ABSTRACT
Staufens (Stau) are RNA-binding proteins involved in mRNA transport, localization, decay and translational control. The Staufen 1 (Stau1) isoform was recently identified as necessary for the protein synthesis-dependent late phase long-term potentiation (late-LTP) and for the maintenance of mature dendritic spines and synaptic activity in hippocampal CA1 pyramidal cells, strongly suggesting a role of mRNA regulation by Stau1 in these processes. However, the causal relationship between these impairments in synaptic function (spine shape and basal synaptic activity) and plasticity (late-LTP) remains unclear. Here, we determine that the effects of Stau1 knockdown on spine shape and size are mimicked by blocking NMDA receptors (or elevating extracellular Mg2+) and that Stau1 knockdown in the presence of NMDA receptor blockade (or high Mg2+) has no further effect on spine shape and size. Moreover, the effect of Stau1 knockdown on late-LTP cannot be explained by these effects, since when tested in normal medium, slice cultures that had been treated with high Mg2+ (to impair NMDA receptor function) in combination with a control siRNA still exhibited late-LTP, while siRNA to Stau1 was still effective in blocking late-LTP. Our results indicate that Stau1 involvement in spine morphogenesis is dependent on ongoing NMDA receptor-mediated plasticity, but its effects on late-LTP are independent of these changes. These findings clarify the role of Stau1-dependent mRNA regulation in physiological and morphological changes underlying long-term synaptic plasticity in pyramidal cells.
Subject(s)
Dendritic Spines/metabolism , Neuronal Plasticity , Pyramidal Cells/metabolism , RNA-Binding Proteins/metabolism , Receptors, N-Methyl-D-Aspartate/metabolism , Synapses/metabolism , Animals , Colforsin/pharmacology , Dendritic Spines/drug effects , Gene Knockdown Techniques , In Vitro Techniques , Long-Term Potentiation/drug effects , Magnesium/pharmacology , Neuronal Plasticity/drug effects , Protein Binding/drug effects , Pyramidal Cells/drug effects , RNA, Messenger/metabolism , RNA, Small Interfering/metabolism , Rats , Receptors, N-Methyl-D-Aspartate/antagonists & inhibitors , Synapses/drug effectsABSTRACT
The two members of the Staufen family of RNA-binding proteins, Stau1 and Stau2, are present in distinct ribonucleoprotein complexes and associate with different mRNAs. Stau1 is required for protein synthesis-dependent long-term potentiation (L-LTP) in hippocampal pyramidal cells. However, the role of Stau2 in synaptic plasticity remains unexplored. We found that unlike Stau1, Stau2 is not required for L-LTP. In contrast, Stau2, but not Stau1, is necessary for DHPG-induced protein synthesis-dependent long-term depression (mGluR-LTD). While Stau2 is involved in early development of spines, its down-regulation does not alter spine morphology or spontaneous miniature synaptic activity in older cultures where LTD occurs. In addition, Stau2, but not Stau1, knockdown reduces the dendritic localization of Map1b mRNA, a specific transcript involved in mGluR-LTD. Moreover, mGluR stimulation with DHPG induces Map1b, but not Map2, mRNA dissociation from mRNA granules containing Stau2 and the ribosomal protein P0. This dissociation was not observed in cells in which Stau2 was depleted. Finally, Stau2 knockdown reduces basal Map1b protein expression in dendrites and prevents DHPG-induced increases in dendritic Map1b protein level. We suggest a role for Stau2 in the generation and regulation of Map1b mRNA containing granules that are required for mGluR-LTD.
Subject(s)
Long-Term Synaptic Depression/physiology , Microtubule-Associated Proteins/metabolism , Nerve Tissue Proteins/metabolism , Neurons/metabolism , RNA-Binding Proteins/metabolism , Receptors, Metabotropic Glutamate/metabolism , Animals , Blotting, Western , HEK293 Cells , Hippocampus/metabolism , Humans , Microscopy, Confocal , Microtubule-Associated Proteins/genetics , Organ Culture Techniques , RNA, Messenger/analysis , RNA, Small Interfering , Rats , Rats, Sprague-Dawley , TransfectionABSTRACT
Staufen1 (Stau1) is an RNA-binding protein involved in transport, localization, decay, and translational control of mRNA. In neurons, it is present in cell bodies and also in RNA granules which are transported along dendrites. Dendritic mRNA localization might be involved in long-term synaptic plasticity and memory. To determine the role of Stau1 in synaptic function, we examined the effects of Stau1 down-regulation in hippocampal slice cultures using small interfering RNA (siRNA). Biolistic transfection of Stau1 siRNA resulted in selective down-regulation of Stau1 in slice cultures. Consistent with a role of Stau1 in transporting mRNAs required for synaptic plasticity, Stau1 down-regulation impaired the late form of chemically induced long-term potentiation (L-LTP) without affecting early-LTP, mGluR1/5-mediated long-term depression, or basal evoked synaptic transmission. Stau1 down-regulation decreased the amplitude and frequency of miniature excitatory postsynaptic currents, suggesting a role in maintaining efficacy at hippocampal synapses. At the cellular level, Stau1 down-regulation shifted spine shape from regular to elongated spines, without changes in spine density. The change in spine shape could be rescued by an RNA interference-resistant Stau1 isoform. Therefore, Stau1 is important for processing and/or transporting in dendrites mRNAs that are critical in regulation of synaptic strength and maintenance of functional connectivity changes underlying hippocampus-dependent learning and memory.
