Conserved regulation of ZC3H14/Nab2 in circRNA biogenesis
ABSTRACT: Circular RNAs (circRNAs) are natural outputs of eukaryotic transcription and RNA processing and have emerged as critical regulators in physiology and human diseases. Although a series of cis-elements and trans-factors are reported to globally regulate circRNA biogenesis, most of these regulations are unconserved or at most mammalian conserved. Here, using a genome-wide CRISPR knockout screen, we have identified an evolutionarily conserved polyadenosine RNA-binding protein ZC3H14 to regulate circRNA biogenesis in eukaryotes. Mechanistically, ZC3H14 associates with spliceosome to bind to 3' and 5' exon-intron boundaries of circularized exons, and forms a dimer to promote circRNA biogenesis. Zc3h14-/- mice exhibit disrupted spermatogenesis and reduced testicular circRNA levels. Additionally, human ZC3H14 is associated with male infertility. Our findings reveal a conserved requirement for ZC3H14/Nab2 in the modulation of eukaryotic backsplicing and link ZC3H14 along with circRNAs to mammalian testicular disorders.
ORGANISM(S): Mus musculus Schizosaccharomyces pombe Homo sapiens
Project description:Circular RNAs (circRNAs) are a large class of animal RNAs. To investigate possible circRNA functions, it is important to understand circRNA biogenesis. Besides human Alu repeats, sequence features that promote exon circularization are largely unknown. We experimentally identified new circRNAs in C. elegans. Reverse complementary sequences between introns bracketing circRNAs were significantly enriched compared to linear controls. By scoring the presence of reverse complementary sequences in human introns we predicted and experimentally validated novel circRNAs. We show that introns bracketing circRNAs are highly enriched in RNA editing or hyper-editing events. Knockdown of the double-strand RNA editing ADAR1 enzyme significantly and specifically up-regulated circRNA expression. Together, our data support a model of animal circRNA biogenesis in which competing RNA:RNA interactions of introns form larger structures which promote circularization of embedded exons, while ADAR1 antagonizes circRNA expression by melting stems within these interactions. Thus, we assign a new function to ADAR1. Examination of 12 samples in different stages of C.elegans development.
Project description:Circular RNAs (circRNAs) are found across eukaryotes and can function in post-transcriptional gene regulation. Their biogenesis through a circle-forming backsplicing reaction is facilitated by reverse-complementary repetitive sequences promoting pre-mRNA folding. Orthologous genes from which circRNAs arise overall, contain more strongly conserved splice sites and exons than other genes, yet it remains unclear to what extent this conservation reflects purifying selection acting on the circRNAs themselves. Our analyses of circRNA repertoires across five species representing three mammalian lineages (marsupials, eutherians: rodents, primates) reveal that surprisingly few circRNAs arise from orthologous genes from different species. Even the circRNAs from shared loci are associated with young, recently active and species-specific transposable elements, rather than with common, ancient transposon integration events. These observations suggest that many circRNAs emerged convergently during evolution – as a byproduct of splicing in orthologs prone to transposable element insertion. Overall, our findings argue against widespread functional circRNA conservation.
Project description:Circular RNAs (circRNAs) are an endogenous class of animal RNAs. Despite their abundance, their function and expression in the nervous system are unknown. Therefore, we sequenced RNA from different brain regions, primary neurons, isolated synapses, as well as during neuronal differentiation. Using these and other available data, we discovered and analyzed thousands of neuronal human and mouse circRNAs. circRNAs were extraordinarily enriched in the mammalian brain, well conserved in sequence, often expressed as circRNAs in both human and mouse, and sometimes even detected in Drosophila brains. circRNAs were overall upregulated during neuronal differentiation, highly enriched in synapses, and often differentially expressed compared to their mRNA isoforms. circRNA expression correlated negatively with expression of the RNA-editing enzyme ADAR1. Knockdown of ADAR1 induced elevated circRNA expression. Together, we provide a circRNA brain expression atlas and evidence for important circRNA functions and values as biomarkers. To assess circRNA expression in mammalian brain, we sequenced and analyzed mouse brain regions (hippocampus, cerebellum, prefrontal cortex and olfactory bulb), various neuronal differentiation (mouse P19 and human SH-SY5Y cells) and maturation (mouse cortical neurons) stages, and subcellular compartments in mouse (synaptoneurosomal fraction, cytoplasmic fraction, whole brain lysate).
