AIY, a primary interneuron in C. elegans, receives inputs from multiple sensory neurons to modulate behaviors such as thermotaxis, locomotion, chemotaxis and learning responses (1-5). Correct synaptic connectivity of AIY pre- and postsynaptic partners is critical for correct formation of the circuits which underlie these behaviors. Although the AIY processes contact multiple potential postsynaptic partners, AIYs form a stereotypical set of synapses with certain neurons at discreet areas of the axons (6). The molecular mechanisms used by AIY to discriminate between potential targets and form functional neuronal circuits are not understood. To understand synaptogenesis in AIY, we have developed a
ttx-3::gfp::
rab-3 marker which allows visualization of synaptic vesicle clusters in these neurons (Michael Nonet, personal communiation). The observed pattern of the vesicles clusters was consistent with the ultrastructural EM pattern reported for AIY presynaptic sites (6). Furthermore GFP::RAB-3 was absent from the AIY processes in
unc-104 mutants, suggesting that the observed clusters are synaptic vesicles transported by the synaptic vesicle kinesin UNC-104 to the presynaptic sites. Interestingly we observed normal synaptic cluster pattern for AIY in
syg-1(
ky652),
syg-2 (
ky671) or
syd-2 (
ju37) mutants, suggesting that these molecules, important for synaptogenesis in other neurons, are not required for synaptogenesis in AIY. However, axon guidance molecules SAX-3 and UNC-6 were critical for normal synaptic cluster pattern, even when they did not severely disrupt axon guidance in AIY. We are currently carrying out genetic screens to better characterize how AIY finds its correct postsynaptic targets in the complex nerve ring environment. Bibliography1.I. Mori, Y. Ohshima, Nature 376, 344 (Jul 27, 1995). 2.M. Gomez et al., Neuron 30, 241 (Apr, 2001). 3.T. Ishihara et al., Cell 109, 639 (May 31, 2002). 4.J. M. Gray, J. J. Hill, C. I. Bargmann, Proc Natl Acad Sci U S A 102, 3184 (Mar 1, 2005). 5.E. L. Tsalik, O. Hobert, J Neurobiol 56, 178 (Aug, 2003). 6.J. G. White, E. Southgate, J. N. Thomson, S. Brenner, Philos Trans R Soc Lond B Biol Sci 275, 327 (Aug 10, 1976).