A gradient molecule in developing rat retina: Expression of 9‐O‐acetyl GD3 in relation to cell type, developmental age, and GD3 ganglioside

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Abstract
In the embryonic and postnatal rat retina a cell surface antigen that is detected by monoclonal antibody JONES is distributed in a dorsoventral gradient. Biochemical analysis has determined that the antigen is a modified ganglioside, 9‐O‐acetyl GD3. In the present study, the distributions of 9‐O‐acetyl GD3 and its possible precursor GD3 in developing rat retina were compared immunocytochemically using specific monoclonal antibodies JONES and R24. On embryonic day 13 (E13) immunoreactivity to JONES was localized to central retina; however, R24 stained throughout the retinal epithelium. By E20, when JONES binding was distributed in a gradient along the dorsoventral axis, R24 again stained dorsal and ventral regions with uniform intensity. Analysis of freshly dissociated retinal cells further revealed that GD3 and 9–O‐acetyl GD3 expressions do not necessarily coincide. At E15 and postnatal day 2 (PN2), the majority of cells (78 and 92%, respectively) were immunolabeled by antibody to GD3, while between E15 and PN2 the percentage of cells immunolabeled by antibody to 9–O‐acetyl GD3 rose from 19 to 68%. By PN4, labeling decreased for both molecules; however, the rate of decline in 9–O‐acetyl GD3 labeling was more pronounced. Regulation of the numbers of JONES‐positive cells does not appear to depend on interaction with the extraretinal environment, for in neural retina explanted at E15 the proportions of 9–O‐acetyl GD3–bearing cells was found to be similar to the percentage observed in neural retina developing to an equivalent age in vivo. Experiments to identify the retinal cell types bearing 9‐O‐acetyl GD3 revealed that it is expressed by both neurons and glia growing in monolayer cultures of rat perinatal neural retina. Examination of freshly dissociated retinal cells following simultaneous labeling for some specific cell types and 9–O‐acetyl GD3 demonstrated that the latter determinant is present on photoreceptor, amacrine, and ganglion cells. For each neuronal cell type, however, not all of the cells were immunoreactive with JONES.We conclude that the differences in the percentages of JONES‐ and R24‐positive cells, and in particular the different rates at which JONES and R24 staining declined with age, indicate that the expression of the JONES epitope is regulated with some independence from parent ganglioside GD3. In addition, since JONES is expressed on a variety of retinal cells, both neurons and glia, and since the rate of decline in proportions of JONES‐labeled cells was found to be the same for at least two neuronal cell types, regulation of the expression of the JONES epitope, in keeping with its dorsoventral gradient of distribution, is probably not based on cell type.