EPILEPSIA, Issue 7 2003
Graeme J. Sills
Summary: Purpose: The antiepileptic drug (AED) vigabatrin (VGB), which exerts its pharmacologic effects on the ,-aminobutyric acid (GABA) system, causes concentric visual field constriction in >40% of exposed adults. This may be a class effect of all agents with GABA-related mechanisms of action. We compared the concentration-related effects of VGB in rat brain and eye with those of gabapentin (GBP) and topiramate (TPM), both of which have been reported to elevate brain GABA concentrations in humans. Methods: Adult male rats (n = 10) were administered 0.9% saline (control), VGB (250, 500, 1,000 mg/kg), GBP (50, 100, 200 mg/kg), or TPM (12.5, 25, 50, 100 mg/kg). At 2 h after dosing, animals were killed, a blood sample obtained, the brain dissected into eight distinct regions, and the retina and vitreous humor isolated from each eye. Samples were analyzed for several GABA-related neurochemical parameters, and serum and tissue drug concentrations determined. Results: VGB treatment produced a significant (p < 0.05) dose-related increase in GABA concentrations and decrease in GABA-transaminase activity in all tissues investigated. This effect was most pronounced in the retina, where VGB concentrations were 18.5-fold higher than those in brain. In contrast, GBP and TPM were without effect on any of the neurochemical parameters investigated and did not accumulate appreciably in the retina. Conclusions: These findings corroborate a previously reported accumulation of VGB in the retina, which may be responsible for the visual field constriction observed clinically. This phenomenon does not appear to extend to other GABAergic drugs, suggesting that these agents might not cause visual field defects. [source]

Retina expresses a novel variant of the ryanodine receptor

EUROPEAN JOURNAL OF NEUROSCIENCE, Issue 11 2007
Varda Shoshan-Barmatz
Abstract Calcium released from intracellular stores via the ryanodine receptor (RyR) mediates a variety of signalling processes. We previously showed that retina expresses the three known types of RyR, but retinal membrane preparations exhibit unique characteristics such as Ca2+ -independent [3H]ryanodine-binding and inhibition by caffeine. We have heretofore suggested that the major retinal RyR isoform is novel. The present study aimed to identify this receptor isoform and to localize RyR in mammalian retina. Immunoblotting with specific and pan-antibodies showed that the major retinal RyR has a mobility similar to that of RyR2 or RyR3. Real-time PCR revealed that the major type is RyR2, and RT-PCR followed by sequencing showed a transcript that encodes a protein with ~ 99% identity to RyR2, yet lacking two regions of seven and 12 amino acids and including an additional insertion of eight amino acids. An antibody against RyR2 localized this type to somas and primary dendrites of most retinal neurons. An antibody against RyR1 localized RyR to most somas but also revealed staining in photoreceptor outer segments, concentrated on the disk membranes at their rim. The ryanodine-binding properties and the electrophoretic mobility of RyR from the outer segments were similar to those of the whole retinal preparation. The results thus identify a novel variant of RyR2 which can contribute to regulating photoreceptor Ca2+ concentrations. The restricted localization of the outer segment RyR to the disk rim suggests that its activation mechanism involves a coupling between retinal RyR and the cGMP-gated channel. [source]

Visual Signals in the Retina: From Photons to Synapses

EXPERIMENTAL PHYSIOLOGY, Issue 1 2000
Leon Lagnado
The ability to see the world around us is an immediate and striking example of the abilities of the nervous system, and perhaps for this reason, vision is one of the most intensively studied aspects of brain function (Hubel, 1995). This paper examines some of the earliest steps in vision occurring in the retina (Dowling, 1987; Rodieck, 1998). [source]

New Cells for the Human Retina

GERMAN RESEARCH, Issue 2-3 2002
Gabriele Thumann PD Dr.
Age-dependent damage to the retina can lead to blindness. It may be possible to restore vision by transplanting cells from the iris onto the retina [source]

Genetic, Temporal and Developmental Differences Between Melatonin Rhythm Generating Systems in the Teleost Fish Pineal Organ and Retina

JOURNAL OF NEUROENDOCRINOLOGY, Issue 4 2003
J. Falcón
Abstract Complete melatonin rhythm generating systems, including photodetector, circadian clock and melatonin synthesis machinery, are located within individual photoreceptor cells in two sites in Teleost fish: the pineal organ and retina. In both, light regulates daily variations in melatonin secretion by controlling the activity of arylalkylamine N -acetyltransferase (AANAT). However, in each species examined to date, marked differences exist between the two organs which may involve the genes encoding the photopigments, genes encoding AANAT, the times of day at which AANAT activity and melatonin production peak and the developmental schedule. We review the fish pineal and retinal melatonin rhythm generating systems and consider the evolutional pressures and other factors which led to these differences. [source]

