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PubMed2005

Tbx2b is essential for neuronal differentiation along the dorsal/ventral axis of the zebrafish retina.

The mechanisms by which retinal neurons are patterned along the dorsal/ventral axis remain largely unknown, yet this patterning is integral for the topographic mapping of visual space. With an interest in elucidating the mechanisms that regulate the development of this retinal axis, we have characterized a T-box family transcription factor, Tbx2b, during zebrafish retinogenesis. Tbx2b is expressed throughout all phases of retinal development with a striking asymmetry of distribution highest dorsally to lowest ventrally. To examine Tbx2b function during retinal development, two morpholino antisense oligonucleotides were created; one blocking the translational start site of Tbx2b and the other interfering with Tbx2b mRNA splicing. Injection of either of these morpholinos resulted in profound defects in the development of the dorsal retina. By using molecular markers for neuronal subtypes, the ventral retina contained all cell types, whereas in the dorsal retina, only retinal ganglion cells expressed markers of differentiation. The cells of the dorsal retina were postmitotic, however, as demonstrated by a lack of BrdUrd incorporation during the normal periods of retinal differentiation. Markers for dorsal and ventral retinal compartments were also expressed normally in Tbx2b morphants. Combined, these observations suggest that the cellular mechanisms regulating neuronal differentiation within the retina are asymmetric about the dorsal/ventral axis and that Tbx2b mediates this process within the dorsal retina.

Animals↗
PubMed1978

Amplification of DNA sequences during chicken cartilage and neural retina differentiation.

[3H]BrdUrd-substituted DNA probes were prepared from organ cultures of differentiating chicken neural retina and cell cultures of stage 24 chicken limb buds. Reassociation reactions using the neural retina probe demonstrated amplification of DNA sequences during differentiation of neural retina. This probe also contained sequences present in greater numbers in heart DNA than in DNA from undifferentiated neural retina. Reassociation reactions of both differentiated cartilage and differentiated neural retina DNA with both the neural retina probe and the cartilage probe demonstrated that at least part of the amplified sequences are tissue specific.

Animals↗
PubMed1981

A topographic gradient of molecules in retina can be used to identify neuron position.

A monoclonal antibody was obtained that binds to cell membrane molecules distributed in a topographic gradient in avian retina. Thirty-five-fold more antigen was detected in dorsoposterior retina that in ventroanterior retina. Most of the antigen was associated with the synaptic layers of the retina. Less antigen was detected in cerebrum, thalamus, cerebellum, and optic tectum, but little or none was found in non-neural tissues tested. The antigen was found on most or all cell types in retina, and the concentration of antigen found is a function of the square of the circumferential distance from the ventroanterior pole of the gradient toward the dorsoposterior pole. Thus, the antigen can be used as a marker of cell position along the ventroanterior-dorsoposterior axis of the retina.

Animals↗
PubMed1982

Immunocytochemical localization of enkephalin-like immunoreactivity in the retina of the guinea pig.

The distribution of enkephalin-like immunoreactivity in the retina of the guinea pig was studied. Indirect immunofluorescence techniques were used on retinae with and without colchicine pretreatment. In retinae not receiving colchicine pretreatment, enkephalin-like immunoreactivity was seen in fibers in the inner plexiform layer, predominantly in laminae 1, 3, and 5. In colchicine-pretreated retinae, enkephalin immunofluorescent cell bodies were seen in the inner margin of the inner nuclear layer in addition to the immunoreactive fibers. These cells showed morphological characteristics of amacrine cells. No enkephalin-like immunofluorescence was seen in the optic nerve, ganglion cell layer, or outer nuclear or plexiform layers. These findings of enkephalin-like immunoreactive cells and fibers in a mammalian retina add to the findings in nonmammalian retinae and suggest that the enkephalins play a role in primary sensory systems of mammalian and nonmammalian species.

Animals↗
PubMed1986

Developmental regulation of glutamine synthetase and carbonic anhydrase II in neural retina.

