Neurexin in embryonic Drosophila neuromuscular junctions.
BACKGROUND
Neurexin is a synaptic cell adhesion protein critical for synapse formation and function. Mutations in neurexin and neurexin-interacting proteins have been implicated in several neurological diseases. Previous studies have described Drosophila neurexin mutant phenotypes in third instar larvae and adults. However, the expression and function of Drosophila neurexin early in synapse development, when neurexin function is thought to be most important, has not been described.


RESULTS
We use a variety of techniques, including immunohistochemistry, electron microscopy, in situ hybridization, and electrophysiology, to characterize neurexin expression and phenotypes in embryonic Drosophila neuromuscular junctions (NMJs). Our results surprisingly suggest that neurexin in embryos is present both pre and postsynaptically. Presynaptic neurexin promotes presynaptic active zone formation and neurotransmitter release, but along with postsynaptic neurexin, also suppresses formation of ectopic glutamate receptor clusters. Interestingly, we find that loss of neurexin only affects receptors containing the subunit GluRIIA.


CONCLUSIONS
Our study extends previous results and provides important detail regarding the role of neurexin in Drosophila glutamate receptor abundance. The possibility that neurexin is present postsynaptically raises new hypotheses regarding neurexin function in synapses, and our results provide new insights into the role of neurexin in synapse development.
Chen
Kaiyun
K
Biological Sciences, University of Illinois at Chicago, Chicago, Illinois, United States of America.
Gracheva
Elena O
EO
Yu
Szi-Chieh
SC
Sheng
Qi
Q
Richmond
Janet
J
Featherstone
David E
DE
D000818:Animals; D030801:Animals, Genetically Modified; D015816:Cell Adhesion Molecules, Neuronal / Q000235:genetics / Q000378:metabolism*; D004330:Drosophila / Q000196:embryology*; D029721:Drosophila Proteins / Q000235:genetics / Q000378:metabolism*; D017403:In Situ Hybridization; D016253:Microscopy, Immunoelectron; D009469:Neuromuscular Junction / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics
D015816:Cell Adhesion Molecules, Neuronal; D029721:Drosophila Proteins; C491321:Nrx protein, Drosophila; D012333:RNA, Messenger