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PubMed1997

Functional significance of recoverin localization in multiple retina cell types.

Knowledge of the cellular localization of recoverin in photoreceptor cells has enabled its interaction with other proteins to be postulated, tested and verified. Recoverin, a calcium sensing protein, is now thought to act by prolongation of the light state through interference with the interaction of arrestin and rhodopsin. Because of the detection of recoverin in multiple cell populations, the specificity of the cellular localization of recoverin was investigated in the retina of the mouse, rat, rabbit, chicken, frog, and chameleon and compared to that for opsin, phosducin, and arrestin. In addition to photoreceptor cell staining, the application of affinity-purified antibodies against recoverin demonstrated immunoreactive cells in the inner nuclear layer and a rare immunopositive cell in the ganglion cell layer of the mouse, rat and rabbit retina. Only photoreceptor cells were stained with recoverin antibodies in the chameleon and frog retina, whereas no cells were recoverin-positive in the chicken retina. In all six species studied, only photoreceptor cells were labelled with antibodies against opsin, phosducin or arrestin. Based on intensity of staining, two distinct populations of anti-recoverin-immunoreactive cells were distinguished in the photoreceptor cell layer of the retinas of the rat and rabbit, with the more darkly stained cells (probably cones) representing about 3% of the photoreceptor cells. The presence of recoverin in cells other than photoreceptors suggests it has an alternative or additional function and indicates the presence of multiple cell type-specific expression signals in the regulatory region of the recoverin gene.

Amino Acid Sequence↗
PubMed1998

A transient role for ciliary neurotrophic factor in chick photoreceptor development.

Previous studies suggest that ciliary neurotrophic factor (CNTF) may represent one of the extrinsic signals controlling the development of vertebrate retinal photoreceptors. In dissociated cultures from embryonic chick retina, exogenously applied CNTF has been shown to act on postmitotic rod precursor cells, resulting in an two- to fourfold increase in the number of cells acquiring an opsin-positive phenotype. We now demonstrate that the responsiveness of photoreceptor precursors to CNTF is confined to a brief phase between their final mitosis and their terminal differentiation owing to the temporally restricted expression of the CNTF receptor (CNTFR alpha). As shown immunocytochemically, CNTFR alpha expression in the presumptive photoreceptor layer of the chick retina starts at embryonic day 8 (E8) and is rapidly down-regulated a few days later prior to the differentiation of opsin-positive photoreceptors, both in vivo and in dissociated cultures from E8. We further show that the CNTF-dependent in vitro differentiation of rods is followed by a phase of photoreceptor-specific apoptotic cell death. The loss of differentiated rods during this apoptotic phase can be prevented by micromolar concentrations of retinol. Our results provide evidence that photoreceptor development depends on the sequential action of different extrinsic signals. The time course of CNTFR alpha expression and the in vitro effects suggest that CNTF or a related molecule is required during early stages of rod differentiation, while differentiated rods depend on additional protective factors for survival.

Animals↗
PubMed2000

Nocturnal tarsier retina has both short and long/medium-wavelength cones in an unusual topography.

The evolutionary position of tarsiers with respect to primates is still debated. The type of photoreceptors in the nocturnal Tarsius spectrum retina has been compared with the nocturnal New World monkey Aotus trivulgaris and the Old World monkey Macaca nemestrina by using immunocytochemical labeling for antisera known to be specific for primate cone and rod proteins. In all three species, antisera to long/medium (L/M) -wavelength specific cone opsin and cone-specific alpha-transducin detected a single row of cones. Only Macaca and tarsier retina contained cones labeled by antiserum to short (S) -wavelength specific cone opsin. Tarsier rod cell bodies were 6-12 deep, depending on retinal eccentricity. Tarsier central cones had 2-microm-wide outer (OS) and inner segments, which came straight off the cell body. Cone morphology differed little from rods except OS were shorter. Macaca cones labeled for 7G6 and calbindin, Aotus cones did not label for calbindin, and Tarsius cones did not label for 7G6 or calbindin. In tarsier retinal whole-mounts, peak cone density ranged from 11,600-14,200/cones mm(2). The 11- to 12-mm-wide peak region centered roughly on the optic disc, although foveal counts remain to be completed. Density decreased symmetrically to a far peripheral band of 4,200-7, 000/cones mm(2). In contrast, S cone density was very low in central retina (0-300/mm(2)), rose symmetrically with eccentricity, and peaked at 1,100-1,600/mm(2) in a 2- to 3-mm-wide zone in the far periphery. In this zone, S cones were 9-14% of all cones. L/M cones were regularly spaced, whereas S cones showed no regular distribution pattern. Although the functional characteristics of the tarsier S and L/M cone systems are yet to be determined, tarsier cone proteins and distribution have some similarities to both New and Old World monkey retinas.

