Neuronal differentiation of retinoblastoma cells induced by medium conditioned by human RPE cells

Tumor cells can be induced to differentiate in vitro by biochemical manipulation of their culture environment. In the studies described here, the effects of medium conditioned by human retinal pigmented epithelial (RPE) cells on Y79 human retinoblastoma cells have been examined. RPE-conditioned medium in conjunction with laminin and a poly-D-lysine substratum is observed to induce neuronal differentiation of Y79 cells. The cells extend long cellular processes and exhibit immunologically detectable neurotypic properties. In contrast, control Y79 cells not exposed to medium conditioned by RPE cells exhibit only infrequent neuronal phenotypes. This response of Y79 cells to RPE-conditioned medium indicates that factors secreted by RPE cells can act as inducers of neuronal differentiation in retinoblastoma cells and suggest that such factors may be of importance in the development and differentiation of the neural retina.

Collagen-induced alterations in intercellular adhesion and antigen expression in retinoblastoma cells

Y79 human retinoblastoma cells, which typically grow as suspension cultures in vitro, show increased intercellular and cell-substratum adhesion, and form compact cellular aggregates when cultured on a collagen substratum. Concomitant with collagen-induced formation of compact cellular aggregates, is an increase in the binding of peanut lectin, especially at points of intercellular apposition. In addition, increases in the binding of antibodies against neuron-specific enolase and the cone-specific monoclonal antibody CSA-1 are noted following attachment and growth on collagen. In contrast, a decrease in the binding of antibodies against the glial marker, glial fibrillary acidic protein, is observed in collagen-attached cells. Thus, both the adhesive properties and the biochemical composition of Y79 retinoblastoma cells are altered by their attachment to and growth upon a collagenous substratum.

Ultrastructural evidence that specialized regions of the murine oviduct contribute a glycoprotein to the extracellular matrix of mouse oocytes

Previous studies have identified a glycoprotein (GP215) that is secreted by the murine oviductal epithelium and subsequently becomes sequestered within the perivitelline space of oocytes and developing embryos (Kapur and Johnson, Dev. Biol. 112:89-93, 1985; J. Exp. Zool. 238:249-260, 1986). The ultrastructural localizations of GP215 in the perivitelline space of ovulated oocytes and in the oviductal epithelium are described here. The glycoprotein is shown to be associated with a morphologically discrete extracellular matrix that provides a unique microenvironment for fertilization and early developmental events. In addition, putative secretory granules that contain this glycoprotein are observed in specific segments of the murine oviductal epthelium, suggesting regional differences in the composition of oviductal secretions.

Ultrastructural visualization of primate cone photoreceptor matrix sheaths

Glycoconjugates, including glycolipids, glycoproteins, and proteoglycans, are present in the plasma membrane of photoreceptor cells and in the interphotoreceptor matrix surrounding photoreceptor cell ellipsoids and outer segments. Although the precise function of these molecules is unknown, they may be important in mediating photoreceptor-pigment epithelial cell interactions, outer segment membrane assembly, and/or disc shedding. Lectins, affinity ligands for defined carbohydrate sequences, have proven particularly useful in studying the glycoconjugate composition of the interphotoreceptor matrix. The peanut lectin selectively binds to domains of the interphotoreceptor matrix surrounding cone ("cone matrix sheaths"), but not rod inner and outer segments. This is evidence for the existence of chemical and structural heterogeneity within the interphotoreceptor matrix. The studies described herein utilized ultrastructural pre-embedding histochemical labeling to assess whether, in addition to the surrounding interphotoreceptor matrix, peanut lectin binding is associated directly with that plasma membrane of cone inner and outer segments. This study confirms that ferritin-conjugated peanut agglutinin binds to cone matrix sheaths, and, in addition, provides ultrastructural evidence for the presence of binding to the plasma membrane surrounding cone inner and outer segments. The data suggest that cone membrane-associated peanut agglutinin-binding molecules may differ from those located within cone matrix sheaths.

