and dark-adapted, during both day and night. We observed retinomotor responses characteristic of light- and dark-adaptation, but found no difference in the number of synaptic ribbons in the retina. The morpho-physiological changes, appearing as retinomotor responses, are thus not expressed at the synaptic level.     

Dopamine Induces Light-Adaptive Retinomotor Movements in Bullfrog Cones via D2 Receptors and in Retinal Pigment Epithelium via D1 Receptors

In the eyes of lower vertebrates, retinal photoreceptors and melanin pigment granules of the retinal pigment epithelium (RPE) exhibit characteristic retinomotor movements in response to changes in ambient illumination and to signals from an endogenous circadian clock. We previously reported that 3,4-dihydroxyphenylethylamine (dopamine) mimicked the effect of light on these movements in photo-receptors and RPE cells of green sunfish, Lepomis cyanellus, by interacting with D2 dopaminergic receptors. Here, we report that dopamine also mimics the effect of light on cone and RPE retinomotor movements in bullfrogs, Rana catesbeiana, i.e., dopamine induces cone contraction and RPE pigment dispersion. Dopamine induced cone contraction in isolated dark-adapted bullfrog retinas incubated in constant darkness in the presence of the phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine (IBMX). This effect of dopamine was inhibited by a D2 but not a D1 antagonist and mimicked by a D2 but not a D1 agonist. These results suggest that induction of cone contraction by dopamine is mediated by D2 dopaminergic receptors and that cone adenylate cyclase activity is inhibited. Thus, dopamine acts via the same type of receptor in both bullfrog and green sunfish retinas to induce cone contraction. In contrast, dopamine influences RPE retinomotor movement via different receptors in fish and bullfrog. Dopamine induced light-adaptive pigment dispersion in isolated dark-adapted bullfrog RPE-eyecups incubated in constant darkness in normal Ringer's solution. Because the retina was not present, these experiments demonstrate a direct effect of dopamine on bullfrog RPE. This effect of dopamine on bullfrog RPE was inhibited by a D1 but not a D2 antagonist and mimicked by a D1 but not a D2 agonist. Furthermore, agents that increase the concentration of intracellular cyclic AMP also induced pigment dispersion in dark-adapted bullfrog RPE-eyecups incubated in the dark. These results suggest that dopamine induces pigment dispersion in bullfrog RPE via D1 dopaminergic receptors. Thus, dopamine acts via different receptors on bullfrog (D1) versus green sunfish (D2) RPE to induce pigment dispersion. In addition, inhibitor studies indicate that pigment dispersion is actin dependent in teleost but not in bullfrog RPE. Dopamine-induced pigment dispersion was inhibited by cytochalasin D in isolated RPE sheets of green sunfish but not in RPE-eyecups of bullfrogs. Together, these observations indicate that dopamine mimics the effect of light on cone and RPE retinomotor movements in both fish and bullfrogs. However, in the RPE, different receptors mediate the effect of dopamine, and different cytoskeletal mechanisms are used to affect pigment transport.(ABSTRACT TRUNCATED AT 400 WORDS)     

Dopaminergic Regulation of Cone Retinomotor Movement in Isolated Teleost Retinas: I. Induction of Cone Contraction Is Mediated by D2 Receptors

In the retinas of lower vertebrates, retinal photoreceptors and melanin pigment granules of the retinal pigment epithelium (RPE) undergo characteristic movements in response to changes in light intensity and to signals from an endogenous circadian clock. To identify agents responsible for mediating light and/or circadian regulation of these retinomotor movements, we investigated the effects of hormones and neurotransmitters on cone, rod, and RPE movements in the green sunfish, Lepomis cyanellus. We report here that 3,4-dihydroxyphenylethylamine (dopamine) mimics the effect of light by inducing light-adaptive retinomotor movements in all three cell types. In isolated dark-cultured retinas, dopamine induced light-adaptive cone contraction with a half-maximal effect at 10(-8) M. This effect of dopamine was inhibited by antagonists with a potency order characteristic of D2 receptor mediation. The dopamine uptake blocker benztropine also induced light-adaptive cone contraction in isolated dark-cultured retinas, suggesting that there is continuous dopamine release in the dark but that concomitant uptake normally prevents activation of cone contraction. That dopamine plays a role in light regulation of cone movement is further suggested by the observation that light-induced cone contraction was partially inhibited by sulpiride, a selective D2 dopamine antagonist, or by Co2+, a blocker of synaptic transmission. Sulpiride also promoted dark-adaptive cone elongation in isolated light-adapted retinas, suggesting that continuous dopamine action is required in the light to maintain the light-adapted cone position. Dopamine can act directly on D2 receptors located on rod and cone inner/outer segments: dopamine induced light-adaptive retinomotor movements in isolated distal fragments of dark-adapted photoreceptors cultured in the dark. Together our results indicate that dopamine induces light-adaptive retinomotor movements in cones, rods, and RPE cells by activating D2 receptors. We suggest that, in vivo, dopamine plays a role in both light and circadian regulation of retinomotor movements.     

