Spatial regulation of synapse formation by Plexin signaling in C. elegans
Mizumoto1, K., Chen1, K.C.
1Department of Zoology, University of British Columbia, Vancouver, Canada
Development of a multi-cellular organism involves extensive inter-cellular interactions. In the nervous system, neurons are connected via special cell-cell interface called synapse. In addition to the synaptic connection, neurons interact with their neighboring neurons that are not their synaptic target cells. Using roundworm (Caenorhabditis elegans) as a model system, we have shown that inter-axonal interaction between neighboring neurons is critical for spatial regulation of synapse formation. In an interaxonal interaction dependent manner, Plexin was localized to the specific subaxonal domain where it restricts synapse formation (Mizumoto and Shen, Neuron 2013).
To understand the molecular mechanism of Plexin-dependent synapse pattern formation, we sought to identify downstream signaling effectors of Plexin. Recent structural and biochemical experiments showed that the cytoplasmic domain of Plexin acts as a RapGAP (Rap GTPase activating protein), which inactivates Rap GTPases (Wang et al., 2012, 2013). Among 3 Rap GTPases in C. elegans, we found that rap-2 was preferentially expressed in the nervous system. Consistent with the Plexin function as a negative regulator of Rap GTPase, gain-of-function alleles of rap-2 generated by CRISPR/Cas9 mimicked the phenotype of plexin mutants, which is an expansion of synaptic region within axon. Surprisingly, loss of function of rap-2 also showed the same synapse distribution defects, suggesting that the activity of Rap-2 GTPase is spatially regulated within axon. In an attempt to identify further downstream of Plexin signaling, we found that mig-15, Nck-interacting kinase, also showed the same synapse patterning defects as plexin and rap-2 mutants. Interestingly, while loss of function of mig-15 caused ectopic synapse formation, its overexpression eliminated synapses from neurons, suggesting that MIG-15 is a key regulator to inhibit synapse formation. Together, we revealed the novel role of Plexin signaling in spatial patterning of synapse formation. At the meeting, I will also discuss other projects in my lab.
HFSP Career Development Award (Award year 2014)
MIZUMOTO, Kota