Characterization of molecules bound by the cone photoreceptor-specific monoclonal antibody CSA-1

The cone-specific monoclonal antibody, CSA-1, selectively labels cone photoreceptors in the neural retina. Immunofluorescence assays reveal that CSA-1 binds cone outer and inner segments, cell bodies, axons and synaptic pedicles. The binding of the antibody is membrane-associated, not cytoplasmic. Several lines of evidence, including sensitivity to mild alkaline hydrolysis and galactosidic enzymes, suggest that the CSA-1 detected determinant is a galactose-containing carbohydrate moiety. Immunoblotting analyses show CSA-1 immunoreactivity with at least two molecules of 54,000 daltons that differ slightly in isoelectric point, and an additional, higher molecular weight species. CSA-1 should prove to be of value in studies of cone photoreceptor biology, in analyses of the development and differentiation of these cells, and in assessing their fate in various retinal pathologies.

Enzymatic characterization of peanut agglutinin-binding components in the retinal interphotoreceptor matrix

Previous histochemical and biochemical studies have documented the presence of carbohydrate-containing molecules in the retinal interphotoreceptor matrix (IPM). The lectin peanut agglutinin (PNA), which preferentially binds galactose-containing carbohydrates, especially galactose-galactosamine linkages, selectively labels cone photoreceptor-associated domains of the IPM ('cone matrix sheaths') in a variety of vertebrate retinas. In the studies described here, the nature of these PNA-binding components was investigated by monitoring the effects of proteolytic and glycosidic enzymes on binding of the lectin in the retina and IPM. All proteolytic enzymes tested cause a marked reduction in PNA-binding to cone matrix sheaths, suggesting that proteinaceous components are important to their organization. Exposure to O-glycanase, but not N-glycanase, markedly reduces binding of PNA to cone matrix sheaths indicating that O-linked oligosaccharides are probably responsible for its binding. Galactose oxidase treatment reduces PNA-binding throughout the retina and IPM, confirming that galactose moieties are involved in its binding. beta-Galactosidase (either before or after neuraminidase treatment) does not alter the pattern of PNA binding, suggesting that neither terminal nor penultimate beta-linked galactose residues constitute a major proportion of the lectin's binding sites in the retina. Neuraminidase treatment markedly increases the density and distribution of PNA binding throughout the retina and IPM, however, this effect appears to be, at least in part, the result of the binding of the lectin to neuraminidase molecules that become associated with tissue sections in addition to binding to carbohydrate groups unmasked by desialation. Exposure to chondroitinases causes disruption of the morphological integrity of cone matrix sheaths and slight diminution of PNA binding. Other enzymes acting on common constituents of extracellular matrices do not have similar effects. Taken together, these observations suggest that PNA-binding to cone matrix sheaths is due to the presence of glycoconjugates with galactose-containing, O-linked oligosaccharide chains.

Chondroitin 6-sulfate glycosaminoglycan is a major constituent of primate cone photoreceptor matrix sheaths

Recent work suggests that chemically and structurally distinct domains of the interphotoreceptor matrix ("cone matrix sheaths") surround cone photoreceptor outer segments and ellipsoids. This specific regionalization of at least some molecular constituents of the interphotoreceptor matrix may establish a unique cone-associated microenvironment. Previous histochemical and biochemical investigations have shown that a variety of glycosaminoglycans are components of the interphotoreceptor matrix and that the structural integrity of cone sheaths is slightly disrupted by glycosaminoglycan-degrading enzymes. In order to pursue the possibility that specific glycosaminoglycan species establish cone matrix sheath domains, monoclonal antibodies directed against various unsaturated glycosaminoglycans have been screened on sections of primate retina. The results of these studies identify chondroitin 6-sulfate glycosaminoglycan as a specific component of primate cone matrix sheaths.

Vascular atrophy in the retinal degenerative rd mouse

We have observed that the lectin Ricinus communis agglutinin I (RCA), which binds to terminal galactose moieties, serves as a marker for vasculature in the mouse retina. The binding of fluorescein-isothiocyanate-conjugated RCA was used to study the development of retinal vasculature in normal mice and in rd (retinal degeneration) mutant mice, which exhibit a massive loss of photoreceptor cells during the first month of life. In the normal mouse, retinal capillaries develop in an ordered manner and are concentrated in three major zones between the inner limiting membrane and the outer plexiform layer. In the rd mouse, the vessels appear to form normally but begin to degenerate by the end of the second postnatal week. By the end of the fourth postnatal week there is approximately a 35% reduction in the total number of vascular profiles in the rd retina compared to normal littermate controls. This reduction in vascularity is temporally associated with the photoreceptor degeneration.