Animals↗
PubMed2001

Distribution of S- and M-cones in normal and experimentally detached cat retina.

The lectin peanut agglutinin (PNA) and antibodies to short (S)- and medium to long wavelength (M/L)-sensitive cones were utilized in order to define the relative distributions of the two spectral types of cone across the domestic cat's retina. These values, in turn, were compared to those from retinas that had been experimentally detached from the retinal pigment epithelium. The pattern of cone distribution in the normal cat's retina is established by the preponderance of M-cones that constitute between 80% and 90% of all cones. Their peak density of over 26,000 cells/mm(2) resides at the area centralis. Though M-cone density decreases smoothly to the ora serrata where they have densities as low as 2,200 cells/mm(2), the density decrease along the nasotemporal axis is slower,creating a horizontal region of higher cone density. S-cones constitute between 10% and 20% of all cones, the number being quite variable even between individual animals of similar age. The highest S-cone densities are found in three distinct locations: at the superior far periphery near the ora serrata, immediately at the area centralis itself, and in a broad zone comprising the central and lower half of the inferior hemiretina. S-cones in the cat retina do not form a regular geometrical array at any eccentricity. As for the detached cat retina, the density of labeled S-cone outer segments (OS) decreases rapidly as early as 1 day postdetachment and continues decreasing to day 28 when the density of cones labeling with anti-S opsin has dropped to less than 10% of normal. This response points to a profound difference between rods and cones; essentially all rods, including those without OS, continue to express their opsin even in long-term detachments. The implications of these results for visual recovery after retinal reattachment are discussed.

Animals↗
PubMed2001

Short and mid-wavelength cone distribution in a nocturnal Strepsirrhine primate (Microcebus murinus).

Strepsirrhines are of considerable interest for understanding the evolution of cone photoreceptors because they represent the most ancestral living primates. The retina of nocturnal Strepsirrhines is reported to contain a single population of medium/long wavelength (MW/LW) cones whereas short wavelength (SW) cones are totally absent. The area centralis of nocturnal Strepsirrhines also lacks the degree of central specialization seen in the fovea of diurnal primates. In this study of a nocturnal Strepsirrhine, the gray mouse lemur (Microcebus murinus), we used specific antibodies that recognize SW and MW/LW opsins to determine the presence of different cone subtypes and their distribution in relation to that of rods and ganglion cells. The results are compared to two diurnal Haplorhine species, a New World (Callithrix jacchus) and an Old World (Macaca fascicularis) monkey. In the mouse lemur, both antibodies to MW/LW cone opsin (COS-1 and CERN956) label the same population of cones. A small proportion of SW cones is only stained by the JH455 antiserum whereas the monoclonal OS-2 antibody shows negative staining. These two antibodies label the same SW cone population in other primates. The extracellular matrix of all cones is also labeled by the peanut agglutinin (PNA) lectin. In mouse lemur retinal wholemounts, peak cone density is localized at the area centralis and ranged from 7,500 to 8,000 cones/mm(2). SW cones represent less than 0.2 % of the total cone population and are mainly located in the nasal part of the retina. SW cones show an irregular distribution and densities never exceed 49 cones/mm(2). The distribution of neurons in the ganglion cell layer shows a distinct centroperipheral gradient with a peak of 28,000 cells/mm(2) at the area centralis. Rod distribution shows a centroperipheral gradient with the peak (850,000 rods/mm(2)) including and extending slightly dorsal to the area centralis. The theoretical spatial resolution of the mouse lemur (4.9 cycles/degree) is slightly lower to that of other nocturnal primates. The densities of rods, cones, and ganglion cell layer neurons represent a compromise between spatial resolution and sensitivity for both photopic and scotopic vision.

Animals↗
PubMed2006

Presence of glutamate, glycine, and gamma-aminobutyric acid in the retina of the larval sea lamprey: comparative immunohistochemical study of classical neurotransmitters in larval and postmetamorphic retinas.

