Synapsin III: Developmental expression, subcellular localization, and rolein axon formation

We have investigated the developmental expression and subcellular localizat ion of synapsin III, the newest member of the synapsin family, in cultured mouse hippocampal neurons. Our results indicate that synapsin III is expres sed early during development, with levels peaking 7 d after plating and dec lining thereafter. Synapsin III is highly concentrated in growth cones. Usi ng specific antisense oligonucleotides, we have also examined the effect of depleting synapsin III on neurite elongation and synaptogenesis. When syna psin III was suppressed immediately after plating, hippocampal neurons exte nded minor processes but failed to differentiate one of them as the axon. T he suppression of synapsin III after axonal elongation did not affect the t ime course of synapse formation. The results indicate that synapsin III has a developmental time course, a subcellular localization, and a development al function very different from those of synapsin I and synapsin II.