title: Differential regulation of the postsynaptic clustering of γ-aminobutyric acid type A (GABAA) receptors by collybistin isoforms.
abstract: Collybistin promotes submembrane clustering of gephyrin and is essential for the postsynaptic localization of gephyrin and γ-aminobutyric acid type A (GABA(A)) receptors at GABAergic synapses in hippocampus and amygdala. Four collybistin isoforms are expressed in brain neurons; CB2 and CB3 differ in the C terminus and occur with and without the Src homology 3 (SH3) domain. We have found that in transfected hippocampal neurons, all collybistin isoforms (CB2(SH3+), CB2(SH3-), CB3(SH3+), and CB3(SH3-)) target to and concentrate at GABAergic postsynapses. Moreover, in non-transfected neurons, collybistin concentrates at GABAergic synapses. Hippocampal neurons co-transfected with CB2(SH3-) and gephyrin developed very large postsynaptic gephyrin and GABA(A) receptor clusters (superclusters). This effect was accompanied by a significant increase in the amplitude of miniature inhibitory postsynaptic currents. Co-transfection with CB2(SH3+) and gephyrin induced the formation of many (supernumerary) non-synaptic clusters. Transfection with gephyrin alone did not affect cluster number or size, but gephyrin potentiated the clustering effect of CB2(SH3-) or CB2(SH3+). Co-transfection with CB2(SH3-) or CB2(SH3+) and gephyrin did not affect the density of presynaptic GABAergic terminals contacting the transfected cells, indicating that collybistin is not synaptogenic. Nevertheless, the synaptic superclusters induced by CB2(SH3-) and gephyrin were accompanied by enlarged presynaptic GABAergic terminals. The enhanced clustering of gephyrin and GABA(A) receptors induced by collybistin isoforms was not accompanied by enhanced clustering of neuroligin 2. Moreover, during the development of GABAergic synapses, the clustering of gephyrin and GABA(A) receptors preceded the clustering of neuroligin 2. We propose a model in which the SH3- isoforms play a major role in the postsynaptic accumulation of GABA(A) receptors and in GABAergic synaptic strength.
authors.affiliation: Department of Physiology and Neurobiology, University of Connecticut, Storrs, Connecticut 06269, USA.
authors.forename: Tzu-Ting
authors.initials: TT
authors.lastname: Chiou
authors.forename: Bevan
authors.initials: B
authors.lastname: Bonhomme
authors.forename: Hongbing
authors.initials: H
authors.lastname: Jin
authors.forename: Celia P
authors.initials: CP
authors.lastname: Miralles
authors.forename: Haiyan
authors.initials: H
authors.lastname: Xiao
authors.forename: Zhanyan
authors.initials: Z
authors.lastname: Fu
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Harvey
authors.forename: Kirsten
authors.initials: K
authors.lastname: Harvey
authors.forename: Stefano
authors.initials: S
authors.lastname: Vicini
authors.forename: Angel L
authors.initials: AL
authors.lastname: De Blas
mesh_terms: D000818:Animals; D002352:Carrier Proteins / Q000378:metabolism; D020662:Guanine Nucleotide Exchange Factors / Q000737:chemistry / Q000378:metabolism*; D057809:HEK293 Cells; D006801:Humans; D053444:Inhibitory Postsynaptic Potentials; D008565:Membrane Proteins / Q000378:metabolism; D009474:Neurons / Q000378:metabolism; D020033:Protein Isoforms / Q000737:chemistry / Q000378:metabolism; D021381:Protein Transport; D051381:Rats; D017207:Rats, Sprague-Dawley; D011963:Receptors, GABA-A / Q000378:metabolism*; D064067:Rho Guanine Nucleotide Exchange Factors; D013569:Synapses / Q000378:metabolism*; D014162:Transfection; D005680:gamma-Aminobutyric Acid / Q000378:metabolism; D018909:src Homology Domains
chemical_list: C577404:Arhgef9 protein, rat; D002352:Carrier Proteins; D020662:Guanine Nucleotide Exchange Factors; D008565:Membrane Proteins; D020033:Protein Isoforms; D011963:Receptors, GABA-A; D064067:Rho Guanine Nucleotide Exchange Factors; C073441:gephyrin; D005680:gamma-Aminobutyric Acid