The neurochemistry of the retina of the larval and postmetamorphic sea lamprey was studied via immunocytochemistry using antibodies directed against the major candidate neurotransmitters [glutamate, glycine, gamma-aminobutyric acid (GABA), aspartate, dopamine, serotonin] and the neurotransmitter-synthesizing enzyme tyrosine hydroxylase. Immunoreactivity to rod opsin and calretinin was also used to distinguish some retinal cells. Two retinal regions are present in larvae: the central retina, with opsin-immunoreactive photoreceptors, and the lateral retina, which lacks photoreceptors and is mainly neuroblastic. We observed calretinin-immunostained ganglion cells in both retinal regions; immunolabeled bipolar cells were detected in the central retina only. Glutamate immunoreactivity was present in photoreceptors, ganglion cells, and bipolar cells. Faint to moderate glycine immunostaining was observed in photoreceptors and some cells of the ganglion cell/inner plexiform layer. No GABA-immunolabeled perikarya were observed. GABA-immunoreactive centrifugal fibers were present in the central and lateral retina. These centrifugal fibers contacted glutamate-immunostained ganglion cells. No aspartate, serotonin, dopamine, or TH immunoreactivity was observed in larvae, whereas these molecules, as well as GABA, glycine, and glutamate, were detected in neurons of the retina of recently transformed lamprey. Immunoreactivity to GABA was observed in outer horizontal cells, some bipolar cells, and numerous amacrine cells, whereas immunoreactivity to glycine was found in amacrine cells and interplexiform cells. Dopamine and serotonin immunoreactivity was found in scattered amacrine cells. Amacrine and horizontal cells did not express classical neurotransmitters (with the possible exception of glycine) during larval life, so transmitter-expressing cells of the larval retina appear to participate only in the vertical processing pathway.

Animals↗
PubMed2006

Degeneration and regeneration of ultraviolet cone photoreceptors during development in rainbow trout.

Ultraviolet-sensitive (UVS) cones disappear from the retina of salmonid fishes during a metamorphosis that prepares them for deeper/marine waters. UVS cones subsequently reappear in the retina near sexual maturation and the return migration to natal streams. Cellular mechanisms of this UVS cone ontogeny were investigated using electroretinograms, in situ hybridization, and immunohistochemistry against opsins during and after thyroid hormone (TH) treatments of rainbow trout (Oncorhynchus mykiss). Increasing TH levels led to UVS cone degeneration. Labeling demonstrated that UVS cone degeneration occurs via programmed cell death and caspase inhibitors can inhibit this death. After the cessation of TH treatment, UVS cones regenerated in the retina. Bromodeoxyuridine (BrdU) was applied after the termination of TH treatment and was detected in the nuclei of cells expressing UVS opsin. BrdU was found in UVS cones but not other cone types. The most parsimonious explanation for the data is that UVS cones degenerated and UVS cones were regenerated from intrinsic retinal progenitor cells. Regenerating UVS cones were functionally integrated such that they were able to elicit electrical responses from second-order neurons. This is the first report of cones regenerating during natural development. Both the death and regeneration of cones in retinae represent novel mechanisms for tuning visual systems to new visual tasks or environments.

Animals↗
PubMed1992

Interphotoreceptor matrix in the human retina: cone-like domains surround a small population of rod photoreceptors.

The interphotoreceptor matrix (IPM) in mammalian retinas is subdivided into rod and cone specific compartments: peanut agglutinin (PNA) binding glycoconjugates are associated with cones, whereas wheat germ agglutinin (WGA) binding glycoconjugates are associated with rods. To establish the identity of a photoreceptor cell type in the human retina with rod dimensions but with a matrix domain which stains with PNA, double label studies, using PNA-ferritin to decorate the extracellular domains and immunocytochemical techniques using a rod specific anti-opsin antibody were conducted. The PNA-binding domains were observed in the cone-associated IPM as well as in the IPM surrounding a small population of rod-shaped photoreceptors. The outer segments of these rod-shaped photoreceptors showed intense labeling with a rod specific anti-opsin antibody as did all other rods which were free of PNA-labeling. A quantitative analysis of all retinal quadrants indicates that this novel rod represents approximately 0.3% of the total rod population in the human retina.