Biochemical characterization of the major peanut-agglutinin-binding glycoproteins in vertebrate retinae

Peanut agglutinin (PNA), a lectin that binds D-galactose-beta (1----3) N-acetyl-D-galactosamine disaccharide linkages, selectively labels cone photoreceptors in the retinae of a variety of species. PNA binds consistently to domains of the interphotoreceptor matrix associated with cone, but not rod, inner and outer segments, to cone cell body and axonal membranes, to cone synaptic pedicles, and to portions of the inner plexiform layer. In order to begin the characterization of the molecular species responsible for cone-specific PNA binding, chick, turkey, rat, dog, pig, monkey, and human retinal extracts were separated by SDS-polyacrylamide gel electrophoresis and probed with peroxidase-conjugated PNA. The results reveal the presence of six major groups of PNA-binding glycoproteins ranging from 30 to 88 kilodaltons. Most of these are shared by the seven species examined; however, some interspecies variation is present. Three groups, designated GP39/40, GP42/45, and GP60, are the most intensely labeled by PNA and are common to all species analyzed, while groups GP29/31 and GP88 are less intensely labeled and are present in most but not all of the species investigated. Labeling of the GP54 group is variable but is most consistently associated with extracts of rat and pig retinae. Trypsin treatment, which results in the loss of cone-associated PNA binding in the interphotoreceptor matrix, causes a visually detectable reduction in three of the six groups of PNA-binding glycoproteins in porcine retinal extracts. Of these, GP54 is the most sensitive, being undetectable on PNA-stained blots after only 5 minutes of enzyme exposure; GP88 and GP45 are less sensitive but both are markedly reduced after 15 minutes of trypsinization. Trypsin-sensitive molecules thus may be involved in the establishment of the cone-specific domains of interphotoreceptor matrix identified by PNA binding. These, as well as the other groups of PNA-binding molecules, are being utilized to develop more specific immunologic probes with which to further study of their distribution and function.

Selective sequestration of an oviductal fluid glycoprotein in the perivitelline space of mouse oocytes and embryos

Previously, we identified a 215 kd glycoprotein, GP215, which is associated with postovulatory oocytes and embryos, but not with preovulatory oocytes (Kapur and Johnson, '85). In this paper a polyclonal antibody that specifically recognizes GP215 has been used to study the distribution of the molecule in association with ova and preimplantation embryos and in the female reproductive tract. GP215 is present in epithelial cells lining the cranial portions of the oviduct and in oviductal fluid, ovarian bursal fluid, and medium conditioned by oviductal tissue in vitro. Immunofluorescence assays of the ovum and early embryo show that GP215 is sequestered in the perivitelline space. Since preovulatory oocytes exposed to bursal fluid in vitro acquire GP215, we hypothesize that GP215 is synthesized and secreted by the oviductal epithelium and secondarily associates with the ovulated oocyte. Sequestration of GP215 within the perivitelline space is relatively specific since mouse serum albumin, a major constituent of oviductal fluid, and other high molecular weight proteins are not similarly retained. These observations indicate that the composition of the perivitelline space may be significantly different from the greater environment external to the zona pellucida such that fertilization and early development of mammalian ova potentially take place in a distinct perivitelline microenvironment.

Interphotoreceptor matrix domains ensheath vertebrate cone photoreceptor cells

The retinal interphotoreceptor matrix (IPM) occupies the space between the neural retina and the retinal pigmented epithelium (RPE), two neuroectoderm-derived epithelia. While the IPM appears to be a major route by which photoreceptor cells receive vital metabolic factors, relatively little is known concerning its structure and function. The studies reported here describe the presence of specialized domains of the IPM that ensheath cone, but not rod, inner and outer segments in pig, monkey, and human retinae. These cone extracellular matrix sheaths are chemically and structurally distinct from the remainder of the IPM as revealed by their specific binding of the lectin peanut agglutinin (PNA) and their structural stability during physical dissociation of the retina. Biochemical studies suggest that the PNA-binding components of the cone matrix sheaths are trypsin-sensitive glycoproteins. These structures may play a role in establishing a specialized microenvironment for cone photoreceptors, maintaining proper orientation of cone outer segments, and/or facilitating cone-RPE interactions.

