Project description:Regulation of microRNA (miR) biogenesis is complex and stringently controlled. Here we identify the kinase GSK3B as an important modulator of global miR biogenesis at microprocessor level. Repression of GSK3B activity reduces Drosha activity towards pri-miRs, leading to accumulation of unprocessed pri-miRs and reduction of pre-miRs and mature miRs without altering levels or cellular localisationof miR biogenesisproteins. Conversly, GSK3B activation increases Drosha activityand mature miR accumulation. GSK3B achieves this through promoting Drosha:cofactor and Drosha:pri-miR interactions: it binds to DGCR8 and p72 in the Microprocessor, an effect dependent of RNA. Indeed GSK3B itself can immunoprecipitate pri-miRs, suggesting possible RNA binding capacity. Kinase assays identify the mechanism for GSK3B-enhansed Drosha activity, which requires GSK3B nuclear localisation, as phosphorylation of Drosha at s300 and/or s302 confirmed by enhanced Drosha activity and association with cofactors, and increased abundance of mature microRNAs in the presence of phospho-mimetic Drosha. Functional implicatons of GSK3B-enhanced miR biogenesis are illustrated by increased levels of GSK3B-upregulatd miR targets following GSK3B inhibition. These data, the first link GSK3B with the miR cascade in humans, hilight a novel pro-biogenesis role for GSK3B in increasing miR biogenesis as a component of the Microprocessor complex with wide ranging consiquences.
Project description:The Microprocessor plays an essential role in canonical miRNA biogenesis by facilitating cleavage of stem-loop structures in primary transcripts to yield pre-miRNAs. Although miRNA biogenesis has been extensively studied through biochemical and molecular genetic approaches, it has yet to be addressed to what extent the current miRNA biogenesis models hold true in intact cells. To address the issues of in vivo recognition and cleavage by the Microprocessor, we investigate RNAs that are associated with DGCR8 and Drosha by using immunoprecipitation coupled with next-generation sequencing. Here, we present global protein-RNA interactions with unprecedented sensitivity and specificity. Our data indicate that precursors of canonical miRNAs and miRNA-like hairpins are the major substrates of the Microprocessor. As a result of specific enrichment of nascent cleavage products, we are able to pinpoint the Microprocessor-mediated cleavage sites per se at single-nucleotide resolution. Unexpectedly, a 2-nt 3M-bM-^@M-^Y overhang invariably exists at the ends of cleaved bases instead of nascent pre-miRNAs. Besides canonical miRNA precursors, we find that two novel miRNA-like structures embedded in mRNAs are cleaved to yield pre-miRNA-like hairpins, uncoupled from miRNA maturation. Our data provide a framework for in vivo Microprocessor-mediated cleavage and a foundation for experimental and computational studies on miRNA biogenesis in living cells. CLIP-seq for DGCR8 and Drosha, RIP-seq for DGCR8, sequencing of AGO2-assocated miRNA
Project description:The Drosha-DGCR8 complex (Microprocessor) is required for microRNA (miRNA) biogenesis. DGCR8 contains two double-stranded RNA binding motifs that recognize the RNA substrate, whereas Drosha functions as the endonuclease. We have used high-throughput sequencing of RNAs isolated by crosslinking immunoprecipitation (HITS-CLIP) to identify endogenous RNA targets of DGCR8 in mammalian cells. Unexpectedly, miRNAs were not the most abundant targets. DGCR8-bound RNAs comprised several hundred mRNAs as well as snoRNAs and long non-coding RNAs. We found that DGCR8 together with Drosha controls the abundance of several mRNAs, as well as long non-coding RNAs, such as MALAT-1. By contrast, the DGCR8-mediated cleavage of snoRNAs is independent of Drosha, suggesting the involvement of DGCR8 in cellular complexes with other endonucleases. Interestingly, binding of DGCR8 to cassette exons, acts as a novel mechanism to regulate the relative abundance of alternatively spliced isoforms. Collectively, these data provide new insights in the complex role of DGCR8 in controlling the fate of several classes of RNAs. Comparison of RNAs associated to both endogenous (D8) and overexpressed (T7) DGCR8 in HEK293T cells
Project description:The human Microprocessor complex cleaves primary microRNA (miRNA) transcripts (pri-miRNAs) to initiate miRNA synthesis. Microprocessor consists of DROSHA (an RNase III enzyme), and DGCR8. DROSHA has two conserved RNase III domains, which make double cuts on each of pri-miRNA strands. In this study, we show that Microprocessor has an unexpected single-cut activity, which creates a single cut on just one of the pri-miRNA strands using one of the two RNase III domains of DROSHA. This cleavage does not lead to the production of miRNA but instead it downregulates miRNA expression. We also demonstrate that certain RNA elements facilitate the single-cut activity of Microprocessor, and by manipulating these elements, we can regulate the ratio of single-cut to double-cut activities, thus controlling miRNA production both in vitro and in vivo.
Project description:Using a protein interaction screen, we identify the Microprocessor component Drosha as a novel Dnmt1-interactor. Drosha-deficient ES cells display genomic hypomethylation which is not accounted for by changes in the levels of Dnmt proteins. Both genetic and transfection studies show that Drosha stimulates Dnmt1 methyltransferase activity. We identify two transcripts that are specifically upregulated in Drosha but not Dicer-deficient ES cells. Regions within these transcripts predicted to form stem-loop structures are processed by Microprocessor and can inhibit DNMT1-mediated methylation in vitro. Our results highlight Drosha as a novel regulator of mammalian DNA methylation and we propose that Drosha-mediated processing of RNA is necessary to ensure full Dnmt1 activity. This adds to the Drosha repertoire of non-miRNA dependent functions as well as implicating RNA in regulating Dnmt1 activity and correct levels of genomic methylation.
