SORTING AND TRANSPORT OF SPECIFIC NEURONAL GLYCOPROTEINS

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The work in this proposal addresses two issues of fundamental importance to our understanding of neuronal function and development. The first is to determine how membrane glycoproteins synthesized in the cell body of a neuron are selectively routed to the pre- and postsynaptic terminal. These processes are central to the proper assembly of surface membranes and to how distinct regions of the neuronal plasma membrane are maintained in a functionally and structurally differentiated state. The second concerns the possible role of glycoproteins as mediators of interneuronal recognition and adhesion. My colleagues and I intend to explore these points using a single cell - R2 the giant neuron of Aplysia californica. R2's cell body, presynaptic, and postsynaptic regions are anatomically accessible. Moreover, R2 synthesizes only ten membrane glycoproteins, a remarkable simplicity relative to the complexity of glycoprotein fractions from vertebrate nervous tissue. Two of R2's glycoproteins have distinctly different destinations in the cell: glycoprotein-I is the major glycoprotein on the cell surface of the cell soma whereas glycoprotein-V is preferentially exported into the axon where it is rapidly transported towards R2's synapses. The site at which the two glycoproteins are sorted will be determined by immunocytochemistry at the ultrastructural level using monoclonal antibodies raised to each glycoprotein. In addition, the oligosaccharide chains of both glycoproteins will be characterized with the idea that a modification of a glycosyl moiety is the signal responsible for the sorting. R2, GCN, and R15 are three large identified neurons that differ in function, location, and neurotransmitter type. We will examine the glycoproteins present on the surface of the cell body and terminals of these neurons in order to test directly the hypothesis that neurons can be distinguished by their glycoprotein constituents. Many features of the proposed experiments are unique and present a unified, multidisciplinary approach to issues of major importance to our knowledge of the neuron.