Insights into snoRNA biogenesis and processing from PAR-CLIP of snoRNA core proteins and small RNA sequencing
ABSTRACT: Background: In recent years, a variety of small RNAs derived from other RNAs with well-known functions such as tRNAs and snoRNAs, have been identified. The functional relevance of these RNAs is largely unknown. To gain insight into the complexity of snoRNA processing and the functional relevance of snoRNA-derived small RNAs, we sequenced long and short RNAs, small RNAs that co-precipitate with the Argonaute 2 protein and RNA fragments obtained in photoreactive nucleotide-enhanced crosslinking and immunoprecipitation (PAR-CLIP) of core snoRNA-associated proteins. Results: Analysis of these data sets revealed that many loci in the human genome reproducibly give rise to C/D box-like snoRNAs, whose expression and evolutionary conservation are typically less pronounced relative to the snoRNAs that are currently catalogued. We further found that virtually all C/D box snoRNAs are specifically processed inside the regions of terminal complementarity, retaining in the mature form only 4-5 nucleotides upstream of the C box and 2-5 nucleotides downstream of the D box. Sequencing of the total and Argonaute 2-associated populations of small RNAs revealed that despite their cellular abundance, C/D box-derived small RNAs are not efficiently incorporated into the Ago2 protein. Conclusions: We conclude that the human genome encodes a large number of snoRNAs that are processed along the canonical pathway and expressed at relatively low levels. Generation of snoRNA-derived processing products with alternative, particularly miRNA-like, functions appears to be uncommon. PAR-CLIP profiling for snoRNP core proteins NOP56, NOP58, Fibrillarin, and Dyskerin in HEK293 cells. Small RNA profiling using RNA-seq in HEK293 and HeLa cells, small RNA profiling using IP-seq of Ago2 associated small RNAs.
Project description:The endoribonuclease Dicer is known for its central role in the biogenesis of eukaryotic small RNAs/microRNAs. Despite its importance, Dicer target transcripts have not been directly mapped. Here, we apply biochemical methods to human cells and C. elegans and identify thousands of Dicer binding sites. We find known and hundreds of novel miRNAs with high sensitivity and specificity. We also report structural RNAs, promoter RNAs, and mitochondrial transcripts as Dicer targets. Interestingly, most Dicer binding sites reside on mRNAs/lncRNAs and are not significantly processed into small RNAs. These passive sites typically harbor small, Dicer-bound hairpins within intact transcripts and generally stabilize target expression. We show that passive sites can sequester Dicer and reduce microRNA expression. mRNAs with passive sites were in human and worm significantly associated with processing-body/granule function. Together, we provide the first transcriptome-wide map of Dicer targets and suggest conserved binding modes and functions outside the miRNA pathway. PAR-CLIP basically as described previously (Hafner et al. 2010).
Project description:The paired-end next-generation sequencing of all small RNAs of less than 200 nucleotides in length from four different human cell lines (SKOV3ip1, MCF-7, BJ-Tielf, INOF) allowed us to determine the exact sequence(s) and variations of human box C/D snoRNAs (small nucleolar RNAs), revealing processing patterns of this class of molecules. Two distinct groups of box C/D snoRNAs were identified based on the position of their ends with respect to their characteristic boxes and the terminal base pairing potential. Short box C/D snoRNAs start sharply 4 or 5 nucleotides upstream of their box C and end 2 or 3 nucleotides downstream of their box D. In contrast, long box C/D snoRNAs start 5 or 6 nucleotides upstream of their box C and end 4 or 5 nucleotides downstream of their box D, increasing the likelihood of formation of a k-turn between their boxes C and D. Sequencing of SKOV3ip1 cells following the depletions of NOP58, a core box C/D snoRNA-binding protein and of RBFOX2, a splicing factor, shows that the short box C/D snoRNA forms are significantly more affected by the depletion of RBFOX2 while the long snoRNA forms, which display more canonical box C/D snoRNA features, are significantly more affected by the depletion of NOP58. Together the data suggest that box C/D snoRNAs are divided into at least two groups of RNA with distinct maturation and functional preferences. Small RNAs (<200 nucleotides) were isolated from different human cell lines that were either untreated or depleted of NOP58 or RBFOX2 using specific siRNAs. The resulting libraries were multiplexed and paired-end sequenced using Illumina HiSeq.
