Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Photoreceptor”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 73 records · Page 4Linked to original sources
PubMed2005

Synaptic pathology, altered gene expression, and degeneration in photoreceptors impacted by drusen.

PURPOSE: Drusen are risk factors for age-related macular degeneration and have been shown to negatively impact cells of the RPE and retina. In this study, the effects of drusen on the synaptic machinery of retinal photoreceptors are investigated. METHODS: Human donor eye tissue containing retina, RPE, and choroid was processed for confocal immunofluorescence microscopy, laser capture microdissection, and light and electron microscopy. Tissue sections were immunostained with a panel of antibodies to synapse-associated proteins. Populations of photoreceptors over drusen and normal populations of photoreceptors were microdissected from fresh frozen tissue, RNA was purified, and quantitative PCR was performed to compare relative levels of gene expression. RESULTS: The number of photoreceptor synaptic terminals is reduced in regions of the outer plexiform layer over drusen, synaptic proteins are mislocalized in photoreceptor cells, and synaptic terminals are often observed within the outer nuclear layer. Photoreceptors over drusen also increase expression of the stress response proteins apolipoprotein E and alphaB-crystallin. Abnormal immunolabeling patterns are not restricted to photoreceptors directly over drusen but are also observed in cells flanking drusen. Gene expression analysis confirms reductions in the expression of genes coding for synapse-associated proteins and signal transduction proteins and increases in the expression of apolipoprotein E and alphaB-crystallingene transcripts. Ultrastructural analysis of photoreceptor synaptic terminals over drusen reveals significant abnormalities, and cell counts show a reduction in photoreceptor density directly over, and lateral to, drusen of all sizes. CONCLUSIONS: Photoreceptors overlying and flanking drusen exhibit morphologic and biochemical signs of degeneration. The expression of synapse-associated proteins decreases in photoreceptor synaptic terminals, whereas the expression of stress-response proteins increases. Reductions in photoreceptor cell densities over, and flanking, drusen suggest that these degenerative effects eventually result in the death of photoreceptors.

Aged↗
PubMed2005

Predominant rod photoreceptor degeneration in Leber congenital amaurosis.

PURPOSE: An unusual retinal vascular morphology in an enucleated eye from a patient with Leber congenital amaurosis (LCA) has been associated with a mutation in AIPL1. The AIPL1 protein is expressed in the pineal gland and retinal photoreceptors. In the retina, AIPL1 is expressed in both developing cone and rod photoreceptors, but it is restricted to rod photoreceptors in the adult human retina. Therefore, this study was conducted to determine the photoreceptor phenotype in this LCA patient to determine if photoreceptors were differentially affected. METHODS: Additional genetic screening was performed and the consequences of the H82Y amino acid substitution characterized in an in vitro assay of NUB1 modulation. The morphology of the photoreceptors was examined by light and electron microscopy. Immunohistochemistry and immunofluorescent confocal microscopy was performed using a range of retinal photoreceptor markers. RESULTS: Transfection of the H82Y mutant AIPL1 in SK-N-SH cells revealed a normal subcellular localization and solubility but resulted in an increased ability of AIPL1 to redistribute GFP-NUB1 to the cytoplasm and resolve NUB1 fragment inclusion formation. Morphologically, the LCA retina appeared to be cone-dominant with a single layer of cone-like cells remaining in the central retina. Photoreceptor outer segments were absent and the surviving residual inner segments were severely shortened. Severe degeneration of the LCA retina was associated with upregulation of glial fibrillary acidic protein (GFAP). No signal was detected for AIPL1, rhodopsin, or L/M and S cone opsins in the LCA retina. Double labeling with peanut agglutinin (PNA) and wheat germ agglutinin (WGA) supported a cone-dominant phenotype for the surviving photoreceptors in the LCA retina, as did double labeling for cone arrestin, and rod and cone recoverin. The cone arrestin signal was restricted to the residual photoreceptor inner segments and was not detected in the cell bodies, axons, or axon terminals of the surviving photoreceptors. Recoverin immunoreactivity was most intense in the residual photoreceptor inner segments. CONCLUSIONS: The phenotype in this patient suggests that although AIPL1 is required for the development of normal rod and cone photoreceptor function, it might only be essential for rod and not cone survival in the adult.

