Trends in Neurosciences
Volume 23, Issue 9, 1 September 2000, Pages 429-435
Journal home page for Trends in Neurosciences

Review
Clustering of inhibitory neurotransmitter receptors at developing postsynaptic sites: the membrane activation model

https://doi.org/10.1016/S0166-2236(00)01627-1Get rights and content

Abstract

Recent studies indicate an important role of cytoskeleton-associated and lipid-anchored proteins in the formation of inhibitory postsynaptic membrane specializations. Membrane apposition of the tubulin-binding protein gephyrin is essential for the recruitment of inhibitory glycine receptors and GABAA receptors to developing postsynaptic sites. Newly disclosed interactions between gephyrin, exchange factors for G proteins of the Rho and Rac families, the translational regulator RAFT1, and actin-binding proteins like profilin might integrate activity-dependent and trophic-factor-mediated signals at developing postsynaptic sites. A model of inhibitory neurotransmitter receptor clustering, is proposed, in which this process is initiated by receptor-driven activation of phosphatidylinositol 3-kinase.

Section snippets

Gephyrin is essential for the formation of postsynaptic GlyR and GABAA-receptor clusters

Gephyrin22 was originally identified as a peripheral membrane protein23 that co-purified with the mammalian GlyR (24, 25). Biochemical and electron microscopy studies have shown that gephyrin is a major structural component of inhibitory postsynaptic membranes that anchors GlyRs to the subsynaptic cytoskeleton8. First, gephyrin decorates the cytoplasmic face of postsynaptic membrane specializations in spinal cord and other regions of the CNS and co-extends with the GlyR immunoreactive receptor

Gephyrin, a synaptic scaffolding protein?

Gephyrin is encoded by a large and highly mosaic gene that is expressed in all mammalian tissues examined22. Its coding region encompasses at least 29 exons, seven of which are subject to alternative splicing to generate a diverse set of gephyrin isoforms48. The N- and C-terminal regions of gephyrin display high homology to proteins involved in molybdenum cofactor (MoCo) biosynthesis, and gephyrin has been shown to be essential for the synthesis of this coenzyme in peripheral organs (Box 1).

Lipid-anchored gephyrin interaction partners

Recent biochemical and yeast two-hybrid experiments have identified a number of gephyrin binding partners (Table 1). These include the lipid-binding proteins collybistin and profilin and the kinase RAFT1 (rapamycin and FKBP12 target); the latter might be implicated in the regulation of subsynaptic protein synthesis (Box 2).

The gephyrin-binding protein collybistin11 belongs to the family of diffuse B-cell lymphoma-like (dbl-like) GDP/GTP-exchange factors (GEFs), which activate small G proteins

Signaling mechanisms involved in inhibitory receptor clustering

One of the central questions of synapse formation is how the pre- and postsynaptic compartments become aligned. Studies at the neuromuscular junction have shown that electrical activity has an important role in restricting ACh-receptor synthesis to synaptic sites55. In embryonic spinal neurons, inhibition of GlyR activation by the specific antagonist strychnine prevents postsynaptic GlyR clustering and induces the internalization of GlyRs into putative endosomal structures46, 56. Similarly,

Concluding remarks

The recent identification of lipid-anchored binding partners of gephyrin has opened novel concepts on how Ca2+ and PI3K-driven activation of trinucleotide-dependent signaling cascades might contribute to the postsynaptic localization and translational control of inhibitory neurotransmitter receptors. The effector proteins involved are likely to also control the dynamic changes of the actin, and possibly tubulin, cytoskeleton that accompany synaptogenesis, and to trigger MAPK and other kinases

Note added in proof

The authors wish to acknowledge recent data70, which shows that in highly mature hippocampal cultures postsynaptic gephyrin clusters are not disrupted by microtubule and actin filament depolymerizing agents. Thus, the gephyrin scaffold that forms at developing synaptic sites might become stabilized at later developmental stages.

