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The catalytic function of the gephyrin‐binding protein IQSEC 3 regulates neurotransmitter‐specific matching of pre‐ and post‐synaptic structures in primary hippocampal cultures
Author(s) -
Früh Simon,
Tyagarajan Shiva K.,
Campbell Benjamin,
Bosshard Giovanna,
Fritschy JeanMarc
Publication year - 2018
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1111/jnc.14572
Subject(s) - gephyrin , pdz domain , scaffold protein , microbiology and biotechnology , neurotransmission , glutamatergic , mutant , biology , hippocampal formation , neuroscience , receptor , glutamate receptor , glycine receptor , biochemistry , signal transduction , gene , amino acid , glycine
In dissociated neuronal cultures the absence of spatial and temporal cues causes the emergence of mismatched synapses, where post‐synaptic proteins of GABA ergic synapses are in part apposed to glutamatergic pre‐synaptic terminals and vice versa. This mismatch offers an opportunity to study the mechanisms that regulate correct apposition of pre‐ and post‐synaptic elements. We report here that the IQ motif and Sec7 domain‐containing protein 3 ( IQSEC 3; BRAG 3; synArf GEF ) specifically regulates the mislocalization of GABA ergic post‐synaptic density ( PSD ) proteins. Over‐expression of IQSEC 3 constructs harboring mutations that ablate Sec7 domain or IQ motif function revealed that IQSEC 3 catalytic activity is involved in the control of apposition between the GABA ergic PSD and glutamatergic terminals. Neurons co‐expressing eGFP ‐gephyrin with IQSEC 3 Sec7 mutant displayed a drastically increased fraction of mismatched eGFP ‐gephyrin clusters compared to other IQSEC 3 constructs. Along with eGFP ‐gephyrin, endogenous GABA A receptor cluster mismatching was increased by IQSEC 3 Sec7 mutant over‐expression. Conversely, GFP ‐ PSD ‐95 clusters were unaffected by over‐expression of any IQSEC 3 construct. The GABA ergic PSD mismatch phenotype was recapitulated by Arf6 dominant‐negative mutant over‐expression, suggesting that Arf6 activation by IQSEC 3 is an essential step in this pathway. In addition, we provide biochemical evidence to confirm gephyrin/ IQSEC 3 interaction near the IQSEC 3 IQ motif, which in turn binds calmodulin at low Ca 2+ concentrations. Taken together, our findings identify a post‐synaptic protein which specifically regulates correct apposition of the GABA ergic PSD to pre‐synaptic terminals.