Glutamine synthetase (GS) is expressed in the neural retina only in Muller glia cells and is inducible with cortisol. A chicken genomic clone that contains at least part of the coding region for the GS enzyme was used to investigate developmental changes in the level of GS mRNA in embryonic chicken retina. A major GS transcript (approximately equal to 3 kilobases) detected by the probe begins to accumulate sharply on day 15 of embryonic development. When cortisol is prematurely supplied to early embryonic retina, it induces precocious accumulation of GS mRNA and of the GS enzyme. At later ages, these effects of cortisol are significantly greater, which suggests that competence to transcribe or stabilize GS mRNA in response to stimulation with cortisol increases with development. Carbonic anhydrase II (CA-II) is expressed in early retina in all the cells, but it becomes later restricted to Muller glia. Using cloned CA-II cDNA, we detected a high level of CA-II mRNA in early retina, followed by a decline due to arrest of CA-II mRNA accumulation in differentiated neurons. As glia cells mature, CA-II mRNA and the enzyme increase to a new high level. Therefore, changes in CA-II gene expression during retina development reflect differentiation-dependent cell-type-specific control of CA-II mRNA accumulation.

Age Factors↗
PubMed1997

Identification and quantitation of the fatty acids composing the CoA ester pool of bovine retina, heart, and liver.

Several proteins found in retinal photoreceptor cells (guanylate cyclase activating protein, protein kinase A, recoverin, and transducin) are N-terminally modified with the fatty acids 12:0, 14:0, 14:1n-9, and 14:2n-6, whereas similar proteins in other tissues contain only 14:0. It has been hypothesized that the acyl-CoA pool of the retina contains amounts of 12:0, 14:1n-9, and 14:2n-6 elevated over 14:0, in comparison to other tissues, and this accounts for the specificity of N-terminal fatty acylation. To test this hypothesis, we performed fatty acid analysis on total acyl-CoAs purified from bovine retina (light-adapted), heart, and liver. We also examined the N- and S-linked fatty acid composition of the total protein pools from these tissues. Acyl-CoAs were prepared from heart, liver, and retina and separated by high performance liquid chromatography (HPLC). Identities of peaks were based on HPLC of standard 12:0, 14:0, 14:1n-9, and 14:2n-6 CoAs. Total protein was subjected to base hydrolysis followed by acidic methanolysis to release S- and N-linked fatty acids, respectively, and fatty acid phenacyl esters were prepared for HPLC analysis. Retina had levels of 12:0 (2.7 +/- 2.1%), 14:1n-9 (2.9 +/- 2.2%), and 14:2n-6 (1.6 +/- 0.7%) CoAs below that of 14:0 CoA (7.0 +/- 1.8%). Likewise, heart levels of 14:2n-6 CoA (3.7 +/- 0.1%) were near and 12:0 (2.6 +/- 0. 6%) and 14:1n-9 (0.7 +/- 0.3%) CoAs were below that of 14:0 CoA (3.8 +/- 1.0%). Liver had levels of 12:0 (16.1 +/- 5.7%) and 14:2n-6 (8.1 +/- 1.2%) CoAs above and 14:1n-9 CoA (1.2 +/- 0.6%) below that of 14:0 CoA (5.9 +/- 0.8%). Fatty acid analysis of total protein showed that all tissues contained S-linked 16:0, 18:0, and 18:1n-9. Retina proteins contained N-linked 14:0, 14:1n-9, and 14:2n-6, whereas heart and liver had only 14:0. Our findings do not support the hypothesis that the CoA ester pool of the retina is enriched with 12:0, 14:1n-9, and 14:2n-6 over 14:0, in comparison to other tissues. This suggests that alternative models must be considered for the regulation of N-terminal fatty acylation of proteins in photoreceptor cells.

Acyl Coenzyme A↗
PubMed2001

Differential regulation of the aldehyde dehydrogenase 1 gene in embryonic chick retina and liver.