Adaptor Proteins, Signal Transducing↗
PubMed1997

Aberrant expression of c-Fos accompanies photoreceptor cell death in the rd mouse.

Selective degeneration of rod photoreceptor cells in the retinal degenerative (rd) mouse prior to their complete maturation is thought to result from elevated cyclic guanosine monophosphate (cGMP) levels owing to the inherited defect in cGMP-phosphodiesterase. To investigate potential signaling pathways which might lead to apoptotic death of photoreceptors in the rd retina, the expression of immediate-early genes (IEG) of the activating protein-1 transcription factor (AP-1) family was examined. Increasing numbers of apoptotic photoreceptor nuclei were observed in the outer nuclear layer of the rd mouse beginning at postnatal day (P) 10. The peak incidence of apoptotic cells was observed at P13; by P16, almost the entire population of photoreceptors had been lost. Although c-Fos-like immunoreactivity was absent in photoreceptors of normal retinas, we observed that commencing at around P10, increasing numbers of rod photoreceptors in the rd retina exhibited nuclear staining for c-Fos protein. While no change in the distribution patterns of other members of the AP-1 family (c-Jun, JunB, and JunD) was observed in photoreceptors, Müller cell nuclei were transiently immunoreactive for c-Jun on P11. The incidence of c-Fos-positive photoreceptors peaked sharply at P12, 1 day earlier than the peak in apoptosis. Furthermore, the population of c-Fos-positive photoreceptors was distinct from apoptotic photoreceptors exhibiting chromatin condensation. The aberrant expression of c-Fos protein in rod photoreceptors immediately prior to their death in the rd mouse raises the possibility that c-Fos may be directly or indirectly involved in triggering the apoptotic cascade. Furthermore, the additional finding of c-Jun induction in Müller glia suggests that the IEG response to photoreceptor degeneration involves both intra- and intercellular signal transduction pathways.

Aging↗
PubMed1998

Photoreceptor allografts in a feline model of retinal degeneration.

BACKGROUND: Photoreceptor transplants provide a potential means to restore function in a degenerate retina and/or rescue degenerating host photoreceptors by trophic influences. We have examined photoreceptor allografts in the Abyssinian cat model of hereditary photoreceptor degeneration to determine the viability and influence of such transplants on the host retina. METHODS: Small pieces of 3- to 5-day-old normal kitten retina containing undifferentiated photoreceptors were injected into the subretinal space of adult Abyssinian cats at an early stage of retinal degeneration using standard vitreo-retinal surgical techniques. The retinas were examined by ophthalmoscopy and fundus photography, then by light and electron microscopy at different times after surgery. RESULTS: Such allografts survive for at least 6 months after surgery. The photoreceptors develop outer segments, invariably in rosettes. The transplants gradually integrate with the host retina but detach the host photoreceptor layer from the retinal pigment epithelium (RPE), which tends to reduce the number of host photoreceptors over the transplant. There is no slowing of the photoreceptor degeneration in neighboring non-detached retina. Inflammation or rejection was not detected. CONCLUSION: Undifferentiated, neonatal photoreceptor allografts survive and develop outer segments in the subretinal space of the Abyssinian mutant feline retina. The allografts gradually integrate with the host neural retina without inducing rejection. In the vicinity of the transplant there is increased loss of host photoreceptors, considered to be due to their detachment from the RPE layer. There is no evidence of any rescue of host photoreceptors elsewhere in this mutant retina.

Animals↗
PubMed2006

Multiple, parallel cellular suicide mechanisms participate in photoreceptor cell death.

