Loss of the RNA trimethylguanosine cap is compatible with nuclear accumulation of spliceosomal snRNAs but not pre-mRNA splicing or snRNA processing during animal development
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ABSTRACT:
PROVIDER: PRJNA600752 | ENA |
REPOSITORIES: ENA
Dataset's files
| Action | DRS | |||
|---|---|---|---|---|
| SRR10874371_1.fastq.gz | Fastqsanger.gz | |||
| SRR10874371_2.fastq.gz | Fastqsanger.gz | |||
| SRR10874372_1.fastq.gz | Fastqsanger.gz | |||
| SRR10874372_2.fastq.gz | Fastqsanger.gz | |||
| SRR10874373_1.fastq.gz | Fastqsanger.gz |
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Project description:The 2,2,7-trimethylguanosine (TMG) cap is synthesized by the conserved Tgs1 enzyme, which is abundantly present on snRNAs essential for pre-mRNA splicing. In our study, we characterize new mutations in the Drosophila tgs1 gene and studied their effects on development and on splicing. Utilizing a hypomorphic tgs1 mutation, we uncovered a prominent role of Tgs1 in pre-mRNA splicing, particularly of introns with smaller sizes and weaker splice sites. Remarkably, stronger tgs1 mutations generated by CRISPR-Cas9 cause lethality without disrupting splicing, likely due to the preponderance of a maternal contribution and stable TMG capped snRNAs maintaining a near normal level of TMG modified snRNAs, which further proved that the TMG modification is important in splicing.
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Project description:Exogenous signals from drug-stressed cancer cells accelerate the proliferation of neighboring tumor cells and promote them to acquire a more aggressive phenotype. We have recently found an exciting phenomenon: drug-stressed cancer cells secrete various components of the spliceosome: proteins and a number of snRNAs. We have observed this phenomenon both in vitro (culture media from cancer cell lines [Pavluykov M. et al.//Cancer Cell, 2018]) and in vivo (ovarian cancer ascites after chemotherapy [Shender V. et al//Mol. Сell. Proteomics, 2014]). The aim of this study was to elucidate the role of secreted spliceosomal snRNAs in intercellular communication. We constructed synthetic U12 and U6atac snRNAs close to the natural structure, including some non-canonical nucleotides imitating post-transcriptional RNA modification. Proteomic analysis of SKOV3 cells transfected with U6atac or U12 snRNA analogs has shown that both exogenous snRNAs lead to an increase of abundance of proteins related to cell cycle regulation and M phase. It has been recently shown that a number of spliceosomal proteins affect regulation of the cell cycle, in particular the M phase (Maslon et al., 2014). Here we demonstrated that not only spliceosomal proteins but also spliceosomal snRNAs (U12 and U6atac) affect activation of mitotic cell cycle genes. This study reveals previously unknown signaling molecules in the microenvironment of ovarian cancer that have potential clinical significance.
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Project description:Exogenous signals from drug-stressed cancer cells accelerate the proliferation of neighboring tumor cells and promote to acquire a more aggressive phenotype. We have recently found an exciting phenomenon: drug-stressed cancer cells secrete various components of the spliceosome: proteins and a number of snRNAs. We have observed this phenomenon both in vitro (culture media from cancer cell lines [Pavluykov M. et al., 2018]) and in vivo (ovarian cancer ascites after chemotherapy [Shender V. et al., 2014]). The aim of this study was to elucidate the role of secreted spliceosomal snRNAs in intercellular communication. We constructed synthetic U12 and U6atac snRNAs close to the natural structure, including some non-canonical nucleotides imitating post-transcriptional RNA modifications. RNAseq analysis of SKOV3 cells transfected with U6atac or U12 snRNA analogs has shown that both exogenous snRNAs lead to an increase of abundance of proteins related to cell cycle regulation and M phase. It has been recently shown that a number of spliceosomal proteins affect regulation of the cell cycle, in particular the M phase [Maslon et al., 2014]. Here we demonstrated that not only spliceosomal proteins but also spliceosomal snRNAs (U12 and U6atac) affect cell cycle gene expression. This study revealed previously unknown signaling molecules in the microenvironment of ovarian cancer that have potential clinical significance.
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Project description:Sequencing-based profiling of ribose methylations is a new approach that allows for experiments adrressing dynamic changes on a large scale. Here, we apply such a method to spliceosomal snRNAs present in human whole cell RNA. Analysis of solid tissue samples confirmed all previously known sites and demonstrated close to full methylation at almost all sites. Methylation changes were revealed in biological experimental settings, using T cell activation as an example, and in the T cell leukemia model, Jurkat cells. Such changes could impact the dynamics of snRNA interactions during the spliceosome cycle and affect mRNA splicing efficiency and splicing patterns.
