Trans-Golgi network delivery of synaptic proteins in synaptogenesis.

Synapse formation, stabilization and maintenance comprise several remarkably precise and rapid stages. The initial steps involve delivery to the site of initial contact between axon and dendrite of transport carriers containing several sets of synaptic proteins necessary for proper synaptic function. This occurs both pre- and postsynaptically and is mediated by apparently distinct vesicular carriers that fuse with the synaptic plasma membrane to deliver receptors for neurotransmitters, ion channels, transporters and pumps. The presynaptic carriers in the developing axon give rise to synaptic vesicles. On the postsynaptic side, the so-called spine apparatus may represent a tubular reservoir that gives rise to the postsynaptic players in synaptic function. Recent evidence indicates that recognition molecules, particularly neural cell adhesion molecule (NCAM), are associated with trans-Golgi-network-derived structures and thus can provide a signal for accumulation of these transport carriers at nascent synapses.