The brain-specific double-stranded RNA-binding protein Staufen2 is required for dendritic spine morphogenesis.
ABSTRACT: Mammalian Staufen2 (Stau2) is a member of the double-stranded RNA-binding protein family. Its expression is largely restricted to the brain. It is thought to play a role in the delivery of RNA to dendrites of polarized neurons. To investigate the function of Stau2 in mature neurons, we interfered with Stau2 expression by RNA interference (RNAi). Mature neurons lacking Stau2 displayed a significant reduction in the number of dendritic spines and an increase in filopodia-like structures. The number of PSD95-positive synapses and miniature excitatory postsynaptic currents were markedly reduced in Stau2 down-regulated neurons. Akin effects were caused by overexpression of dominant-negative Stau2. The observed phenotype could be rescued by overexpression of two RNAi cleavage-resistant Stau2 isoforms. In situ hybridization revealed reduced expression levels of beta-actin mRNA and fewer dendritic beta-actin mRNPs in Stau2 down-regulated neurons. Thus, our data suggest an important role for Stau2 in the formation and maintenance of dendritic spines of hippocampal neurons.
Project description:Messenger ribonucleoprotein particles (mRNPs) are used to transport mRNAs along neuronal dendrites to their site of translation. Numerous mRNA-binding and regulatory proteins within mRNPs finely regulate the fate of bound-mRNAs. Their specific combination defines different types of mRNPs that in turn are related to specific synaptic functions. One of these mRNA-binding proteins, Staufen2 (Stau2), was shown to transport dendritic mRNAs along microtubules. Its knockdown expression in neurons was shown to change spine morphology and synaptic functions. To further understand the molecular mechanisms by which Stau2 modulates synaptic function in neurons, it is important to identify and characterize protein co-factors that regulate the fate of Stau2-containing mRNPs. To this end, a proteomic approach was used to identify co-immunoprecipitated proteins in Staufen2-containing mRNPs isolated from embryonic rat brains. The proteomic approach identified mRNA-binding proteins (PABPC1, hnRNP H1, YB1 and hsc70), proteins of the cytoskeleton (alpha- and beta-tubulin) and RUFY3 a poorly characterized protein. While PABPC1 and YB1 associate with Stau2-containing mRNPs through RNAs, hsc70 is directly bound to Stau2 and this interaction is regulated by ATP. PABPC1 and YB1 proteins formed puncta in dendrites of embryonic rat hippocampal neurons. However, they poorly co-localized with Stau2 in the large dendritic complexes suggesting that they are rather components of Stau2-containing mRNA particles. All together, these results represent a further step in the characterization of Stau2-containing mRNPs in neurons and provide new tools to study and understand how Stau2-containing mRNPs are transported, translationally silenced during transport and/or locally expressed according to cell needs.
Project description:Dendritic localization and hence local mRNA translation contributes to synaptic plasticity in neurons. Staufen2 (Stau2) is a well-known neuronal double-stranded RNA-binding protein (dsRBP) that has been implicated in dendritic mRNA localization. The specificity of Stau2 binding to its target mRNAs remains elusive. Using individual-nucleotide resolution CLIP (iCLIP), we identified significantly enriched Stau2 binding to the 3'-UTRs of 356 transcripts. In 28 (7.9%) of those, binding occurred to a retained intron in their 3'-UTR The strongest bound 3'-UTR intron was present in the longest isoform of Calmodulin 3 (Calm3L ) mRNA Calm3L 3'-UTR contains six Stau2 crosslink clusters, four of which are in this retained 3'-UTR intron. The Calm3L mRNA localized to neuronal dendrites, while lack of the 3'-UTR intron impaired its dendritic localization. Importantly, Stau2 mediates this dendritic localization via the 3'-UTR intron, without affecting its stability. Also, NMDA-mediated synaptic activity specifically promoted the dendritic mRNA localization of the Calm3L isoform, while inhibition of synaptic activity reduced it substantially. Together, our results identify the retained intron as a critical element in recruiting Stau2, which then allows for the localization of Calm3L mRNA to distal dendrites.