Photoreceptor degeneration in human photoreceptor dystrophies and in the relevant animal models has been thought to be executed by one common mechanism -- caspase-mediated apoptosis. However, recent experiments have challenged this concept. In previous experiments, analyzing gene expression in the degenerating rd/rd mouse retina, we have suggested that the gene defect leads to oxidative stress and altered metabolism, which may induce caspase-dependent and caspase-independent cell death mechanisms such as the activation of cystein-proteases, lysosomal proteases, autophagy and complement-mediated lysis. In this study we asked two questions. First, whether a temporal analysis of these different mechanisms during the course of degeneration would enable us to establish a causal relationship between these events; and second, whether photoreceptor degeneration in different models of photoreceptor dystrophies occurs by activating the same mechanisms. Three models of photoreceptor degeneration were chosen in which photoreceptor degeneration is caused by different events: the rd/rd mouse (calcium overload); the rds/rds mouse (structural defect); and light-damage (LD; oxidative stress). Marker genes were selected for the identified processes. PCR-analysis on laser capture microdissection samples was used to verify the expression of these genes in the rod photoreceptor layer. A temporal relationship between the processes was established at the mRNA level, using quantitative RT-PCR. The time course of gene expression was compared to that of cell loss (loss of rows of photoreceptor nuclei) and apoptosis (TUNEL labeling). Apoptosis and autophagy was analyzed using enzymatic assays. The time course of apoptosis and TUNEL labeling coincide in all three models. Complement-activated lysis was found to either parallel (rd/rd and rds/rds) or precede (LD) the development of TUNEL-positive cells. Autophagy was determined to parallel (rd/rd and LD) or lag (rds/rds) behind the development of TUNEL-positive cells. In all three models, glucose metabolism was found to be increased significantly prior to the onset of cell death, but then dropped in parallel with the loss of cells. The presence of the marker genes was verified by laser capture microdissection, and apoptosis (caspase activity) and autophagy (lysozyme and cathepsin activity) were verified in retina extracts. These results provide evidence that irrespective of whether photoreceptor degeneration is triggered by gene defects (lack of beta-PDE or rds/peripherin) or environmental stress (light-damage), a number of pro-apoptotic mechanisms are triggered leading to the degeneration of the photoreceptor cells. The temporal pattern of the different pathways suggests that the non-caspase-dependent mechanisms may actively participate in the demise of the photoreceptors, rather than represent a passive response of the retina to the presence of dying cells. Thus, unless the common upstream initiator for a given photoreceptor dystrophy is found, multiple rescue paradigms need to be used to target all active pathways.

Animals↗
PubMed2006

Ceramide is a mediator of apoptosis in retina photoreceptors.

PURPOSE: The precise mechanisms involved in photoreceptor apoptosis are still unclear. In the present study, the role of ceramide, a sphingolipid precursor that induces apoptosis on cellular stress, was investigated in relation to the activation of cell death in photoreceptors. METHODS: Rat retina neuronal cultures, with or without docosahexaenoic acid (DHA), were treated with the ceramide analogue acetylsphingosine (C2-ceramide), and with a glucosylceramide synthase inhibitor. Ceramide synthesis in cultures treated with the oxidant paraquat was evaluated with [3H]palmitate. The effect of inhibitors of ceramide de novo synthesis, fumonisin B1 and cycloserine, on photoreceptor apoptosis was investigated. Apoptosis, mitochondrial membrane potential, and Bcl-2 expression were determined. RESULTS: Addition of C2-ceramide induced photoreceptor apoptosis. Paraquat increased formation of [3H]ceramide in photoreceptors, compared with the control, whereas inhibition of ceramide synthesis, immediately before paraquat treatment, prevented paraquat-induced photoreceptor apoptosis. Fumonisin also reduced photoreceptor apoptosis during early development in vitro. DHA, the retina major polyunsaturated fatty acid, which protects photoreceptors from oxidative stress-induced apoptosis, completely blocked C2-ceramide-induced photoreceptor death, simultaneously increasing Bcl-2 expression. Inhibiting glucosylceramide synthase, which catalyzes ceramide glucosylation, before ceramide or paraquat treatment blocked DHA's protective effect. CONCLUSIONS: The results suggest that oxidative stress stimulated an increase in ceramide levels that induced photoreceptor apoptosis. DHA prevented oxidative stress and ceramide damage by upregulating Bcl-2 expression and glucosylating ceramide, thus decreasing its intracellular concentration. This shows for the first time that ceramide is a critical mediator for triggering photoreceptor apoptosis in mammalian retina and suggests that modulating ceramide levels may provide a therapeutic tool for preventing photoreceptor death in neurodegenerative diseases.

Animals↗
PubMed2002

DNA damage and repair in light-induced photoreceptor degeneration.

