Changes in ganglioside profile in chick embryo retina: Studies on tissue and cell cultures

Ganglioside expression during differentiation of chick retinal cells in vitro

The neural retina has been widely used to study the developmental patterns of ganglioside metabolism. Recent findings about in vitro differentiating chick embryo retina cells showed that: a) GD3 and GD1a ganglioside patterns undergo the most dramatic changes; b) when the cells emit neurites, GD3 ganglioside and a group of complex gangliotetraosylgangliosides (GTOG) are transiently coexpressed; c) synchronized developmental phenomena are dissociated by anti-GM1 antibodies; d) GD3 remains as a major ganglioside in differentiated neurons, though it is almost not immunoexpressed; e) GTOG affect antibody binding to GD3; f) the content of gangliosides involved in neural differentiation modifies their immunostain localization on cell membrane; g) after exogenous GTOG uptake, immature neurons mimic GD3 immunofluorescent localization of mature cells; h) a subset of purified retinal ganglion cells express GTOG characteristic of mature neurons.

Appearance of beta 1,4 N-acetylgalactosaminyltransferase (glycosphingolipids GA2/GM2/GD2 synthase) in embryonic chicken vitreous humor during development

PURPOSE

beta 1,4 N-Acetylgalactosaminyltransferase (GalNAcT) is a type II integral membrane protein of the Golgi apparatus that catalyzes the synthesis of the glycosphingolipids GM2, GD2, and GA2. The activity of GalNAcT in chick retinal cells increases 6-fold between embryonic days 7 and 14. Because GalNAcT, like many Golgi glycosyltransferases, is proteolytically cleaved from Golgi membranes to release a soluble form into the culture medium of cells transfected with the cloned human enzyme, we tested whether GalNAcT might be released from embryonic retinal cells into the vitreous humor.

METHODS

Samples of vitreous humor and plasma and extracts of retinal cells were assayed for GalNAcT activity.

RESULTS

The activity of a soluble form of GalNAcT in embryonic chick vitreous humor was nearly undetectable until embryonic day 10, then increased more than six fold until day 16, and remained at that level until birth. The activity was identified as authentic GalNAcT based on a requirement for Mn++, GSL substrate specificity, and product characterization. GalNAcT activity in embryonic plasma was roughly 10% that of the corresponding vitreous humor, suggesting that the plasma was not the source of the activity in the vitreous.

CONCLUSIONS

GalNAcT in embryonic chicken vitreous humor is likely due either to a specific release from neural retinal cells or due to non-specific lysis of these cells during apoptosis associated with the development of the retina. Regardless of the source, GalNAcT in the vitreous humor has the potential to function as a lectin by binding to gangliosides GD3 and GM3 on the surface of retinal cells and, thereby, to influence neuronal development.

The effect of fumonisin B1 on developing chick embryos: correlation between de novo sphingolipid biosynthesis and gross morphological changes

Fumonisins, mycotoxins produced by Fusarium moniliforme and a number of other fungi, are potent inhibitors of the sphinganine-N-acyltransferase, a key enzyme of sphingolipid biosynthesis, and cause neuronal degeneration, liver and renal toxicity, cancer and other injury to animals. In this study we investigated the effect of fumonisin B1 on the sphingolipids of developing chick embryos. After yolk sac injection of fumonisin B1 a concentration and time dependent increase of the sphinganine-over-sphingosine ratio of the embryos could be demonstrated. Studies were done to evaluate the effect of fumonisin B1 on the glycophingolipid pattern of the chick embryos. In the presence of 72 micrograms fumonisin B1 per egg the incorporation of [14C]galactose and of [14C]serine into embryonic glycosphingolipids was reduced by about 70%, although the mass of glycosphingolipids was not affected by the toxin. However, a reduction of the wet weight of the treated embryos was observed. Additionally, histological examinations of whole embryo sections of control and fumonisin B1 treated embryos are presented. Fumonisin B1 caused haemorrhages under the skin as well as in the liver of treated embryos. A close correlation between disruption of sphingoid metabolism and light microscopic detectable tissue lesions could be observed.