Project description:Dendritic messenger RNA (mRNA) localization and subsequent local translation in dendrites critically contributes to synaptic plasticity and learning and memory. Little is known, however, about the contribution of RNA-binding proteins (RBPs) to these processes in vivo.To delineate the role of the double-stranded RBP Staufen2 (Stau2), we generate a transgenic rat model, in which Stau2 expression is conditionally silenced by Cre-inducible expression of a microRNA (miRNA) targeting Stau2 mRNA in adult forebrain neurons. Known physiological mRNA targets for Stau2, such as RhoA, Complexin 1, and Rgs4 mRNAs, are found to be dysregulated in brains of Stau2-deficient rats. In vivo electrophysiological recordings reveal synaptic strengthening upon stimulation, showing a shift in the frequency-response function of hippocampal synaptic plasticity to favor long-term potentiation and impair long-term depression in Stau2-deficient rats. These observations are accompanied by deficits in hippocampal spatial working memory, spatial novelty detection, and in tasks investigating associative learning and memory.Together, these experiments reveal a critical contribution of Stau2 to various forms of synaptic plasticity including spatial working memory and cognitive management of new environmental information. These findings might contribute to the development of treatments for conditions associated with learning and memory deficits.
Project description:dendritic mRNA transport machines. Although Stau2 is thought to be involved in the dendritic targeting of several mRNAs in neurons, the mechanism whereby Stau2 regulates these mRNAs is unknown. To elucidate the functions of Stau2, we screened for novel binding partners by affinity purification of GST-tagged Stau2 from 293F cells.Three RNA helicases, RNA helicase A, Upf1 and Mov10, were identified in Stau2-containing complexes. We focused our studies on Upf1, a key player in nonsense-mediated mRNA decay. Stau2 was found to bind directly to Upf1 in an RNA-independent manner in vitro. Tethering Stau2 to the 3'-untranslated region (UTR) of a reporter gene had little effect on its expression in HeLa cells. In contrast, when the same tethering assay was performed in 293F cells, we observed an increase in reporter protein levels. This upregulation of protein expression by Stau2 turned out to be dependent on Upf1. Moreover, we found that in 293F cells, Stau2 upregulates the reporter mRNA level in an Upf1-independent manner.These results indicate that the recruitment of Stau2 alone or in combination with Upf1 differentially affects the fate of mRNAs. Moreover, the results suggest that Stau2-mediated fate determination could be executed in a cell type-specific manner.
Project description:Messenger RNAs are associated with multiple RNA-binding proteins to form ribonucleoprotein (mRNP) complexes. These proteins are important regulators of the fate of their target mRNAs. In human cells, Staufen1 and Staufen2 proteins, coded by two different genes, are double-stranded RNA-binding proteins involved in several cellular functions including mRNA localization, translation, and decay. Although 51% identical, these proteins are nevertheless found in different RNA particles. In addition, differential splicing events generate Staufen2 isoforms that only differ at their N-terminal extremities. In this paper, we used a genome-wide approach to identify and compare the mRNA targets of mammalian Staufen proteins. The mRNA content of Staufen mRNPs was identified by probing DNA microarrays with probes derived from mRNAs isolated from immunopurified Staufen-containing complexes following transfection of HEK293T cells with Stau1(55)-HA, Stau2(59)-HA, or Stau2(62)-HA expressors. Our results indicate that 7% and 11% of the cellular RNAs expressed in HEK293T cells are found in Stau1- and in Stau2-containing mRNPs, respectively. A comparison of Stau1- and Stau2-containing mRNAs identifies a relatively low percentage of common mRNAs; the percentage of common mRNAs highly increases when mRNAs in Stau2(59)-HA- and Stau2(62)-containing mRNPs are compared. There is a predominance of mRNAs involved in cell metabolism, transport, transcription, regulation of cell processes, and catalytic activity. All these subsets of mRNAs are mostly distinct from those associated with FMRP or IMP, although some mRNAs overlap. Consistent with a model of post-transcriptional gene regulation, our results show that Stau1- and Stau2-mRNPs associate with distinct but overlapping sets of cellular mRNAs.