Project description:Small non-coding RNAs function in concert with Argonaute (Ago) proteins to regulate gene expression at the level of transcription, mRNA stability or translation. Ago proteins bind small RNAs and form the core of silencing complexes. Here we report the analysis of small RNAs associated with human Ago1 and Ago2 revealed by immunoprecipitation and deep sequencing. Among the reads we find small RNAs originating from the small nucleolar RNA (snoRNA) ACA45. Moreover, processing of ACA45 requires Dicer activity but is independent of Drosha/DGCR8. Using bio-informatic prediction algorithms and luciferase reporter assays, we uncover the mediator subunit CDC2L6 as one potential mRNA target of ACA45 small RNAs suggesting a role for ACA45 processing products in post-transcriptional gene silencing. We further identify a number of human snoRNAs with microRNA (miRNA)- like processing signatures. We have therefore identified a novel class of small RNAs in human cells that originate from snoRNAs and can function like miRNAs. Two samples examined. Small RNAs associated to human Argonaute 1 and human Argonaute 2
Project description:Dicer is a deeply conserved endoribonuclease with key functions in small RNA biogenesis. Here we employed PAR-CLIP/iPAR-CLIP to identify direct Dicer binding sites in the transcriptomes of human cells and human. We found hundreds of novel miRNAs and non-canonical Dicer substrates with high sensitivity. Small RNA production depended on structure of the binding site and is globally biased towards the 5' arm of hairpins. Unexpectedly, in both species Dicer bound numerous hairpins inside mRNAs without observable small RNA production. Our data revealed ~100 mRNAs of protein coding genes to be targeted in both human and worm. These mRNAs significantly overlapped with the RNAi pathway. We also, unexpectedly, found that mitochondrial transcripts are Dicer targets in both species. We demonstrate functional consequences of Dicer binding by perturbation analysis. Taken together,we provide the first genome-wide catalog of direct Dicer targets. Our results suggest widespread function outside of miRNA biogenesis. PAR-CLIP basically as described previously (Hafner et al. 2010).
Project description:To exert regulatory function, miRNAs guide Argonaute (AGO) proteins to partially complementary sites on target RNAs. Crosslinking and immunoprecipitation (“re state-of-the-art to map AGO binding sites, but assigning the targeting miRNA to these sites relies on bioinformatics predictions and is therefore indirect. To directly and unambiguously identify miRNA:target site interactions, we modified our CLIP methodology in C. elegans to experimentally ligate miRNAs to their target sites. Unexpectedly, ligation reactions also occurred in absence of the exogenous ligase. Our in vivo dataset and re-analysis of published mammalian AGO-CLIP data for miRNA-chimeras yielded >17,000 miRNA:target site interactions. Analysis of interactions and extensive experimental validation of chimera-discovered targets of viral miRNAs suggest that our strategy identifies canonical, non-canonical, and non-conserved miRNA interactions. Our data suggest that ~80% of miRNA:targets have perfect or partial seed complementarity. In summary, analysis of miRNA:target chimeras enables the systematic, context-specific, in vivo discovery of miRNA interactions. In vivo PAR-CLIP basically as described previously (Jungkamp et al. 2011) using GFP-tagged ALG-1 expressing worms in L3 stage. Worm lysate was treated with RNase T1. Following immunoprecipitation and a second RNase T1 digest, it was proceeded as described in Hafner et al. 2010. For the modified iPAR-CLIP ligation samples and its control samples immuno-purified complexes were treated with PNK phospathase minus, subjected to ligation with T4 RNA ligase/no ligase added and subsequently phosphorylated with PNK. Protein purification and RNA library preparation essentially as described in Hafner et al., but with the selection of longer RNA products.
Project description:We developed a method for measuring non-specific background in PAR-CLIP data demonstrating that covalently crosslinked background binding is common, reproducible and apparently universal. Furthermore, we show that quantitative determination of background is essential for identifying targets of weakly binding RNA-binding proteins and can substantially improve motif analysis. To define background binding events in PAR-CLIP data we performed the standard PAR-CLIP protocol (Hafner et al., Cell 2010.) on lysates expressing a commonly used non-RBP control, FLAG-GFP. After FLAG-tag immunopurification of UV 365nm irradiated lysates prepared from cells supplemented with 4-thiouridine (4SU), RNA was partially digested with RNase T1, radiolabeled and separated by SDS-PAGE. Reads were sequenced by Illumina HiSeq. PAR-CLIP was also performed for HuR. Included as well is a total from lysates treated like PAR-CLIP, but without immunoprecipitation (see sample description for more detail).
