Malformation of embryonic neural retina elicited by BrdU

Transplantation of embryonic retina to the subretinal space in rabbits

Embryonic rabbit retina can be transplanted to the subretinal space of adult rabbit with a new method, which gives a high rate of successful short-term transplants. Embryonic (stage E 15) neural retina cells were injected through an incision just behind the sclerocorneal border with a thin (inner diameter 0.15-0.4 mm, outer diameter 0.3-0.5 mm) plastic tube attached to a specially designed instrument, by which the length of the protruding plastic tip could be controlled. The retina was penetrated from the vitreous side and the donor tissue was injected into the subretinal space. The cells survived in the host for at least 5 months, although the long-term survival rate tended to decrease. The transplanted cells matured and differentiated, forming an approximation of the layered, retinal structure with some anomalies (e.g. rosettes). The subretinal location offers an interesting and convenient way of studying the development of retinal cell transplants in rabbits. Large transplants can be produced, and the risk for failures due to erroneous vitreous placement is small.

Embryonic cell recognition: uncoupling tissue-specific affinities from cell-type specificities

We have experimentally defined the two major aspects of embryonic cell recognition-adhesion (ReAd), tissue type-specific ReAd and cell type-specific ReAd; we showed that they arise consecutively during cell differentiation, and that the former can function in the absence of the latter. Embryonic chick cells (retina and chondroblasts) in which differentiation was arrested by BrdU at an early stage, failed to express cell-type ReAd, yet they continued to display tissue-type ReAd: they distinguished tissue-self from non-self and selectively cohered with self. Our results indicate that tissue-type and cell-type ReAd represent distinct, separately controlled mechanisms. BrdU appears to be useful as a probe for investigating the regulation of these mechanisms, and as an experimental effector of differentiation abnormalities associated with defects in cell recognition.

Cell disorganization and malformation in neural retina caused by antibodies to R-cognin: ultrastructural study

Retina tissue from 6-day chick embryos was organ-cultured for 3 days in the presence of antibodies to R-cognin, a surface antigen of retina cells. The antibodies which are known to bind to this antigen caused a striking malformation: interruption of the outer limiting membrane and extensive cell disorganization resulting in exteriorization of many cells and forming of chaotic masses on the surface of the tissue. Controls did not show these effects. These results further confirm that R-cognin is involved in the mechanism of histotypic contacts and recognition of retina cells, and that it plays an essential role in cell organization and histogenesis in the retina.

Biosynthesis of gangliosides in cultured retina from chick embryos

Retina tissue from 7-day chick embryos was maintained in culture for up to 10 days. After 5 days in culture the incorporation of [3H]leucine into proteins and of [3H]glucosamine into gangliosides was similar to that found in retinas from 12-day embryos. The incorporation of [3H]thymidine into DNA decreased steadily with time in culture; after 5 days it was about 20% of the initial value and approximately twice that determined in retinas from 12-day embryos. The radioactivity pattern of gangliosides labeled with [3H]glucosamine showed a predominance of the label in disialosyllactosylceramide (GD3); up to the 3rd day of culture. From then on, there was a progressive increase in the labeling of disialosylgangliotetraosylceramide (GD1a); by day 7 of culture, labeling of GD1a predominated and the labeling pattern was indistinguishable from that found in retinas from 12-day-old embryos. The specific activities of the CMP-NeuAc:GM3 sialosyl- and UDP-GalNAc:GM3 N-acetylgalactosaminyl-transferases decreased to 15% and increased to 400%, respectively, of the values determined in the retinas of 7-day embryos. The cultured retinas progressed in their organization into layers with culture time. The labeling transition from GD3 to GD1a was also detected after inhibition of the histotypic organization by addition of 5-bromo 2-deoxyuridine to the culture medium. Results suggest that high activity of GM3:sialosyl transferase and high labeling of GD3 are associated with the proliferative state of retina cells, while high activity of GM3:N-acetylgalactosaminyltransferase and high labeling of GD1a are associated with the non-proliferative, differentiated state of these cells.

Localization of retina cognin in embryonic neural retina tissue by immuno-scanning electron microscopy

The retina cognin (a retina-specific cell-surface glycosylated protein that mediates self-recognition and morphogenetic contact associations of embryonic retina cells) was visualized by immunolabeling and scanning electron microscopy on the surface of cells within retina tissue of 9- and 16-day chick embryos. The photoreceptor processes which are free of contact with cells in the neural retina, were found to be devoid of surface cognin from early on in their development. These results extend previous studies on cognin localization and regeneration on separated retina cells in vitro and conclusively correlate its presence and surface topology with its postulated role.

Antimitotic drugs that enhance neuronal survival in olfactory bulb cell cultures

Cell cultures of olfactory bulb from 2-3-day-old rats were used to evaluate 6 antimitotic drugs for their effects on neuronal survival. In cultures grown in medium without drugs for 7 days, neurons died as a layer of non-neuronal cells proliferated. A series of experiments were performed to determine dilutions and exposure times that allow maximum neuronal survival for each of the antimitotic drugs. Use of bromodeoxyuridine (BUdR) at 10(-5) M with a 5 day exposure gave cultures with large aggregates of neurons and an extensive network of interconnecting neurites. Cytosine arabinoside (Ara-C) at 8 X 10(-6) M for 5 days of exposure was also effective but the aggregates contained cellular debris. Fluorodeoxyuridine (FUdR) at 10(-4) for 5 days was less effective in flowing neurons to survive. Methotrexate (MTX), high thymidine and hydroxyurea were all not effective in allowing neuronal survival. In all cases there was an inverse relationship between the survival of neurons and proliferation of non-neuronal cells. Additional experiments were performed to determine how proliferating non-neuronal cells can lead to the death of neurons. In a series of transfer experiments, cultures were exposed to conditioned medium. Cultured olfactory bulb neurons grown on small cover slips were exposed to BUdR under optimal conditions and after 7 days were transferred to cultures treated or not treated with BUdR. In cultures not treated with BUdR, most of the transferred BUdR treated neurons died, while in cultures treated with BUdR the BUdR treated neurons survived. These results suggest that antimitotics enhance olfactory bulb neuronal survival by reducing the number of non-neuronal cells. In addition, it appears that proliferating non-neuronal cells are responsible for neuronal cell death by a medium factor and not by contact with the dividing non-neuronal cells.