Project description:<h4>Background</h4>Staufen2 (STAU2) is an RNA-binding protein involved in the post-transcriptional regulation of gene expression. This protein was shown to be required for organ formation and cell differentiation. Although STAU2 functions have been reported in neuronal cells, its role in dividing cells remains deeply uncharacterized. Especially, its regulation during the cell cycle is completely unknown.<h4>Results</h4>In this study, we showed that STAU2 isoforms display a mitosis-specific slow migration pattern on SDS-gels in all tested transformed and untransformed cell lines. Deeper analyses in hTert-RPE1 and HeLa cells further indicated that the slow migration pattern of STAU2 isoforms is due to phosphorylation. Time course studies showed that STAU2 phosphorylation occurs before prometaphase and terminates as cells exit mitosis. Interestingly, STAU2 isoforms were phosphorylated on several amino acid residues in the C-terminal half via the cyclin-dependent kinase 1 (Cdk1), an enzyme known to play crucial roles during mitosis. Introduction of phospho-mimetic or phospho-null mutations in STAU2 did not impair its RNA-binding capacity, its stability, its interaction with protein co-factors or its sub-cellular localization, suggesting that STAU2 phosphorylation in mitosis does not regulate these functions. Similarly, STAU2 phosphorylation is not likely to be crucial for cell cycle progression since expression of phosphorylation mutants in hTert-RPE1 cells did not impair cell proliferation.<h4>Conclusions</h4>Altogether, these results indicate that STAU2 isoforms are phosphorylated during mitosis and that the phosphorylation process involves Cdk1. The meaning of this post-translational modification is still elusive.
Project description:Staufen2 (Stau2) is an RNA-binding protein involved in cell fate decision by controlling several facets of mRNA processing including localization, splicing, translation and stability. Herein we report that exposure to DNA-damaging agents that generate replicative stress such as camptothecin (CPT), 5-fluoro-uracil (5FU) and ultraviolet radiation (UVC) causes downregulation of Stau2 in HCT116 colorectal cancer cells. In contrast, other agents such as doxorubicin and ionizing radiation had no effect on Stau2 expression. Consistently, Stau2 expression is regulated by the ataxia telangiectasia and Rad3-related (ATR) signaling pathway but not by the DNA-PK or ataxia telangiectasia mutated/checkpoint kinase 2 pathways. Stau2 downregulation is initiated at the level of transcription, independently of apoptosis induction. Promoter analysis identified a short 198 bp region which is necessary and sufficient for both basal and CPT-regulated Stau2 expression. The E2F1 transcription factor regulates Stau2 in untreated cells, an effect that is abolished by CPT treatment due to E2F1 displacement from the promoter. Strikingly, Stau2 downregulation enhances levels of DNA damage and promotes apoptosis in CPT-treated cells. Taken together our results suggest that Stau2 is an anti-apoptotic protein that could be involved in DNA replication and/or maintenance of genome integrity and that its expression is regulated by E2F1 via the ATR signaling pathway.
