Temporal appearance of the presynaptic cytomatrix protein bassoon during synaptogenesis

Bassoon is a 420-kDa presynaptic cytomatrix protein potentially involved in the structural organization of neurotransmitter release sites. In this study, we have investigated a possible role for Bassoon in synaptogenesis and in defining synaptic vesicle recycling sites. We find that it is expressed at early stages of neuronal differentiation in which it is selectively sorted into axons. As synaptogenesis begins, Bassoon clusters appear along dendritic profiles simultaneously with synaptotagmin I, sites of synaptic vesicle recycling, and the acquisition of functional excitatory and inhibitory synapses. A role for Bassoon in the assembly of excitatory and inhibitory synapses is supported by the colocalization of Bassoon clusters with clusters of GKAP and AMPA receptors as well as GABA(A) receptors. These data indicate that the recruitment of Bassoon is an early step in the formation of synaptic junctions.