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Revealing molecular mechanisms for synaptic strength regulation.
Information storage in the brain involves long-term changes in excitatory synaptic strength. Excitatory synaptic transmission is mediated by glutamate acting on three classes of ligand-gated ion channels, which are classified pharmacologically as AMPA receptors, NMDA receptors, and kainate (KA) receptors. These three receptors show characteristic localizations and function differently to modulate synaptic strength in long-term plasticity.
Three types of long-term plasticity are well established. 1. PKC and CaMKII, activated by calcium influx through NMDA receptors, increase post-synaptic expression of AMPA receptors in hippocampal CA1 cells. 2. PKC, activated by metabotropic glutamate receptors, decreases post-synaptic expression of AMPA receptors in cerebellar Purkinje cells. 3. KA receptors participate in a presynaptic form of long-term plasticity at hippocampal mossy fiber-CA3 synapses.
The main objective of the research in my laboratory is to elucidate molecular mechanisms for glutamate receptor regulation in these distinct forms of long-term plasticity. To understand these mechanisms, our laboratory uses several techniques including biochemistry, molecular biology, immunocytochemistry and gene-targeted animals. To detect channel activity of receptors or to reconstruct properties of native receptors, our laboratory also uses electrophysiology, especially focusing on cRNA injected Xenopus laevis oocytes as a model system.
We previously identified stargazin-like TARPs as key molecules to stabilize AMPA receptors at synapses. TARPs both modulate trafficking of AMPA receptors to the synapses and control the gating and pharmacology of the channel. Stargazin is quantitatively phosphorylated in the brain, and stargazin phosphorylation promotes synaptic trafficking of AMPA receptors. NMDA receptor activity can induce stargazin phosphorylation via activation of CaMKII and PKC, which directly phosphorylate stargazin in vitro. At hippocampal synapses, long-term potentiation (LTP) requires stargazin phosphorylation; thus, stargazin is a critical substrate in LTP in hippocampal CA1 cells.
These studies will provide fundamental insights into the mechanisms of the regulation of synaptic strength at excitatory synapses. Furthermore, these studies will help us to understand molecular mechanisms for various types of synaptic plasticity in learning and memory.
Figure caption:
A, TARPs consist of four isoforms (stargazin, g -3, g -4, and g -8), which show distinct expression patterns in the brain . B, TARPs (green) colocalize with the glutamatergic markers AMPA receptors (red)(left panel), but not with the GABAergic marker GAD65 (red)(right panel). C, TARPs both modulate trafficking of AMPA receptors to the synapses and control the gating and pharmacology of the channel. Oocytes injected with GluR1 alone are more sensitive to glutamate (Glu) than to kainate (KA). D, AMPA receptor subunits GluR1, GluR2 and GluR4 co-immunoprecipitate with stargazin (STG) in brain extracts from +/stg mice (+/-), but not in extracts from stg/stg mice (-/-). E, TARPs stabilize AMPA receptors at synapses through its C-terminal PDZ domain binding motif.
Selected publications:
Tomita S, Adesnik H , Sekiguchi M , Zhang W, Wada K, Howe JR, Nicoll RA, Bredt DS. (2005) Stargazin modulates AMPA receptor gating and trafficking by distinct domains. Nature, 435, 1052-1058
Tomita S, Stein V , Stocker TJ, Nicoll RA, Bredt DS. (2005) Bi-directional synaptic plasticity regulated by phosphorylation of stargazin-like TARPs. Neuron, 45, 269-277
Tomita S.,Fukata,M., Nicoll,RA., Bredt, DS. (2004) Dynamic interaction of stargazin-like TARPs with cycling AMPA receptors at synapses. Science, 303, 1508-11.
Tomita S, Chen L, Kawasaki Y, Petralia RS, Wenthold RJ, Nicoll RA, Bredt DS. (2003) Functional studies and distribution define a family of transmembrane AMPA receptor regulatory proteins. J Cell. Biol., 161,805-16.
Email: susumu.tomita@yale.edu
Phone: 203-785-7201
Research opportunities for post-doc and graduate students
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