Reese Thomas S.

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Reese
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Thomas S.
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Author: Dosemeci, Ayse × Has files: Yes ×

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  • Preprint
    Inhibition of phosphatase activity facilitates the formation and maintenance of NMDA-induced calcium/calmodulin-dependent protein kinase ii clusters in hippocampal neurons
    ( 2004-10-04) Tao-Cheng, Jung-Hwa ; Vinade, Lucia ; Winters, Christine A. ; Reese, Thomas S. ; Dosemeci, Ayse
    The majority of hippocampal neurons in dissociated cultures and in intact brain exhibit clustering of CaMKII into spherical structures with an average diameter of 110 nm when subjected to conditions that mimic ischemia and excitotoxicity (Tao-Cheng et al., 2001). Because clustering of CaMKII would reduce its effective concentration within the neuron, it may represent a cellular strategy to prevent excessive CaMKII-mediated phosphorylation during episodes of Ca2+ overload. Here we employ a relatively mild excitatory stimulus to promote sub-maximal clustering for the purpose of studying the conditions for the formation and disappearance of CaMKII clusters. Treatment with 30 µM NMDA for 2 min produced CaMKII clustering in ~15 percent of dissociated hippocampal neurons in culture, as observed by pre-embedding immunogold electron microscopy. These CaMKII clusters could be labeled with antibodies specific to the phospho form (Thr286) of CaMKII, suggesting that at least some of the CaMKII molecules in clusters are autophosphorylated. To test whether phosphorylation is involved in the formation and maintenance of CaMKII clusters, the phosphatase inhibitors calyculin A (5 nM) or okadaic acid (1 µM) were included in the incubation medium. With inhibitors more neurons exhibited CaMKII clusters in response to 2 min NMDA treatment. Furthermore, 5 min after the removal of NMDA and Ca2+, CaMKII clusters remained and could still be labeled with the phospho-specific antibody. In contrast, in the absence of phosphatase inhibitors, no clusters were detected 5 min after the removal of NMDA and Ca2+ from the medium. These results suggest that phosphatases type 1 and/or 2A regulate the formation and disappearance of CaMKII clusters.
  • Article
    Distribution of postsynaptic density (PSD)-95 and Ca2+/calmodulin-dependent protein kinase II at the PSD
    (Society for Neuroscience, 2003-12-03) Petersen, Jennifer D. ; Chen, Xiaobing ; Vinade, Lucia ; Dosemeci, Ayse ; Lisman, John E. ; Reese, Thomas S.
    Postsynaptic densities (PSDs) contain proteins that regulate synaptic transmission. We determined the positions of calcium/calmodulin-dependent protein kinase II (CaMKII) and PSD-95 within the three-dimensional structure of isolated PSDs using immunogold labeling, rotary shadowing, and electron microscopic tomography. The results show that all PSDs contain a central mesh immediately underlying the postsynaptic membrane. Label for PSD-95 is found on both the cytoplasmic and cleft sides of this mesh, averaging 12 nm from the cleft side. All PSDs label for PSD-95. The properties of CaMKII labeling are quite different. Label is virtually absent on the cleft sides of PSDs, but can be heavy on the cytoplasmic side at a mean distance of 25 nm from the cleft. In tomograms, CaMKII holoenzymes can be visualized directly, appearing as labeled, tower-like structures reflecting the 20 nm diameter of the holoenzyme. These towers protrude from the cytoplasmic side of the central mesh. There appears to be a local organization of CaMKII, as judged by fact that the nearest-neighbor distances are nearly invariant over a wide range of labeling density for CaMKII. The average density of CaMKII holoenzymes is highly variable, ranging from zero to values approaching a tightly packed state. This variability is significantly higher than that for PSD-95 and is consistent with an information storage role for CaMKII.
  • Article
    Persistent accumulation of calcium/calmodulin-dependent protein kinase II in dendritic spines after induction of NMDA receptor-dependent chemical long-term potentiation
    (Society for Neuroscience, 2004-10-20) Otmakhov, Nikolai ; Tao-Cheng, Jung-Hwa ; Carpenter, Stephen ; Asrican, Brent ; Dosemeci, Ayse ; Reese, Thomas S. ; Lisman, John E.
    Calcium/calmodulin-dependent protein kinase II (CaMKII) is a leading candidate for a synaptic memory molecule because it is persistently activated after long-term potentiation (LTP) induction and because mutations that block this persistent activity prevent LTP and learning. Previous work showed that synaptic stimulation causes a rapidly reversible translocation of CaMKII to the synaptic region. We have now measured green fluorescent protein (GFP)-CaMKIIα translocation into synaptic spines during NMDA receptor-dependent chemical LTP (cLTP) and find that under these conditions, translocation is persistent. Using red fluorescent protein as a cell morphology marker, we found that there are two components of the persistent accumulation. cLTP produces a persistent increase in spine volume, and some of the increase in GFP-CaMKIIα is secondary to this volume change. In addition, cLTP results in a dramatic increase in the bound fraction of GFP-CaMKIIα in spines. To further study the bound pool, immunogold electron microscopy was used to measure CaMKIIα in the postsynaptic density (PSD), an important regulator of synaptic function. cLTP produced a persistent increase in the PSD-associated pool of CaMKIIα. These results are consistent with the hypothesis that CaMKIIα accumulation at synapses is a memory trace of past synaptic activity.