Project description:Nab2 encodes a polyadenosine RNA-binding protein (RBP) with broad roles in post-transcriptional regulation, including in RNA export, poly(A) tail length control, and mRNA splicing, and loss of its human ortholog ZC3H14 gives rise to a form of autosomal recessive intellectual disability. Understanding of Nab2/ZC3H14 function in metazoan nervous systems is limited, in part, because no comprehensive identification of metazoan-Nab2-associated RNA transcripts has yet been conducted. Moreover, many Nab2/ZC3H14 functional protein partnerships likely remain unidentified. Here we present evidence that Drosophila melanogaster Nab2 interacts with the RBP Ataxin-2 (Atx2), a neuronal translational regulator, and implicate these proteins in coordinate regulation of neuronal morphology and adult viability. We then present the first high-throughput identifications of RNAs associating with Nab2 and Atx2 in Drosophila brain neurons using an RNA immunoprecipitation-sequencing (RIP-Seq) approach. Critically, the RNA interactomes of each RBP overlap. The identities of shared associated transcripts (e.g. drk, me31B, stai) and of transcripts specific to Nab2 or Atx2 (e.g. Arpc2, tea, respectively) promise insight into the neuronal functions of and interactions between each RBP. Significantly, we find Nab2 exhibits high specificity in its RNA associations in neurons in vivo, associating with only a fraction of all polyadenylated RNAs. These Nab2-associated RNAs are overrepresented for internal A-rich motifs, suggesting such sequences may partially mediate Nab2 target selection. Taken together, these data demonstrate 1)Nab2 opposingly regulates neuronal morphology and shares associated neuronal RNAs with Atx2 and 2)Drosophila Nab2 associates with a more specific subset of polyadenylated mRNAs than its polyadenosine affinity alone may suggest.
Project description:Circular RNAs (circRNAs) are broadly expressed in eukaryotic cells, but their role in human health and disease remains obscure. Here, we show that circular antisense non-coding RNA in the INK4 locus (circANRIL), which is transcribed at a locus of atherosclerotic cardiovascular disease on chromosome 9p21, confers athero-protection by controlling ribosomal RNA (rRNA) maturation and modulating pathways of atherogenesis. At the molecular level, circANRIL competes with precursor rRNA (pre-rRNA) for binding to pescadillo homolog 1 (PES1), an essential 60S-preribosomal assembly factor, thereby impairing exonuclease-mediated pre-rRNA processing and ribosome biogenesis. As a consequence, circANRIL induces nucleolar stress and p53 activation, resulting in the induction of apoptosis and inhibition of proliferation, which are key athero-protective cell functions within the arterial wall. Collectively, these findings identify circANRIL as a prototype of a circRNA regulating ribosome biogenesis and conferring athero-protection, thereby unveiling a therapeutic potential of certain circRNAs in human disease. Analysis of transcriptome-wide expression level in HEK293 cells with stable overexpression of circular ANRIL (n=3) compared to a vector control (n=3).
Project description:The polyadenosine RNA binding proteins (Pabs) represent one class of RNA binding proteins that play critical roles in gene expression. This class includes the well-studied nuclear and cytoplasmic Pabs, PABPN1 and PABPC1, respectively, as well as the newly characterized nuclear Pab, zinc finger CCCH-type containing #14, or ZC3H14. ZC3H14 was recently linked to a form of intellectual disability, suggesting a critical role for ZC3H14 in neurons; however, the post-transcriptional function of ZC3H14 is unknown. In this study, we performed a microarray analysis of cells depleted of ZC3H14 or PABPN1 in MCF-7 breast cancer cells. These results revealed that PABPN1 significantly affected ~17% of expressed transcripts as compared to ZC3H14, which affected ~1% of expressed transcripts, suggesting that ZC3H14 has specific mRNA targets. The differentially expressed mRNAs identified in this analysis not only provide information about the classes and types of transcripts that are regulated by these proteins, but also represent a set of transcripts that could be directly bound by ZC3H14 and/or PABPN1. Total RNA isolated from MCF-7 cells treated for 48 hours with siRNA targeting PABPN1, ZC3H14 (all splice variants), or a control scramble siRNA.