Project description:The Drosha-DGCR8 complex (Microprocessor) is required for microRNA (miRNA) biogenesis. DGCR8 contains two double-stranded RNA binding motifs that recognize the RNA substrate, whereas Drosha functions as the endonuclease. We have used high-throughput sequencing of RNAs isolated by crosslinking immunoprecipitation (HITS-CLIP) to identify endogenous RNA targets of DGCR8 in mammalian cells. Unexpectedly, miRNAs were not the most abundant targets. DGCR8-bound RNAs comprised several hundred mRNAs as well as snoRNAs and long non-coding RNAs. We found that DGCR8 together with Drosha controls the abundance of several mRNAs, as well as long non-coding RNAs, such as MALAT-1. By contrast, the DGCR8-mediated cleavage of snoRNAs is independent of Drosha, suggesting the involvement of DGCR8 in cellular complexes with other endonucleases. Interestingly, binding of DGCR8 to cassette exons, acts as a novel mechanism to regulate the relative abundance of alternatively spliced isoforms. Collectively, these data provide new insights in the complex role of DGCR8 in controlling the fate of several classes of RNAs.
Project description:Neural stem cell regulation is essential for the formation of the central nervous system and homeostatic neurogenesis in the adult mammalian brain. The RNAseIII Drosha, a key component of the miRNA microprocessor, plays a central role in regulating NSC maintenance partially through a miRNA-independent mechanism. Drosha controls mRNA expression levels by targeting and cleaving evolutionary conserved stem-loop hairpins located in the mRNAs of stem cell-related transcription factors. However, it is unknown how the Drosha-mediated endonucleolytic cleavage of mRNA is regulated. Here, we identify novel Drosha and NFIB interactors in hippocampal NSCs by in vitro pull-down assays followed by Mass Spectrometry. We unravel the RNA binding proteins implicated in Drosha-mediated regulation of neurogenesis and we find Scaffold Attachment Factor B1 to play a novel and essential role in NFIB mRNA regulation during neural stem cell differentiation.
Project description:The Microprocessor plays an essential role in canonical miRNA biogenesis by facilitating cleavage of stem-loop structures in primary transcripts to yield pre-miRNAs. Although miRNA biogenesis has been extensively studied through biochemical and molecular genetic approaches, it has yet to be addressed to what extent the current miRNA biogenesis models hold true in intact cells. To address the issues of in vivo recognition and cleavage by the Microprocessor, we investigate RNAs that are associated with DGCR8 and Drosha by using immunoprecipitation coupled with next-generation sequencing. Here, we present global protein-RNA interactions with unprecedented sensitivity and specificity. Our data indicate that precursors of canonical miRNAs and miRNA-like hairpins are the major substrates of the Microprocessor. As a result of specific enrichment of nascent cleavage products, we are able to pinpoint the Microprocessor-mediated cleavage sites per se at single-nucleotide resolution. Unexpectedly, a 2-nt 3’ overhang invariably exists at the ends of cleaved bases instead of nascent pre-miRNAs. Besides canonical miRNA precursors, we find that two novel miRNA-like structures embedded in mRNAs are cleaved to yield pre-miRNA-like hairpins, uncoupled from miRNA maturation. Our data provide a framework for in vivo Microprocessor-mediated cleavage and a foundation for experimental and computational studies on miRNA biogenesis in living cells.
Project description:The Microprocessor complex (DGCR8/Drosha) is required for microRNA (miRNA) biogenesis but also binds and regulates the stability of several types of cellular RNAs. Of particular interest, DGCR8 controls the stability of mature small nucleolar RNA (snoRNA) transcripts independently of Drosha, suggesting the existence of alternative DGCR8 complex/es with other nucleases to process a variety of cellular RNAs. Here, we found that DGCR8 co-purifies with subunits of the nuclear exosome, preferentially associating with its hRRP6-containing nucleolar form. Importantly, we demonstrate that DGCR8 is essential for the recruitment of the exosome to snoRNAs and to human telomerase RNA. In addition, we show that the DGCR8/exosome complex controls the stability of the human telomerase RNA component (hTR/TERC). Altogether, these data suggests that DGCR8 acts as a novel adaptor to recruit the exosome complex to structured RNAs and induce their degradation.
Project description:The Microprocessor, composed of Drosha and Pasha/DGCR8, is necessary for the biogenesis of canonical microRNAs (miRNAs), and required for animal embryogenesis. However, the cause for this requirement is largely unknown. The Microprocessor may be required to produce one or few essential miRNAs, or alternatively, many individually non-essential miRNAs. Additionally, Drosha and Pasha/DGCR8 may be required for processing non-miRNA substrates. To distinguish between these possibilities, we developed a system in C. elegans to stringently deplete embryos from the Microprocessor and miRNAs. We show that the early embryonic arrest upon loss of the Microprocessor is rescued by the addition of two individual miRNAs from the miR-35 and miR-51 families, resulting in morphologically normal larvae. Thus, just two canonical miRNAs are sufficient for morphogenesis and organogenesis in C. elegans, and indicate that miRNA processing explains the essential requirement for the Microprocessor during embryogenesis.