Arachis↗
PubMed2005

Rhodopsin-iCre transgenic mouse line for Cre-mediated rod-specific gene targeting.

Retinal photoreceptors are highly differentiated postmitotic neurons that transduce photons into electrical signals. While the functions of many photoreceptor-specific genes can be evaluated by direct gene targeting, here we facilitate the studies of nonphotoreceptor-specific genes in these cells by developing an Opsin-iCre transgenic mouse line, iCre-75, in which a 4-kb mouse rod opsin promoter drives the expression of bacteriophage P1 Cre recombinase. Immunohistochemical analysis demonstrated that Cre recombinase is present exclusively in the outer nuclear layer of iCre75 mouse retina. Cre expression is found only in rods and not in cones. The expression level reached 188+/-44 ng per retina at postnatal day (pnd) 11 and increased to 687+/-56 ng at 2 months and older. Cre-mediated excision of floxed genomic DNA was absent at pnd 4, became detectable at pnd 7, and was completed by pnd 18. Retinal morphology and electroretinograms were normal in 8-month-old transgenic animals. The iCre-75 transgenic mice are thus suitable for future genetic studies of essential genes in retinal rod photoreceptors.

Animals↗
PubMed1994

Retinal GlcNAc-transferases and the glycosylation of rhodopsin.

The major oligosaccharide chains of bovine, frog and human rhodopsins are identical in structure. These molecules are unique in terms of their abridged size as compared to other asparagine-linked glycoproteins, a property which must be reflected in the activities and properties of the glycosyltransferases of the retina that are concerned with their biosynthesis. One of the unusual characteristics of the major oligosaccharide chain is its lack of branching. A key enzymatic step required for branching to occur would be the transfer of a residue of N-acetylglucosamine to the terminal unsubstituted mannose residue of the major rhodopsin oligosaccharide. We have investigated the kinetic properties of enzymes that would catalyse this process. The N-acetylglucosaminyl-transferases (GlcNAc-transferases) of Golgi-enriched fractions of bovine retina, human retina, rat liver Golgi and a partially purified GlcNAc-transferase II from rat liver were examined using as acceptors rhodopsin, opsin and the oligosaccharide isolated from rhodopsin. The identification of the substrates and products of the reactions was carried out by chromatographic means. From an evaluation of the Vmax/K(m) ratios it was observed that bovine and human retinas have very limited abilities compared to the rat liver enzymes to carry out the transfer of GlcNAc to these acceptors, showing from 100- to about 800-fold lower efficiency in this regard. A comparison of the activities obtained with intact rhodopsin or opsin and the rhodopsin oligosaccharide indicated that the activity of GlcNAc-transferase II was not appreciably influenced by the polypeptide portion of the molecule. It was also observed that prior galactosylation of rhodopsin blocked the addition of GlcNAc to rhodopsin. It is suggested that these properties contribute to the assembly of the abridged structures that have been observed in the oligosaccharides of rhodopsins of all species thus far examined.

Acetylglucosamine↗
PubMed2001

Development of normal and injury-induced gene expression of aFGF, bFGF, CNTF, BDNF, GFAP and IGF-I in the rat retina.