Crayfish Procambarus clarkii Retina and Nervous System Exhibit Antioxidant Circadian Rhythms Coupled with Metabolic and Luminous Daily Cycles

PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 1 2009
María Luisa Fanjul-Moles
Based on previous work in which we proposed midgut as a putative peripheral oscillator responsible for circadian reduced glutathione (GSH) crayfish status, herein we investigated the retina and optic lobe-brain (OL-B) circadian GSH system and its ability to deal with reactive oxygen species (ROS) produced as a consequence of metabolic rhythms and light variations. We characterized daily and antioxidant circadian variations of the different parameters of the glutathione system, including GSH, oxidized glutathione (GSSG), glutathione reductase (GR) and glutathione peroxidase (GPx), as well as metabolic and lipoperoxidative circadian oscillations in retina and OL-B, determining internal and external GSH-system synchrony. The results demonstrate statistically significant bi- and unimodal daily and circadian rhythms in all GSH-cycle parameters, substrates and enzymes in OL-B and retina, as well as an apparent direct effect of light on these rhythms, especially in the retina. The luminous condition appears to stimulate the GSH system to antagonize ROS and lipid peroxidation (LPO) daily and circadian rhythms occurring in both structures, oscillating with higher LPO under dark conditions. We suggest that the difference in the effect of light on GSH rhythmic mechanisms of both structures for antagonizing ROS could be due to differences in glutathione-system coupling strength with the circadian clock. [source]

9- cis Retinal Increased in Retina of RPE65 Knockout Mice with Decrease in Coat Pigmentation,

PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 6 2006
Jie Fan
The protein RPE65 is essential for the generation of the native chromophore, 11- cis retinal, of visual pigments. However, the Rpe65 knockout (Rpe65 -1- ) mouse shows a minimal visual response due to the presence of a pigment, isorhodopsin, formed with 9- cis retinal. Isorhodopsin accumulates linearly with prolonged dark-rearing of the animals. The majority of Rpe65 -/- mice have an agouti coat color. A tan coat color subset of Rpe65 -/- mice was found to have an enhanced visual response as measured by electroretinograms. The enhanced response was found to be due to increased levels of 9- cis retinal and isorhodopsin pigment levels. Animals of both coat colors reared in cyclic light have minimal levels of regenerated pigment and show photoreceptor degeneration. On dark-rearing, pigment accumulates and photoreceptor degeneration is decreased. In the tan Rpe65 -/- mice, the level of photoreceptor degeneration is less than in the agouti animals, which have an increased pigment and decreased free opsin level. Therefore, photoreceptor damage correlates with the amount of the apoprotein present, supporting findings that the activity from unregenerated opsin can lead to photoreceptor degeneration. [source]

Effect of Visible Light on Normal and P23H-3 Transgenic Rat Retinas: Characterization of a Novel Retinoic Acid Derivative Present in the P23H-3 Retina

PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 3 2006
Todd Duncan
ABSTRACT Transgenic rats with the P23H mutation in rhodopsin exhibit increased susceptibility to light damage, compared with normal animals. It is known that light-induced retinal damage requires repetitive bleaching of rhodopsin and that photoreceptor cell loss is by apoptosis; however, the underlying molecular mechanism(s) leading to photoreceptor cell death are still unknown. Photoproducts, such as all- trans retinal or other retinoid metabolites, released by the extensive bleaching of rhodopsin could lead to activation of degenerative processes, especially in animals genetically predisposed to retinal degenerations. Using wild-type and transgenic rats carrying the P23H opsin mutation, we evaluated the effects of acute intense visible light on retinoid content, type and distribution in ocular tissues. Rats were exposed to green light (480,590 nm) for 0, 5, 10, 30 and 120 min. Following light treatment, rats were sacrificed and neural retinas were dissected free of the retinal pigment epithelium. Retinoids were extracted from retinal tissues and then subjected to HPLC and mass spectral analysis. We found that the light exposure affected relative levels of retinoids in the neural retina and retinal pigment epithelium of wild-type and P23H rat eyes similarly. In the P23H rat retina but not the wild-type rat retina, we found a retinoic acid-like compound with an absorbance maximum of 357 nm and a mass of 304 daltons. Production of this retinoic acid-like compound in transgenic rats is influenced by the age of the animals and the duration of light exposure. It is possible that this unique retinoid may be involved in the process of light-induced retinal degeneration. [source]

Dose-Dependent Immunohistochemical Changes in Rat Cornea and Retina after Oral Methylphenidate Administration