Complex gangliosides affect GD3 accessibility to antibody in developing neuronal cells

Ganglioside expression of embryonic chick retina cells developed in vitro was analyzed by indirect immunofluorescence. Immature neurons were GD3 positive cells and the labeling was chiefly distributed all over their cell membrane. Mature neurons became GD3 negative and expressed complex gangliosides of the a- and b-pathways; nevertheless, the content of GD3 accounted for approximately 40% of the total gangliosides in these cells. Neuraminidase hydrolysis pointed out that GD3 was located in membrane of differentiated cells. The frequency of cells with the GD3 immunostain localized in restricted area of membrane of undifferentiated neurons increased significantly after adding a mixture of bovine brain gangliosides (largely complex gangliosides). Antibody binding to immobilized GD3 showed a dose-dependent inhibition by adding a mixture of bovine brain gangliosides, GM1, GD1a or asialo-GM1. Glycosphingolipids with shorter oligosaccharide chains, as cerebrosides or sulfatides, did not affect this binding. These results suggest that, concomitant with the accretion of content of complex gangliosides, a rearrangement in the membrane would occur, which progressively masks GD3 to its antibody. This rearrangement might affect putative ganglioside functions involved in neuronal differentiation.

In vitro modulation of changes in ganglioside patterns of differentiating neurons in the presence of an anti-GM1 antibody

Retinal cells from 7-day-old chicken embryos were cultured in the presence of a polyclonal anti-GM1 antibody, at low and high density in a "sandwich cell culture". Cells that were about 80% neurofilament positive at all times, changed their morphology and emitted processes as controls. By examining immunocytochemical expression of gangliosides, cells cultured in the presence of the antibody maintained GD3 expression longer than controls, albeit the expression of the gangliotetraosylgangliosides (GTOG) was not considerably affected. This leads to an extension of the transient period in which differentiating cells coexpressed both types of gangliosides (GD3 and GTOG). At 3-4 days in vitro the relative synthesis of GD3 was about 30% higher and that of GD1a about 40% lower than in controls, indicating a delay in the shift of the synthesis pattern. Nevertheless, the pattern of ganglioside composition resembled at 4 days in vitro. Results indicate that the anti-GM1 antibody may modulate the expression and synthesis of gangliosides without a detectable decrease in neuritogenesis. Considering that the emission of neurites occurs in coexpressing GD3 and GTOG neurons, it is suggested that neuritogenesis could be irrespective of losing the GD3 expression.

Gangliosides and neuronal differentiation

Using the GD3-specific mAb R24 we demonstrate by immunohistochemistry that the first embryonic cells of chicken expressing GD3 represent heavily proliferating cells of mesodermal origin (mesenchymal stem and endothelial cells). At this developmental stage (E1-1.5) neuroectodermal cells of the forming neural tube are not stained by R24 or any other available anti-ganglioside antibodies. These cells of the neural tube start to express GD3 at around E1.5 in parallel with increasing proliferative activity. Likewise proliferating and migrating neuronal crest derivates as well as undifferentiated retinal cells, the forming lens and otic placodes increasingly express GD3 in an organ-specific pattern following the spatiotemporal increase in mitotic activity. Immunostaining of GD1b (mAb D21b) or c-pathway polysialogangliosides (mAb Q211) is not obtained before E2.5, is nervous tissue specific and restricted to "new-born" neurons, which start to migrate and form first neurites. This striking change in ganglioside synthesis and expression also occurs in primary cell cultures (after or without previous Q211-mediated complement kill of neurons) during differentiation of mitotic progenitor cells to neurons (neurogenesis). In cell culture, the fluorescence staining is evenly distributed over the whole neuronal surface including filopodia at the growth cones. Monensin (10(-8) M) prevents expression of GD1b and c-polysialogangliosides and simultaneously differentiation of neuronal morphology (neurogenesis). The presence of exogenous gangliosides from bovine brain leads to a decrease of the monensin effect or even abolishes it.

