Synelfin is a presynaptic
protein of unknown function that is differentially regulated in the avian song control circuit during the critical period for song learning; in humans, it gives rise to an amyloidogenic
peptide found in
senile plaques of
Alzheimer's disease. To gain insight into the potential involvement of
synelfin in synapse development, we investigated its expression in neurons cultured from the embryonic rat hippocampus. These neurons express a variety of defined synaptic
proteins, and form numerous synaptic connections after several days in culture.
Synapsin I, a synaptic vesicle-associated
protein, was detected within one day after the neurons were put in culture, but significant immunoreactivity for
synelfin was not detected until approximately 5 days in vitro (DIV). By 3 DIV,
synapsin-positive puncta (previously shown to correspond to presynaptic specializations) were detected surrounding the
soma and proximal dendritic processes, whereas comparable aggregations of
synelfin did not appear until several days later. By 14 DIV the punctate concentrations of
synelfin and
synapsin overlapped completely. Thus
synelfin is expressed in these cultured neurons and eventually becomes localized to presynaptic terminals, but it is absent from these specializations when they first form. We conclude that presynaptic terminals can change in molecular composition, and that
synelfin is associated with later stages in synaptic development or modulation.