ANATOMIA, HISTOLOGIA, EMBRYOLOGIA, Issue 2 2009
E. Tunc
Summary Methylphenidate hydrochloride (MPH), more commonly known as Ritalin, is a piperidine derivative and is the drug most often used to treat attention deficit/hyperactivity disorder, one of the most common behavioural disorders of children and young adults. The aim of this study was to investigate dose-dependent immunohistochemical Dopamine 2 receptor (D2) expression and apoptosis in the rat cornea and cornea. In this study, 27 female pre-pubertal Wistar albino rats, divided into three different dose groups (5, 10 and 20 mg/kg) and their control groups, were used. They were treated orally with methylphenidate dissolved in saline solution for 5 days per week during 3 months. At the end of the third month, after perfusion fixation, eye tissue was removed. Paraffin sections were collected for immunohistochemical and terminal deoxynucleotidyl-transferase-mediated dUTP-biotin nick end labelling assay studies. In our study, we observed that the cornea D2 receptor reactivity showed a dose-related increase after MPH treatment, especially in basal cells of the epithelium and a dose-dependent decrease in the retinal ganglion cell which was statistically meaningful. Analysis of the cornea thickness results showed no meaningful difference between groups. Apoptotic cell number showed a meaningful increase in the high dose treated group compared to the other groups of the study. The data suggest that Ritalin has degenerative effect on the important functional part of the eye, such as cornea and retina and its activating dopaminergic mechanism via similar neuronal paths, functionally and structurally, to induce morphological changes. As a result, we believe that this morphological changes negatively effecting functional organization of the affected cornea and retina. [source]

Optimized Architecture for Nutrition in the Avascular Retina of Megachiroptera

ANATOMIA, HISTOLOGIA, EMBRYOLOGIA, Issue 5 2007
D. K. Brudenall
Summary Investigations were undertaken to evaluate the unique choroidal vascular system of the Megachiroptera (fruit bats) and its possible significance for retinal nutrition. Fluorescein angiography was performed and documented on Pteropus poliocephalus. Vascular casts were made of the eye of Pteropus scapulatus. Histologic evaluation was performed on P. scapulatus. Results confirmed that each papilla has a vascular core, and a unique vascular system emanating from the optic disc. The histological appearance of the choroid and retina of P. scapulatus confirmed a vascular core to the papillae with a thin, but definite Bruch's membrane. Megachiroptera have a unique vascular system to supply nutrition to the retina consisting of capillary loops within a dense, uniform mosaic of choroidal projections or papillae, which permit the diffusion of metabolites to the retina and a heretofore undescribed vascular tuft emanating from the optic disc. We suggest that this vascular system provides nutrition by diffusion to a thick avascular retina, without any shadowing by vessels, and allows for nocturnal visual acuity and light-gathering capabilities. [source]

The Distribution of Ganglion Cells in the Equine Retina and its Relationship to Skull Morphology

ANATOMIA, HISTOLOGIA, EMBRYOLOGIA, Issue 2 2007
K. E. Evans
Summary It has recently been reported that a strong correlation exists between the distribution of retinal ganglion cells and nose length in the domestic dog. To determine if this phenomenon occurs in another domestic species with diverse skull morphology, the current study examined the distribution of retinal ganglion cells in 30 horses from a variety of breeds. There was a significant variation in the density of ganglion cells found across the retinae. Breed was a significant predictor for ganglion cell density within the visual streak. A strong positive correlation exists between the density of ganglion cells in the visual streak and nasal length. Significant variation was also seen in the area centralis but did not correlate with any of the recorded skull measurements. The findings of this study provide us with further understanding of the equine visual system and the level of variation that exists between individuals of the same species. [source]

Defining Cytochemical Markers for Different Cell Types in the Equine Retina

ANATOMIA, HISTOLOGIA, EMBRYOLOGIA, Issue 6 2006
C. A. Deeg
Summary The major cell types in the mammalian retina are photoreceptors, amacrine, horizontal, bipolar, ganglion and Mueller glial cells. Most of the specific cell types are conserved, but cytochemical markers vary between species. The aim of our study was to characterize cytochemically distinctive markers for different cell types in the equine retina. We were able to define specific markers for equine Mueller glial cells and photoreceptor cells. Furthermore, we describe markers for large ganglion cells, horizontal and amacrine cells and a subpopulation of bipolar cells. Additionally, discrimination between the inner plexiform layer and nerve fibre layer can be achieved by expression of syntaxin and neurofilament 200 respectively. [source]

The Presence of Megamitochondria in the Ellipsoid of Photoreceptor Inner Segment of the Zebrafish Retina