Scanning electron microscopy of photoreceptor cells in the light- and dark-adapted retina of Haplochromis burtoni (Cichlidae,Teleostei)

Summary The photoreceptor layer in the retina of Haplochromis burtoni (Cichlidae, Teleostei) was studied by scanning electron microscopy. Three types of receptors were identified: rods, single-cones and double-cones. The three-dimensional arrangement of these photoreceptors is described in the light- and dark-adapted retina. The surface of the inner segment of the photoreceptor cells displays fine vertical fissures which give rise to slender processes. These so called calycal processes which are of different lengths in rods and cones, surround the beginning of the smooth-surfaced outer segment. The myoid, the contractile part of the receptor, which is located beneath the ellipsoid, was examined in the single-cones of the dark-adapted retina. It is a slender structure with surface infoldings. The myoid, studied by transmission electron microscopy, contains bundles of parallel myofilaments, which are thought to be contractile.This investigation was supported by grants of the Deutsche Forschungsgemeinschaft (Sonderforschungsbereich 51-E/10)     

Retinal photoreceptor fine structure in the red-backed salamander (Plethodon cinereus).

The retinal photoreceptors of the red-backed salamander (Plethodon cinerus) have been studied by light and electron microscopy. Rods and single cones are present in this duplex retina in a ratio of about 25:1. The photoreceptors in this amphibian species are much larger than is reported for most vertebrates. In the light-adapted state, rods reach deep into the retinal epithelial (RPE) layer. The rod outer segment is composed of discs of uniform diameter displaying several very deep incisors. The rod inner segment displays a distal elliposid of mitochondria and a short stout myoid region. Rod nuclei are electron dense and often protrude through the external limiting membrane. Rod synaptic spherules are large and display several invaginated synaptic sites as well as superficial synapses. It is felt that the rods do not undergo retinomotor movements. The cone photoreceptors are much smaller than the rods and display a tapering outer segment, an unusual modified ellipsoid and a large parabolid of glycogen in the inner segment. Cone nuclei are less electron dense than rods and are located at all levels within the outer nuclear layer. The synaptic pedicle of the cones is larger, more electron lucent and display more synaptic sites (both invaginated and superficial) than that of rods. It is felt that cone photomechanical responses are minimal.     

Fine structure of the retina of black bass, Micropterus salmoides (Centrarchidae, Teleostei).

The structure of light- and dark-adapted retina of the black bass, Micropterus salmoides has been studied by light and electron microscopy. This retina lacks blood vessels at all levels. The optic fiber layer is divided into fascicles by the processes of Müller cells and the ganglion cell layer is represented by a single row of voluminous cells. The inner nuclear layer consists of two layers of horizontal cells and bipolar, amacrine and interplexiform cells. In the outer plexiform layer we observed the synaptic terminals of photoreceptor cells, rod spherules and cone pedicles and terminal processes of bipolar and horizontal cells. The spherules have a single synaptic ribbon and the pedicles possess multiple synaptic ribbons. Morphologically, we have identified three types of photoreceptors: rods, single cones and equal double cones which undergo retinomotor movements in response to changes in light conditions. The cones are arranged in a square mosaic whereas the rods are dispersed between the cones.     