Aldehyde dehydrogenase (ALDH1) is highly expressed in the dorsal cells of the undifferentiated retina, where it has been proposed to play a role in the formation of a retinoic acid gradient along the ventrodorsal axis. In contrast to the retina, ALDH1 levels increase with differentiation in the liver and remain elevated in the adult tissue. To understand the molecular basis for differential expression of ALDH1 during development, we characterized the ALDH1 transcripts expressed in chick retina and liver. By sequencing, primer extension, and S1 nuclease analysis, we show that retina ALDH1 mRNA has an additional 300 nucleotides of 5'-untranslated sequence resulting from the transcription of two 5' noncoding exons. There is a 24-29-kilobase pair (kb) gap between exons 1 and 2 and a 290-base pair gap between exons 2 and 3. Exon 3, which contains the ALDH1 start codon, represents the first exon of the liver transcript. Using a reporter gene assay, we have identified tissue-specific regulatory elements that govern ALDH1 expression in primary retina and liver cultures. Constructs with >1.6 kb of DNA flanking the 5'-end of exon 1 showed elevated activity in retinal cultures but only basal activity in liver cultures. In contrast, constructs with <1 kb of 5'-flanking DNA were active in both retina and liver cultures. Our results suggest that an important mechanism for the control of ALDH1 transcriptional activity is through the presence of inhibitory elements located 0.7-1.6 kb upstream of the ALDH1 gene. DNase I footprint analysis reveal four sites of protein-DNA interaction within this region, one of which is specific to the liver and corresponds to a NF-kappaB/Rel binding site.

Aldehyde Dehydrogenase↗
PubMed2002

How does the eye breathe? Evidence for neuroglobin-mediated oxygen supply in the mammalian retina.

Visual performance of the vertebrate eye requires large amounts of oxygen, and thus the retina is one of the highest oxygen-consuming tissues of the body. Here we show that neuroglobin, a neuron-specific respiratory protein distantly related to hemoglobin and myoglobin, is present at high amounts in the mouse retina (approximately 100 microm). The estimated concentration of neuroglobin in the retina is thus about 100-fold higher than in the brain and is in the same range as that of myoglobin in the muscle. Neuroglobin is expressed in all neurons of the retina but not in the retinal pigment epithelium. Neuroglobin mRNA was detected in the perikarya of the nuclear and ganglion layers of the neuronal retina, whereas the protein was present mainly in the plexiform layers and in the ellipsoid region of photoreceptor inner segment. The distribution of neuroglobin correlates with the subcellular localization of mitochondria and with the relative oxygen demands, as the plexiform layers and the inner segment consume most of the retinal oxygen. These findings suggest that neuroglobin supplies oxygen to the retina, similar to myoglobin in the myocardium and the skeletal muscle.

Animals↗
PubMed2005

Divergent distribution in vascular and avascular mammalian retinae links neuroglobin to cellular respiration.

The visual function of the vertebrate retina relies on sufficient supply with oxygen. Neuroglobin is a respiratory protein thought to play an essential role in oxygen homeostasis of neuronal cells. For further understanding of its function, we compared the distribution of neuroglobin and mitochondria in both vascular and avascular mammalian retinae. In the vascular retinae of mouse and rat, oxygen is supplied by the outer choroidal, deep retinal, and inner capillaries. We show that in this type of retina, mitochondria are concentrated in the inner segments of photoreceptor cells, the outer and the inner plexiform layers, and the ganglion cell layer. These are the same regions in which oxygen consumption takes place and in which neuroglobin is present at high levels. In the avascular retina of guinea pig the deep retinal and inner capillaries are absent. Therefore, only the inner segments of the photoreceptors adjacent to choroidal capillaries display an oxidative metabolism. We demonstrate that in the retina of guinea pigs both neuroglobin and mitochondria are restricted to this layer. Our results clearly demonstrate an association of neuroglobin and mitochondria, thus supporting the hypothesis that neuroglobin is a respiratory protein that supplies oxygen to the respiratory chain.

Amino Acid Sequence↗
PubMed2004

S-crystallin and arginine kinase bind F-actin in light- and dark-adapted octopus retinas.