ANATOMIA, HISTOLOGIA, EMBRYOLOGIA, Issue 6 2005
J. Kim
Summary Although the megamitochondria (MM) were localized in various pathological conditions, normal retina of some mammalian species was reported to include MM for various physiological roles. However, it was not clearly confirmed whether the MM is present in the retina of lower vertebrate as well. In this study, we tried to show the presence of the MM in the zebrafish retina using electron microscopic technique. In all the photoreceptors including rods, cones and double cones of the zebrafish retina, MM were observed in the ellipsoid of inner segment. In the photoreceptor epllipsoid of the zebrafish retina, the mitochondria located in the central portion of the ellipsoid had a highly electron-dense matrix, which were accompanied by the mitochondria with electron-lucent matrix in the apical portion of the ellipsoid. The presence of MM was more clearly discernable in the rods, which were localized under the double cones. This finding is somewhat different from those observed in the previous studies because MM were localized in the inner segment of cones, but were not in those of rods in the case of mammalian retina. Although the exact physiological meaning for the presence of MM in some vertebrate species should be further studied, the present study could show that the MM in the ellipsoid of the retinal photoreceptors was not only restricted in some mammalian species. [source]

Postnatal innervation of the rat superior colliculus by axons of late-born retinal ganglion cells

EUROPEAN JOURNAL OF NEUROSCIENCE, Issue 7 2002
Elizabeth J. Dallimore
Abstract Rat retinal ganglion cells (RGCs) are generated between embryonic day (E) 13 and E19. Retinal axons first reach the superior colliculus at E16/16.5 but the time of arrival of axons from late-born RGCs is unknown. This study examined (i) whether there is a correlation between RGC genesis and the timing of retinotectal innervation and (ii) when axons of late-born RGCs reach the superior colliculus. Pregnant Wistar rats were injected intraperitoneally with bromodeoxyuridine (BrdU) on E16, E18 or E19. Pups from these litters received unilateral superior colliculus injections of fluorogold (FG) at ages between postnatal (P) day P0 and P6, and were perfused 1,2 days later. RGCs in 3 rats from each BrdU litter were labelled in adulthood by placing FG onto transected optic nerve. Retinas were cryosectioned and the number of FG, BrdU and double-labelled (FG+/BrdU+) RGCs quantified. In the E16 group, the proportion of FG-labelled RGCs that were BrdU+ did not vary with age, indicating that axons from these cells had reached the superior colliculus by P0/P1. In contrast, for the smaller cohorts of RGCs born on E18 or E19, the proportion of BrdU+ cells that were FG+ increased significantly after birth; axons from most RGCs born on E19 were not retrogradely FG-labelled until P4/P5. Thus there is a correlation between birthdate and innervation in rat retinotectal pathways. Furthermore, compared to the earliest born RGCs, axons from late-born RGCs take about three times longer to reach the superior colliculus. Later-arriving axons presumably encounter comparatively different growth terrains en route and eventually innervate more differentiated target structures. [source]

Effect of Visible Light on Normal and P23H-3 Transgenic Rat Retinas: Characterization of a Novel Retinoic Acid Derivative Present in the P23H-3 Retina

The role of CTGF in the diabetic rat retina and its relationship with VEGF and TGF-,2, elucidated by treatment with CTGFsiRNA

ACTA OPHTHALMOLOGICA, Issue 6 2010
Hongwei Yang
Acta Ophthalmol. 2010: 88: 652,659 Abstract. Purpose:, The critical association of connective tissue growth factor (CTGF) with diabetic retinopathy (DR) remains to be clarified. We detected alterations in the gene and protein expression of CTGF and related cytokines, including vascular endothelial growth factor (VEGF) and transforming growth factor-,2 (TGF-,2), and their response to small interfering RNA (siRNA) targeting the CTGF (CTGFsiRNA) in the retina of diabetic rats. The relationships between CTGF, VEGF and TGF-,2 levels, as well as the degree of apoptosis in the diabetic retina, were also investigated. Methods:, Diabetes was induced in rats by the ,-cell toxin streptozotocin (STZ). Retinas were obtained from control and diabetic rats and similar animals treated with CTGFsiRNA by intravitreal injection. mRNA level and protein expression of CTGF, VEGF and TGF-,2 were measured by reverse transcription-polymerase chain reaction (RT-PCR) and Western blotting, and located by immunohistochemistry. Retinal apoptosis was detected by TUNEL staining. Results:, The levels of CTGF, VEGF and TGF-,2 and the number of TUNEL-positive nuclei were significantly higher in diabetic retinas than in control retinas (p < 0.01). The level of CTGF rose at 8 weeks, earlier than levels of VEGF and TGF-,2, which rose at 12 weeks after the onset of diabetes. The difference was significant (p < 0.05). siRNA-mediated inhibition of CTGF mRNA inhibited retinal VEGF and TGF-,2 and also resulted in a significant decrease in apoptosis. Significant correlations were found between CTGF and VEGF (p = 0.009), CTGF and TGF-,2 (p = 0.01), and apoptosis and these three cytokines (p < 0.01) in the rat retina early in diabetes. Conclusions:, These results suggest that the diabetes-mediated increase in CTGF upregulates VEGF and TGF-,2 expression and induces apoptosis in the retina. This elevation may be inhibited by treatment with CTGFsiRNA. Connective tissue growth factor may serve as a potential target for the prevention and treatment of DR. [source]