GD3 prevalence in adult rat retina correlates with the maintenance of a high GD3-/GM2-synthase activity ratio throughout development

Unlike neurons from avian retina and other regions of avian and mammalian brain, neurons from mammalian retina not only contain gangliosides of the gangliotetraosyl ceramide series but also maintain a prevalence of GD3, a ganglioside of the lactosylceramide series characteristic of proliferative neural cells, when they are fully differentiated. We show here that GD3 is prevalent at all developmental periods of the rat retina from birth [50% of total gangliosidic N-acetylneuraminic acid (NeuNAc)] to adult (30% of total gangliosidic NeuNAc). GD3-synthase specific activity increased about 1.5-fold from birth to day 7 and essentially plateaued thereafter. The GD3-/GM2-synthase specific activity ratio was compared in rat and chicken retina at early and late developmental stages. In chicken retina the ratio was about 0.7 at early (when GD3 is prevalent) and decreased to 0.07 at late (when GD1a is prevalent) developmental stages. In rat retina the ratio was about 13 and 6 at, respectively, early and late developmental stages. These findings suggest that the prevalence of GD3 and of other "b" pathway gangliosides in adult rat retina neurons could be due in part to the maintenance of a high GD3-/GM2-synthase activity ratio throughout development of the tissue.

Internalization of the inhibitor of the N-acetylgalactosaminyltransferase by chicken embryonic retina cells: reversibility of the inhibitor effects

Retina cells from 6-day-old chicken embryos were cultured in the presence of an 125I-labeled protein inhibitor of the UDP-N-acetylgalactosamine:GM3,N-acetylgalactosaminyltransferase. The cells were labeled and did not lose the incorporated radioactivity when treated with 0.125% trypsin or 1 M NaCl at 37 degrees C for 1 hr, indicating that the iodinated inhibitor was inside the cells. Immunostaining procedures using an anti-inhibitor antibody were applied to the cells cultured in the presence of the inhibitor after permeabilization of the cells. The inhibitor was found inside the round cells virtually devoid of neurites, but not in flat glial-like cells or in process-bearing neural cells. Also found was an apparent self-recovery effect of the cells for both the anti-neuritogenic effect and the modification of the pattern of labeled gangliosides produced by the inhibitor when the agent was withdrawn from the culture medium after the initial period of 20 hr. This recovery was clearly observed 72 hr after the removal of the inhibitor.

The expression of a fucosyl-ganglioside in the molecular layer of the dentate gyrus following entorhinal cortical lesions

alpha-Galactosyl (alpha-fucosyl) GM1 is a ganglioside present in the outer two-thirds of the molecular layer of the dentate gyrus of the rat. This region is the terminal zone for afferents from the entorhinal cortex. In order to evaluate changes in ganglioside expression in this region following deafferentation, a monoclonal antibody (WCC4) was used to monitor the ganglioside from 3 to 30 days following a lesion to the entorhinal cortex. From 7 to 14 days postlesion, there was a relative decrease in the width of the band of immunohistochemical staining on the ipsilateral (lesioned) as compared with the contralateral (non-lesioned) side. The results of these studies indicate that alpha-galactosyl (alpha-fucosyl) GM1 is likely to be associated with dendritic shafts in the dentate molecular layer.

Studies of the developing chick retina using monoclonal antibody 8A2 that recognizes a novel set of gangliosides

A monoclonal antibody, Mab 8A2, that recognizes a novel set of gangliosides was produced by immunizing a mouse with Embryonic Day 14 chick optic nerve. Immunohistochemical studies of the developing chick retina revealed a complex pattern of Mab 8A2 immunoreactivity. Initially, staining is concentrated in the optic fiber layer in the central retina. Later in development, the most intense staining is seen at the periphery of the retina and 8A2 immunoreactivity appears in other retina layers. In the adult retina, 8A2 immunoreactivity is lost from the optic fiber layer but persists in the inner plexiform layer, inner nuclear layer, and outer plexiform layer. Cell culture experiments showed intense staining of neurites from retinal ganglion cells but no staining of Muller cells. Biochemical characterization of the epitope recognized by Mab 8A2 suggests that it includes a 9-O-acetyl group that is present on five different gangliosides. The 8A2 immunoreactive gangliosides are distinct from and have slower mobilities on thin-layer chromatographs than those recognized by Mab D1.1 which recognizes 9-O-acetyl GD3.