PURPOSE: Rhabdomere microvilli dramatically reorganize in conditions of light and dark. This reorganization involves remodeling of the microvillus actin cytoskeleton. We are using the rhabdomeric retina of Octopus bimaculoides to identify actin-binding proteins that may be involved in this remodeling. METHODS: Octopus were light-/dark-adapted, retinas separated into dorsal and ventral halves, and homogenized. Actin-binding proteins were recognized using F-actin overlay blot assays and selected proteins from the overlays were identified using N-terminal sequencing methods or mass spectroscopy. Protein concentrations were quantified and compared by statistical analysis. RESULTS: Total protein gels of light-/dark-adapted, ventral/dorsal halves were almost identical except for a protein band at 26 kD. The relative amount of this protein in the dark was almost double that found in the light. The levels of other proteins did not vary significantly between the light and dark. F-actin overlays also showed matching patterns of actin-binding proteins except for the 26 kD protein. Although the 26 kD protein from light-adapted retinas transferred to the blotting membranes, it did not bind F-actin while the 26 kD protein on overlays from dark-adapted retinas always demonstrated F-actin binding. Besides the 26 kD protein, other proteins at 200 kD, 80 kD, 40 kD appeared on the overlays. These proteins and the 26 kD protein were sequenced and identified as hemocynanin, transitional ER ATPase, arginine kinase and S-crystallin, respectively. CONCLUSIONS: The amount of S-crystallin present in the octopus retina is significantly greater in dark-adapted retinas and it binds to F-actin. In the light, the level of S-crystallin is greatly reduced and there is no apparent F-actin binding. No other studies, to our knowledge, show that S-crystallin binds to the actin cytoskeleton or that its expression is regulated by light. Arginine kinase may provide energy for cytoskeletal remodeling as it may in other neural tissues.

Actins↗
PubMed2004

Identification of angiotensin converting enzyme 2 in the rodent retina.

PURPOSE: An active renin-angiotensin system has been found in the retina of rats and humans. Angiotensin-converting enzyme 2 (ACE2) is a recently discovered enzymatic homologue of Angiotensin-converting enzyme (ACE) that may be an important new component of the renin-angiotensin system (RAS). This study assesses the involvement of ACE2 in the normal and diabetic rodent retina and its modulation by ACE inhibition. METHODS: Sprague-Dawley rats were randomised into three groups, control, diabetes, and diabetes plus ramipril, with diabetes induced with the cell toxin streptozocin and the study run for 24 weeks. ACE2 and ACE gene levels were measured using quantitative real-time polymerase chain reaction (QRT-PCR), ACE2 protein expression was confirmed by Western blotting, and ACE and ACE2 catalytic activity were measured using specific activity assays in the rat retina. Localisation of ACE2 mRNA and protein were determined by in situ hybridisation and immunohistochemistry, respectively. RESULTS: ACE mRNA levels were decreased to approximately 50% in the diabetic retina, but ACE2 mRNA levels were not significantly changed. ACE but not ACE2 gene expression was influenced by ramipril treatment. Following immunostaining, both ACE2 and ACE protein were localised predominantly to the inner nuclear layer (INL) but also to photoreceptors. In the diabetic retina, ACE enzyme activity was decreased, whereas ACE2 enzyme activity was increased. CONCLUSIONS: This study has identified ACE2 gene and catalytically active protein in the rodent retina. In diabetes, the major changes were a decrease in ACE but an increase in ACE2 enzymatic activity. The ACE inhibitor ramipril did not reduce ACE2 enzymatic activity.

Angiotensin-Converting Enzyme 2↗
PubMed2006

Daily oscillation in melatonin synthesis in the Turkey pineal gland and retina: diurnal and circadian rhythms.

The aim of the present study was to examine arylalkylamine N-acetyltransferase (AANAT) activity and melatonin content in the pineal gland and retina as well as the melatonin concentration in plasma of the turkey (Meleagris gallopavo), an avian species in which several physiological processes, including reproduction, are controlled by day length. In order to investigate whether the analyzed parameters display diurnal or circadian rhythmicity, we measured these variables in tissues isolated at regular time intervals from birds kept either under a regular light-dark (LD) cycle or under constant darkness (DD). The pineal gland and retina of the turkey rhythmically produced melatonin. In birds kept under a daily LD cycle, melatonin levels in the pineal gland and retina were high during the dark phase and low during the light phase. Rhythmic oscillations in melatonin, with high night-time concentrations, were also found in the plasma. The pineal and retinal melatonin rhythms mirrored oscillations in the activity of AANAT, the penultimate enzyme in the melatonin biosynthetic pathway. Rhythmic oscillations in AANAT activity in the turkey pineal gland and retina were circadian in nature, as they persisted under conditions of constant darkness (DD). Transferring birds from LD into DD, however, resulted in a potent decline in the amplitude of the AANAT rhythm from the first day of DD. On the sixth day of DD, pineal AANAT activity was still markedly higher during the subjective dark than during the subjective light phase; whereas, AANAT activity in the retina did not exhibit significant oscillations. The results indicate that melatonin rhythmicity in the turkey pineal gland and retina is regulated both by light and the endogenous circadian clock. The findings suggest that environmental light may be of primary importance in the maintenance of the high-amplitude melatonin rhythms in the turkey.