The translocation of signaling molecules in dark adapting mammalian rod photoreceptor cells is dependent on the cytoskeleton

CYTOSKELETON, Issue 10 2008
Boris Reidel
Abstract In vertebrate rod photoreceptor cells, arrestin and the visual G-protein transducin move between the inner segment and outer segment in response to changes in light. This stimulus dependent translocation of signalling molecules is assumed to participate in long term light adaptation of photoreceptors. So far the cellular basis for the transport mechanisms underlying these intracellular movements remains largely elusive. Here we investigated the dependency of these movements on actin filaments and the microtubule cytoskeleton of photoreceptor cells. Co-cultures of mouse retina and retinal pigment epithelium were incubated with drugs stabilizing and destabilizing the cytoskeleton. The actin and microtubule cytoskeleton and the light dependent distribution of signaling molecules were subsequently analyzed by light and electron microscopy. The application of cytoskeletal drugs differentially affected the cytoskeleton in photoreceptor compartments. During dark adaptation the depolymerization of microtubules as well as actin filaments disrupted the translocation of arrestin and transducin in rod photoreceptor cells. During light adaptation only the delivery of arrestin within the outer segment was impaired after destabilization of microtubules. Movements of transducin and arrestin required intact cytoskeletal elements in dark adapting cells. However, diffusion might be sufficient for the fast molecular movements observed as cells adapt to light. These findings indicate that different molecular translocation mechanisms are responsible for the dark and light associated translocations of arrestin and transducin in rod photoreceptor cells. Cell Motil. Cytoskeleton 65: 785,800, 2008. © 2008 Wiley-Liss, Inc. [source]

The unconventional myosin-VIIa associates with lysosomes

CYTOSKELETON, Issue 1 2005
Lily E. Soni
Abstract Mutations in the myosin-VIIa (MYO7a) gene cause human Usher disease, characterized by hearing impairment and progressive retinal degeneration. In the retina, myosin-VIIa is highly expressed in the retinal pigment epithelium, where it plays a role in the positioning of melanosomes and other digestion organelles. Using a human cultured retinal pigmented epithelia cell line, ARPE-19, as a model system, we have found that a population of myosin-VIIa is associated with cathepsin D- and Rab7-positive lysosomes. Association of myosin-VIIa with lysosomes was Rab7 independent, as dominant negative and dominant active versions of Rab7 did not disrupt myosin-VIIa recruitment to lysosomes. Association of myosin-VIIa with lysosomes was also independent of the actin and microtubule cytoskeleton. Myosin-VIIa copurified with lysosomes on density gradients, and fractionation and extraction experiments suggested that it was tightly associated with the lysosome surface. These studies suggest that myosin-VIIa is a lysosome motor. Cell Motil. Cytoskeleton 62:13,26, 2005. © 2005 Wiley-Liss, Inc. [source]

Actin-dependent motility of melanosomes from fish retinal pigment epithelial (RPE) cells investigated using in vitro motility assays

CYTOSKELETON, Issue 2 2004
E. L. McNeil
Melanosomes (pigment granules) within retinal pigment epithelial (RPE) cells of fish and amphibians undergo massive migrations in response to light conditions to control light flux to the retina. Previous research has shown that melanosome motility within apical projections of dissociated fish RPE cells requires an intact actin cytoskeleton, but the mechanisms and motors involved in melanosome transport in RPE have not been identified. Two in vitro motility assays, the Nitella assay and the sliding filament assay, were used to characterize actin-dependent motor activity of RPE melanosomes. Melanosomes applied to dissected filets of the Characean alga, Nitella, moved along actin cables at a mean rate of 2 ,m/min, similar to the rate of melanosome motility in dissociated, cultured RPE cells. Path lengths of motile melanosomes ranged from 9 to 37 ,m. Melanosome motility in the sliding filament assay was much more variable, ranging from 0.4,33 ,m/min; 70% of velocities ranged from 1,15 ,m/min. Latex beads coated with skeletal muscle myosin II and added to Nitella filets moved in the same direction as RPE melanosomes, indicating that the motility is barbed-end directed. Immunoblotting using antibodies against myosin VIIa and rab27a revealed that both proteins are enriched on melanosome membranes, suggesting that they could play a role in melanosome transport within apical projections of fish RPE. Cell Motil. Cytoskeleton 58:71,82, 2004. © 2004 Wiley-Liss, Inc. [source]