Wheat germ agglutinin induces compaction- and cavitation-like events in two-cell mouse embryos

The lectin wheat germ agglutinin (WGA) has been observed to induce morphological events similar to compaction and cavitation in 2-cell mouse embryos. In vitro exposure of embryos to WGA results in increased apposition between blastomeres and the subsequent formation of a large intercellular cavity. As is the case for cavitation normally associated with blastocyst formation, WGA-induced cavitation can be inhibited by ouabain, suggesting a requirement for ATPase activity. However, WGA-induced effects are not inhibited by cytoskeletal disruptive agents or inhibitors of a variety of synthetic and metabolic functions. WGA may induce the observed effects by triggering the premature onset of developmental events normally involved in the processes of compaction and cavitation or, perhaps, by inducing morphologically similar changes as a result of the crosslinking of cell surface lectin-binding molecules and regional inhibition of ATPase function.

An oviductal fluid glycoprotein associated with ovulated mouse ova and early embryos

This study documents a molecular change in the murine ovum related to its exposure to oviductal fluid. Wheat germ agglutinin (WGA) identifies a 215-kDa glycoprotein band (GP215) that is associated with ovulated oocytes and early embryos obtained from the oviduct, but is absent from preovulatory oocytes. GP215 is present in ovarian bursal fluid, oviductal fluid, oviductal epithelial cell extracts, and medium conditioned by oviductal tissue in vitro. Preovulatory oocytes acquire GP215 after in vitro incubation in ovarian bursal fluid. Thus, it appears likely that GP215 is secreted by the oviductal epithelium and becomes intimately associated with the ovum following ovulation.

Application of acrylamide as an embedding medium in studies of lectin and antibody binding in the vertebrate retina

The use of acrylamide as an embedding medium for vertebrate retinal tissue and its applicability to lectin and antibody-based cytochemical studies is described. The acrylamide technique has numerous advantages over those using fresh-frozen or paraffin embedded material. The morphological integrity of retinal tissue prepared in acrylamide is equivalent to that obtainable with paraffin and superior to that of fresh-frozen material. In addition, this technique alleviates problems often encountered with the thermal and chemical treatments required in the paraffin method. The acrylamide technique allows the localization of lectin and antibody-binding sites essentially unaltered by the fixation and embedding protocol, as in frozen sections, while maintaining tissue morphology similar to that of paraffin-embedded tissue. It is hoped that this approach will be useful to other workers in vision research employing lectin, antibody or other cytochemical approaches to the study of cellular structure and function.

Specific binding of peanut lectin to a class of retinal photoreceptor cells. A species comparison

Although lectins have been used to study surface oligosaccharides of photoreceptor cells in intact retinas and dissociated retinal cells, the specificity of lectin binding to cones versus rods in a variety of species has not been examined closely. The authors previously found that application of fluorescein isothiocyanate (FITC)-conjugated peanut agglutinin (PNA), a lectin with high affinity for galactose-galactosamine disaccharide residues, to cryostat sections of unfixed mouse retina results in staining that is confined to synaptic regions and a subpopulation of photoreceptor cells. To further investigate the possibility that PNA binding is specific for cone photoreceptors, the authors extended their studies to include the duplex retinas of fish, rabbit, monkey, and human in addition to the cone-dominant retina of the chick. These studies show that PNA binding is specific for cone inner and outer segments and also is likely to be associated with the large synaptic pedicles of cone photoreceptor cells. In addition, the authors compared PNA binding with that of Ricinus communis agglutinin I (RCA), another lectin that preferentially binds terminal D-galactose moieties. While RCA does bind to cones in the species examined, it also binds to a lesser extent to rod photoreceptor inner segments. The pattern of binding of RCA in other regions of the retina differs markedly from that of PNA. Significantly, RCA serves as a specific marker for retinal vasculature in the human, monkey, and mouse. These results suggest that certain PNA-binding macromolecules may be important in defining the molecular and cellular specificity of cone photoreceptor cells and that PNA may provide a means for the isolation of cones and cone-specific molecules. RCA may prove to be of value in monitoring vascular changes associated with normal development and pathologic conditions.

