title: Selective localization of collybistin at a subset of inhibitory synapses in brain circuits.
abstract: Collybistin is a brain-specific guanine nucleotide exchange factor (GEF) that is crucial for the postsynaptic accumulation of gephyrin and γ-aminobutyric acid A receptors (GABA(A) Rs) at a specific subset of inhibitory synapses. Our understanding of the in vivo function of collybistin has been hampered by lack of information about the synaptic localization of this protein in brain circuits. Here we describe the subcellular localization of endogenous collybistin by using antibodies raised against distinct molecular domains that should recognize the majority of endogenous collybistin isoforms. We show that collybistin co-clusters with gephyrin and GABA(A) Rs in synaptic puncta and is recruited to postsynaptic specializations early during synapse development. Notably, collybistin is present in only a subset of gephyrin-positive synapses, with variable co-localization values in different brain regions. Moreover, collybistin co-localizes with GABA(A) Rs containing the α1, α2, or α3 subunits, arguing against a selective association with specific GABA(A) R subtypes. Surprisingly, we found that collybistin is expressed only transiently in Purkinje cells, suggesting that in these cerebellar neurons collybistin plays a selective role during the initial assembly of postsynaptic specializations. These data reveal a remarkable heterogeneity in the organization of GABAergic synapses and provide an anatomical basis for interpreting the variable effects caused by disruption of the collybistin gene in human X-linked intellectual disability and mouse knockout models.
authors.affiliation: Department of Anatomy, Pharmacology, and Forensic Medicine, National Institute of Neuroscience, Turin, Italy.
authors.forename: Annarita
authors.initials: A
authors.lastname: Patrizi
authors.forename: Laura
authors.initials: L
authors.lastname: Viltono
authors.forename: Elena
authors.initials: E
authors.lastname: Frola
authors.forename: Kirsten
authors.initials: K
authors.lastname: Harvey
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Harvey
authors.forename: Marco
authors.initials: M
authors.lastname: Sassoè-Pognetto
mesh_terms: D000818:Animals; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism; D020662:Guanine Nucleotide Exchange Factors / Q000235:genetics / Q000378:metabolism*; D057809:HEK293 Cells; D006801:Humans; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D009415:Nerve Net / Q000033:anatomy & histology / Q000502:physiology*; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism*; D021122:Protein Subunits / Q000235:genetics / Q000378:metabolism; D011689:Purkinje Cells / Q000166:cytology / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D011963:Receptors, GABA-A / Q000235:genetics / Q000378:metabolism*; D064067:Rho Guanine Nucleotide Exchange Factors; D013569:Synapses / Q000378:metabolism*
chemical_list: C577403:Arhgef9 protein, mouse; C577404:Arhgef9 protein, rat; D002352:Carrier Proteins; D020662:Guanine Nucleotide Exchange Factors; D008565:Membrane Proteins; D020033:Protein Isoforms; D021122:Protein Subunits; D011963:Receptors, GABA-A; D064067:Rho Guanine Nucleotide Exchange Factors; C073441:gephyrin