PURPOSE: Intense light causes photoreceptor death that is greatest in the superior central retina. Short-duration treatment in a light-damage model results in TUNEL-positive photoreceptor nuclei within this region. However, cells lost 10 days after light treatment are fewer than the TUNEL-labeled cells observed earlier. Therefore, this study was undertaken to monitor DNA fragmentation and cell death to explain the discrepancy. METHODS: Eyes of dark-adapted rats were light damaged for 4 or 5 hours. DNA fragmentation was measured by TUNEL, laddering, and highly repetitive short interspersed nuclear element (SINE) analysis in dark-adapted, nondamaged control (dark-control) retinas and in retinas collected at 6-hour intervals after light treatment. TUNEL-positive photoreceptor nuclei were counted in these samples along a superior-to-inferior meridian and compared with control and damaged 10-day retinas. Monocytes and DNA polymerase beta were monitored by immunohistochemistry. RESULTS: TUNEL-positive staining of photoreceptors was centered around the superior central retina. At 10 days, photoreceptor loss had occurred in this region. In graphs of 6-hour-interval data, two DNA-fragmentation peaks, 24 hours apart, were evident. Monocytes appeared after nuclear damage. Total TUNEL-positive cells under both peaks exceeded the number of photoreceptors lost. The DNA-repair enzyme, polymerase beta, was induced in the superior central retina, within photoreceptor inner segments, 24 hours after light treatment, but declined thereafter. CONCLUSIONS: One population of damaged cells may mend DNA until the repair mechanism is exceeded and then revert to apoptosis, or, alternatively, two populations may undergo DNA fragmentation 24 hours apart. Either DNA fragmentation is masked at midpoint by temporary repair, or two waves of damage occur, but repair rescues the first set, not the second. Photoreceptors lost are fewer than TUNEL-positive cells. Thus, both possibilities suggest photoreceptor DNA repair. The transient appearance of DNA polymerase beta in photoreceptors under these experimental conditions further suggests nuclear repair. Thus, maintenance of in-house DNA-repair mechanisms may provide an alternate approach for the rescue of photoreceptors, as well as other neurons with stress-induced damage. These events may provide useful drug targets to promote photoreceptor survival in various forms of retinal degeneration.

Animals↗
PubMed1998

Effects of retinal laser photocoagulation on photoreceptor basic fibroblast growth factor and survival.

PURPOSE: In an unpublished study, the authors found that immunoreactivity for basic fibroblast growth factor (bFGF) is increased in rod photoreceptors adjacent to long-standing laser burns in human diabetic retinas. The goal of this study was to determine whether laser photocoagulation produces a similar increase in photoreceptor bFGF and promotes survival of these cells in dystrophic rodent retinas. METHODS: Threshold (whitening) and subthreshold (nonwhitening) laser burns were made in retinas of normal and Royal College of Surgeons (RCS) rats and normal and rds mice. The retinas were processed for immunocytochemical and morphometric analyses. RESULTS: In nonlasered normal rat and mouse retinas, bFGF immunoreactivity was prominent in the nuclei of Müller cells and astrocytes. Photoreceptors were bFGF negative except for a zone of bFGF-immunoreactive rods near the ora serrata. Some photoreceptors in nonlasered retinas of RCS rats and rds mice became bFGF immunoreactive. After laser treatment, bFGF immunoreactivity was markedly increased in all photoreceptors flanking the threshold burns and within the subthreshold burns in normal and mutant rats and mice. In RCS rat retinas, photoreceptor bFGF immunoreactivity remained elevated within subthreshold burns and flanking the threshold burns, and photoreceptor survival was prolonged. In rds mouse retinas, increased bFGF immunoreactivity in photoreceptors was not sustained and their degeneration was not retarded. CONCLUSIONS: Laser treatment of RCS rat retinas produced a sustained increase in bFGF immunoreactivity in photoreceptors and prolonged their survival, but laser treatment of rds mouse retinas did not have a long-term effect on photoreceptor bFGF immunoreactivity or survival. Although species differences in laser effects on photoreceptor bFGF and survival are apparent, the finding that rods flanking laser burns in human retinas have sustained increases in bFGF immunoreactivity suggests that laser treatment may be useful for prolonging survival of mutant photoreceptors in retinas of patients with retinitis pigmentosa.