Selective lectin binding of the developing mouse retina

A battery of eight lectins with different carbohydrate specificities was used to study changes in glycoconjugate expression during cell differentiation in the mouse retina. The lectins tested included concanavalin A (Con A), wheat germ agglutinin (WGA), soybean agglutinin (SBA), peanut agglutinin (PNA), Ulex europaeus agglutinin (UEA), Ricinus communis agglutinin I (RCA), Dolichos biflorus agglutinin (DBA), and Limulus polyphemus agglutinin (LPA). Unfixed frozen sections of adult and early postnatal mouse retina were treated with fluorescein isothiocyanate-conjugated lectins and examined by fluorescence microscopy. The results showed selective lectin binding in both cellular and synaptic retinal layers of the adult mouse and throughout postnatal development. In general, an increase in intensity of fluorescent lectin staining during retinal development was observed for Con A, WGA, DBA, LPA, RCA, and PNA. This suggests an increase in the expression or accessibility of carbohydrate moieties during development. SBA and UEA showed little to no binding to adult or neonatal retina. Retinal vasculature was intensely stained by RCA, both during development and in the adult. All lectins binding to adult or neonatal retinal layers showed some degree of reactivity with the inner segment region of photoreceptor cells. However, only Con A, PNA and WGA bound to photoreceptor outer segments, suggesting significant differences in the glycosylated components of inner and outer segment membranes. PNA bound specifically to a subpopulation of photoreceptor cells and to discrete regions within the outer synaptic layer. The pattern of PNA binding suggests that this lectin binds preferentially to cone photoreceptor inner and outer segments and cone synaptic pedicles rather than to rod photoreceptor cells. This marked specificity of PNA binding suggests that it may provide a basis for the physical separation of cone and rod photoreceptor cells.

Decreased uptake and retention of rhodamine 123 by mitochondria in feline sarcoma virus-transformed mink cells

A reduce uptake and retention of the mitochondria-specific membrane potential probe rhodamine 123 by feline sarcoma virus (FeSV)-transformed mink fibroblasts (64F3) has been detected. The decreased accumulation of rhodamine 123 by 64F3 mitochondria is not due to abnormal plasma membrane dye permeability, since after microinjection of the dye these cells are still unable to retain the dye at levels comparable to the untransformed parental cells, CCL 64. Nigericin, an ionophore that mediates an electrically neutral exchange of protons for potassium ions resulting the elimination of the pH gradient across the mitochondrial membrane and a compensatory increase in mitochondrial membrane potential with continued respiration, increases both the dye uptake and the retention time in transformed 64F3 cells. These results suggest that mitochondria in FeSV-transformed mink cells may have an abnormally low mitochondrial membrane potential accompanied by a relatively high pH gradient. Since anioic metabolites such as pyruvate and glutamate are accumulated by mitochondria in proportion to the delta pH across the mitochondrial membrane, the abnormal mitochondria described here may contribute to the abnormal metabolic state of FeSV-transformed cells.

Monitoring of relative mitochondrial membrane potential in living cells by fluorescence microscopy

Permeant cationic fluorescent probes are shown to be selectively accumulated by the mitochondria of living cells. Mitochondria-specific interaction of such molecules is apparently dependent on the high trans-membrane potential (inside negative) maintained by functional mitochondria. Dissipation of the mitochondrial trans-membrane and potential by ionophores or inhibitors of electron transport eliminates the selective mitochondrial association of these compounds. The application of such potential-dependent probes in conjunction with fluorescence microscopy allows the monitoring of mitochondrial membrane potential in individual living cells. Marked elevations in mitochondria-associated probe fluorescence have been observed in cells engaged in active movement. This approach to the analysis of mitochondrial membrane potential should be of value in future investigations of the control of energy metabolism and energy requirements of specific biological functions at the cellular level.

Localization of mitochondria in living cells with rhodamine 123

The laser dye rhodamine 123 is shown to be a specific probe for the localization of mitochondria in living cells. By virtue of its selectivity for mitochondria and its fluorescent properties, the detectability of mitochondria stained with rhodamine 123 is significantly improved over that provided by conventional light microscopic techniques. With the use of rhodamine 123, it is possible to detect alterations in mitochondrial distribution following transformation by Rous sarcoma virus and changes in the shape and organization of mitochondria induced by colchicine treatment.