Migration and aggregation of embryonic chicken neurons in vitro: possible functional implication of polysialogangliosides

The presented study reports a primary culture system of embryonic chicken optic lobe neurons, which turned out to be a suitable model for cell migration and aggregation: Freshly dissociated neurons developed short processes, contacted one another and formed fasciculated bundles, on which neurons migrated as long-shaped cells, similar to migrating neurons in vivo. We used this system to study the possible involvement of c-pathway polysialogangliosides for neuronal migration and aggregation. These highly negative charged glycosphingolipids are the predominant gangliosides of migrating and outgrowing neurons in vivo. Addition of a purified ganglioside mixture (50 microM), extracted from brains of the corresponding embryonic stage, strongly enhanced neuronal migration and aggregation, while incubation of the cells with monoclonal antibody Q211, specifically binding c-polysialogangliosides, reduced aggregate formation in a dose-dependent manner. Cultures treated with 10 micrograms/ml Q211, instead, displayed a more divergent growth, leading to the formation of a fine network of single neuronal processes. These results suggest a functional implication of c-polysialogangliosides in neuronal fasciculation, migration and aggregation.

c-pathway polysialogangliosides in the nervous tissue of vertebrates, reacting with the monoclonal antibody Q211

The mouse monoclonal antibody Q211, previously shown to recognize a common epitope of chicken brain GP1c and of two other polysialogangliosides containing 4 and 6 sialic acid residues respectively, is demonstrated to bind to gangliosides with identical thin-layer chromatography (TLC) migration in the brain of representatives of boney fish, rays, reptiles and mammals, including man. In the boney fish brains, the Q211 binding gangliosides were found to be alkali-labile, the Q211 epitope, however, is alkali-stable. After alkaline treatment, the cichlid fish contained at least 4 Q211-binding gangliosides, migrating as GT1c, GQ1c, GP1c and 'GH'. In the trout brain only one Q211 antigenic fraction was found, migrating as GQ1c. In the brains of ray, turtle and embryonic chicken an identical pattern of Q211-binding gangliosides (GQ1c, GP1c, 'GH') occurred. In the embryonic rat and human brain, the content of Q211-binding gangliosides was much lower as compared to the other vertebrate species. The epitope was found in two fractions, migrating like GQ1c (human and rat) and GP1c (rat). The presence of Q211 epitope in all species was confirmed by immunohistochemistry. These data confirm that the Q211-epitope contains a complete c-ganglio-tetraose structure, carrying 3 sialic residues at the inner galactose. They furthermore demonstrate that the expression of c-pathway polysialogangliosides is a general feature of the vertebrate nervous tissue, either during whole life (fish, reptiles) or more or less transient during embryonic development (birds, mammals).

Gangliosides in lesion-induced synaptogenesis: studies in the hippocampus of the rat brain

Changes in ganglioside composition, biosynthesis and individual distribution were studied in hippocampal regions after unilateral destruction of the entorhinal cortex. After 1 and 3 days postlesion (dpl), a decrease in ganglioside content was detected in area dentata (AD) and pyramidal cell regions CA1-CA3 (CA), both ipsilateral and contralateral to the lesion. By 5 dpl all the values had returned to control values, except in AD which showed a dramatic increase in total ganglioside content reaching a maximum at 12 dpl. By 30 dpl this area also showed control content. A significant increase in biosynthesis of gangliosides was observed at 5 and 8 dpl in the hippocampus ipsilateral to the lesion without changes in the contralateral counterpart. Individual ganglioside distribution showed a pronounced change in GM1 and GQ1b with small changes in the other major gangliosides. Significant differences were observed in the distribution of gangliosides between the two hippocampal regions studied in unoperated control animals. GD1a was more concentrated in AD, whereas GQ1b, GT1b and GD1b predominated in CA. The data presented here indicate that important modifications in ganglioside content as well as pattern occur in the deafferented hippocampus a phenomenon that could be related with the known effect of gangliosides on neuritogenesis observed in cell culture studies.