Outer retinal fine structure of the garfish Belone belone (L.) (Belonidae, Teleostei) during light and dark adaptation – photoreceptors, cone patterns and densities

In the present EM study, we investigate the retina of Belone belone , a visually-orientated marine predator living close to the water surface. In the duplex retina, four morphologically different cone types are observed: unequal and equal double cones, long single cones and triple cones. In the light-adapted state, five different cone patterns occur: row, twisted row, square, pentagonal and hexagonal patterns. High double cone densities are found ventro-nasally, ventro-temporally and dorso-temporally. Throughout the retina the double cone/single cone ratio is 2 : 1, in the ventral part, however, a 1 : 1 ratio occurs. In the vitreous body we found a curtain-like intraocular septum dividing the retina into two morphologically different regions. In most areas of the dark-adapted retina the cone patterns are absent at the ellipsoid level, with long single cones standing more vitreally in the light path than double cones. The mosaics are retained, however, in the outer nuclear layer. Typical dark adaptation, i.e. the retinomotor movements of the retinal pigment epithelium and photoreceptors in response to the dark adaptation (light change) is not present in the peripheral ventral and parts of the central ventral area. In both regions we found a twisted row pattern of cones having a vitreal position. The findings are discussed with respect to the photic habitat and feeding habits of this species.     

Oxygen distribution and consumption in the macaque retina

The oxygen distribution in the retina of six anesthetized macaques was investigated as a model for retinal oxygenation in the human retina in and adjacent to the fovea. P(O2) was measured as a function of retinal depth under normal physiological conditions in light and dark adaptation with O(2) microelectrodes. Oxygen consumption (Q(O2)) of the photoreceptors was extracted by fitting a steady-state diffusion model to P(O2) measurements. In the perifovea, the P(O2) was 48 +/- 13 mmHg (mean and SD) at the choroid and fell to a minimum of 3.8 +/- 1.9 mmHg around the photoreceptor inner segments in dark adaptation, rising again toward the inner retina. The P(O2) in the inner half of the retina in darkness was 17.9 +/- 7.8 mmHg. When averaged over the outer retina, photoreceptor Q(O2) (called Q(av)) was 4.6 +/- 2.3 ml O(2).100 g(-1).min(-1) under dark-adapted conditions. Illumination sufficient to saturate the rods reduced Q(av) to 72 +/- 11% of the dark-adapted value. Both perifoveal and foveal photoreceptors received most of their O(2) from the choroidal circulation. While foveal photoreceptors have more mitochondria, the Q(O2) of photoreceptors in the fovea was 68% of that in the perifovea. Oxygenation in macaque retina was similar to that previously found in cats and other mammals, reinforcing the relevance of nonprimate animal models for the study of retinal oxygenation, but there was a smaller reduction in Q(O2) with light than observed in cats, which may have implications for understanding the influence of light under some clinical conditions.     

Electron microscopic observations on the retinal pigment epithelium and choroid in the domestic pig (Sus scrofa)

Summary The morphology of the retinal pigment epithelium (RPE) and adjacent choroid has been investigated by electron microscopy in the domestic pig. The RPE consists of a single layer of cells which are columnar posteriorly but become cuboidal and even squamous moving peripherally in the fundus. The cells of the RPE layer regardless of location display basal (scleral) infoldings and apical (vitreal) processes and are joined laterally by junctional complexes. Throughout the retina the epithelial cells are rich in smooth endoplasmic reticulum and mitochondria but less so in rough endoplasmic reticulum and polysomes. The epithelial nucleus is vesicular and basally located. In the superior fundus an area of the RPE is very lightly pigmented and richer in lysosomes than is this layer in the inferior and peripheral fundus. The choroid overlying this area is also lightly pigmented and contains much collagen in a lamellar arrangement. This region may represent a vestigial tapetum fibrosum. Bruch's membrane is slightly thicker posteriorly but is everywhere seen to have a pentalaminate substructure. The choriocapillaris is a single layer of large capillaries which show numerous fenestrations facing the RPE. In the superior fundus the choriocapillaris is also highly fenestrated facing the choroid.     

Dopamine Inhibits Forskolin- and 3-Isobutyl-1-Methylxanthine-Induced Dark-Adaptive Retinomotor Movements in Isolated Teleost Retinas