Project description:Box C/D-type small nucleolar RNAs (snoRNAs) are functional RNAs responsible for mediating 2’-O-ribose methylation of ribosomal RNAs (rRNAs) within the nucleolus. Previously, in relation to a novel chromosomal translocation in a human B-cell lymphoma, we identified U50HG, a non-protein-coding gene that hosted a box C/D-type U50 snoRNA within its intron. To investigate the physiological importance of the U50 snoRNA and its involvement in tumorigenesis, we generated a mouse model deficient in mouse U50 (mU50) snoRNA expression without altering the expression of mouse mU50 host-gene, mU50HG-b. The established mU50 snoRNA-deficient mice showed a significant reduction of mU50 snoRNA expression and the corresponding target rRNA methylation in various organs. Lifelong phenotypic monitoring showed that the mU50-deficient mice looked almost normal without accelerated tumorigenicity; however, a notable difference was the propensity for anomalies in the lymphoid organs. B-cells were isolated from spleens of DmU50(HG-b) mice or wild-type C57BL/6J with antibody-conjugated magnetic beads system (Myltenyi Biotec). Total RNA was purified with QIAGEN RNeasy Micro kit. Affymetrix GeneChip® Microarrays (Mouse Expression 430 2.0 Array) were used.
Project description:Leukemogenesis requires enhanced self-renewal activity, which is induced by specific oncogenes. The underlying molecular mechanisms remain incompletely understood. We transduced mouse lineage negative bone marrow cells (enriched for hematopoietic stem and progenitor cells) with retrovirus expressing leukemic oncogene AML1-ETO9a, MYC and MLL-AF9 as well as empty vector (MIG). We found that all three oncogenes enhanced snoRNA formation. High abundance of snoRNAs was observed in primary human AML specimens with the notable exception of NPM1 mutant AML. Leukemogenesis by AML1-ETO required expression of the groucho related Amino Enhancer of Split (AES). AES functioned by inducing snoRNA/RNP formation via interaction with the RNA helicase DDX21. Similarly, loss of C/D box snoRNAs with concomitant loss of rRNA 2’-O-methylation resulted in decreased leukemia self-renewal potential.In summary, we identified C/D box snoRNAs and rRNA 2’-O-methylation as critical determinants of leukemic stem cell activity. Overall design: We used small RNA-Seq to determine the expression profile of small nucleolar RNA (snoRNA) in 63 primary AML patient samples. To further investigate the role of AES and DDX21 in snoRNA formation we also analyzed kasumi-1 cell lines with shRNA based downregulation of AES or DDX21. Furthermore, we show that mouse snoRNAs are induced by leukemia oncogene AML-ETO9a, MLL-AF9 and MYC in mouse lineage negative bone marrow cells.
Project description:The conserved human LIN28 RNA-binding proteins function in development, maintenance of pluripotency and oncogenesis. We used PAR-CLIP and a newly developed variant of this method, iDo-PAR-CLIP, to identify LIN28B targets as well as sites bound by the individual RNA binding domains of LIN28B in the human transcriptome at nucleotide resolution. The position of target binding sites reflected the known structural relative orientation of individual LIN28B binding domains, validating iDo-PAR-CLIP. Our data suggest that LIN28B directly interacts with most expressed mRNAs and members of the let-7 microRNA family. The Lin28 binding motif detected in pre-let-7 was enriched in mRNA sequences bound by LIN28B. Upon LIN28B knock down, cell proliferation and the cell cycle were strongly impaired. Quantitative shotgun proteomics of LIN28B depleted cells revealed significant reduction of protein synthesis from its RNA targets that function in translation, mRNA splicing and cell cycle control. Computational analyses provided evidence that the strength of protein synthesis reduction correlated with the location of LIN28B binding sites within target transcripts. We used PAR-CLIP and a newly developed variant of this method, iDo-PAR-CLIP, to identify LIN28B targets as well as sites bound by the individual RNA binding domains of LIN28B in the human transcriptome at nucleotide resolution.
Project description:Small nucleolar RNAs (snoRNAs) dysfunction have been associated with cancer development. We investigated the function of an orphan C/D box class snoRNA, SNORD126, in hepatocellular carcinoma (HCC) and colorectal cancer (CRC) cells We used microarrays to identify targets with roles in SNORD126’s activity in Huh-7 cells SNORD126- or EGFP-overexpressed Huh-7 cells were collected and followed by RNA extraction, then hybridized with Affymetrix microarrays. We sought to obtain the differentially expressed genes between the two groups.