In vivo and in vitro expression of gangliosides in chick retina Müeller cells

The expression of gangliosides of the lactosylceramide (LC) and of the gangliotetraosylceramide (GTC) series on the surface of cells from the chick neural retina was investigated by double-color indirect immunofluorescence. GD3 was assumed to be representative of LC and was detected using a specific monoclonal antibody. GM1 was assumed to be representative of GTC and was detected using the binding of cholera toxin followed by the binding of cholera toxin antibodies. The expression of polysialosylated GTC (polysialosyl-GTC) was detected using the cholera toxin-cholera toxin antibody experimental approach, after conversion of polysialosyl-GTC to GM1 by treatment of the cells with neuraminidase. In retinas from 6-day-old embryos (R6), most cells (approximately 80%) expressed GD3 but not GTC. After culturing for 7 days, (R6+7), the expression of GTC was found confined to neuron-like cells; flat cells derived from Müller cells expressed GD3 but were negative for GTC expression. On the other hand, postmitotic Müller cells obtained from 13-day-old embryo (R13) or 1-day-old hatched chick retina (RP1) expressed GD3, GM1, and polysialosyl-GTC but were unable to maintain the expression of these GTCs when kept in culture for several days. According to these results, retinal cells can be defined on the basis of their ganglioside expression as follows: (a) retinoblasts, by the expression of GD3; (b) postmitotic neuronal cells, by the expression of GTC; and (c) postmitotic Müller cells, by the expression of GD3 and GTC.(ABSTRACT TRUNCATED AT 250 WORDS)

Ganglioside composition of normal and mutant mouse embryos

The enrichment of gangliosides in neuronal membranes suggests that they play an important role in CNS development. We recently found a marked tetrasialoganglioside deficiency in twl/twl mutant mouse embryos at embryonic day (E)-11. The recessive twl/twl mutants die at embryonic ages E-9 to E-18 from failed neural differentiation in the ventral portion of the neural tube. In the present study, we examined the composition and distribution of gangliosides in twl/twl mutant mouse embryos at E-12. The total ganglioside sialic acid concentration was significantly lower in the mutants than in normal (+/-) embryos. The mutants also expressed significant deficiencies of gangliosides in the "b" metabolic pathway (GD3, GD1b, GT1b, and GQ1b) and elevations in levels of gangliosides in the "a" metabolic pathway (GM3, GM2, GM1, and GD1a). These findings suggest that the mutants have a partial deficiency in the activity of a specific sialyltransferase in the b pathway. Regional ganglioside distribution was also studied in E-12 normal mouse embryos. The ganglioside composition in heads and bodies was similar to each other and to whole embryos. Total ganglioside concentration and the distribution of b pathway gangliosides were significantly higher in neural tube regions than in nonneural tube regions. These findings suggest that b pathway gangliosides accumulate in differentiating neural cells and that the deficiency of these gangliosides in the twl/twl mutants is closely associated with failed neural differentiation.

Gangliosides of the mouse spinal cord: a comparison in in vivo and in vitro tissues

Ganglioside profiles in spinal cord from 13-day mouse fetuses, 21-day postnatal and adult mice were compared with those harvested from organotypic cross-sections of fetal mouse spinal cord grown for 28 days in vitro in a serum-free medium. All the major species of gangliosides reported for brain were present both in the in vivo tissue and cultured spinal cord, though not necessarily at each developmental stage examined. Fresh tissues showed increases and decreases in various gangliosides as have been reported for higher brain centers at similar stages of development in mammals and birds. However, qualitative and quantitative differences exist between fresh spinal cord and cultured cord explants as well as between galactose-grown and galactose-free cultures. Spinal cord explants grown in the presence of galactose showed measurable amounts of GM2 and GM3 which were not detected in the control-defined medium-grown cultures. The differences between the two culture groups may be related to interneuronal connectivity patterns.