Project description:In human cells, Staufen2 is a double-stranded RNA-binding protein involved in several cellular functions. Although 51% identical to Staufen1, these proteins are nevertheless found in different RNA particles. In addition, differential splicing events generate Staufen2 isoforms that only differ at their N-terminal extremities. We used a genome wide approach to identify and compare the mRNA targets of mammalian Staufen2 isoforms. The mRNA content of Staufen mRNPs was identified by probing DNA microarrays with probes derived from mRNAs isolated from immunopurified Staufen2-containing complexes following transfection of HEK293T cells with Stau2-HA (59kDa) or Stau2-HA (62kDa) expressors. Our results indicate that 11% of the cellular RNAs expressed in HEK293T cells are found in Stau2-containing mRNPs. There is a predominance of mRNAs involved in cell metabolism, transport, transcription, regulation of cell processes and catalytic activity. Keywords: Immunoprecipitation, Staufen, microarray Overall design: HEK293 cells were transiantly transfected with plasmids coding for Staufen2-HA isoforms. Cell extracts were immunoprecipitated using anti-HA antibodies and co-immunoprecipitated mRNAs were purified and used to hybridize microarrays. As control, cell extract from mock transfected cells were used.
Project description:In human cells, Staufen2 is a double-stranded RNA-binding protein involved in several cellular functions. Although 51% identical to Staufen1, these proteins are nevertheless found in different RNA particles. In addition, differential splicing events generate Staufen2 isoforms that only differ at their N-terminal extremities. We used a genome wide approach to identify and compare the mRNA targets of mammalian Staufen2 isoforms. The mRNA content of Staufen mRNPs was identified by probing DNA microarrays with probes derived from mRNAs isolated from immunopurified Staufen2-containing complexes following transfection of HEK293T cells with Stau2-HA (59kDa) or Stau2-HA (62kDa) expressors. Our results indicate that 11% of the cellular RNAs expressed in HEK293T cells are found in Stau2-containing mRNPs. There is a predominance of mRNAs involved in cell metabolism, transport, transcription, regulation of cell processes and catalytic activity. Experiment Overall Design: HEK293 cells were transiantly transfected with plasmids coding for Staufen2-HA isoforms. Cell extracts were immunoprecipitated using anti-HA antibodies and co-immunoprecipitated mRNAs were purified and used to hybridize microarrays. As control, cell extract from mock transfected cells were used.
Project description:In neurons, many mRNAs are transported along neuronal dendrites to their site of translation by ribonucleoprotein complexes (mRNPs). Numerous mRNA-binding, motor and regulatory proteins within mRNPs finely regulate the fate of each of these mRNAs and their specific combination is likely to define different types of mRNA complexes and their neuronal functions. Staufen2 is a well known mRNA-binding protein present in distinct population of mRNPs in neurons and is implicated in the transport of mRNAs along the dendritic microtubules. However, little is known about the associated mRNAs in Staufen2 neuronal mRNPs complexes. As a means to understand its role in neuronal processes, a genome wide approach has been used to identify mRNAs that are co-immunoprecipitated with Staufen2 complexes from embryonic rat brains. The genome wide approach identified 1780 mRNAs associated with Staufen2 mRNPs that code for proteins involved in cellular processes such as post-translational protein modifications, RNA metabolism, intracellular transport and translation. All these mRNAs are consistent with the role of Staufen2 in synaptogenesis. Overall design: Immunoprecipitation of Staufen2-containing mRNPs was performed on cell extracts prepared from whole brains of E17-E18 Sprague Dawley rat embryos. Cells were dissociated with a manual putter and lysed in 50 mM Tris-HCl (pH 7.5), 100 mM NaCl, 0.5% Triton X-100, 15 mM EGTA, 1 mM DTT and complete EDTA-free protease inhibitor cocktail (Roche). Cell lysates were centrifuged at 10 000 rpm for 10 min. After centrifugation, the supernatants were incubated with a rabbit polyclonal anti-Staufen2 or preimmune antibodies for 2 hours at 4°C, then with a 50% protein A-sepharose slurry for 2 hours at 4°C. Immune complexes were washed five times with the lysis buffer and eluted from the resin by heating at 95°C for 5 minutes in elution buffer (100 mM Tris-HCl pH 7.4, 200 mM DTT and 4% SDS). RNAs were isolated by Trizol (Invitrogen) extraction. Experiments were repeated several times (Anti-Stau2: n = 6; control preimmune: n = 6).