Adult↗
PubMed2005

Retinal regional differences in photoreceptor cell death and regeneration in light-lesioned albino zebrafish.

Teleost fish regenerate retinal cells from a population of inner nuclear layer (INL) stem cells. To characterize photoreceptor regeneration in zebrafish (Danio rerio), adult albino fish were subjected to constant intense light to cause photoreceptor cell death. Retinal morphometry was performed on histological sections of control and light-lesioned albino retinas to compare the extent of light damage in the ventral, central and dorsal retinal regions. In addition, opsin immunohistochemistry and TUNEL were used to compare photoreceptor cell death in these different retinal areas, while PCNA immunolabeling quantified the cell proliferation that precedes the photoreceptor regeneration. Transgenic albino; Tg(alpha1-tubulin:egfp) zebrafish were also exposed to the intense light in order to examine regeneration-related gene expression changes. The light-lesioned retinas are characterized by extensive rod and cone photoreceptor cell death in the central and dorsal regions. In contrast, many of the rods and cones survive in the ventral retina. The highest levels of INL cell proliferation, which occurs subsequent to photoreceptor death, correspond to the retinal regions that suffer the greatest levels of photoreceptor damage. In the ventral retina, where photoreceptor cell death is minimal, cell proliferation is confined to the ONL. In addition, EGFP expression from the alpha1-tubulin promoter is increased in Müller glial cells in the light-damaged central and dorsal retina, while transgene expression in the ventral retina is restricted to small, round INL cells. Furthermore, expression of the HuC/D neuronal antigen is detected in a subpopulation of the Müller cells in the light-damaged superior retinal region. These data demonstrate that adult albino zebrafish display retinal regional differences in photoreceptor cell death and in the regeneration-related INL cell proliferation response. The high levels of INL cell proliferation and alpha1-tubulin:egfp transgene expression in the Müller cells may be graded in response to the degree of photoreceptor cell death. This suggests that the levels of photoreceptor damage may directly influence cell responses in the underlying retinal layers.

Animals↗
PubMed2005

Targeted effects of retinoic acid signaling upon photoreceptor development in zebrafish.

Retinoic acid (RA) is a signaling molecule important for photoreceptor development in vertebrates. The purpose of this study was to examine the mechanisms of the effects of RA upon developing rod and cone photoreceptors in the embryonic zebrafish. Exposure to exogenous RA increased the number of photoreceptors expressing rod opsin and red cone opsin, and decreased the number of photoreceptors expressing the blue and UV cone opsins, suggesting targeted effects of RA on photoreceptor development. RA exposure also increased opsin expression in individual rods and red cones, but decreased opsin expression in individual blue and UV cones, as indicated by differences in the strength of opsin hybridization in identified photoreceptors. RA exposure did not, however, significantly alter quantitative measures of photoreceptor pattern in a manner expected for changes in photoreceptor fate. These observations collectively indicate that RA treatment does not affect photoreceptor fate, but rather differentially influences opsin transcription in determined photoreceptors. An enzyme involved in RA synthesis, RALDH2, was immunocytochemically localized to retinal progenitor cells and the retinal pigmented epithelium (RPE), suggesting the presence of RA in the vicinity of developing photoreceptors. However, expression of an RA response element-driven transgene was restricted to the RPE, retinal progenitors, and a small population of neurons in ventral retina, suggesting that the endogenous RA signaling system is spatially limited within the eye.

Aldehyde Oxidoreductases↗
PubMed1981

Multiple classes of photoreceptors and neurons in the frontal organ of Rana pipiens.

An attempt has been made to characterize the photoreceptors and neurons of the frontal organ of Rana pipiens and the synaptic contacts of these cells, in order to provide morphological correlates for previous physiological findings. Neurons, glial cells, and photoreceptors with two different appearances can be seen in normal anatomical preparations. The photoreceptors make ribbon synaptic contacts onto both neurons and other photoreceptors. Retrograde transport of either cobalt or horseradish peroxidase through the frontal nerve results in labeling of neurons which are often located near the exit point of the frontal nerve from the frontal organ. Some of the dendritic processes of these neurons ramify among the neurons themselves, while others ramify among the photoreceptors. In addition, the frontal organ contains two photoreceptor types which synaptically contact both neurons and other photoreceptors. In some frontal organs labeled with cobalt (but never in peroxidase-labeled preparations) certain photoreceptors were also labeled. The labeled photoreceptors were probably the result of transcellular cobalt movement from labeled neurons, and not the result of some photoreceptors having axons in the frontal nerve. These results are discussed in conjunction with physiological evidence that chromatic interactions occur within single photoreceptors, each of which contains a single visual pigment with two physiologically active states.