Animals↗
PubMed2003

Effects of long-term vitamin K (phylloquinone) intake on retina aging.

Emerging evidence suggests neuroprotective functions of vitamin K and/or vitamin K-dependent proteins. We investigated the effect of dietary vitamin K on retina aging (thinning). Female Sprague-Dawley rats were maintained from weaning on low (80 microg kg(-1) diet), adequate (500 microg kg(-1) diet) or high (2000 microg kg(-1) diet) levels of vitamin K1 (phylloquinone). Relative concentrations of brain vitamin K associated with these diets were 1: 3.3: 25 (K1) and 1: 2.7: 9.0 (menaquinone-4). Histomorphometry of old (21 month) rats revealed positive associations between vitamin K and thickness of retina layers, especially in the equatorial/peripheral retina. No association of diet and retina thickness was detected among young (6 month) animals. The sparing effect of vitamin K in the retina was most evident in the inner plexiform layer and in the photoreceptor inner and outer segments. Surprisingly, we observed no effect of vitamin K on the age-dependent loss of photoreceptor cells, interneurons or ganglion cells. These data suggest a role for vitamin K in maintaining the aging retina and suggest that the sparing effect of vitamin K does not reflect the survival-promoting (anti-apoptotic) activities of vitamin K-dependent proteins.

Aging↗
PubMed2000

Melatonin circadian rhythm in the retina of mammals.

Melatonin has been traditionally considered to be derived principally from the pineal gland. However, several investigations have now demonstrated that melatonin synthesis occurs also in the retina (and in other organs as well) of several vertebrate classes, including mammals. As in the pineal, melatonin synthesis in the retina is elevated at night and reduced during the day. Since melatonin receptors are present in the retina and retinal melatonin does not contribute to the circulating levels, retinal melatonin probably acts locally as a neuromodulator. Melatonin synthesis in the retinas of mammals is under control of a circadian oscillator located within the retina itself, and circadian rhythms in melatonin synthesis and/or release have been described for several species of rodents. These rhythms are present in vivo, persist in vitro, are entrained by light, and are temperature compensated. The recent cloning of the gene responsible for the synthesis of the enzyme arylalkylamine N-acetyltransferase (the only enzyme unique to the melatonin synthetic pathway) will facilitate localizing the cellular site of melatonin synthesis in the retina and investigating the molecular mechanism responsible for the generation of retinal melatonin rhythmicity. Melatonin has been implicated in many retinal functions, and the levels of melatonin and dopamine appear to regulate several aspects of retinal physiology that relate to light and dark adaptation. In conclusion, it seems that retinal melatonin is involved in several functions, but its precise role is yet to be understood.

Animals↗
PubMed1985

Isolation of a cell-surface receptor for chick neural retina adherons.

Embryonic chick neural retina cells release glycoprotein complexes, termed adherons, into their culture medium. When absorbed onto the surface of petri dishes, neural retina adherons increase the initial rate of neural retina cell adhesion. In solution they increase the rate of cell-cell aggregation. Cell-cell and adheron-cell adhesions of cultured retina cells are selectively inhibited by heparan-sulfate glycosaminoglycan, but not by chondroitin sulfate or hyaluronic acid, suggesting that a heparan-sulfate proteoglycan may be involved in the adhesion process. We isolated a heparan-sulfate proteoglycan from the growth-conditioned medium of neural retina cells, and prepared an antiserum against it. Monovalent Fab' fragments of these antibodies completely inhibited cell-adheron adhesion, and partially blocked spontaneous cell-cell aggregation. An antigenically and structurally similar heparan-sulfate proteoglycan was isolated from the cell surface. This proteoglycan bound directly to adherons, and when absorbed to plastic, stimulated cell-substratum adhesion. These data suggest that a heparan-sulfate proteoglycan on the surface of chick neural retina cells acted as a receptor for adhesion-mediating glycoprotein complexes (adherons).