Coordinated regulation of dorsal bone morphogenetic protein 4 and ventral Sonic hedgehog signaling specifies the dorso-ventral polarity in the optic vesicle and governs ocular morphogenesis through fibroblast growth factor 8 upregulation

DEVELOPMENT GROWTH & DIFFERENTIATION, Issue 4 2010
Takuma Kobayashi
Dorsal and ventral specification in the early optic vesicle plays a crucial role in vertebrate ocular morphogenesis, and proper dorsal-ventral polarity in the optic vesicle ensures that distinct structures develop in separate domains within the eye primordium. The polarity is determined progressively during development by coordinated regulation of extraocular dorsal and ventral factors. In the present study, we cultured discrete portions of embryonic chick brains by preparing anterior cephalon, anterior dorsal cephalon and anterior ventral cephalon, and clearly demonstrate that bone morphogenetic protein 4 (BMP4) and Sonic hedgehog (Shh) constitute a dorsal-ventral signaling system together with fibroblast growth factor 8 (FGF8). BMP4 and Shh upregulate Tbx5 and Pax2, as reported previously, and at the same time Shh downregulates Tbx5, while BMP4 affects Pax2 expression to downregulate similarly. Shh induces Fgf8 expression in the ventral optic vesicle. This, in turn, determines the distinct boundary of the retinal pigmented epithelium and the neural retina by suppressing Mitf expression. The lens develops only when signals from both the dorsal and ventral regions come across together. Inverted deposition of Shh and BMP4 signals in organ-cultured optic vesicle completely re-organized ocular structures to be inverted. Based on these observations we propose a novel model in which the two signals govern the whole of ocular development when they encounter each other in the ocular morphogenic domain. [source]

Cath6, a bHLH atonal family proneural gene, negatively regulates neuronal differentiation in the retina

DEVELOPMENTAL DYNAMICS, Issue 9 2010
Fumi Kubo
Abstract Basic helix,loop,helix (bHLH) transcription factors play important roles in cell type specification and differentiation during the development of the nervous system. In this study, we identified a chicken homolog of Atonal 8/ath6 (Cath6) and examined its role in the developing retina. Unlike other Atonal-family proneural genes that induce neuronal differentiation, Cath6 was expressed in stem cell-like progenitor cells in the marginal region of the retina, and its overexpression inhibited neuronal differentiation. A Cath6 fused with a VP16 transactivation domain recapitulated the inhibitory effect of Cath6 on neuronal differentiation, indicating that Cath6 functions as a transcription activator. These results demonstrate that Cath6 constitutes a unique member of the Atonal-family of genes in that it acts as a negative regulator of neuronal differentiation. Developmental Dynamics 239:2492,2500, 2010. © 2010 Wiley-Liss, Inc. [source]

Cloning and characterization of voltage-gated calcium channel alpha1 subunits in Xenopus laevis during development

DEVELOPMENTAL DYNAMICS, Issue 11 2009
Brittany B. Lewis
Abstract Voltage-gated calcium channels play a critical role in regulating the Ca2+ activity that mediates many aspects of neural development, including neural induction, neurotransmitter phenotype specification, and neurite outgrowth. Using Xenopus laevis embryos, we describe the spatial and temporal expression patterns during development of the 10 pore-forming alpha1 subunits that define the channels' kinetic properties. In situ hybridization indicates that CaV1.2, CaV2.1, CaV2.2, and CaV3.2 are expressed during neurula stages throughout the neural tube. These, along with CaV1.3 and CaV2.3, beginning at early tail bud stages, and CaV3.1 at late tail bud stages, are detected in complex patterns within the brain and spinal cord through swimming tadpole stages. Additional expression of various alpha1 subunits was observed in the cranial ganglia, retina, olfactory epithelium, pineal gland, and heart. The unique expression patterns for the different alpha1 subunits suggests they are under precise spatial and temporal regulation and are serving specific functions during embryonic development. Developmental Dynamics 238:2891,2902, 2009. © 2009 Wiley-Liss, Inc. [source]

