Regulation of stargazin synaptic trafficking by C-terminal PDZ ligand phosphorylation in bidirectional synaptic plasticity.
ABSTRACT Stargazin is a transmembrane alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor regulatory protein that controls the surface and synaptic expression of AMPA-type glutamate receptors (AMPARs). Synaptic anchoring of AMPARs is influenced by the interaction between stargazin's C-terminal post-synaptic density-95 (PSD-95)/discs large/zona occludens-1 (PDZ) ligand and the synaptic scaffolding protein PSD-95. Phosphorylation of the stargazin PDZ ligand by protein kinase A (PKA) disrupts stargazin's interaction with PSD-95, but whether this phosphorylation plays a role in activity-dependent regulation of stargazin/AMPAR synaptic trafficking is unknown. Here, we show that stargazin is phosphorylated within the PDZ ligand at threonine residue 321 (T321) by mitogen-activated protein kinases (MAPKs) as well as PKA. By expressing constructs that selectively block T321 phosphorylation by either PKA or MAPKs, we show that stargazin T321 phosphorylation is required for activity-dependent changes in stargazin synaptic clustering in dissociated rat hippocampal neuron cultures. Specifically, we find that mutations that block stargazin T321 phosphorylation by PKA prevent activity-dependent increases in stargazin synaptic clustering, whereas a point mutant that blocks MAPK phosphorylation of T321 prevents activity-dependent decreases in stargazin synaptic clustering. Taken together, our studies implicate phosphorylation of stargazin T321 by PKA and MAPKs in bidirectional control of stargazin/AMPAR synaptic clustering during synaptic plasticity.
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ABSTRACT: Observations of distant galaxies are important both for understanding how galaxies form and for probing the physical conditions of the Universe at early times. It is, however, very difficult to identify galaxies at redshifts z > 5, because they are so faint and have few spectral characteristics. We previously reported the probable identification of a galaxy at z = 6.68, based on one line and an apparent break in the spectrum just shortwards of that, which we interpreted as Lyman alpha emission and the Lyman alpha break, where photons with shorter wavelengths are absorbed by the intervening neutral hydrogen gas. Here we present optical photometry that shows moderate detections of light in the B- and V-band images, which are inconsistent with the expected absence of flux shortwards of the Lyman alpha break for alpha galaxy at z > 5, and inconsistent with the previous flux measurement. Moreover, the spectral energy distribution for this object cannot readily be fitted by any known galaxy spectral template at any redshift, so the redshift is undetermined.Nature 11/2000; 408(6812):562-4. · 38.60 Impact Factor
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ABSTRACT: We investigated whether the interaction between the N-ethyl-maleimide-sensitive fusion protein (NSF) and the AMPA receptor (AMPAR) subunit GluR2 is involved in synaptic plasticity in the CA1 region of the hippocampus. Blockade of the NSF-GluR2 interaction by a specific peptide (pep2m) introduced into neurons prevented homosynaptic, de novo long-term depression (LTD). Moreover, saturation of LTD prevented the pep2m-induced reduction in AMPAR-mediated excitatory postsynaptic currents (EPSCs). Minimal stimulation experiments indicated that both pep2m action and LTD were due to changes in quantal size and quantal content but were not associated with changes in AMPAR single-channel conductance or EPSC kinetics. These results suggest that there is a pool of AMPARs dependent on the NSF-GluR2 interaction and that LTD expression involves the removal of these receptors from synapses.Neuron 11/1999; 24(2):389-99. · 15.77 Impact Factor
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ABSTRACT: Electrophysiology, immunostaining and time lapse imaging techniques were employed to study the mechanism of long-term depression (LTD) induced by DHPG, a specific group I metabotropic glutamate receptor (mGluR) agonist. Experiments were performed in primary hippocampal culture or in the CA1 area of acute rat hippocampal slices. In agreement with previous results by others, we show that DHPG (200 microM, 10 min) can induce LTD (DHPG-LTD) in acute slices, in the presence or absence of synaptic inhibition. In addition, in voltage clamp whole cell experiments we find that accompanying the reduction in the evoked excitatory postsynaptic current (EPSC), miniature EPSC amplitude and frequency are reduced. Similar results were obtained in cultured neurons. Immunostaining and time lapse imaging showed a long-lasting loss of AMPA receptors from the membrane surface of cultured neurons after DHPG treatment, which appears to occur in only a subset of the puncta. Further electrophysiological recordings on slices showed that blocking postsynaptic endocytosis by introducing a blocking peptide named D15 in recording pipettes abolished the DHPG-LTD. In conclusion, these data suggest that LTD induced by mGluR activation is due to a rapid removal of AMPA receptors from the postsynaptic membrane.Neuropharmacology 12/2001; 41(6):664-71. · 4.11 Impact Factor