References (71)

  • C.M. Becker

    Glycine receptor heterogeneity in rat spinal cord during postnatal development

    EMBO J.

    (1988)
  • W. Hoch

    Primary cultures of mouse spinal cord express the neonatal isoform of the inhibitory glycine receptor

    Neuron

    (1989)
  • A. Triller

    Gamma-aminobutyric acid-containing terminals can be apposed to glycine receptors at central synapses

    J. Cell Biol.

    (1987)
  • A.J. Todd

    Colocalization of GABA, glycine and their receptors at synapses in the rat spinal cord

    J. Neurosci.

    (1996)
  • M. Sassoé-Pognetto

    Colocalization of gephyrin and GABAA receptor subunits in the rat retina

    J. Comp. Neurol.

    (1995)
  • H. Betz

    Gephyrin, a major player in GABAergic postsynaptic membrane assembly?

    Nat. Neurosci.

    (1998)
  • M. Kneussel

    The GABAA receptor associated protein GABARAP interacts with gephyrin but is not involved in receptor anchoring at the synapse

    Proc. Natl. Acad. Sci. U. S. A.

    (2000)
  • J. Kirsch et al.

    Glycine-receptor activation is required for receptor clustering in spinal neurons

    Nature

    (1998)
  • M.T.W. Liu

    Crystal structure of the gephyrin-related molybdenum cofactor biosynthesis protein MogA from Escherichia coli

    J. Biol. Chem.

    (2000)
  • U. Maier

    Roles of non-catalytic subunits in gbetagamma-induced activation of class I phosphoinositide 3-kinase isoforms beta and gamma

    J. Biol. Chem.

    (1999)
  • W. Hoch

    Formation of the neuromuscular junction. Agrin and its unusual receptors

    Eur. J. Biochem.

    (1999)
  • M.A. Abbott

    The insulin receptor tyrosine kinase substrate p58/53 and the insulin receptor are components of CNS synapses

    J. Neurosci.

    (1999)
  • O. Wan

    Recruitment of functional GABAA receptors to postsynaptic domains by insulin

    Nature

    (1997)
  • M.M. Chou et al.

    The 70kDa S6 kinase complexes with and is activated by the Rho family G proteins cdc42 and Rac1

    Cell

    (1996)
  • M. Sheng

    PDZs and receptor/channel clustering: rounding up the latest suspects

    Neuron

    (1996)
  • S.E. Craven et al.

    PDZ proteins organize synaptic signaling pathways

    Cell

    (1998)
  • J. Kirsch

    Assembly of signaling machinery at the postsynaptic membrane

    Curr. Opin. Neurobiol.

    (1999)
  • J. Kirsch

    Gephyrin antisense oligonucleotides prevent glycine receptor clustering in spinal neurons

    Nature

    (1993)
  • C. Essrich

    Postsynaptic clustering of major GABAA receptor subtypes requires the γ2 subunit and gephyrin

    Nat. Neurosci.

    (1998)
  • M. Kneussel

    Loss of postsynaptic GABAA receptor clustering in gephyrin-deficient mice

    J. Neurosci.

    (1999)
  • J. Kirsch et al.

    The postsynaptic localization of the glycine receptor-associated protein gephyrin is regulated by the cytoskeleton

    J. Neurosci.

    (1995)
  • S. Kins

    Collybistin, a novel brain specific GEF, induces submembrane clustering of gephyrin

    Nat. Neurosci.

    (2000)
  • D.M. Sabatini

    Interaction of RAFT1 with gephyrin required for rapamycin-sensitive signaling

    Science

    (1999)
  • H. Wang

    GABAA-receptor-associated protein links GABAA receptors and the cytoskeleton

    Nature

    (1999)
  • H. Wang et al.

    Binding of GABARAP to microtubules and microfilaments suggests involvement of cytoskeleton in GABARAP-GABAA receptor interaction

    J. Neurochem.

    (2000)
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