Glycoconjugates of the avian eye: the development and maturation of the neural retina as visualized by lectin binding

The distribution of binding sites for four rhodamine-conjugated lectins has been examined in paraffin-embedded tissue sections of the developing and mature avian neural retina. The method of fixation employed here (95% ethanol:glacial acetic acid) is shown to conserve substantially more in vivo labeled 3H-glycoprotein or 3H-ganglioside than fixation with either 3.7% formaldehyde or 2% glutaraldehyde. Each lectin was shown to be optimally active by direct hemagglutination and inhibitable by the appropriate hapten in the cytochemical assay. Staining with wheat germ agglutinin (leads to N-acetylglucosamine) occurs predominantly to each of the anuclear retinal layers and progressively disappears from each of the nuclear layers. By adulthood, the inner nuclear layer is stained in a gradient which is highest adjacent to the inner nuclear layer while the nuclear layers are virtually unstained. Although similar to wheat germ agglutinin, staining with concanavalin A (leads to mannose) is less intense and persists in the adult nuclear layers. Dolichos biflorus agglutinin (leads to N-acetylgalactosamine) predominantly stains the embryonic ganglion cell layer. With development, this lectin demonstrates profound differences between the major cell types of the inner nuclear layer and the inner (negative) and outer (positive) plexiform layers. Differences between the principal synaptic layers are further accentuated by Ulex europaeus agglutinin I (leads to fucose): Binding sites are virtually absent from the 12th day embryonic retina, but are abundant throughout the retina by the 18th day and persist after hatching. However, in the adult retina staining persists in the outer plexiform layer but is lost from the inner plexiform and nerve fiber layers. In contrast to Dolichos biflorus agglutinin, Ulex europaeus agglutinin I stains the inner nuclear layer uniformly. Temporal differences in the characteristic lectin binding patterns exhibited by each of the major nuclear and anuclear layers of the developing avian neural retina are thus documented.

Development of differential affinities and positional information in embryonic retina cells: inhibition by BrdU

Embryonic neural retina cells fail to develop surface properties for type-specific cell recognition if they are transiently exposed to BrdU during an early, critical age. Such cells do not proceed with histogenetic positioning, organization and differentiation and, instead, form a malformed cell mass. This effect of BrdU is correlated with BrdU incorporation into DNA, and it can be prevented by simultaneous treatment of the cells with cytosine arabinoside. The proposed working hypothesis is that, in this system, BrdU interferes with expression of genes controlling cognitive specification of the cell surface.

Separation of cell subpopulations from embryonic chick neural retina with fluorescence-activated cell sorting

Fluorescence-activated cell analysis and sorting was used to characterize and separate cell subpopulations from the developing chick retina according to size, stage in the cell cycle and location in the tissue. It was shown that uptake of rhodamine B isothiocyanate (RITC) protein stain, light-scattering at large angles, and the time of flight of cells through the laser beam all correlate with cell size. Vital staining of DNA by H33342 permits cell separation according to phase in the cell cycle (G1, S, G2 + M). Further, a method was developed for separating postmitotic cells, based upon the quenching of H33342 fluorescence by the incorporation of 5-bromo-2'-deoxyuridine (BrdU) into DNA. Quantitative data reflect the decrease of DNA-synthesizing cells and the increase of postmitotic cells as the development of the retina proceeds. Isolation of cells on the basis of their location in the whole tissue is achieved by exposing the desired surface (e.g. the inner (concave) surface of the retina, which is rich in ganglion cells) to a suspension of Fluorescamine, which stains only cell layers close to the surface. Sorting out the fluorescing cells yields a high proportion of cells with the appearance, size and postmitotic characteristics of ganglion cells.

The development of inducibility for glutamine synthetase in embryonic neural retina: inhibition by BrdU

The hydrocortisone-mediated induction of glutamine synthetase (GS) in the neural retina of the chick embryo is a characteristic and unique feature of differentiation of this tissue. The induction involves genomic activity elicited by the inducer resulting in synthesis and accumulation of the enzyme. We describe correlations between the growth of embryonic retina tissue in vivo and in vitro and the development of its inducibility for GS, and demonstrate that this development proceeds through two phases: competence-acquisition phase (before the 7th day of development), and maturation phase. BrdU applied for 24 h to retinas of 5-day embryos irreversibly suppresses the development of induction-competence. However, BrdU does not affect the progressive maturation of inducibility when applied to retinas that already are fully induction-competent (8 days and older). The short treatment with BrdU of 5-day retinas also causes defective histogenesis resulting in drastic malformation of the tissue. The nature of the processes involved in competence-acquisition and in the maturation of inducibility for GS are examined. Possible mechanisms by which BrdU prevents the development of induction-competence for GS in the early embryonic retina and elicits defective histogenesis are discussed.