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Carr BJ, Skitsko D, Song J, Li Z, Ju MJ, Moritz OL. Prominin-1 null Xenopus laevis develop subretinal drusenoid-like deposits, cone-rod dystrophy, and RPE atrophy. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.06.03.597229. [PMID: 38895468 PMCID: PMC11185615 DOI: 10.1101/2024.06.03.597229] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/21/2024]
Abstract
Mutations in the PROMININ-1 (PROM1) gene are associated with inherited, non-syndromic vision loss. Here, we used CRISPR/Cas9 to induce truncating prom1-null mutations in Xenopus laevis to create a disease model. We then tracked progression of retinal degeneration in these animals from the ages of 6 weeks to 3 years old. We found that retinal degeneration caused by prom1-null is age-dependent and likely involves death or damage to the retinal pigment epithelium (RPE) that precedes photoreceptor degeneration. As prom1-null frogs age, they develop large cellular debris deposits in the subretinal space and outer segment layer which resemble subretinal drusenoid deposits (SDD) in their location, histology, and representation in color fundus photography and optical coherence tomography (OCT). In older frogs, these SDD-like deposits accumulate in size and number, and they are present before retinal degeneration occurs. Evidence for an RPE origin of these deposits includes infiltration of pigment granules into the deposits, thinning of RPE as measured by OCT, and RPE disorganization as measured by histology and OCT. The appearance and accumulation of SDD-like deposits and RPE thinning and disorganization in our animal model suggests an underlying disease mechanism for prom1-null mediated blindness of death and dysfunction of the RPE preceding photoreceptor degeneration, instead of direct effects upon photoreceptor outer segment morphogenesis, as was previously hypothesized.
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Affiliation(s)
- Brittany J Carr
- The University of Alberta, Faculty of Medicine and Dentistry, Department of Ophthalmology and Visual Sciences
| | - Dominic Skitsko
- The University of British Columbia, Faculty of Medicine, Department of Ophthalmology and Visual Sciences
| | - Jun Song
- The University of British Columbia, Faculty of Applied Science, Faculty of Medicine, School of Biomedical Engineering
| | - Zixuan Li
- The University of Alberta, Faculty of Medicine and Dentistry, Department of Ophthalmology and Visual Sciences
| | - Myeong Jin Ju
- The University of British Columbia, Faculty of Medicine, Department of Ophthalmology and Visual Sciences
- The University of British Columbia, Faculty of Applied Science, Faculty of Medicine, School of Biomedical Engineering
| | - Orson L Moritz
- The University of British Columbia, Faculty of Medicine, Department of Ophthalmology and Visual Sciences
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D'Angelo R, Donato L, Venza I, Scimone C, Aragona P, Sidoti A. Possible protective role of the ABCA4 gene c.1268A>G missense variant in Stargardt disease and syndromic retinitis pigmentosa in a Sicilian family: Preliminary data. Int J Mol Med 2017; 39:1011-1020. [PMID: 28290600 DOI: 10.3892/ijmm.2017.2917] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2016] [Accepted: 02/07/2017] [Indexed: 11/05/2022] Open
Abstract
In the wide horizon of ophthalmologically rare diseases among retinitis pigmentosa forms, Stargardt disease has gradually assumed a significant role due to its heterogeneity. In the present study, we aimed to support one of two opposite hypotheses concerning the causative or protective role of heterozygous c.1268A>G missense variant of the ABCA4 gene in Stargardt disease and in syndromic retinitis pigmentosa. This study was based on a family consisting of three members: proband, age 54, with high myopia, myopic chorioretinitis and retinal dystrophy; wife, age 65, with mild symptoms; daughter, age 29, asymptomatic. After genetic counseling, ABCA4 and RP1 gene analysis was performed. The results highlighted an important genetic picture. The proband was found to carry two variant RP1 SNPs, rs2293869 (c.2953A>T) and rs61739567 (c.6098G>A), and, a wild-type condition for four RP1 polymorphisms, rs444772 (c.2623G>A) and three SNPs in the 'hot-spot' region, exon 4. The proband's wife, instead, showed an opposite condition compared to her husband: a homozygous mutated condition for the first four SNPs analyzed, while the last two were wild-type. Regarding the ABCA4 gene, the proband evidenced a wild-type condition. Furthermore, the wife showed a heterozygous condition of ABCA4 rs3112831 (c.1268A>G). As expected, the daughter presented heterozygosity for all variants of both genes. In conclusion, even though the c.1268A>G missense variant of the ABCA4 gene has often been reported as causative of disease, and in other cases protective of disease, in our family case, the variant appears to reduce or delay the risk of onset of Stargardt disease.