We have been investigating the mechanisms of diurnal and circadian regulation of teleost retinomotor movements. In the retinas of lower vertebrates, photoreceptors and melanin pigment granules of the retinal pigment epithelium (RPE) undergo movements at dawn and dusk. These movements continue to occur at subjective dawn and dusk in animals maintained in constant darkness. Cone myoids contract at dawn and elongate at dusk; RPE pigment disperses into the epithelial cells' long apical processes at dawn and aggregates into the cell bodies at dusk. We report here that forskolin, an adenylate cyclase activator, and 3-isobutyl-1-methylxanthine (IBMX), a phosphodiesterase inhibitor, each induces dark-adaptive cone and RPE retinomotor movements in isolated light-adapted green sunfish retinas cultured in constant light. Forskolin induces a 22-fold elevation in retinal cyclic AMP content. Forskolin- and IBMX-induced movements are inhibited approximately 65% and 95%, respectively, by 3,4-dihydroxyphenylethylamine (dopamine). However, dopamine does not inhibit dark-adaptive movements induced by dibutyryl cyclic AMP. Epinephrine is much less effective than dopamine in inhibiting forskolin-induced movements, while phenylephrine and clonidine are totally ineffective. These results are consistent with our previous findings that treatments that increase intracellular cyclic AMP content promote dark-adaptive retinomotor movement. They further suggest that dopamine inhibits adenylate cyclase activity in photoreceptors and RPE cells and thereby favors light-adaptive retinomotor movements.     

Effects of hypoxia on potassium homeostasis and pigment epithelial cells in the cat retina

Intracellular recordings show that light-evoked hyperpolarizations of the apical and basal membranes of the cat retinal pigment epithelium (RPE) are altered by mild hypoxia. RPE cells, like glia, have a high K+ conductance, and measurements with K+-sensitive microelectrodes show that the hypoxic changes in the RPE cell are largely the result of changes in extracellular [K+] in the subretinal space [( K+]o) rather than direct effects on RPE cells. During hypoxia, light-evoked [K+]o responses and membrane responses have longer times to peak, slower and less complete recovery during illumination, and larger amplitudes. In addition to the effects on light-evoked responses, hypoxia causes a depolarization of first the apical and then the basal membranes of RPE cells under dark-adapted conditions. The basal depolarization is accompanied by a decrease in basal membrane resistance. These depolarizations appear to be caused by a rapid increase in [K+]o at the onset of hypoxia, which is maximal in dark adaptation, and smaller if the retina is subjected to maintained illumination. All of the effects are graded with the severity of hypoxia and can be observed at arterial oxygen tensions as high as 65 mmHg, although the threshold may be even higher. We argue that the origin of hypoxic [K+]o changes is probably an inhibition of the photoreceptors' Na+/K+ pump. This work then suggests that photoreceptors are more sensitive to hypoxia than previously believed, and that the high oxygen tension normally provided by the choroidal circulation is necessary for normal photoreceptor function.     

Dopaminergic Regulation of Cone Retinomotor Movement in Isolated Teleost Retinas: II. Modulation by γ-Aminobutyric Acid and Serotonin

In the accompanying paper we reported that 3,4-dihydroxyphenylethylamine (dopamine) induced light-adaptive retinomotor movements in teleost photoreceptors and that this effect was mediated by D2 dopamine receptors located on the photoreceptors themselves. In this study, we investigated the effects on cone retinomotor movement of three agents that have been reported by others to modulate retinal dopamine release: gamma-aminobutyric acid (GABA), 5-hydroxytryptamine (5-HT, serotonin), and melatonin. We report here that the GABA antagonists bicuculline and picrotoxin induced light-adaptive cone contraction in dark-adapted green sunfish retinas cultured in constant darkness; thus they mimic the effect of light or exogenously applied dopamine. Since their effects were blocked by either the D2 dopamine antagonist sulpiride or by Co2+, it seems likely that these agents act by enhancing retinal dopamine release. The GABA agonist muscimol produced effects opposite to those of GABA antagonists. Muscimol inhibited light-induced cone contraction in previously dark-adapted retinas and induced dark-adaptive cone elongation in light-adapted retinas. These results suggest that in green sunfish retinas, as has been reported for other retinas, GABA inhibits dopamine release. 5-HT induced light-adaptive cone contraction in dark-adapted retinas; thus 5-HT also mimics the effect of light or exogenously applied dopamine. The effect of 5-HT was blocked by sulpiride, Co2+, or the 5-HT antagonist mianserin. These results suggest that 5-HT induces cone contraction by stimulating dopamine release. Melatonin neither inhibited dopamine-induced cone contraction in retinas cultured in the dark nor induced cone elongation in retinas cultured in the light. Our results suggest that both GABA and 5-HT (but not melatonin) affect cone retinomotor movements in green sunfish by modulating dopamine release: GABA by inhibiting and 5-HT by stimulating dopamine release. We report in the companion paper that dopamine induced contraction in isolated cone fragments. Together these observations strongly suggest that dopamine serves as the final extracellular messenger directly inducing light-adaptive cone retinomotor movement, and that GABA and 5-HT affect these movements by modulating dopamine release.     

