Project description:Local translation is a conserved molecular mechanism. It allows a cell with a complex shape to bypass somatic protein synthesis and transport, and thus to respond quickly to a local stimulus. Local translation also contributes to the establishment of molecular and functional polarity. In the brain, it has been extensively studied in neurons and has also been described more recently in astrocytes - a type of glial cell with specialized extensions that contact vessels and synapses. Here, we studied perisynaptic astrocytic processes (PAPs) in the dorsal hippocampus and showed that they contain RNAs, ribosomes, the endoplasmic reticulum-Golgi intermediate compartment, particles of the Golgi apparatus, and protein synthesis events. We used our recently refined polysome immunoprecipitation technique to characterize the pool of polysomal mRNAs in PAPs (which we refer to as the “PAPome”) from the dorsal hippocampus and compared it with the polysomal mRNAs found in the astrocyte as a whole. The polysomal transcripts that were enriched in the PAPome encoded mostly cytoplasmic proteins and defined an unexpected molecular repertoire with the most enriched transcripts coding for proteins involved in iron homeostasis, translation, cell cycle and cytoskeleton. Interestingly, among them Erz, Fth1, and Rplp1 were enriched in PAPs compared to perivascular astrocytic processes indicating that local translation differ at these two interfaces and may sustain distinct molecular properties. The PAP-enriched transcripts Flt1, Fth1, Ccnd2, Mdm2, Gnb2l1 and Eef1a1 code for proteins involved in memory and learning mechanisms. We therefore studied their local translation in the context of fear conditioning (i.e. behavior involving the dorsal hippocampus). We observed changes in the density and/or distribution of these mRNAs in astrocytes processes as well as a drop of their translation specifically in PAPs. Our results highlight unexpected molecular properties of hippocampal PAPs and suggest for the first time that local translation in this perisynaptic compartment is linked to fear-related memory.
Project description:The subcellular localization and translation of messenger RNA (mRNA) supports functional differentiation between cellular compartments. In neuronal dendrites, local translation of mRNA provides a rapid and specific mechanism for synaptic plasticity and memory formation, and might be involved in the pathophysiology of certain brain disorders. Despite the importance of dendritic mRNA translation, little is known about which mRNAs can be translated in dendrites in vivo and when their translation occurs. Here we collect ribosome-bound mRNA from the dendrites of CA1 pyramidal neurons in the adult mouse hippocampus. We find that dendritic mRNA rapidly associates with ribosomes following a novel experience consisting of a contextual fear conditioning trial. High throughput RNA sequencing followed by machine learning classification reveals an unexpected breadth of ribosome-bound dendritic mRNAs, including mRNAs expected to be entirely somatic. Our findings are in agreement with a mechanism of synaptic plasticity that engages the acute local translation of functionally diverse dendritic mRNAs. RNA-Seq of ribosome-bound mRNA immunoprecipitated from dendrites and soma of CA1 pyramidal neurons in the mouse hippocampus
Project description:We present a genome-wide assessment of small open reading frames (smORF) translation by ribosomal profiling of polysomal fractions in Drosophila S2 cell. In this way, mRNAs bound by multiple ribosomes and hence actively translated can be isolated and distinguished from mRNAs bound by sporadic, putatively non-productive single ribosomes or ribosomal subunits. Ribosomal profiling of large and small polysomal fractions in Drosophila S2 cells to assess translation of smORFs
Project description:The subcellular localization and translation of messenger RNA (mRNA) supports functional differentiation between cellular compartments. In neuronal dendrites, local translation of mRNA provides a rapid and specific mechanism for synaptic plasticity and memory formation, and might be involved in the pathophysiology of certain brain disorders. Despite the importance of dendritic mRNA translation, little is known about which mRNAs can be translated in dendrites in vivo and when their translation occurs. Here we collect ribosome-bound mRNA from the dendrites of CA1 pyramidal neurons in the adult mouse hippocampus. We find that dendritic mRNA rapidly associates with ribosomes following a novel experience consisting of a contextual fear conditioning trial. High throughput RNA sequencing followed by machine learning classification reveals an unexpected breadth of ribosome-bound dendritic mRNAs, including mRNAs expected to be entirely somatic. Our findings are in agreement with a mechanism of synaptic plasticity that engages the acute local translation of functionally diverse dendritic mRNAs.