What drives cell morphogenesis: A look inside the vertebrate photoreceptor

DEVELOPMENTAL DYNAMICS, Issue 9 2009
Breandán Kennedy
Abstract Vision mediating photoreceptor cells are specialized light-sensitive neurons in the outer layer of the vertebrate retina. The human retina contains approximately 130 million of such photoreceptors, which enable images of the external environment to be captured at high resolution and high sensitivity. Rod and cone photoreceptor subtypes are further specialized for sensing light in low and high illumination, respectively. To enable visual function, these photoreceptors have developed elaborate morphological domains for the detection of light (outer segments), for changing cell shape (inner segments), and for communication with neighboring retinal neurons (synaptic terminals). Furthermore, rod and cone subtypes feature unique morphological variations of these specialized characteristics. Here, we review the major aspects of vertebrate photoreceptor morphology and key genetic mechanisms that drive their formation. These mechanisms are necessary for cell differentiation as well as function. Their defects lead to cell death. Developmental Dynamics 238:2115,2138, 2009. © 2009 Wiley-Liss, Inc. [source]

The embryonic expression patterns and the knockdown phenotypes of zebrafish ADP-ribosylation factor-like 6 interacting protein gene

DEVELOPMENTAL DYNAMICS, Issue 1 2009
Hsing-Yen Huang
Abstract ADP-ribosylation factor-like 6 (Arl6) mutation is linked to human disease and Arl6 interacts with Arl6 interacting protein (Arl6ip). However, the expression pattern and function of Arl6ip during embryogenesis are unknown. To confirm whether abnormal Arl6ip function might result in embryonic defects in zebrafish, we examined the expression patterns of arl6ip during embryogenesis, and they were maternally expressed and exhibited in the brain, optic primordia, hypochord, spinal cord, myotome, heart, fin-bud, kidney, trunk, and retina. Knockdown of Arl6ip revealed the following phenotypic defects: microphthalmia, disorganized pigment pattern, flat head, defective tectum, deficient pectoral fins, abnormal pneumatic duct, pericardial edema, and deformed trunk. Particularly, histological dissection of the retinae of arl6ip -morphants revealed that neuronal differentiation is severely delayed, resulting in no formation of retinal layers. We further confirmed that opsins of arl6ip -morphants were not transcribed. Based on this evidence, Arl6ip may play important roles in zebrafish ocular, heart, and fin-bud development. Developmental Dynamics 238:232,240, 2009. © 2008 Wiley-Liss, Inc. [source]

Expression of AP-2, in the developing chick retina

DEVELOPMENTAL DYNAMICS, Issue 11 2008
Xiaodong Li
Abstract AP-2 is a family of transcription factors that play important roles during embryonic development. Two AP - 2 genes, AP - 2, and AP - 2,, have previously been characterized in chick retina. Here, we demonstrate that a third member of the chicken AP-2 family, AP - 2,, is primarily expressed in the retina and brain, with highest levels at embryonic days 7 to 11. By in situ hybridization and immunohistochemical analysis, we show that AP - 2, RNA and protein are found in a subset of ganglion cells in embryonic chick retina. Co-immunostaining with anti-Brn3a and anti,AP-2, antibodies indicates that approximately one-third of Brn3a-positive ganglion cells express AP-2,. AP - 2, RNA but not AP-2, protein is also found in cells located in the outer half of the inner nuclear layer. The spatial and temporal distribution of AP-2, protein in the retina suggests a transient role in a subset of late-born ganglion cells likely involving axonal trafficking or pathfinding. Developmental Dynamics 237:3210,3221, 2008. © 2008 Wiley-Liss, Inc. [source]

Androgen receptor gene expression in the developing and adult zebrafish brain

DEVELOPMENTAL DYNAMICS, Issue 10 2008
Daniel A. Gorelick
Abstract Androgens play a central role in the regulation of male sexual differentiation and behavior in many vertebrates, including zebrafish. Their signaling is mediated by activation of the androgen receptor. A single androgen receptor (ar) gene was recently identified in zebrafish, which encodes a protein that binds androgens in vitro. However, the tissue-specific expression pattern of this receptor in vivo has not been described. Using whole-mount RNA in situ hybridization, we characterized expression of the ar gene in developing zebrafish and in the adult brain. In embryos, transcripts were found in the presumptive pronephros and in olfactory placodes. By 3,5 days postfertilization, ar transcripts were also detected in the pineal organ anlage and the retina. In the adult brain, ar was expressed in discrete regions of the telencephalon, in the preoptic area, and throughout the periventricular hypothalamus, regions previously implicated in the regulation of sexually dimorphic behaviors in mammals. Developmental Dynamics 237:2987,2995, 2008. © 2008 Wiley-Liss, Inc. [source]

Expression patterns of the opsin 5,related genes in the developing chicken retina