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Affiliation(s)
- Rosalia D'Angelo
- Department of Biomedical Sciences, Odontoiatric and Morphofunctional Images, University of Messina, I-98125 Messina, Italy
| | - Luigi Donato
- Department of Biomedical Sciences, Odontoiatric and Morphofunctional Images, University of Messina, I-98125 Messina, Italy
| | - Isabella Venza
- Department of Clinical and Experimental Medicine, University of Messina, I-98125 Messina, Italy
| | - Concetta Scimone
- Department of Biomedical Sciences, Odontoiatric and Morphofunctional Images, University of Messina, I-98125 Messina, Italy
| | - Pasquale Aragona
- Department of Biomedical Sciences, Odontoiatric and Morphofunctional Images, University of Messina, I-98125 Messina, Italy
| | - Antonina Sidoti
- Department of Biomedical Sciences, Odontoiatric and Morphofunctional Images, University of Messina, I-98125 Messina, Italy
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Goldberg AFX, Moritz OL, Williams DS. Molecular basis for photoreceptor outer segment architecture. Prog Retin Eye Res 2016; 55:52-81. [PMID: 27260426 DOI: 10.1016/j.preteyeres.2016.05.003] [Citation(s) in RCA: 122] [Impact Index Per Article: 15.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2016] [Revised: 05/27/2016] [Accepted: 05/29/2016] [Indexed: 01/11/2023]
Abstract
To serve vision, vertebrate rod and cone photoreceptors must detect photons, convert the light stimuli into cellular signals, and then convey the encoded information to downstream neurons. Rods and cones are sensory neurons that each rely on specialized ciliary organelles to detect light. These organelles, called outer segments, possess elaborate architectures that include many hundreds of light-sensitive membranous disks arrayed one atop another in precise register. These stacked disks capture light and initiate the chain of molecular and cellular events that underlie normal vision. Outer segment organization is challenged by an inherently dynamic nature; these organelles are subject to a renewal process that replaces a significant fraction of their disks (up to ∼10%) on a daily basis. In addition, a broad range of environmental and genetic insults can disrupt outer segment morphology to impair photoreceptor function and viability. In this chapter, we survey the major progress that has been made for understanding the molecular basis of outer segment architecture. We also discuss key aspects of organelle lipid and protein composition, and highlight distributions, interactions, and potential structural functions of key OS-resident molecules, including: kinesin-2, actin, RP1, prominin-1, protocadherin 21, peripherin-2/rds, rom-1, glutamic acid-rich proteins, and rhodopsin. Finally, we identify key knowledge gaps and challenges that remain for understanding how normal outer segment architecture is established and maintained.
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Affiliation(s)
- Andrew F X Goldberg
- Eye Research Institute, Oakland University, 417 Dodge Hall, Rochester, MI, 48309, USA.
| | - Orson L Moritz
- Department of Ophthalmology & Visual Sciences, University of British Columbia, Vancouver, BC, Canada
| | - David S Williams
- Department of Ophthalmology and Jules Stein Eye Institute, Department of Neurobiology, David Geffen School of Medicine at UCLA, University of California, Los Angeles, CA, USA
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4
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Hárosi FI, Novales Flamarique I. Functional significance of the taper of vertebrate cone photoreceptors. ACTA ACUST UNITED AC 2012; 139:159-87. [PMID: 22250013 PMCID: PMC3269789 DOI: 10.1085/jgp.201110692] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Vertebrate photoreceptors are commonly distinguished based on the shape of their outer segments: those of cones taper, whereas the ones from rods do not. The functional advantages of cone taper, a common occurrence in vertebrate retinas, remain elusive. In this study, we investigate this topic using theoretical analyses aimed at revealing structure–function relationships in photoreceptors. Geometrical optics combined with spectrophotometric and morphological data are used to support the analyses and to test predictions. Three functions are considered for correlations between taper and functionality. The first function proposes that outer segment taper serves to compensate for self-screening of the visual pigment contained within. The second function links outer segment taper to compensation for a signal-to-noise ratio decline along the longitudinal dimension. Both functions are supported by the data: real cones taper more than required for these compensatory roles. The third function relates outer segment taper to the optical properties of the inner compartment whereby the primary determinant is the inner segment’s ability to concentrate light via its ellipsoid. In support of this idea, the rod/cone ratios of primarily diurnal animals are predicted based on a principle of equal light flux gathering between photoreceptors. In addition, ellipsoid concentration factor, a measure of ellipsoid ability to concentrate light onto the outer segment, correlates positively with outer segment taper expressed as a ratio of characteristic lengths, where critical taper is the yardstick. Depending on a light-funneling property and the presence of focusing organelles such as oil droplets, cone outer segments can be reduced in size to various degrees. We conclude that outer segment taper is but one component of a miniaturization process that reduces metabolic costs while improving signal detection. Compromise solutions in the various retinas and retinal regions occur between ellipsoid size and acuity, on the one hand, and faster response time and reduced light sensitivity, on the other.
