Synaptic clustering of Fascilin II and Shaker: essential targeting sequences and role of Dlg.

Previous studies have shown that both the Fasciclin II (Fas II) cell adhesion molecule and the Shaker potassium channel are localized at the Drosophila neuromuscular junction, where they function in the growth and plasticity of the synapse. Here, we use the GAL4-UAS system to drive expression of the chimeric proteins CD8-Fas II and CD8-Shaker and show that the C-terminal sequences of both Fas II and Shaker are necessary and sufficient to drive the synaptic localization of a heterologous protein. Moreover, we show that the PDZ-containing protein Discs-Large (Dlg) controls the localization of these proteins, most likely through a direct interaction with their C-terminal amino acids. Finally, transient expression studies show that the pathway these proteins take to the synapse involves either an active clustering or a selective stabilization in the synaptic membrane.