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Abstract
The neuronal actin-binding protein drebrin A forms a stable structure with F-actin in dendritic spines. NMDA receptor activation causes an exodus of F-actin bound by drebrin A (DA-actin) from dendritic spines, suggesting a pivotal role for DA-actin exodus in synaptic plasticity. We quantitatively assessed the extent of DA-actin localization to spines using the spine-dendrite ratio of drebrin A in cultured hippocampal neurons, and found that (1) chemical long-term potentiation (LTP) stimulation induces rapid DA-actin exodus and subsequent DA-actin re-entry in dendritic spines, (2) Ca2+ influx through NMDA receptors regulates the exodus and the basal accumulation of DA-actin, and (3) the DA-actin exodus is blocked by myosin II ATPase inhibitor, but is not blocked by myosin light chain kinase (MLCK) or Rho-associated kinase (ROCK) inhibitors. These results indicate that myosin II mediates the interaction between NMDA receptor activation and DA-actin exodus in LTP induction. Furthermore, myosin II seems to be activated by a rapid actin-linked mechanism rather than slow MLC phosphorylation. Thus the myosin-II mediated DA-actin exodus might be an initial event in LTP induction, triggering actin polymerization and spine enlargement.
Highlights
Drebrin A is a neuron-specific actin-binding protein that is located at the base of dendritic spine heads [1,2,3]
The spine-dendrite ratio (SDR) used in this study is the average fluorescence signal of the molecule of interest in a dendritic spine head divided by the average fluorescence signal of that molecule in the dendritic shaft at the foot of the spine (Fig. 1A)
In the present study we demonstrated that (1) chemical longterm potentiation stimulation induces rapid DA-actin exodus and subsequent DA-actin re-entry in dendritic spines, (2) Ca2+ influx through NMDA receptors regulates both the exodus and the basal accumulation of DA-actin, and (3) the DA-actin exodus is blocked by a myosin II ATPase inhibitor, but is not blocked by either myosin light chain kinase (MLCK) or Rho-associated kinase (ROCK) inhibitors
Summary
Drebrin A is a neuron-specific actin-binding protein that is located at the base of dendritic spine heads [1,2,3]. Drebrin A binding modifies the pitch of actin filaments [4,5] and forms stable F-actin that is resistant to depolymerization by cytochalasin D [6,7]. Mikati et al [8] have recently shown that F-actin that is bound by drebrin A (DA-actin) is stable, and the depolymerization of DA-actin is suppressed at both ends of the filaments. DA-actin is not observed in dynamic dendritic filopodia, but is observed in more stable dendritic spines [9]. It is suggested that DA-actin forms stable structures of F-actin at the base of dendritic spine heads
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