Pigmented epithelium to retinal transdifferentiation and Pax6 expression in larval Xenopus laevis

This study examines the retinal transdifferentiation (TD) of retinal pigmented epithelium (RPE) fragments dissected from Xenopus laevis larvae and implanted into the vitreous chamber of non-lentectomized host eyes. In these experimental conditions, most RPE implants transformed into polarized vesicles in which the side adjacent to the lens maintained the RPE phenotype, while the side adjacent to the host retina transformed into a laminar retina with the photoreceptor layer facing the cavity of the vesicle and with the ganglionar cell layer facing the host retina. The formation of a new retina with a laminar organization is the result of depigmentation, proliferation and differentiation of progenitor cells under the influence of inductive factors from the host retina. The phases of the TD process were followed using BrdU labelling as a marker of the proliferation phase and using a monoclonal antibody (mAbHP1) as a definitive indicator of retina formation. Pigmented RPE cells do not express Pax6. In the early phase of RPE to retinal TD, all depigmented and proliferating progenitor cells expressed Pax6. Changes in the Pax6 expression pattern became apparent in the early phase of differentiation, when Pax6 expression decreased in the presumptive outer nuclear layer (ONL) of the new-forming retina. Finally, during the late differentiation phase, the ONL, which contains photoreceptors, no longer expressed Pax6, Pax6 expression being confined to the ganglion cell layer and the inner nuclear layer. These results indicate that Pax6 may have different roles during the different phases of RPE to retinal TD, acting as an early retinal determinant and later directing progenitor cell fate.     

Role of lysophosphatidic acid in the retinal pigment epithelium and photoreceptors

The human retina is a complex structure of organised layers of specialised cells that support the transmission of light signals to the visual cortex. The outermost layer of the retina, the retinal pigment epithelium (RPE), forms part of the blood retina barrier and is implicated in many retinal diseases. Lysophosphatidic acid (LPA) is a bioactive lipid exerting pleiotropic effects in various cell types, during development, normal physiology and disease. Its producing enzyme, AUTOTAXIN (ATX), is highly expressed by the pigmented epithelia of the human eye, including the RPE. Using human pluripotent stem cell (hPSC)-derived retinal cells, we interrogated the role of LPA in the human RPE and photoreceptors. hPSC-derived RPE cells express and synthesize functional ATX, which is predominantly secreted apically of the RPE, suggesting it acts in a paracrine manner to regulate photoreceptor function. In RPE cells, LPA regulates tight junctions, in a receptor-dependent mechanism, with an increase in OCCLUDIN and ZONULA OCCLUDENS (ZO)-1 expression at the cell membrane, accompanied by an increase in the transepithelial resistance of the epithelium. High concentration of LPA decreases phagocytosis of photoreceptor outer segments by the RPE. In hPSC-derived photoreceptors, LPA induces morphological rearrangements by modulating the actin myosin cytoskeleton, as evidenced by Myosin Light Chain l membrane relocation. Collectively, our data suggests an important role of LPA in the integrity and functionality of the healthy retina and blood retina barrier.     

Light-Induced Dopamine Release from Teleost Retinas Acts as a Light-Adaptive Signal to the Retinal Pigment Epithelium

In the retinal pigment epithelium (RPE) of lower vertebrates, melanin pigment granules migrate in and out of the cells' long apical projections in response to changes in light condition. When the RPE is in its normal association with the retina, light onset induces pigment granules to disperse into the apical projections; dark onset induces pigment granules to aggregate into the cell bodies. However, when the RPE is separated from the retina, pigment granule movement in the isolated RPE is insensitive to light onset. It thus seems likely that a signal from the retina communicates light onset to the RPE to initiate pigment dispersion. We have examined the nature of this retina-to-RPE signal in green sunfish, Lepomis cyanellus. In isolated retinas with adherent RPE, light-induced pigment dispersion in the RPE is blocked by treatments known to block Ca2+-dependent transmitter release in the retina. In addition, the medium obtained from incubating previously dark-adapted retinas in the light induces light-adaptive pigment dispersion when added to isolated RPE. In contrast, the medium obtained from incubating dark-adapted retinas in constant darkness does not affect pigment distribution when added to isolated RPE. These results are consistent with the idea that RPE pigment dispersion is triggered by a substance that diffuses from the retina at light onset. The capacity of the conditioned medium from light-incubated retinas to induce pigment dispersion in isolated RPE is inhibited by a D2 dopamine antagonist, but not by D1 or alpha-adrenergic antagonists. Light-induced pigment dispersion in whole RPE-retinas is also blocked by a D2 dopamine antagonist.(ABSTRACT TRUNCATED AT 250 WORDS)     