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Affiliation(s)
- Ferenc I Hárosi
- Laboratory of Sensory Physiology, Marine Biological Laboratory, Woods Hole, MA 02543, USA
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Solessio E, Mani SS, Cuenca N, Engbretson GA, Barlow RB, Knox BE. Developmental regulation of calcium-dependent feedback in Xenopus rods. ACTA ACUST UNITED AC 2005; 124:569-85. [PMID: 15504902 PMCID: PMC2234010 DOI: 10.1085/jgp.200409162] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The kinetics of activation and inactivation in the phototransduction pathway of developing Xenopus rods were studied. The gain of the activation steps in transduction (amplification) increased and photoresponses became more rapid as the rods matured from the larval to the adult stage. The time to peak was significantly shorter in adults (1.3 s) than tadpoles (2 s). Moreover, adult rods recovered twice as fast from saturating flashes than did larval rods without changes of the dominant time constant (2.5 s). Guanylate cyclase (GC) activity, determined using IBMX steps, increased in adult rods from ∼1.1 s−1 to 3.7 s−1 5 s after a saturating flash delivering 6,000 photoisomerizations. In larval rods, it increased from 1.8 s−1 to 4.0 s−1 9 s after an equivalent flash. However, the ratio of amplification to the measured dark phosphodiesterase activity was constant. Guanylate cyclase–activating protein (GCAP1) levels and normalized Na+/Ca2+, K+ exchanger currents were increased in adults compared with tadpoles. Together, these results are consistent with the acceleration of the recovery phase in adult rods via developmental regulation of calcium homeostasis. Despite these large changes, the single photon response amplitude was ∼0.6 pA throughout development. Reduction of calcium feedback with BAPTA increased adult single photon response amplitudes threefold and reduced its cutoff frequency to that observed with tadpole rods. Linear mathematical modeling suggests that calcium-dependent feedback can account for the observed differences in the power spectra of larval and adult rods. We conclude that larval Xenopus maximize sensitivity at the expense of slower response kinetics while adults maximize response kinetics at the expense of sensitivity.
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Affiliation(s)
- Eduardo Solessio
- Center for Vision Research, Weiskotten Hall, SUNY Upstate Medical University, 750 East Adams St., Syracuse, NY 13210, USA.
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Liu Q, Lyubarsky A, Skalet JH, Pugh EN, Pierce EA. RP1 is required for the correct stacking of outer segment discs. Invest Ophthalmol Vis Sci 2003; 44:4171-83. [PMID: 14507858 PMCID: PMC1904498 DOI: 10.1167/iovs.03-0410] [Citation(s) in RCA: 94] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
PURPOSE Mutations in RP1 are a common cause of dominant retinitis pigmentosa (RP), but the mechanism by which the identified mutations lead to photoreceptor cell death and blindness has not been determined. To investigate the function of the RP1 protein in photoreceptors and gain insight into the mechanism of disease, gene-targeting techniques were used to produce mice with a mutant Rp1 allele that mimics the truncation alleles found to cause disease. METHODS RT-PCR was used to amplify illegitimate RP1 transcripts from lymphoblasts. Gene targeting was used to create mice with a mutant Rp1-myc allele. Confocal immunofluorescence microscopy was used to identify the location of the mutant Rp1-myc protein in photoreceptors. The structure of the photoreceptors in the resultant Rp1-myc mice was studied by light and electron microscopy. The retinal function of the mutant mice was investigated using analysis of full-field ERGs. RESULTS Wild-type and mutant RP1 mRNA were both detected in lymphoblasts from patients with RP1 disease. Rp1-myc mice produced a truncated version of the Rp1 protein, containing the N-terminal 662 amino acids, which localized correctly to the axoneme of the photoreceptor outer segments. Mice homozygous for the mutant Rp1-myc allele underwent a rapid-onset retinal degeneration characterized by incorrectly oriented outer segment discs that failed to stack properly into outer segments. In contrast, the photoreceptors of heterozygous mice remained relatively healthy. CONCLUSIONS The presence of mutant RP1 mRNA in lymphoblasts from patients with RP1 disease implies that the mutant message can escape nonsense-mediated mRNA decay and that a truncated RP1 protein may be produced in the retina. The truncated Rp1-myc protein appears to be nonfunctional, and not to exert a dominant negative effect in the photoreceptors of heterozygous mice. Results from homozygous Rp1-myc mice indicate that RP1 is required for the correct orientation and higher order stacking of outer segment discs.