DEVELOPMENTAL DYNAMICS, Issue 7 2008
Sayuri Tomonari
Abstract The opsin gene family encodes G protein,coupled seven-transmembrane proteins that bind to a retinaldehyde chromophore for photoreception. It has been reported that opsin 5 is expressed in mammalian neural tissue, but its function has been elusive. As a first step to understand the function for opsin 5 in the developing eye, we searched for chicken opsin 5 -related genes in the genome by a bioinformatic approach and isolated opsin 5 cDNA fragments from the embryonic retina by RT-PCR. We found that there are three opsin 5,related genes, designated cOpn5m (chicken opsin 5, mammalian type), cOpn5L1 (chicken opsin 5 - like 1), and cOpn5L2 (chicken opsin 5 - like 2), in the chicken genome. Quantitative PCR analysis has revealed that cOpn5m is the most abundant in the developing and early posthatching neural retina. In situ hybridization analysis has shown that cOpn5m is specifically expressed in subsets of differentiating ganglion cells and amacrine cells. These results suggest that the mammalian type opsin 5 may contribute to the development of these retinal cells in the chicken. Developmental Dynamics 237:1910,1922, 2008. © 2008 Wiley-Liss, Inc. [source]

Relationship between delta-like and proneural bHLH genes during chick retinal development

DEVELOPMENTAL DYNAMICS, Issue 6 2008
Branden R. Nelson
Abstract Notch signaling in the retina maintains a pool of progenitor cells throughout retinogenesis. However, two Notch-ligands from the Delta-like gene family, Dll1 and Dll4, are present in the developing retina. To understand their relationship, we characterized Dll1 and Dll4 expression with respect to proliferating progenitor cells and newborn neurons in the chick retina. Dll4 matched the pattern of neural differentiation. By contrast, Dll1 was primarily expressed in progenitor cells. We compared Dll1 and Dll4 kinetic profiles with that of the transiently up-regulated cascade of proneural basic helix,loop,helix (bHLH) genes after synchronized progenitor cell differentiation, which suggested a potential role for Ascl1 in the regulation of Delta-like genes. Gain-of-function assays demonstrate that Ascl1 does influence Delta-like gene expression and Notch signaling activity. These data suggest that multiple sources of Notch signaling from newborn neurons and progenitors themselves coordinate retinal histogenesis. Developmental Dynamics 237:1565,1580, 2008. © 2008 Wiley-Liss, Inc. [source]

Expression patterns and cell cycle profiles of PCNA, MCM6, cyclin D1, cyclin A2, cyclin B1, and phosphorylated histone H3 in the developing mouse retina

DEVELOPMENTAL DYNAMICS, Issue 3 2008
Kirston M. Barton
Abstract A challenge in studying organogenesis is the ability to identify progenitor cell populations. To address this problem, we characterized the expression patterns of cell cycle proteins during mouse retinal development and used flow cytometry to determine the expression profiles in the cell cycle. We found that MCM6 and PCNA are expressed in essentially all retinal progenitor cells throughout the proliferative period and these proteins are readily detectable in all cell cycle phases. Furthermore, their expression levels are downregulated as cells exit the cell cycle and differentiate. We also analyzed the expression of Cyclins D1, A2, and B1, and phosphorylated Histone H3 and found unexpected expression patterns and cell cycle profiles. The combined utilization of the markers tested and the use of flow cytometry should further facilitate the study of stem and progenitor cell behavior during development and in adult tissues. Developmental Dynamics 237:672,682, 2008. © 2008 Wiley-Liss, Inc. [source]

Expression of multiple class three semaphorins in the retina and along the path of zebrafish retinal axons

DEVELOPMENTAL DYNAMICS, Issue 10 2007
Davon C. Callander
Abstract Retinal ganglion cells (RGCs) extend axons that exit the eye, cross the midline at the optic chiasm, and synapse on target cells in the optic tectum. Class three semaphorins (Sema3s) are a family of molecules known to direct axon growth. We undertook an expression screen to identify sema3s expressed in the retina and/or brain close to in-growing RGC axons, which might therefore influence retinal-tectal pathfinding. We find that sema3Aa, 3Fa, 3Ga, and 3Gb are expressed in the retina, although only sema3Fa is present during the time window when the axons extend. Also, we show that sema3Aa and sema3E are present near or at the optic chiasm. Furthermore, sema3C, 3Fa, 3Ga, and 3Gb are expressed in regions of the diencephalon near the path taken by RGC axons. Finally, the optic tectum expresses sema3Aa, 3Fa, 3Fb, and 3Gb. Thus, sema3s are spatiotemporally placed to influence RGC axon growth. Developmental Dynamics 236:2918,2924, 2007. © 2007 Wiley-Liss, Inc. [source]