Animals↗
PubMed1991

Light-stimulated rhabdom turnover in Limulus ventral photoreceptors maintained in vitro.

The role of light in turnover of photosensitive membranes was studied in isolated photoreceptors maintained in vitro. Ventral photoreceptors of the horseshoe crab, Limulus polyphemus, were used since they have been the subjects of many in vitro physiological studies. This study shows that the two classes of ventral photoreceptors, the large and small photoreceptors (Herman: companion paper), differ in their morphological response to light. The rhabdom of small photoreceptors is remarkable for its regularity, independent of lighting condition. The photosensitive microvilli of the rhabdom of small photoreceptors are narrow and almost always tightly packed in a hexagonal arrangement. In contrast, the morphology of the rhabdom of the large ventral photoreceptors is different in the dark and in the light, and the rhabdom undergoes turnover during lighting transitions. When fully dark-adapted, the photosensitive microvilli of large photoreceptors are narrow and well organized, sometimes in a crystalline array. However, in the light-adapted state, the microvilli are much thicker and very irregular. The transitions between the dark and light-adapted states, examined at midday, are rapid. After 5 minutes light exposure, the microvilli are dilated at their bases and shed membranes are present in the cytoplasm. By 30 minutes after light onset, the appearance of the rhabdom of large photoreceptors is indistinguishable from fully light-adapted cells. The transition to the dark-adapted state is equally rapid. Even at 5 or 12 minutes after light offset, most microvilli are narrow and quite regular, and by 30 minutes, the rhabdom usually appears to be fully dark-adapted. These experiments show that both the synthetic and degradative phases of rhabdom renewal take place in isolated photoreceptors. No efferent neural activity is required to initiate turnover; rather, changes in illumination alone are sufficient to generate rhabdom turnover in large ventral photoreceptors in vitro.

Adaptation, Physiological↗
PubMed2002

Developmental death of photoreceptors in the C57BL/6J mouse: association with retinal function and self-protection.

We have investigated the relationship between cell death among photoreceptors and the expression of function- and stress-related proteins during the development of the retina of the C57BL/6J mouse. Retinas from mice aged P(postnatal day)4 to P63 (adult) were examined for cell death using the TUNEL technique, and for the expression of basic fibroblast growth factor (bFGF), cytochrome oxidase (CO), rod opsin and glial fibrillary acidic protein (GFAP), using immunocytochemistry. At P4, cell death is most prominent in the inner layers of retina, declining to near-zero levels by P16. Cell death among photoreceptors occurs in a discrete wave commencing at approximately P12 and remaining elevated into the 4th postnatal week, beginning, peaking and declining later than in inner retina. The onset of photoreceptor death correlates with the expression of function-related molecules, such as CO and opsin. The decline in photoreceptor death correlates with the expression of the protective factor bFGF in photoreceptors. At the anterior edge of the retina photoreceptor death and the expression of bFGF are accelerated, and the expression of bFGF and GFAP is upregulated, by an edge-specific stress. We conclude that in the mouse photoreceptors undergo a wave of death which culls the neonatal population to adult levels. The onset of photoreceptor death is related to the acceleration of photoreceptor metabolism and function between P12 and P20. The decline of photoreceptor death to the very low levels found in the adult may be mediated by the upregulation of protective factors such as bFGF. Photoreceptor death and the expression of bFGF and GFAP at the edge of the retina are regulated by a still-unidentified, edge-specific stress, from as early as P16.

Aging↗
PubMed1995

Effects of Müller cell disruption on mouse photoreceptor cell development.