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Project description:Competing exonucleases that promote 3’ end maturation or degradation direct quality control of small non-coding RNAs, but how these enzymes distinguish normal from aberrant RNAs is poorly understood. The Pontocerebellar Hypoplasia 7 (PCH7)-associated 3’ exonuclease TOE1 promotes maturation of canonical small nuclear RNAs (snRNAs). Here, we demonstrate that TOE1 achieves specificity towards canonical snRNAs by recognizing Sm complex assembly and cap trimethylation, two features that distinguish snRNAs undergoing correct biogenesis from other small non-coding RNAs. Indeed, disruption of Sm complex assembly via snRNA mutations or protein depletions obstructs snRNA processing by TOE1, and in vitro snRNA processing by TOE1 is stimulated by a trimethylated cap. An unstable snRNA variant that normally fails to undergo maturation becomes fully processed by TOE1 when its degenerate Sm binding motif is converted into a canonical one. Our findings uncover the molecular basis for how TOE1 distinguishes snRNAs from other small non-coding RNAs and explain how TOE1 promotes maturation specifically of canonical snRNAs undergoing proper processing.
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Project description:The 2,2,7-trimethylguanosine (TMG) cap is one of the first identified modifications on eukaryotic RNAs. TMG, synthesized by the conserved Tgs1 enzyme, is abundantly present on snRNAs essential for pre-mRNA splicing. Results from ex vivo experiments in vertebrate cells suggested that TMG ensures nuclear localization of snRNAs. Functional studies of TMG using tgs1 mutations in unicellular organisms yield results inconsistent with TMG being indispensable for either nuclear import or splicing. Utilizing a hypomorphic tgs1 mutation in Drosophila, we show that TMG reduction impairs germline development by disrupting the processing, particularly of introns with smaller sizes and weaker splice sites. Unexpectedly, loss of TMG does not disrupt snRNAs localization to the nucleus, disputing an essential role of TMG in snRNA transport. Tgs1 loss also leads to defective 3' processing of snRNAs. Remarkably, stronger tgs1 mutations cause lethality without severely disrupting splicing, likely due to the preponderance of TMG-capped snRNPs. Tgs1, a predominantly nucleolar protein in Drosophila, likely carries out splicing-independent functions indispensable for animal development. Taken together, our results suggest that nuclear import is not a conserved function of TMG. As a distinctive structure on RNA, particularly non-coding RNA, we suggest that TMG prevents spurious interactions detrimental to the function of RNAs that it modifies.
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Project description:Effect of extracellular spliceosomal snRNAs on the transcriptome of ovarian cancer cells
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Project description:In this study we investigated snRNA-mediated modulation of pre-mRNA splicing across the human transcriptome. We first quantified the relative abundance of snRNAs across a comprehensive range of healthy adult and fetal tissues, revealing a surprising variation in the relative snRNA levels both inter- and intra-tissue. To study the role of snRNAs in cancer-relevant splicing, we used breast cancer as a model, since it exhibits a high rate of aberrant splicing48, but a low frequency of mutations in the splicing machinery52. We observed fluctuations in snRNA adundance across the majority of patients, across all breast cancer subtypes. To investigate the impact of snRNA levels using a controlled system, we knocked down snRNAs in vitro, to analyze splicing both transcriptome-wide and at the level of individual exons and introns. Depletion of each specific snRNA resulted in differential splicing across more than a thousand exon junctions within mRNA transcripts. Knock-down of U1 and U2 levels was primarily associated with changes in exon inclusion rates, whereas U4 and U6 depletion predominantly caused incomplete intron removal and a resulting retention of introns in the mature mRNA. Rather than being driven by a single factor, the observed splicing changes were associated with multiple other splicing-relevant features and mechanisms, including mRNA transcription, intron size, and nucleotide composition. The snRNA-mediated changes to the splicing program were enriched within genes encoding components of core cellular pathways and processes, including multiple aspects of RNA and protein metabolism, and thereby have the potential to impact cell growth and identity. The exons and introns that were sensitive to snRNA levels displayed a high variability in splicing in vivo across primary breast cancer samples, indicating that snRNA dysregulation may contribute to aberrant splicing in cancer. We suggest that the cellular composition of snRNAs constitutes a previously unrecognized layer of splicing regulation within the cell, and that variations or disruptions in the relative abundance of the snRNAs can affect the transcriptome of both healthy and malignant cells.
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