Glycoprotein-associated oligosaccharides from embryonic chick neural retina which contain glucose in phosphodiester-linkage to mannose (ManPGlc) have recently been detected by our laboratory, as has an enzyme responsible for the synthesis of the phosphodiester and a group of peptides that specifically recognize them. This proposal seeks to investigate at a molecular level the changes these proteins undergo during development of the retina and to assess the roles these proteins may play in the physiologic functions of the visual system. Particular attention will be paid to the possibility that this unique oligosaccharide functions as a trafficking signal to segregate these glycoproteins for axoplasmic transport, and that once on the cell surface these glycoproteins function in interneuronal recognition.
The specific aims of this proposal are: I. To pursue further studies of the glycoprotein acceptors in retina recognized in the phosphoglucosyl transferase reaction. Studies will include determinations of the specific activities of the phosphoglucosyltransferase and identification by autoradiographic analyses of gels of its acceptors in chick retina, tectum, and other parts of the CNS. II. To continue our characterization of ManPGlc binding proteins in embryonic chick neural retina. The proposed studies include a determination of the amino acid sequences of these peptides, and of their relationships to one another and to the previously described cell-surface protein ligatin. III. To determine the importance of ManPGlc-containing glycoproteins to cell-to-cell adhesion and, ultimately, to interneuronal synaptic specificity. We propose to pursue studies of intercellular recognition by monitoring the effects of exogenously adding these proteins themselves, their oligosaccharide analogs, or antibodies directed against them, to in vitro assays for intercellular adhesion. IV. To examine the possibility that oligosaccharides containing ManPGlc may be an important feature in the selection of certain glycoproteins for axoplasmic transport in retinal ganglion cells. Experiments in neural retina will determine if the ManPGlc binding proteins and/or glycoproteins carrying phosphodiester-linked glucose are axonally transported and, if so, to determine the importance of this oligosaccharide to this process.
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