All neurons contain synaptic vesicles that package and store neurotransmitter and release their contents during synaptic transmission. All synaptic vesicles appear to share at least three integral membrane proteins of sizes 95, 65 and 38 kd and often associate with a peripheral protein, synapsin 1. The appearance of the first three proteins is a measure, therefore, of the onset of synaptogenesis during development or regeneration. We propose to complete the DNA sequencing of one of these vesicle membrane proteins, and to use the DNA to examine the transcription of vesicle genes during rat brain and retinal development. If as expected the vesicle-specific DNA provides a useful probe, we will examine elements of the 5' flanking sequences involved in gene regulation. An unexpected feature of the three vesicle membrane proteins is that they also found in endocrine cell lines. We propose a concrete model that tries to fit these and other findings into a developmental sequence that all neurons undergo. Two key elements of the model which will be tested here are that synaptic vesicles arise by endocytosis of dense secretory vesicle membranes, and that expression of genes for synaptic vesicle proteins occurs significantly in advance of synaptogenesis and even process extension. Finally to take the model beyond the descriptive, experiments are set up to use the shared vesicle proteins to examine how synaptic vesicles fuse with membranes and how synaptic vesicle proteins but not other membrane proteins recycle from the plasma membrane during coated vesicle-mediated endocytosis. Since these experiments study molecular components present in all synapses, the findings will, we hope, enlighten several areas of neurobiology and be pertinent to a number of neurological disorders.
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