Focal mechanical injury to the retina substantially increases basic fibroblast growth factor (bFGF) and ciliary neurotrophic factor (CNTF) mRNA expression, accompanied by a transient increase in FGFR-1 mRNA, and this response is thought to protect photoreceptors near the injury site from inherited and light-induced retinal degenerations. We have now examined retinal gene expression of the principal survival factors involved in the response to injury in normal rats as a function of postnatal age both in normal and injured retinas. Sprague-Dawley rats were injured in one eye by needle incision through the retina at postnatal day (P) 10, 22, 35, 60, 90, 120 and 180. The other eye was uninjured and served as the control. Retinas were taken 1 day post-injury. Northern blot analysis was performed to determine the mRNA expression of the following factors and receptors: bFGF and acidic fibroblast growth factors (aFGF) and FGF receptor-1 (FGFR-1); CNTF and CNTF receptor alpha (CNTFR-alpha); brain-derived neurotrophic factor (BDNF) and its receptor trk B; and insulin-like growth factor-I (IGF-I) and IGF-I receptor (IGF-IR); glial fibrillary acidic protein (GFAP) and opsin. In the uninjured control eyes, mRNA expression of most of the factors increased with postnatal age, with little expression at P10 and maximal expression levels reached at P22 (opsin), P35 (aFGF), P60 (BDNF) or P90 (bFGF, FGFR-1, CNTF and GFAP). In contrast, IGF-1 mRNA rapidly decreased from a high level of expression at P10 to about 55% of that level by P22, reaching a stable 45-50% of the P10 level at P35 and thereafter. The response to injury of bFGF, FGFR-1, CNTF and GFAP mRNAs increased with postnatal age. Unexpectedly, only minimal increases in bFGF, FGFR-1, CNTF and GFAP over those seen in the control eyes were observed before P35. Thereafter, the increase of bFGF mRNA after injury reached a maximum of three-fold at P60, maintained this level to P120, and slightly decreased to 2.5-fold by P180. Expression of FGFR-1 mRNA showed a maximum increase of 2.6-fold at P90. Expression of CNTF and GFAP mRNAs followed a time course similar to that of bFGF. Mechanical injury did not alter the mRNA levels of aFGF, BDNF, IGF-I, and receptors, CNTFR-alpha, trk B and IGF-IR. These data show that the response to injury is minimal at early postnatal ages but increases with age and peaks at P60-90 for most potential survival factors.

Analysis of Variance↗
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↗
PubMed2000

Degeneration of cone photoreceptors induced by expression of the Mas1 protooncogene.

Although transgenic expression of oncogenes typically leads to tumorigenesis, oncogene expression directed to the rod photoreceptors leads to cell death without tumor formation. To evaluate the cellular and functional changes induced in cone photoreceptors by an oncogene, the Mas1 protooncogene was targeted to the cones of transgenic mice by the human red/green opsin promoter. Mas1 was chosen because of its exclusive expression in the nervous system and its homology to opsin. The overall histologic appearance of the transgenic retina was normal and retinal tumors were never observed. While rod-mediated electroretinograms were normal in all respects, cone-mediated responses were diminished in direct relationship to the level of transgene expression as determined by Northern blot analysis. Responses of UV- and green-sensitive cones were reduced equivalently, and Northern analysis and immunocytochemistry indicated that cone photoreceptor densities were markedly diminished throughout transgenic retinas. These results indicate that oncogene expression in cones induces cell death without tumor formation and support the possibility that aberrant oncogene expression may underlie some forms of hereditary retinal diseases. The Mas1 transgenic mice may be useful in understanding the cone photoreceptor degeneration that occurs in cone dystrophies and age-related macular degeneration and in evaluating potential therapies for these disorders.

Aging↗
PubMed2002

A maximum-likelihood analysis of eight phylogenetic markers in gallwasps (Hymenoptera: Cynipidae): implications for insect phylogenetic studies.

We assessed the utility of eight DNA sequence markers (5.8S rDNA, 18S rDNA, 28S rDNA, ITS regions, long-wavelength opsin, elongation factor 1-alpha, cytochrome b, and cytochrome oxidase I) in reconstructing phylogenetic relationships at various levels of divergence in gallwasps (Hymenoptera: Cynipidae), using a set of eight exemplar taxa. We report sequence divergence values and saturation levels and compare phylogenetic results of these sequences analyzed both separately and combined to a well-corroborated morphological phylogeny. Likelihood ratio tests were used to find the best evolutionary model fitting each of the markers. The likelihood model best explaining the data is, for most loci, parameter rich, with strong A-T bias for mitochondrial loci and strong rate heterogeneity for the majority of loci. Our data suggest that 28S rDNA, elongation factor 1-alpha, and long-wavelength opsin may be potentially useful markers for the resolution of cynipid and other insect within-family-level divergences (circa 50-100 mya old), whereas mitochondrial loci and ITS regions are most useful for lower-level phylogenetics. In contrast, the 18S rDNA marker is likely to be useful for the resolution of above-family-level relationships.

Animals↗
PubMed1986

Immunocytochemical localization of a rhodopsin-like protein in the lipochondria in photosensitive neurons of Aplysia californica.