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Affiliation(s)
- Qin Liu
- Scheie Eye Institute, University of Pennsylvania School of Medicine, Philadelphia, PA 19104, USA
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9
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Gábriel R, Wilhelm M, Straznicky C. Microtubule-associated protein 2 (MAP2)-immunoreactive neurons in the retina of Bufo marinus: colocalisation with tyrosine hydroxylase and serotonin in amacrine cells. Cell Tissue Res 1992; 269:175-82. [PMID: 1358449 DOI: 10.1007/bf00384738] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
Neuron populations in the retina of the toad, Bufo marinus, were labelled with a monoclonal antibody raised against microtubule-associated protein 2 (MAP2). A subpopulation of cones, probably corresponding to the blue-sensitive small single cones, large diameter amacrine cells in the most proximal row of the inner nuclear layer and some large ganglion cells in the ganglion cell layer were labelled. Double labelling experiments were carried out to establish the colocalisation of MAP2 with known putative transmitter substances of the anuran amacrine cells. MAP2 was colocalised in a subpopulation of serotonin-immunoreactive and in all tyrosine hydroxylase-immunoreactive amacrine cells. The results indicate, that the MAP2 content in the neurons of the anuran retina can be correlated with other well-defined neurochemical and/or physiological properties.
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Affiliation(s)
- R Gábriel
- Department of Anatomy and Histology, School of Medicine, Flinders University of South Australia, Adelaide
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10
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Röhlich P, Szél A, Papermaster DS. Immunocytochemical reactivity of Xenopus laevis retinal rods and cones with several monoclonal antibodies to visual pigments. J Comp Neurol 1989; 290:105-17. [PMID: 2592607 DOI: 10.1002/cne.902900107] [Citation(s) in RCA: 31] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Immunocytochemical reactions with several antibodies to visual pigments were used to study visual cells of the Xenopus laevis retina. Monoclonal antibodies to bovine opsin "E," 1D4, and 4B4 (reactive with the N- and C-terminus and with the loop connecting transmembrane segments 5-6, respectively) and to chicken visual pigments COS-1 and OS-2 (binding to mammalian red/green and blue cones, respectively), as well as a rabbit antifrog opsin serum 11-7, were applied to semithin and thin sections of the retina. The bound antibodies were detected with the peroxidase technique at the light microscopic level; a three-stage immunogold procedure was used for electron microscopic immunocytochemistry. The overwhelming majority of rods were labeled by monoclonal antibodies "E," 4B4, 1D4, OS-2, and serum 11-7. A small fraction (2-3%) of rods did not bind monoclonal antibodies "E" and 4B4, but this minor population of rods was strongly reactive with 1D4 and to a lesser extent with OS-2, indicating the presence of different visual pigment. These rods differ in shape from the major rod type; they are thinner, shorter, and may be comparable to the blue-sensitive ("green") rods of other amphibia. Cones were morphologically heterogeneous: double cones, large single cones, and small single cones were found, and the large single and the double cones were occasionally duplicated. Double cones and large single cones (as well as their duplicated varieties) strongly bound monoclonal antibodies COS-1 and were unlabeled by all other monoclonal antibodies, except OS-2. The small single cone was remarkably unreactive with COS-1 and "E," weakly labeled by 1D4 and 4B4, and most reactive with OS-2 and 11-7. This unique pattern of immunocytochemical reactions in the small cone type indicates the uniqueness of its visual pigment from other cone types in the Xenopus retina. The present study shows the existence of two different opsins in morphologically distinct (thick and thin) rod types and at least two cone pigments in the heterogeneous cone population.