Project description:Circular RNAs (circRNAs) constitute an abundant class of covalently closed non-coding RNA molecules that are formed by backsplicing from eukaryotic protein-coding genes. Recent studies have shown that circRNAs can act as microRNA or protein decoys as well as transcriptional regulators. However, the functions of most circRNAs are still poorly understood. Because circRNA sequences overlap with their linear parent transcripts, depleting specific circRNAs without affecting host gene expression remains a challenge. Here, we assessed the utility of LNA-modified antisense oligonucleotides (ASOs) to knock down circRNAs for loss-of-function studies. We identified 5807 circRNAs in total RNA sequencing data from 4 liver cancer cell lines and used the back splice junction (BSJ) sequences of 7 validated circRNAs as target sites for designing different LNA-modified ASOs for circRNA knockdown. We found that while most RNase H-dependent gapmer ASOs mediate effective knockdown of their target circRNAs, some gapmers reduce the levels of the linear parent transcript and may also cause degradation of unintended off-targets. The circRNA targeting specificity can be enhanced using design-optimized gapmer ASOs or LNA/DNA mixmer ASOs, which display potent and specific circRNA knockdown with a minimal effect on the host genes or predicted off-targets. In summary, our results demonstrate that LNA-modified ASOs complementary to BSJ sequences mediate robust knockdown of circRNAs in vitro and, thus, represent a useful tool to explore the biological roles of circRNAs in loss-of-function studies in cultured cells and animal models.
Project description:Circular RNAs (circRNAs) represent an abundant and conserved entity of non-coding RNAs, however the principles of biogenesis are currently not fully understood. To elucidate features important for circRNA production, we performed global analyses of RNA-binding proteins associating with the flanking introns of circRNAs, and we identified two factors, SFPQ and NONO, to be highly enriched with circRNAs. We observe a subclass of circRNAs, coined DALI circRNAs, with distal inverted Alu elements and long introns to be highly deregulated upon SFPQ knockdown. Moreover, SFPQ depletion leads to increased intron retention with concomitant induction of cryptic splicing prevalent for long introns causing in some cases premature transcription termination and polyadenylation. Aberrant splicing in the upstream and downstream regions of circRNA producing exons are critical for shaping the circRNAome, and specifically, we identify a conserved impact of missplicing in the immediate upstream region to drive circRNA biogenesis. Collectively, our data show that SFPQ plays an important role in maintaining intron integrity by ensuring accurate splicing of long introns, and disclose novel features governing Alu-independent circRNA production.
Project description:Circular RNAs (circRNAs) are single-stranded RNAs that are joined head to tail. Initially discovered as pathogen genomes such as hepatitis D virus (HDV) and plant viroids, circRNAs are recently recognized as a pervasive class of noncoding RNAs in eukaryotic cells, generated through back splicing. circRNAs have been postulated to function in cell-to-cell information transfer or memory due to their extraordinary stability. Whether and how circRNAs trigger immune recognition is not known. Here we show that exogenous circular RNAs potently stimulate immune signaling, and mammalian cells sense self vs. nonself circRNAs via circRNA biogenesis. Transfection of purified in vitro spliced circRNA into mammalian cells led to potent induction of innate immunity genes. The nucleic acid sensor RIG-I is necessary and sufficient to sense foreign circRNA, and RIG-I and foreign circRNA co-aggregate in cytoplasmic foci. CircRNA activation of innate immunity is independent of 5’ triphosphate, double-stranded RNA structure, or primary sequence of the foreign circRNA. Instead, self-nonself discrimination depends on the intron that programs the circRNA. Use of a human intron to express a foreign circRNA sequence abrogates immune activation, and the mature human circRNA is associated with diverse RNA binding proteins reflecting its endogenous splicing and biogenesis. These results reveal innate immune sensing of circRNA, a prevalent class of host and pathogen RNAs, and highlight introns—the predominant output of mammalian transcription—as unexpected arbiters of self-nonself identity in the RNA world.