Synapses store information by long-lasting modifications of their structure and molecular composition, but the precise chronology of these changes has not been studied at single-synapse resolution in ...real time. Here we describe the spatiotemporal reorganization of postsynaptic substructures during long-term potentiation (LTP) at individual dendritic spines. Proteins translocated to the spine in four distinct patterns through three sequential phases. In the initial phase, the actin cytoskeleton was rapidly remodeled while active cofilin was massively transported to the spine. In the stabilization phase, cofilin formed a stable complex with F-actin, was persistently retained at the spine, and consolidated spine expansion. In contrast, the postsynaptic density (PSD) was independently remodeled, as PSD scaffolding proteins did not change their amount and localization until a late protein synthesis-dependent third phase. Our findings show how and when spine substructures are remodeled during LTP and explain why synaptic plasticity rules change over time.
•Postsynaptic proteins are reorganized during LTP in three sequential phases•Cofilin is rapidly, persistently enriched in the spine via a stable F-actin complex•Cofilin signaling pathway is necessary for the maintenance of spine expansion•Delayed PSD growth is spine expansion independent but protein synthesis dependent
Bosch et al. describe the spatiotemporal reorganization of postsynaptic substructures during potentiation at single dendritic spines. They uncover the late-phase growth of the postsynaptic density and the unique dynamics of cofilin, which play a critical role in consolidating spine growth.
Long-term synaptic plasticity requires a mechanism that converts short Ca2+ pulses into persistent biochemical signaling to maintain changes in the synaptic structure and function. Here, we present a ...novel mechanism of a positive feedback loop, formed by a reciprocally activating kinase-effector complex (RAKEC) in dendritic spines, enabling the persistence and confinement of a molecular memory. We found that stimulation of a single spine causes the rapid formation of a RAKEC consisting of CaMKII and Tiam1, a Rac-GEF. This interaction is mediated by a pseudo-autoinhibitory domain on Tiam1, which is homologous to the CaMKII autoinhibitory domain itself. Therefore, Tiam1 binding results in constitutive CaMKII activation, which in turn persistently phosphorylates Tiam1. Phosphorylated Tiam1 promotes stable actin-polymerization through Rac1, thereby maintaining the structure of the spine during LTP. The RAKEC can store biochemical information in small subcellular compartments, thus potentially serving as a general mechanism for prolonged and compartmentalized signaling.
•Persistent Rac1 activity is required for structural LTP of dendritic spines•CaMKII stably binds on pseudo-autoinhibitory domain of Tiam1, a Rac-GEF•This binding disinhibits autoinhibition of CaMKII and maintains its activity•Persistently activated CaMKII phosphorylates Tiam1 and maintains Rac1 activity
Saneyoshi et al. find that stimulation of single spine causes rapid formation of a reciprocally activating signaling complex between CaMKII and a Rac-GEF Tiam1, which stably activates Rac1 and maintains enlarged spine structure during LTP.
Glutathione-labile protecting groups for phosphodiester moieties in oligonucleotides were designed, synthesized, and incorporated into oligonucleotides. The protecting groups on the phosphodiester ...moieties were cleaved in a buffer containing 10 mM glutathione, which was used as a model of intracellular fluid. Cellular uptake of oligonucleotides bearing glutathione-labile protecting groups was strongly affected by the location and number of the protecting groups.
Since the discovery of long‐term potentiation (LTP) about a half‐century ago, Ca2+/CaM‐dependent protein kinase II (CaMKII) has been one of the most extensively studied components of the molecular ...machinery that regulate plasticity. This unique dodecameric kinase complex plays pivotal roles in LTP by phosphorylating substrates through elaborate regulatory mechanisms, and is known to be both necessary and sufficient for LTP. In addition to acting as a kinase, CaMKII has been postulated to have structural roles because of its extraordinary abundance and diverse interacting partners. It now is becoming clear that these two functions of CaMKII cooperate closely for the induction of both functional and structural synaptic plasticity of dendritic spines.
Because of its extraordinary abundance within neuronal cells, calmodulin kinase CaMKII has been believed to act as a structural protein as well as an enzyme during synaptic plasticity. In this review, we summarized studies in CaMKII field and provide an insight into how enzymatic and structural functions of CaMKII cooperate with each other for long‐term potentiation (LTP) in neurons.
This article is part of a mini review series: “Synaptic Function and Dysfunction in Brain Diseases”.
Because of its extraordinary abundance within neuronal cells, calmodulin kinase CaMKII has been believed to act as a structural protein as well as an enzyme during synaptic plasticity. In this review, we summarized studies in CaMKII field and provide an insight into how enzymatic and structural functions of CaMKII cooperate with each other for long‐term potentiation (LTP) in neurons.
This article is part of a mini review series: “Synaptic Function and Dysfunction in Brain Diseases”.
Cell-permeable oligodeoxyribonucleotides (ODNs) bearing reduction-activated protecting groups were synthesized as oligonucleotide pro-drugs. Although these oligonucleotides were amenable to ...solid-phase DNA synthesis and purification, the protecting group on their phosphodiester moiety could be readily cleaved by nitroreductase and NADH. Moreover, these compounds exhibited good nuclease resistance against 3′-exonuclease and endonuclease and good stability in human serum. Fluorescein-labeled ODNs modified with reduction-activated protecting groups showed better cellular uptake compared with that of naked ODNs.
