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Novel RNA-binding Proteins Bind U1 snRNA to Promote Splicing of Weak 5' Splice Sites

ABSTRACT: Removal of introns during pre-mRNA splicing, which is central to gene expression, initiates by base pairing of U1 snRNA with a 5' splice site (5'SS). In mammals, many introns contain weak 5'SSs that are not efficiently recognized by the canonical U1 snRNP, suggesting alternative mechanisms exist. Here, we develop a cross-linking immunoprecipitation coupled to a high-throughput sequencing method, BCLIP-seq, to identify NRDE2 (Nuclear RNAi defective-2) and CCDC174 (Coiled-Coil Domain-Containing 174) as novel RNA-binding proteins in mouse ES cells that associate with U1 snRNA and unspliced 5'SSs. Both proteins bind directly to U1 snRNA independently of canonical U1 snRNP specific proteins, and they are required for the selection and effective processing of weak 5'SSs. Our results reveal that mammalian cells use non-canonical splicing factors bound directly to U1 snRNA to effectively select suboptimal 5'SS sequences in hundreds of genes, promoting proper splice site choice and accurate pre-mRNA splicing.

ORGANISM(S): Mus musculus

PROVIDER: GSE179744 | GEO | 2023/05/04

REPOSITORIES: GEO

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Novel RNA-binding Proteins Bind U1 snRNA to Promote Splicing of Weak 5' Splice Sites

Project description:Removal of introns during pre-mRNA splicing, which is central to gene expression, initiates by base pairing of U1 snRNA with a 5' splice site (5'SS). In mammals, many introns contain weak 5'SSs that are not efficiently recognized by the canonical U1 snRNP, suggesting alternative mechanisms exist. Here, we develop a cross-linking immunoprecipitation coupled to a high-throughput sequencing method, BCLIP-seq, to identify NRDE2 (Nuclear RNAi defective-2) and CCDC174 (Coiled-Coil Domain-Containing 174) as novel RNA-binding proteins in mouse ES cells that associate with U1 snRNA and unspliced 5'SSs. Both proteins bind directly to U1 snRNA independently of canonical U1 snRNP specific proteins, and they are required for the selection and effective processing of weak 5'SSs. Our results reveal that mammalian cells use non-canonical splicing factors bound directly to U1 snRNA to effectively select suboptimal 5'SS sequences in hundreds of genes, promoting proper splice site choice and accurate pre-mRNA splicing.

2023-09-07 | PXD029392 | Pride

LUC7 is an U1snRNP component that plays a role in alternative splicing and terminal introns removal in plants

Project description:Introns are removed by the spliceosome, a large complex composed of five ribonucleoprotein subcomplexes (U snRNP). In metazoans, the U1 snRNP, which binds to 5’ splice sites, also fulfills regulatory roles in splice site selection and possesses non-splicing related functions. Here, we show that an Arabidopsis U1 snRNP subunit, LUC7, affects constitutive and alternative splicing. Interestingly, LUC7 specifically promotes splicing of a subset of terminal introns. Splicing of LUC7-dependent terminal introns is a prerequisite for nuclear export and can be modulated by stress. Globally, intron retention under stress conditions occurs preferentially among first and terminal introns, uncovering an unknown bias for splicing regulation in Arabidopsis. Taken together, our study reveals that the Arabidopsis U1 snRNP is important for alternative splicing and removal of terminal introns and it suggests that Arabidopsis terminal introns fine-tune gene expression under stress conditions.

2017-05-24 | GSE98779 | GEO

Intron looping is mediated during transcription by U1 snRNP and RNA polymerase II [RNA-Seq]

Project description:In the earliest step of spliceosome assembly, the two splice sites flanking an intron are brought into proximity by U1 snRNP and U2AF. The mechanism that facilitates this intron looping is poorly understood. Using a CRISPR interference-based approach to halt RNA polymerase II transcription in the middle of introns, we discovered that the 5 splice site base pairs with a U1 snRNA that is tethered to RNA polymerase II during intron synthesis. Correlation with splicing outcomes demonstrate that these associations are functional. The interactions between 5 splice sites, U1 snRNP, and elongating RNA polymerase II occurs genome-wide. Our findings reveal that during intron synthesis the upstream 5 splice site remains attached to the transcriptional machinery and is thus brought into proximity of the 3 splice site to enable rapid splicing.

2021-06-16 | GSE144906 | GEO

Intron looping is mediated during transcription by U1 snRNP and RNA polymerase II [RIP-seq]

2021-06-16 | GSE144905 | GEO

Intron looping is mediated by U1 snRNP and RNA polymerase II co-transcriptionally [ChIP-seq]

2021-06-16 | GSE144874 | GEO

Selected humanization of yeast U1 snRNP leads to global suppression of pre-mRNA splicing and mitochondrial dysfunction in the budding yeast

Project description:The recognition of 5’ splice site (5’ ss) is one of the earliest steps of pre-mRNA splicing. To better understand the mechanism and regulation of 5’ ss recognition, we selectively humanized components of the yeast U1 snRNP to reveal the function of these components in 5’ ss recognition and splicing. We targeted U1C and Luc7, two proteins that interact with and stabilize the yeast U1 (yU1) snRNA and the 5’ ss RNA duplex. We replaced the Zinc-Finger (ZnF) domain of yU1C with its human counterpart, which resulted in cold-sensitive growth phenotype and moderate splicing defects. Next, we added an auxin-inducible degron to yLuc7 protein and found that Luc7-depleted yU1 snRNP resulted in the concomitant loss of PRP40 and Snu71 (two other essential yeast U1 snRNP proteins), and further biochemical analyses suggest a model of how these three proteins interact with each other in the U1 snRNP. The loss of these proteins resulted in a significant growth retardation accompanied by a global suppression of pre-mRNA splicing. The splicing suppression led to mitochondrial dysfunction as revealed by a release of Fe2+ into the growth medium and an induction of mitochondrial reactive oxygen species. Together, these observations indicate that the human U1C ZnF can substitute that of yeast, Luc7 is essential for the incorporation of the Luc7-Prp40-Snu71 trimer into yeast U1 snRNP, and splicing plays a major role in the regulation of mitochondria function in yeast.