Müller cells have been proposed to play an important role in photoreceptor cell development during the final stages of retinal maturation. The effect of disrupting Müller cells during mouse retinal development was investigated using the specific glial cell toxin, DL-alpha-aminoadipic acid (AAA). By giving multiple systemic injections over several days, impairment of Müller cell function was maintained during the period of photoreceptor migration and differentiation. Following three consecutive days of AAA treatment [commencing on post-natal (P) day 3, 5, 7 or 9, and examined at P8-P14], clumps of photoreceptor nuclei were displaced through the inner segments, lying immediately beneath the retinal pigment epithelium (RPE). Apart from the scalloped appearance of the outer retina, the overall lamination pattern of the retina was relatively well preserved. Even when AAA treatment commenced as early as P3, several days prior to the formation of the outer nuclear layer, the majority of photoreceptors migrated to their correct position and formed inner and outer segments. Therefore, the signals for photoreceptor migration are either provided by the Müller cells prior to P3, or, alternatively, are derived from different intrinsic or extrinsic cues. Disruption of Müller cell function was evidenced by decreased glutamine synthetase activity as well as by increased glial fibrillary acidic protein (GFAP) and decreased cellular retinaldehyde-binding protein (CRALBP) immunoreactivity. Immunocytochemistry with an antibody to CD44, which labels the microvilli of Müller cells at the outer limiting membrane, coupled with electron microscopic analysis, demonstrated that the zonulae adherentes between Müller cells and photoreceptors were either irregular or absent in areas adjacent to displaced clumps of photoreceptors. Thus AAA treatment of early post-natal mice results in localized disruption of the contacts between Müller cells and photoreceptors. These pathologic changes persist into adulthood since at P28, while short stretches of photoreceptors appeared relatively normal with fully developed outer segments, periodic clumps of displaced photoreceptor nuclei were still present adjacent to the RPE. In conclusion, Müller cell processes at the outer limiting membrane appear to play a critical role in providing a barrier to aberrant photoreceptor migration into the subretinal space.

2-Aminoadipic Acid↗
PubMedDate not supplied

Chromatin immunoprecipitation identifies photoreceptor transcription factor targets in mouse models of retinal degeneration: new findings and challenges.

The transcription factors, Otx2, Crx, Nrl, and Nr2e3, expressed by retinal photoreceptor cells are essential for photoreceptor gene expression, development, and maintenance. Malfunction of any of these factors due to genetic mutations causes photoreceptor disease. Protein-protein interaction studies suggest that these factors may form a regulatory network centered on Crx. To understand how these factors regulate photoreceptor gene transcription in vivo, we have employed chromatin immunoprecipitation (ChIP) assays to assess the ability of these proteins to bind to regulatory sequences of photoreceptor genes in the retina of wild-type and mutant mice with photoreceptor degeneration. This paper summarizes the advantages and limitations of ChIP, using examples from our studies to demonstrate how this technique has contributed to our understanding of the regulation of photoreceptor gene expression. We report that Crx, Otx2, Nrl, and Nr2e3 co-occupy the promoter/enhancer, but not the region 3' of selected Crx target genes, in a retina-specific fashion. We identified Crx-dependent (Nr2e3) and Crx-independent (Otx2 and Nrl) target binding using Crx knockout mice (Crx-/-), suggesting that individual factors may use distinct mechanism(s) for binding and regulating target genes. Consistent with ChIP results, we also found that Otx2, a close family member of Crx, can activate the promoter of rod and cone genes in HEK293 cells, implicating Otx2 in regulating photoreceptor gene expression. These findings provide important information for understanding how photoreceptor transcription factors regulate photoreceptor gene expression and the mechanisms by which mutations in these factors cause transcriptional dysregulation and photoreceptor degeneration.

Animals↗
PubMed2004

Requirement of neuroD for photoreceptor formation in the chick retina.