Developmental expression in embryonic rat and chicken brain of a polysialoganglioside-antigen reacting with the monoclonal antibody Q 211

The monoclonal mouse antibody Q 211 binds to an antigen, which is expressed by postmitotic growing neurons of embryonic chicken and rat brain. In chicken, thin layer chromatography (TLC) immunostaining confirms the presence of the Q 211 antigen in at least 3 different polysialoganglioside fractions. One comigrates on TLC plates with GP1c and the others with gangliosides, which have been previously preliminary characterized as GQ1c, and as a hexasialoganglioside. Thus, 3 sialic acid residues linked to the inner galactose of a complete tetraose moiety is suggested as the common epitope of the different Q 211-antigen-active gangliosides. Also in the embryonic rat brain, immunohistochemistry reveals a transient expression of the Q 211 antigen in areas containing growing nerve fibres. Unlike chicken, however, in the rat the staining is restricted to early thalamocortical innervations and to a fibre system (probably long distance projections) connecting the mamillary body with the hippocampus formation. In ganglioside extracts from rat forebrain 2 polysialogangliosides are shown by immuno-TLC to bind Q 211. One of these fractions, occurring transiently and in parallel with histochemical staining, comigrates on TLC plates with chicken GP1c. The other comigrates with the second main Q 211 antigen-containing band of chicken, which was preliminary identified as GQ1c.

Biosynthesis and expression of gangliosides during differentiation of chick embryo retina cells in vitro

Cells from neural retina from 7-day chick embryos were cultured on polylysine-coated dishes up to 7 days. The small, round-shaped cells at seeding differentiated progressively, and after 4 days in vitro the majority had enlarged bodies and abundant processes. The content of protein and DNA was essentially unchanged during the entire period of culture. The incorporation of radioactivity from [3H]glucosamine into gangliosides declined slightly, reaching about 65% of the initial values at the end of the culture period. The proliferating activity measured by the incorporation of [3H]thymidine into DNA decreased to 10% or less of the initial value after 3 days in vitro. Almost at the same chronological times as in ovo, the synthesis of GD3 and of a ganglioside partially identified as GT3 decreased from 70 and 19% of the total incorporation into gangliosides in the first 20 h of culture to about 7 and 5%, respectively, after 3 days in vitro. Conversely, the synthesis of GD1a increased from about 6% at the beginning to about 70% at the end of the culture times. Immunocytochemical analyses of the expression of gangliotetraosyl gangliosides in cultured cells showed that these gangliosides appeared in the bodies and processes of cells having neuronal morphology; very little immunostaining of the scarce flattened cells, probably Müller cells, was found. The results indicate that the changes in ganglioside metabolism, which lead to decreased synthesis of gangliosides lacking the galactosyl-N-acetyl-galactosaminyl disaccharide end and to increased synthesis of gangliotetraosyl gangliosides, occur in cells that in culture differentiate into neurons.

Ganglioside abnormalities associated with failed neural differentiation in a T-locus mutant mouse embryo

The T-locus on mouse chromosome 17 contains a number of mutations that disrupt cellular differentiation and embryonic development. Because of their purported role in neuronal differentiation and brain development, gangliosides were studied in mouse embryos homozygous for two T-locus mutations: T and twl. Mice homozygous for the dominant T mutation die from failed mesodermal differentiation in the notochord, whereas mice homozygous for the recessive twl mutation die from failed neural differentiation in the ventral portion of the neural tube. No major ganglioside abnormalities were found in T/T mutant embryos at Embryonic Day 10 (E-10). In contrast, E-11 twl/twl mutants expressed a marked deficiency of the tetrasialoganglioside GQ1. Since this ganglioside migrates with GQ1b in three different thin-layer solvent systems, it may have the same structure as GQ1b. To gain insight into regional distribution, gangliosides were examined in head regions and body regions of normal (+/+) E-11 embryos. The ganglioside composition of these regions was the same as that of the whole embryo, with GM3 and GD3 comprising about 75% of the total ganglioside distribution. Moreover, N-acetylneuraminic acid was the only sialic acid species detectable in the E-10 and the E-11 embryos. These findings indicate that N-acetylneuraminic acid-containing gangliosides are synthesized actively in E-10 and E-11 mouse embryos and also suggest that the GQ1 deficiency in the twl/twl mutants is closely associated with failed neural differentiation.

