Synaptic localization of iGluR complexes is regulated by the modulation of Neto extracellular domain. Young-Jun Kim, Mihaela Serpe. NICHD, National Institute of Health, Bethesda, MD.

   Neurotransmitter receptor subunits are recruited at the opposite of the presynaptic active zones to make postsynaptic clusters upon the arrival of the axon terminals. Juxtaposition of active zones and postsynaptic densities is tightly regulated to make functional synapses. Previously we found Neto is an essential component of iGluR complexes which moves together with the receptor subunits at Drosophila NMJ. Here, we report that extracellular domain of Neto is essential for the regulation of iGluR cluster formation and is regulated by the proteolytic processing. Lethality of neto genetic null mutants could be rescued by the introduction of neto transgene which contains extracellular domain only. Drosophila Neto contains the highly conserved stretch of -RXXR- sequences just before the first CUB domain which is cut by Furin-1 protease. Inhibition of proteolytic activities by expressing Furin-1 RNAi construct both in the muscle and the neuron caused the decrease of iGluR cluster formation and pMad clusters. Two mutant lines were generated; PM (processing mutant)-Neto which contains uncleavable prodomain, and CA (constitutively active)-Neto of which prodomain was removed. According to the rescue analyses, both PM- and CA-Neto could rescue the embryonic lethality of neto null mutants. However, the animals rescued by PM-Neto couldn't make to the adult stages and showed abnormal iGluR and clustering, which means proteolytic processing of Neto prodomain is an important step for the maintainence of iGluR complexes at the synapse.