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Affiliation(s)
- P Röhlich
- Department of Pathology, University of Texas Health Science Center, San Antonio 78284
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11
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Vaughan DK, Fisher SK, Bernstein SA, Hale IL, Linberg KA, Matsumoto B. Evidence that microtubules do not mediate opsin vesicle transport in photoreceptors. J Cell Biol 1989; 109:3053-62. [PMID: 2687292 PMCID: PMC2115958 DOI: 10.1083/jcb.109.6.3053] [Citation(s) in RCA: 29] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023] Open
Abstract
The organization of the rod photoreceptor cytoskeleton suggests that microtubules (MTs) and F actin are important in outer segment (OS) membrane renewal. We studied the role of the cytoskeleton in this process by first quantifying OS membrane assembly in rods from explanted Xenopus eyecups with a video assay for disc morphogenesis and then determining if the rate of assembly was reduced after drug disassembly of either MTs or F actin. Membrane assembly was quantified by continuously labeling newly forming rod OS membranes with Lucifer Yellow VS (LY) and following the tagged membranes' distal displacement along the OS. LY band displacement displayed a linear increase over 16 h in culture. These cells possessed a longitudinally oriented network of ellipsoid MTs between the sites of OS protein synthesis and OS membrane assembly. Incubation of eyecups in nocodazole, colchicine, vinblastine, or podophyllotoxin disassembled the ellipsoid MTs. Despite their absence, photoreceptors maintained a normal rate of OS assembly. In contrast, photoreceptors displayed a reduced distal displacement of LY-labeled membranes in eyecups treated with cytochalasin D, showing that our technique can detect drug-induced changes in basal rod outer segment assembly. The reduction noted in the cytochalasin-treated cells was due to the abnormal lateral displacement of newly added OS disc membranes that occurs with this drug (Williams, D. S., K. A. Linberg, D. K. Vaughan, R. N. Fariss, and S. K. Fisher. 1988. J. Comp. Neurol. 272:161-176). Together, our results indicate that the vectorial transport of OS membrane constituents through the ellipsoid and their assembly into OS disc membranes are not dependent on elliposid MT integrity.
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Affiliation(s)
- D K Vaughan
- Department of Biological Sciences, University of California, Santa Barbara 93106
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12
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Williams DS. Ommatidial structure in relation to turnover of photoreceptor membrane in the locust. Cell Tissue Res 1982; 225:595-617. [PMID: 7127410 DOI: 10.1007/bf00214807] [Citation(s) in RCA: 52] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
In the compound eye of the locust, Locusta, the cross-sectional area of the rhabdoms increases at "dusk" by 4.7-fold due to the rapid assembly of new microvillar membrane, and decreases at "dawn" by a corresponding amount as a result of pinocytotic shedding from the microvilli. The rhabdoms at night have more and longer photoreceptor microvilli than rhabdoms during the day. The orientations of the six rhabdomeres that comprise the distal rhabdom also change. The density of intramembrane particles on the P-face of the microvillar membrane, putatively representing mostly rhodopsin molecules, or aggregates thereof, does not change. An alteration in the size of the ommatidial field-stop, produced by the primary pigment cells, is concomitant with the change in rhabdom size. At night the increase in size of the field-stop must widen the angular acceptance of a rhabdom, increasing the capture of photons from an extended field. Conversely, during the day, when photons are more abundant, its decrease must narrow the acceptance angle, increasing angular resolution. Because of the presence of this field-stop, the optics of the ommatidium would not be greatly affected if the rhabdom were to remain always at its night size. It is argued, therefore, that the variable-size rhabdom must have resulted from some demand other than that of light/dark adaptation. Changes in size and organisation of the rhabdoms in response to various light regimes indicate that: (1) Rapid shedding of photoreceptor membrane is induced by the onset of light, but shedding also occurs slowly in darkness during the day. (2) Microvillar assembly is initiated by the onset of darkness, but also occurs at the normal time of dusk without a change in ambient lighting, provided there has been some light during the day. Therefore, both shedding and assembly of microvillar membrane are affected by the state of illumination, but also appear to be under some endogenous control.