Ganglioside GM1 antibodies and B-cholera toxin bind specifically to embryonic chick dorsal root ganglion neurons but do not modulate neurite regeneration

Polyclonal antibodies to ganglioside GM1 have been prepared and characterised by direct and competitive enzyme-linked immunoassay. An immunoglobulin fraction was prepared from a rabbit antisera showing high specificity and antibody titre for GM1 relative to the other major brain gangliosides. The anti-GM1 immunoglobulin fraction and B-cholera toxin specifically labelled neurons in primary cultures of embryonic chick dorsal root ganglia and there was a good correlation between the relative increase in binding of anti-GM1 immunoglobulin and B-cholera toxin following neuraminidase treatment of a variety of cell types. At antibody concentrations that show saturable binding to endogenous ganglioside in the neuronal membrane, the anti-GM1 immunoglobulin fraction did not interfere with the nerve growth factor (NGF)-mediated fibre outgrowth and neuronal survival as indexed by measurement of neurofilament protein levels. Similarly, at levels in excess of those shown to stimulate thymocyte proliferation, B-cholera toxin was also without effect. These data are not consistent with GM1 in the neuronal membrane functioning as a receptor molecule for NGF and/or other differentiation factors present in the tissue culture media.

Neuritogenic and metabolic effects of individual gangliosides and their interaction with nerve growth factor in cultures of neuroblastoma and pheochromocytoma

The 4 major ganglioside species, GM1, GD1a, GD1b and GT1b (200 micrograms/ml), were tested individually for the ability to stimulate neuronal trophic responses. The growth parameters measured were: morphologic changes, quantitated by computer-assisted morphometry of neurite length and number per soma, and metabolic changes, indicated by alterations in ornithine decarboxylase activity (ODC). In addition, the interaction of each ganglioside with nerve growth factor (NGF) was investigated with an NGF-responsive pheochromocytoma PC12 cell line and NGF-insensitive neuroblastoma Neuro-2a cultures. PC12 cells responded to gangliosides only in the presence of NGF (20 micrograms/ml): GM1 produced the greatest morphologic response, but did not alter metabolic levels; GT1b increased both parameters. The presence (5 micrograms/ml) or absence of NGF did not have an effect on the ganglioside-mediated morphologic responses of Neuro-2a cells to each species: GD1b elicited the greatest increase in neurite length, while GD1a and GT1b stimulated both length and number. In contrast, while GT1b alone was able to elevate ODC activity independently of NGF, the simultaneous exposure of Neuro-2a cultures to NGF and GM1 or GD1a resulted in a stimulation of cellular metabolism. These results indicate that each ganglioside species has a specific target action in the stimulation of different trophic responses and that performance in one category is not a predictor of the result in another. In addition, it is possible to confer a sensitivity to NGF by simultaneous treatment with specific gangliosides. This indicates that membrane gangliosides may modulate the actions of neurotrophic factors.

Gangliosides in postmitotic retina of chick embryo: changes in vivo and in cell cultures

Developmental changes in ganglioside composition of postmitotic neural retina of chick embryo were analyzed by thin-layer chromatography. Gangliosides were identified by comparing their chromatographic mobilities with reference standards. The outstanding changes are decrease in the concentration of GD3L and increase in GD1a and GM1 concentrations. By depleting Müller glia cells from retina tissue of 13- and 16-day embryos (R13, R16) we determined that the bulk of the major gangliosides is associated with the neurons. Analysis of gangliosides in monolayer cultures of R13 and R16 cells highly enriched for Müller cell-derived gliocytes indicated that these cells express the same types of gangliosides as neurons, but in somewhat different concentrations and relative proportions; however, after time in culture these cells showed ganglioside types and changes in ganglioside profile that are not characteristic of normal retina. The latter observation is consistent with other evidence that the phenotype of Müller glia cells becomes altered in monolayer culture. In contrast to cultures of early embryonic retina, in organ cultures of later postmitotic retina, ganglioside composition did not continue to change as in normal development. This suggests that in postmitotic retina, normal developmental progression of ganglioside changes requires systemic and/or other conditions which are missing or altered when this tissue is isolated and cultured in vitro.