Project description:Nuclear transcriptional factors are key regulators of stem cell identity and differentiation, however whether extra-nuclear factors are involved in cell fate decisions remains unclear. Here we report that centrosome-associated spliceosome repression drives the differentiation of immature neuroblasts into neurons. Using neuroblastoma cells undergoing asymmetric division (ACD) as a model, we demonstrate that spliceosome components assemble preferentially at the mother centriole and undergo dynamic relocation in response to retinoic acid (RA) or centrosome ablation. ACD cells require selective Ninein splicing variants to promote the efficient formation of centrosome-associated spliceosome condensates. RA-induced neuron differentiation activates ciliogenesis and alternative splicing patterns, including cytoplasmic intron-retained transcripts in spliceosome-related genes. While pharmacological ablation of cilia impedes RA-dependent neuronal differentiation, inhibition of centriole duplication enhances synapse formation, recapitulating the molecular and morphological features of neurons. Mechanistically, centrosome repression-mediated differentiation of ACD cells into neurons relocates spliceosome factors between the nucleus and centrosome, activating cytoplasmic intron retention and exon inclusion in genes essential for ciliogenesis and cerebral cortical development. Collectively, our findings establish a cellular model for programmed splicing control and a strategy to enhance cytoplasmic spliced genes critical for human brain development.
Project description:The studies of spliceosomal interactions are challenging due to their dynamic nature. Here we developed spliceosome iCLIP, which immunoprecipitates SmB along with snRNPs and auxiliary RNA binding proteins (RBPs) to simultaneously map the spliceosomal binding to human snRNAs and pre-mRNAs. This identified 9 distinct regions on pre-mRNAs, which overlap with position-dependent binding patterns of 15 RBPs. Using spliceosome iCLIP, we additionally identified >50,000 branchpoints (BPs) that have canonical features, unlike those identified by RNA-seq. The iCLIP BPs generally overlap with the computationally predicted BPs, and alternative BPs are associated with extended regions of structurally accessible RNA. We find that the position and strength of BPs defines the binding patterns of SF3 and U2AF complexes, whereas the RNA structure around BPs affects the sensitivity of exons to perturbation of these complexes. Our findings introduce spliceosome iCLIP as a new method for transcriptomic studies of BPs and splicing mechanisms.
Project description:Alternative splicing (AS) can produce multiple transcripts with different exon-intron structures from a single pre-mRNA. Pre-mRNA splicing is catalyzed by a dynamic macromolecular ribonucleoprotein (RNP) complex termed the spliceosome. The spliceosome consists of several small nuclear ribonucleoproteins (snRNPs) that bind uridine-rich small nuclear RNA (snRNA). In U1, U2, U4 and U5 snRNPs, snRNA interacts with the conserved Smith antigen (Sm) proteins via a bipartite Sm sequence motif. In eukaryotes, seven Sm proteins (B, D1/2/3, E, F and G) form a heptameric ring-shaped complex surrounding the snRNA. Here, we performed a tandem affinity purification using SMEB as a bait in Arabidopsis cell suspension cultures. At least 45 known/hypothesized and potential novel spliceosome components were identified in Arabidopsis.
Project description:microRNA dysregulation is a common feature of cancer cells, but the complex roles of microRNAs in cancer are not fully elucidated. Here we used functional genomics to identify oncogenic microRNAs in non-small cell lung cancer and to evaluate their impact on response to EGFR targeting therapy. Our data demonstrate that microRNAs with an AAGUGC-motif in their seed-sequence increase both cancer cell proliferation and sensitivity to EGFR inhibitors. Global transcriptomics, proteomics and target prediction resulted in the identification of several tumor suppressors involved in the G1/S transition as targets of AAGUGC-microRNAs. The clinical implications of our findings were evaluated by analysis of public domain data supporting the link between this microRNA seed-family, their tumor suppressor targets and cancer cell proliferation. In conclusion we propose that AAGUGC-microRNAs are an integral part of an oncogenic signaling network, and that these findings have potential therapeutic implications, especially in selecting patients for EGFR-targeting therapy.
Project description:Extracellular vesicles (EVs) are emerging as novel mediators of cellular communication, in part via the delivery of their contents including microRNAs; small non-coding RNAs that regulate gene expression and are crucial for neuronal circuit formation and function. Whether microRNAs are transferred between differentiated neurons is so far unknown. Moreover, the physiological role of EVs in inter-neuronal signaling is largely elusive. We observed that EVs derived from brain-derived neurotrophic factor (BDNF)-treated neurons induced dendrite complexity, synapse maturation and neuronal firing in recipient hippocampal neurons. This was dependent on the activity of three microRNAs, miR-132-5p, miR-218-5p and miR-690, that were specifically up-regulated in BDNF-induced EVs. Transcriptomic analysis further showed the differential expression of genes related to synaptogenesis in BDNF-EV-treated neurons, many of which are conserved targets of these miRNAs. Overall, this work demonstrates a novel mechanism of inter-neuronal communication, which may be highly relevant in neurological disorders characterized by aberrant BDNF signaling.