Animals↗
PubMed1985

Analysis of pre- and postsynaptic factors of the serotonin system in rabbit retina.

[3H]Serotonin is accumulated by a specific set of amacrine cells in the rabbit retina. These cells also accumulate the neurotoxin, 5,7-dihydroxytryptamine, and show signs of necrosis within 4 h of in vivo exposure to the drug. Biochemical analysis of [3H]serotonin uptake reveal a sodium- and temperature-dependent, high affinity uptake system with a Km of 0.94 microM and Vmax of 1.08 pmol/mg protein/min. [3H]Tryptophan is also accumulated in rabbit retinal homogenates by a high affinity process. Accumulated [3H]serotonin is released in response to potassium-induced depolarization of intact, isolated retinas. In vitro binding studies of rabbit retinal homogenate membranes demonstrate specific sets of binding sites with characteristics of the postsynaptic serotonin receptor. These data strongly suggest that rabbit retina contains virtually all of the molecular components required for a functional serotonergic neurotransmitter system. The only significant difference between the serotonin system in rabbit retina and that in the well-established serotonin transmitter systems in nonmammalin retinas and in brains of most species is the relatively low concentration of endogenous serotonin in rabbit retinas, as demonstrated by high-performance liquid chromatography, histofluorescence, or immunocytochemistry.

5,7-Dihydroxytryptamine↗
PubMed1992

Receptive field properties of rod-driven horizontal cells in the skate retina.

The large receptive fields of retinal horizontal cells result primarily from extensive intercellular coupling via gap (electrical) junctions; thus, the extent of the receptive field provides an index of the degree to which the cells are electrically coupled. For rod-driven horizontal cells in the dark-adapted skate retina, a space constant of 1.18 +/- 0.15 mm (SD) was obtained from measurements with a moving slit stimulus, and a comparable value (1.43 +/- 0.55 mm) was obtained with variation in spot diameter. These values, and the extensive spread of a fluorescent dye (Lucifer Yellow) from the site of injection to neighboring cells, indicate that the horizontal cells of the all-rod retina of skate are well coupled electrically. Neither the receptive field properties nor the gap-junctional features of skate horizontal cells were influenced by the adaptive state of the retina: (a) the receptive field organization was unaffected by light adaptation, (b) similar dye coupling was seen in both dark- and light-adapted retinae, and (c) no significant differences were found in the gap-junctional particle densities measured in dark- and light-adapted retinas, i.e., 3,184 +/- 286/microns 2 (n = 8) and 3,073 +/- 494/microns 2 (n = 11), respectively. Moreover, the receptive fields of skate horizontal cells were not altered by either dopamine, glycine, GABA, or the GABAA receptor antagonists bicuculline and picrotoxin. We conclude that the rod-driven horizontal cells of the skate retina are tightly coupled to one another, and that the coupling is not affected by photic and pharmacological conditions that are known to modulate intercellular coupling between cone-driven horizontal cells in other species.

Animals↗
PubMed1967

Effects of cardiac glycosides on electrical activity in the isolated retina of the frog.

Ouabain added to physiological salt solutions bathing the isolated frog retina irreversibly abolishes the electrical response to light (the electroretinogram or ERG). The time course of abolition depends on the concentration of ouabain in the medium and the surface of the retina to which it is applied. When the glycoside is placed on the receptor surface, in 7 min the ERG is completely eliminated by 10(-4)M ouabain and more than 90% inhibited by 3 x 10(-5)M ouabain. The effect is slower at lower concentrations and when the solution is applied to the vitreous surface of the retina. The evidence suggests that abolition of the ERG by ouabain is due principally to inhibition of the active transport of sodium: (a) Structurally modified glycosides which are considerably less potent inhibitors of alkali cation-activated ATPase activity in preparations of frog retinal outer segments are also poorer inhibitors of electrical activity in isolated retinas. (b) Replacing much of the sodium in the medium bathing the retina by choline, Tris, or sucrose significantly protects the retina from ouabain. It is suggested that in a standard sodium environment essentially constant activity of the sodium pump is required to prevent rapid and irreversible change. The cellular sites most critically dependent on the sodium pump have not been identified.

Adenosine Triphosphate↗