Project description:During neuronal wiring, extrinsic cues trigger the local translation of specific mRNAs in axons via cell surface receptors. The coupling of ribosomes to receptors has been proposed as a mechanism linking signals to local translation but it is not known how broadly this mechanism operates, nor whether it can selectively regulate mRNA translation. We report that receptor-ribosome coupling is employed by multiple guidance cue receptors and this interaction is mRNA-dependent. We find that different receptors bind to distinct sets of mRNAs and RNA-binding proteins. Cue stimulation induces rapid dissociation of ribosomes from receptors and the selective translation of receptor-specific mRNAs in retinal axon growth cones. Further, we show that receptor-ribosome dissociation and cue-induced selective translation are inhibited by simultaneous exposure to translation-repressive cues, suggesting a novel mode of signal integration. Our findings reveal receptor-specific interactomes and provide a general model for the rapid, localized and selective control of cue-induced translation.
Project description:Background Protein synthesis is a highly energy demanding process and is regulated according to energy availability in plant cells. Light and sugar availability affect mRNA translation but the specific roles of these factors remain unclear. In this study, sucrose was applied to Arabidopsis seedlings kept in the light or in the dark, in order to distinguish sucrose and light effects on transcription and translation. These were studied using microarray analysis of steady state mRNA and mRNA bound to translating ribosomes. Results Steady state mRNA levels were affected differently by sucrose in the light and in the dark but general translation increased to a similar extend in both conditions. Alterations in polysomal mRNA association closely followed the changes induced on the transcript level. However, for 243 mRNAs, a change in ribosome occupancy was observed after sucrose treatment in the light, but not in the dark condition. Many of these mRNAs are annotated as encoding ribosomal proteins, supporting specific translational regulation of this group of transcripts. Unexpectedly, the numbers of ribosomes bound to each mRNA decreased for mRNAs with increased ribosome occupancy. Conclusions Our results suggest that sucrose regulate translation of these 243 mRNAs but specifically in the light, through a novel regulatory mechanism. Our data sows that increased polysomal association is not necessarily leading to more ribosomes per transcript, suggesting a mechanism of translational induction not solely dependent on increased translation initiation rates. Four different samples groups were used: Control, Darkness, Sucrose, Simultaneous Darkness and sucrose treatments. All sample groups was represented by both total mRNA hybridization and of mRNAs from polysomal enrichment. All sample groups were represented by three biological replicates.
Project description:mRNAs bound by ribosomes from yeast cells were analysed in order to determine the exact position of ribosomes in the presence or absence of Rio1p. Beside total Ribosome Protected Fragments (RPFs), RPFs from mRNAs protected by immature pre-40S pre-ribosomes was also analysed. The analysis showed that immature 40S ribosomes can carry out translation and their premature entry into translation is hindered by Rio1p.
Project description:We present a genome-wide assessment of small open reading frames (smORF) translation by ribosomal profiling of polysomal fractions in Drosophila S2 cell. In this way, mRNAs bound by multiple ribosomes and hence actively translated can be isolated and distinguished from mRNAs bound by sporadic, putatively non-productive single ribosomes or ribosomal subunits.
Project description:We present a genome-wide assessment of the translation of small open reading frames (smORF) in Drosophila melanogaster mRNAs, using ribosomal profiling of polysomal fractions in three contiguous temporal windows, which encopass all of embryogenesis. We also performed the same protocol using S2 cells. In this way, mRNAs bound by multiple ribosomes can be isolated and distinguished from mRNAs bound by sporadic, putatively non-productive single ribosomes or ribosomal subunits.
Project description:Quaking RNA binding protein(QKI) is essential for oligodendrocyte development as myelination requires MBP mRNA regulation and localization to distal processes by its cytoplasmic isoforms(e.g. QKI-6). QKI-6 is also highly expressed in astrocytes, which we and others recently demonstrated have regulated mRNA localization. Here, we show via CLIPseq that QKI-6 binds 3’UTRs of a subset of astrocytic mRNAs, including many enriched in peripheral processes. Binding is enriched near stop codons, which is mediated partially by QKI binding motifs(QBMs) yet spreads to adjacent sequences. We developed CRISPR TRAPseq: a viral approach for mosaic, cell-type specific gene mutation with simultaneous translational profiling. This enabled study of QKI-6 CLIP targets in QKI-deleted astrocytes in an otherwise normal brain. Astrocyte-targeted QKI deletion altered translation and maturation, while also increasing synaptic density within the astrocyte's territory. Overall, our data indicate QKI is required for astrocyte maturation and demonstrate an approach for a highly targeted translational assessment of gene knockout in specific cell-types in vivo.