Proteome analyses of the postsynaptic density (PSD), a proteinaceous specialization beneath the postsynaptic membrane of excitatory synapses, have identified several thousands of proteins. While ...proteins with predictable functions have been well studied, functionally uncharacterized proteins are mostly overlooked. In this study, we conducted a comprehensive meta-analysis of 35 PSD proteome datasets, encompassing a total of 5,869 proteins. Employing a ranking methodology, we identified 97 proteins that remain inadequately characterized. From this selection, we focused our detailed analysis on the highest-ranked protein, FAM81A. FAM81A interacts with PSD proteins, including PSD-95, SynGAP, and NMDA receptors, and promotes liquid-liquid phase separation of those proteins in cultured cells or in vitro. Down-regulation of FAM81A in cultured neurons causes a decrease in the size of PSD-95 puncta and the frequency of neuronal firing. Our findings suggest that FAM81A plays a crucial role in facilitating the interaction and assembly of proteins within the PSD, and its presence is important for maintaining normal synaptic function. Additionally, our methodology underscores the necessity for further characterization of numerous synaptic proteins that still lack comprehensive understanding.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Dendritic spines constitute the major compartments of excitatory post-synapses. They undergo activity-dependent enlargement, which is thought to increase the synaptic efficacy underlying learning and ...memory. The activity-dependent spine enlargement requires activation of signaling pathways leading to promotion of actin polymerization within the spines. However, the molecular machinery that suffices for that structural plasticity remains unclear. Here, we demonstrate that shootin1a links polymerizing actin filaments in spines with the cell-adhesion molecules N-cadherin and L1-CAM, thereby mechanically coupling the filaments to the extracellular environment. Synaptic activation enhances shootin1a-mediated actin-adhesion coupling in spines. Promotion of actin polymerization is insufficient for the plasticity; the enhanced actin-adhesion coupling is required for polymerizing actin filaments to push against the membrane for spine enlargement. By integrating cell signaling, cell adhesion, and force generation into the current model of actin-based machinery, we propose molecular machinery that is sufficient to trigger the activity-dependent spine structural plasticity.
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•Shootin1a couples F-actin retrograde flow and cell adhesions in dendritic spines•Synaptic activation enhances shootin1a-mediated clutch coupling in spines•Shootin1a-mediated clutch coupling generates force for spine formation•Activity-induced spine enlargement requires shootin1a-mediated clutch coupling
Kastian et al. use gene knockout, protein interaction assays, force microscopy, and speckle imaging to analyze the molecular mechanics driving structural plasticity of dendritic spines. Their data demonstrate that both shootin1a-mediated clutch coupling and actin polymerization are required for the generation of force to trigger activity-induced spine enlargement.
Ca2+/calmodulin-dependent protein kinase II (CaMKII) is a signaling protein required for long-term memory. When activated by Ca2+/CaM, it sustains activity even after the Ca2+ dissipates. In addition ...to the well-known autophosphorylation-mediated mechanism, interaction with specific binding partners also persistently activates CaMKII. A long-standing model invokes two distinct S and T sites. If an interactor binds at the T-site, then it will preclude autoinhibition and allow substrates to be phosphorylated at the S site. Here, we specifically test this model with X-ray crystallography, molecular dynamics simulations, and biochemistry. Our data are inconsistent with this model. Co-crystal structures of four different activators or substrates show that they all bind to a single continuous site across the kinase domain. We propose a mechanistic model where persistent CaMKII activity is facilitated by high-affinity binding partners that kinetically compete with autoinhibition by the regulatory segment to allow substrate phosphorylation.
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•CaMKII kinase domain binds all interactors through a single continuous binding site•A salt bridge interaction far from active site increases binding affinity•αD helix changes conformation between autoinhibited and active “on” states•High-affinity binders may prolong activation by maintaining the “on” state
Özden et al. report high-resolution structures of CaMKII bound to peptides from proteins that are crucial for memory. All interactors dock onto the same single binding site using conserved interactions. A model is proposed for how high-affinity interactors prolong CaMKII activity by competing with autoinhibition.
•A knock-in animal with a mutation in CaMKII binding domain of Tiam1 is generated.•The animal has specific impairment in Rac activation but not in Cdc42.•The hippocampal dendritic spines are smaller ...and failed to undergo structural LTP.•The animals had impaired novel object recognition test seven days after training.
A stimulation inducing long-term potentiation (LTP) of synaptic transmission induces a persistent expansion of dendritic spines, a phenomenon known as structural LTP (sLTP). We previously proposed that the formation of a reciprocally activating kinase-effector complex (RAKEC) between CaMKII and Tiam1, an activator of the small G-protein Rac1, locks CaMKII into an active conformation, which in turn maintains the phosphorylation status of Tiam1. This makes Rac1 persistently active, specifically in the stimulated spine. To understand the significance of the CaMKII-Tiam1 RAKEC in vivo, we generated a Tiam1 mutant knock-in mouse line in which critical residues for CaMKII binding were mutated into alanines. We confirmed the central role of this interaction on sLTP by observing that KI mice showed reduced Rac1 activity, had smaller spines and a diminished sLTP as compared to their wild-type littermates. Moreover, behavioral tests showed that the novel object recognition memory of these animals was impaired. We thus propose that the CaMKII-Tiam1 interaction regulates spine morphology in vivo and is required for memory storage.
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