2024-01-03 | GSE252348 | GEO

Transcriptome changes in splicing inhibited cells

Project description:In eukaryotes, U1 small nuclear ribonucleoprotein (snRNP) forms spliceosomes in equal stoichiometry with U2, U4, U5 and U6 snRNPs; however, its abundance in human far exceeds that of the other snRNPs. Here we used antisense morpholino oligonucleotide to U1 snRNA to achieve functional U1 snRNP knockdown in HeLa cells, and identified accumulated unspliced pre-mRNAs by genomic tiling microarrays. In addition to inhibiting splicing, U1 snRNP knockdown caused premature cleavage and polyadenylation in numerous pre-mRNAs at cryptic polyadenylation signals, frequently in introns near (<5 kilobases) the start of the transcript. This did not occur when splicing was inhibited with U2 snRNA antisense morpholino oligonucleotide or the U2-snRNP-inactivating drug spliceostatin A unless U1 antisense morpholino oligonucleotide was also included. We further show that U1 snRNA–pre-mRNA base pairing was required to suppress premature cleavage and polyadenylation from nearby cryptic polyadenylation signals located in introns. These findings reveal a critical splicing-independent function for U1 snRNP in protecting the transcriptome, which we propose explains its overabundance.

2010-09-29 | GSE24179 | GEO

Frac-Seq Analysis of ZFC3H1 Knockdown U2OS Cells

Project description:We have found that depletion of the zinc finger protein ZFC3H1 inhibits the nuclear retention of these RNAs. ZFC3H1 forms a complex with MTR4 and PABPN1 (the PolyAdenylation EXosome Targeting complex (Meola et al 2016, Ogami et al 2017) and likely recruits the nuclear exosome for RNA degradation. Recently, we found that depletion of U1-70K, one protein component of the U1 snRNP spliceosomal complex, inhibits nuclear retention of 5’SS motif containing RNAs. The U1 snRNP complex recognizes and binds to the 5’SS motif and in vitro studies showed that U1-70K directly interact with a similar 5’SS motif through U1 snRNA binding (Gunderson et al 1999). Interestingly, we found that U1 snRNP is involved in targeting 5’SS motif containing mRNAs to nuclear speckles shortly following RNA transcription. In contrast, ZFC3H1 is involved in nuclear speckle localization post-transcriptionally and actively retain RNAs in these structures. Together, our results suggest a model where U1 snRNP interacts with the RNA via the 5’SS motif and targets mature mRNAs to nuclear speckles. Specifically, it suggests that misprocessed RNAs can be targeted to speckles (or other nucleoplasmic foci) and that these foci serve as a platform to recruit the nuclear exosome via ZFC3H1. Our results highlight a splicing independent role of U1 snRNP and how mRNA nuclear export function in nuclear surveillance to prevent the translation of aberrant proteins.

2022-03-31 | GSE176144 | GEO

Prp4 Kinase Grants the License to Splice: Control of Weak Splice Sites during Spliceosome Activation

Project description:The genome of the fission yeast Schizosaccharomyces pombe encodes 17 kinases that are essential for cell growth. These include the cell-cycle regulator Cdc2, as well as several kinases that coordinate cell growth, polarity, and morphogenesis during the cell cycle. In this study, we further characterized another of these essential kinases, Prp4, and showed that the splicing of many introns is dependent on Prp4 kinase activity. For detailed characterization, we chose the genes res1 and ppk8, each of which contains one intron of typical size and position. Splicing of the res1 intron was dependent on Prp4 kinase activity, whereas splicing of the ppk8 intron was not. Extensive mutational analyses of the 5’ splice site of both genes revealed that proper transient interaction with the 5’ end of snRNA U1 governs the dependence of splicing on Prp4 kinase activity. Proper transient interaction between the branch sequence and snRNA U2 was also important. Therefore, the Prp4 kinase is required for recognition and efficient splicing of introns displaying weak exon1/5’ splice sites and weak branch sequences.

2015-12-01 | GSE75517 | GEO

The Evolutionarily Conserved AU-Dinucleotide at the 5’ End of U1 snRNA is Critical for the Biogenesis and Functionality of U1 snRNP

Project description:Splicing is initiated by a productive interaction of pre-mRNA and the U1 snRNP, which dictates the formation a short RNA duplex between the 5’ splice site of a pre-mRNA and the 5’ end of the U1 snRNA. A long-standing puzzle has been why the AU dincucleotide at the 5’-end of the U1 snRNA shows strict conservation, despite the absence of an apparent role in duplex formation. To explore this conundrum, we varied this AU dinucleotide into to all possible permutations and analyzed the resulting molecular, biochemical, and physiological consequences. This led to the findings that the AU dinucleotide governs the precision of transcription start site, the methylation status of the U1 snRNA 5’-cap, appropriate maturation of a functional U1 snRNP, and its subsequent utilization in the splicing pathway. Our data also provide an insight as to why the identity of the AU dinucleotide is strongly favored during evolution.

2018-02-22 | GSE97015 | GEO

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