THE SYNAPTIC VESICLE AND ITS TARGETS

Synaptic vesicles play the central role in synaptic transmission. They are regarded as key organelles involved in synaptic functions such as uptake, storage and stimulus-dependent release of neurotransmitter. I n the last few years our knowledge concerning the molecular components involved in the functioning of synaptic vesicles has grown impressive ly. Combined biochemical and molecular genetic approaches characterize many constituents of synaptic vesicles in molecular detail and contri bute to an elaborate understanding of the organelle responsible for fa st neuronal signalling. By studying synaptic vesicles from the electri c organ of electric rays and from the mammalian cerebral cortex severa l proteins have been characterized as functional carriers of vesicle f unction, including proteins involved in the molecular cascade of exocy tosis. The synaptic vesicle specific proteins, their presumptive funct ion and targets of synaptic vesicle proteins will be discussed. This p aper focuses on the small synaptic vesicles responsible for fast neuro nal transmission. Comparing synaptic vesicles from the peripheral and central nervous systems strengthens the view of a high conservation in the overall composition of synaptic vesicles with a unique set of pro teins attributed to this cellular compartment. Synaptic vesicle protei ns belong to gene families encoding multiple isoforms present in subpo pulations of neurons. The overall architecture of synaptic vesicle pro teins is highly conserved during evolution and homologues of these pro teins govern the constitutive secretion in yeast. Neurotoxins from dif ferent sources helped to identify target proteins of synaptic vesicles and to elucidate the molecular machinery of docking and fusion. Synap tic vesicle proteins and their markers are useful tools for the unders tanding of the complex life cycle of synaptic vesicles.