Polyclonal antibodies directed against squid opsin were used in immunocytochemical and immunoblot experiments to identify a rhodopsin-like protein in photosensitive neurons of Aplysia. Aldehyde-fixed abdominal and cerebral ganglia were embedded in paraffin for peroxidase anti-peroxidase analysis or used whole for immunofluorescence studies. Ganglia were embedded in Lowicryl K4M for electron-microscope immunocytochemistry. In both the cerebral and abdominal ganglia, light-microscope immunocytochemical results showed reaction product deposited around the neuronal cell periphery corresponding in position to the lipochondria. In the abdominal ganglion, the giant cell R2, located in the right rostral quarter, and neurons in the right caudal quarter were consistently labeled with anti-opsin. Electron-microscopic studies demonstrated ferritin-labeling of the lipochondria in R2 and other immunoreactive neurons. Immunoblot analysis of R2 and cerebral neuron extracts was used to identify two prominent immunoreactive protein bands at 85 000 and 67 500 molecular weight.

Animals↗
PubMed1994

Cone cells fail to develop normally in transgenic mice showing ablation of rod photoreceptor cells.

Transgenic mice were derived containing the cytotoxic dt-alpha gene driven by opsin promoter sequences. Mice expressing this construct showed progressive degeneration of rod photoreceptor cells commencing at birth, with obvious depletion of such cells by postnatal day 7. Ablation of rod photoreceptor cells in the transgenic retina was accompanied by the failure of developing cone cells to elaborate outer segments, although all other aspects of cone cell cytodifferentiation appeared normal. The results suggest that the 1.0-kb opsin promoter segment contains rod cell type specificity and that cone cells require maturation of rod cells to complete the late stages of their terminal differentiation and for their maintenance and cellular integrity.

Animals↗
PubMed1992

Immunocytochemical demonstration of interphotoreceptor retinoid-binding protein in cerebellar medulloblastoma.

Previously, immunoreactive rod-opsin and S-antigen (arrestin), two highly characteristic markers of retinal photoreceptors and pinealocytes, were shown to be present in certain medulloblastoma cells. It, thus, has been suggested that such cells differentiate along the photoreceptor lineage. This is corroborated in the present immunocytochemical investigation using antibodies against another photoreceptor-cell marker, the interphotoreceptor retinoid-binding protein (IRBP). As shown in preparations of human retina and pineal organ, IRBP can be successfully demonstrated in formalin-fixed and paraffin-embedded tissue: the IRBP immunoreaction is located to the outer and inner segments of retinal photoreceptor cells and to perikarya of certain pinealocytes. Examination of formalin-fixed, paraffin-embedded biopsy specimens of 66 cerebellar medullo-blastomas revealed varying numbers of IRBP-immuno-reactive tumor cells in 19 cases that were formerly shown to contain rod-opsin and S-antigen immunoreaction. IRBP-immunoreactive tumor cells were also found in a retinoblastoma and a pineocytoma, but not in neuroblastoma, ganglioneuroblastoma, glioblastoma, oligodendroglioma and astrocytoma. The results indicate: (1) cerebellar medulloblastomas are heterogeneous in their differentiation potential; (2) one type of medulloblastoma displays photoreceptor characteristics; (3) this type appears to be closely related to retinoblastoma and pineal cell tumors; and (4) all three types of tumors may display additional common features to be explored in future studies.

Antigens↗
PubMed1993

Distribution of three retinal proteins in developing octopus photoreceptors.

The expression of proteins unique to plasma membrane domains of developing photoreceptors is used as a marker for retinal differentiation in vertebrates. Invertebrate photoreceptors are also compartmentalized, but little information is available on the development of these compartments or the expression of retinal proteins specific to these cellular regions. Using routine electron microscopy techniques, we have made observations on the formation of photoreceptor organelles, including myeloid bodies and rhabdomeres, in embryonic octopus eyes from an early stage in development through hatching. Immunocytochemical experiments on the embryos demonstrate a timed expression of three retinal proteins during development, and the early separation of the octopus photoreceptor plasma membrane into distinct domains. Using polyclonal antibodies for opsin, retinochrome and retinal binding protein we have shown that opsin appears first and is confined to the distal end of the photoreceptor that will eventually differentiate into rhabdomeres. This membrane domain is separated from the proximal/inner segment plasma membrane by a septate junction. Retinochrome is expressed later when the myeloid bodies appear in the inner segments, and retinal binding protein is apparently not synthesized until sometime after hatching. These results suggest that, in the cephalopod retina, protein components of the retinoid cycling apparatus appear in a specific developmental sequence during the differentiation of this tissue.

Animals↗