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Hollyfield JG, Rayborn ME, Sarthy PV, Lam DM. The emergence, localization and maturation of neurotransmitter systems during development of the retina in Xenopus laevis. I. Gamma aminobutyric acid. J Comp Neurol 1979; 188:587-98. [PMID: 521507 DOI: 10.1002/cne.901880406] [Citation(s) in RCA: 77] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
The high-affinity uptake, biosynthesis and release of GABA have been studied in the retina of Xenopus laevis. In the mature retina, [3H]-GABA is accumulated predominantly by horizontal cells. A second population of cells located in the inner nuclear layer (possibly a type of amacrine cell) also showed a specific GABA uptake. In addition, this retina contains significant activities of L-glutamic acid decarboxylase and also releases [3H]-GABA in response to increasing K+ concentrations in the medium. We have followed the appearance and maturation of these GABA-ergic properties during embryonic development of this retina. Our results indicate that these properties emerge in a precise temporal pattern during retinal differentiation: the specific neuronal uptake of GABA precedes GABA synthesis which is followed by K+-stimulated GABA release.
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Kinney MS, Fisher SK. Changes in length and disk shedding rate of Xenopus rod outer segments associated with metamorphosis. PROCEEDINGS OF THE ROYAL SOCIETY OF LONDON. SERIES B, BIOLOGICAL SCIENCES 1978; 201:169-77. [PMID: 27798 DOI: 10.1098/rspb.1978.0038] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Histological examination of the retinae of
Xenopus
tadpoles undergoing the extensive transformations of metamorphic climax revealed a progressive and dramatic decrease in the length of rod outer segments (r. o. s.) (by 1.22 µm/day), which was reversed after the completion of metamorphosis, when r. o. s. grew longer (by 1.11 µm/day). The rate of r. o. s. disk addition during these two periods was determined by examining the incorporation of [
3
H]-leucine by light microscopic autoradiography. The band of labelled protein in r. o. s. was displaced sclerally at a rate of 1.70 µm/day during the first half of metamorphic climax, and of 1.56 µm/day in young juveniles during the second month after metamorphosis. The similarity of the rate of band displacement at these times indicates that the changes in r. o. s. length associated with metamorphosis result from major changes in the rate of disk shedding and/or phagocytosis, which was about 2.92 µm/day pre-metamorphically and 0.45 µm/day post-metamorphically. E. m. observation at these stages and during the final stages of metamorphic climax revealed no significant alterations in the cellular organization or ultrastructure of rods or pigment epithelium, even though some r. o. s. were only 3 µm long. This large change in r. o. s. length undoubtedly influences the animal’s scotopic sensitivity and the relative mesopic activity of its rods and cones, and may have important effects on the animal’s visual physiology.
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Kinney MS, Fisher SK. The photoreceptors and pigment epithelium of the larval Xenopus retina: morphogenesis and outer segment renewal. PROCEEDINGS OF THE ROYAL SOCIETY OF LONDON. SERIES B, BIOLOGICAL SCIENCES 1978; 201:149-67. [PMID: 27797 DOI: 10.1098/rspb.1978.0037] [Citation(s) in RCA: 53] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Light microscopic autoradiography and electron microscopy were used to examine outer segment renewal and the development of photoreceptors and pigment epithelium in the larvalXenopusretina. Following the injection of [3H]-leucine at stages 37/38–40 (when outer segments first develop) or 53–54 (when rod outer segments (r. o. s.) attain adult length), a band of label accumulated at the base of r. o. s. and was displaced sclerally with time, whereas label was diffusely distributed in cone outer segments (c. o. s.). By taking into account the change in shape of r. o. s. from conical to cylindrical around stage 46, and calculating outer segment growth (determined from the rate of band displacement) asvolumeof material added with time, we found a constant rate of membrane addition (1.59 μm/day) from the time of initial outer segment formation. The changes observed in r. o. s. length therefore indicate variations in the rate of disk shedding and phagocytosis, which is minimal before stage 46 and rises to 1.19 μm/day after stages 53–54. Ultrastructural observation showed that although all photoreceptor outer segments form by the repeated evagination of the plasma membrane of the connecting cilium, r. o. s. and c. o. s. are distinguishable by differences in membrane appearance even before they develop divergent membrane topologies. Fibrous granules near the basal body of young receptors may be precursors to the elongating ciliary microtubules. Clusters of cisternae observed near the ciliary base in photoreceptor inner segments may represent a stage in the transport of newly-synthesized opsin to the outer segment base.
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