Apical polarization of N-CAM in retinal pigment epithelium is dependent on contact with the neural retina

The retinal pigment epithelium (RPE) is unique among epithelia in that its apical surface does not face a lumen, but, instead, is specialized for interaction with the neural retina. The molecules involved in the interaction of the RPE with the neural retina are not known. We show here that the neural cell adhesion molecule (N-CAM) is found both on the apical surface of RPE in situ and on the outer segments of photoreceptors, fulfilling an important requisite for an adhesion role between both structures. Strikingly, culture of RPE results in rapid redistribution of N-CAM to the basolateral surface. This is not due to an isoform shift, since the N-CAM expressed by cultured cells (140 kD) is the same as that expressed by RPE in vivo. Rather, the reversed polarity of N-CAM appears to result from the disruption of the contact between the RPE and the photoreceptors of the neural retina. We suggest that N-CAM in RPE and photoreceptors participate in these interactions.     

Ezrin promotes morphogenesis of apical microvilli and basal infoldings in retinal pigment epithelium

Ezrin, a member of the ezrin/radixin/moesin (ERM) family, localizes to microvilli of epithelia in vivo, where it bridges actin filaments and plasma membrane proteins. Here, we demonstrate two specific morphogenetic roles of ezrin in the retinal pigment epithelium (RPE), i.e., the formation of very long apical microvilli and of elaborate basal infoldings typical of these cells, and characterize the role of ezrin in these processes using antisense and transfection approaches. In the adult rat RPE, only ezrin (no moesin or radixin) was detected at high levels by immunofluorescence and immunoelectron microscopy at microvilli and basal infoldings. At the time when these morphological differentiations develop, in the first two weeks after birth, ezrin levels increased fourfold to adult levels. Addition of ezrin antisense oligonucleotides to primary cultures of rat RPE drastically decreased both apical microvilli and basal infoldings. Transfection of ezrin cDNA into the RPE-J cell line, which has only trace amounts of ezrin and moesin, sparse and stubby apical microvilli, and no basal infoldings, induced maturation of microvilli and the formation of basal infoldings without changing moesin expression levels. Taken together, the results indicate that ezrin is a major determinant in the maturation of surface differentiations of RPE independently of other ERM family members.     

A Highlights from MBoC Selection: Chloride Intracellular Channel 4 Is Critical for the Epithelial Morphogenesis of RPE Cells and Retinal Attachment

Retinal detachment is a sight-threatening condition. The molecular mechanism underlying the adhesion between the RPE and photoreceptors is poorly understood because the intimate interactions between these two cell types are impossible to model and study in vitro. In this article, we show that chloride intracellular channel 4 (CLIC4) is enriched at apical RPE microvilli, which are interdigitated with the photoreceptor outer segment. We used a novel plasmid-based transfection method to cell-autonomously suppress CLIC4 in RPE in situ. CLIC4 silenced RPE cells exhibited a significant loss of apical microvilli and basal infoldings, reduced retinal adhesion, and epithelial-mesenchymal transition. Ectopically expressing ezrin failed to rescue the morphological changes exerted by CLIC4 silencing. Neural retinas adjacent to the CLIC4-suppressed RPE cells display severe dysplasia. Finally, a high level of aquaporin 1 unexpectedly appeared at the apical surfaces of CLIC4-suppressed RPE cells, together with a concomitant loss of basal surface expression of monocarboxylate transporter MCT3. Our results suggested that CLIC4 plays an important role in RPE-photoreceptor adhesion, perhaps by modulating the activity of cell surface channels/transporters. We propose that these changes may be attributable to subretinal fluid accumulation in our novel retinal detachment animal model.