PURPOSE: The genetic control of photoreceptor cell fate in the vertebrate retina is poorly understood. Published studies suggest that the genetic program underlying photoreceptor production involves neuroD, a proneural basic helix-loop-helix (bHLH) gene. The present study investigates whether neuroD is necessary for photoreceptor cell development, by using loss-of-function analyses. METHOD: Engrailed-mediated active repression, antisense oligonucleotides, and small interfering RNA (siRNA) were used to attenuate neuroD expression and function in embryonic chick retina. The development of the retina was subsequently analyzed to determine whether these experimental manipulations would yield photoreceptor deficits in otherwise normal retina. RESULTS: Chick embryos infected with retroviruses expressing an active repression construct, En-NeuroDDeltaC, exhibited severe photoreceptor deficits. The outer nuclear layer (ONL) of the retina was no longer a contiguous structure, but became fragmented with regions that contained fewer or no photoreceptor cells. Photoreceptor deficiency was evident even before the retina became laminated, suggesting that active repression of NeuroD may have affected photoreceptor genesis. No deficiency was observed in other types of retinal cells. Culturing retinal cells in the presence of siRNA against neuroD resulted in a more than 50% reduction in the number of photoreceptor cells and an increase in the number of chx10+ cells. Subjecting the developing retina to antisense oligonucleotides against neuroD yielded fewer photoreceptor cells both in vivo and in vitro. Consistent with these observations, anti-NeuroD antibody specifically labeled the nuclei of the ONL. CONCLUSIONS: The data suggest a specific and an essential role of neuroD in photoreceptor formation in the chick retina.

Animals↗
PubMed2006

Docosahexaenoic acid promotes photoreceptor differentiation without altering Crx expression.

PURPOSE: The precise molecular cues required for photoreceptor development are still unknown. Pax6 and Crx are essential during early retinal development and for photoreceptor differentiation, respectively. The lipid molecule docosahexaenoic acid (DHA) has also been shown to promote photoreceptor differentiation. Pax6 expression during the early steps in photoreceptor development and whether the mutual contribution of Crx and DHA enhances photoreceptor differentiation were investigated. METHODS: Neuroblast proliferation, Crx, and Pax6 expression were investigated in rat retinas in vivo and in neuronal cultures with or without DHA. BrdU incorporation, nestin and opsin expression, apical differentiation, and axonal outgrowth were determined by phase microscopy and immunochemistry. RESULTS: Pax6 expression occurred in all proliferating retinal neuroblasts in vivo; however, after their last mitotic division, photoreceptors stopped expressing Pax6 and started expressing Crx. In vitro, photoreceptor progenitors also showed a switch from Pax6 to Crx expression immediately after they exited the cell cycle and started differentiation. In contrast, those progenitors differentiating into amacrine neurons continued expressing Pax6 and did not express Crx. Most postmitotic photoreceptors expressing Crx showed little axon development and few of them expressed opsin. The addition of DHA dramatically increased differentiation in Crx-positive photoreceptors, enhancing opsin expression, apical differentiation, and axonal outgrowth, without affecting Crx expression. CONCLUSIONS: The results suggest that Pax6 and Crx expression are mutually exclusive during photoreceptor differentiation. Onset of Crx expression may provide a permissive stage that is essential to initiate photoreceptor differentiation, but additional support of DHA, among other environmental signals, is necessary to accomplish further differentiation.

Animals↗
PubMed2005

Function of atypical protein kinase C lambda in differentiating photoreceptors is required for proper lamination of mouse retina.

The photoreceptor is a highly polarized neuron and also has epithelial characteristics such as adherens junctions. To investigate the mechanisms of polarity formation of the photoreceptor cells, we conditionally knocked out atypical protein kinase Clambda (aPKClambda), which has been proposed to play a critical role in the establishment of epithelial and neuronal polarity, in differentiating photoreceptor cells using the Cre-loxP system. In aPKClambda conditional knock-out (CKO) mice, the photoreceptor cells displayed morphological defects and failed to form ribbon synapses. Intriguingly, lack of aPKClambda in differentiating photoreceptors led to severe laminar disorganization not only in the photoreceptor layer but also in the entire retina. Cell fate determination was not affected by total laminar disorganization. After Cre recombinase began to be expressed in the developing photoreceptors at embryonic day 12.5, both the immature photoreceptors and mitotic progenitors were dispersed throughout the CKO retina. We detected that adherens junction formation between the immature photoreceptors and the progenitors was lost in the CKO retina, whereas it was maintained between the progenitors themselves. These results indicate that the expression of aPKClambda in differentiating photoreceptors is required for total retinal lamination. Our data suggest that properly polarized photoreceptors anchor progenitors at the apical edge of the neural retina, which may be essential for building correct laminar organization of the retina.

Animals↗