The Y3** ncRNA promotes the 3' end processing of histone mRNAs

Intracellular localisation and extracellular release of Y RNA and Y RNA binding proteins

Cells can communicate via the release and uptake of extracellular vesicles (EVs), which are nano-sized membrane vesicles that can transfer protein and RNA cargo between cells. EVs contain microRNAs and various other types of non-coding RNA, of which Y RNA is among the most abundant types. Studies on how RNAs and their binding proteins are sorted into EVs have mainly focused on comparing intracellular (cytoplasmic) levels of these RNAs to the extracellular levels in EVs. Besides overall transcriptional levels that may regulate sorting of RNAs into EVs, the process may also be driven by local intracellular changes in RNA/RBP concentrations. Changes in extracellular Y RNA have been linked to cancer and cardiovascular diseases. Although the loading of RNA cargo into EVs is generally thought to be influenced by cellular stimuli and regulated by RNA binding proteins (RBP), little is known about Y RNA shuttling into EVs. We previously reported that immune stimulation alters the levels of Y RNA in EVs independently of cytosolic Y RNA levels. This suggests that Y RNA binding proteins, and/or changes in the local Y RNA concentration at EV biogenesis sites, may affect Y RNA incorporation into EVs. Here, we investigated the subcellular distribution of Y RNA and Y RNA binding proteins in activated and non-activated THP1 macrophages. We demonstrate that Y RNA and its main binding protein Ro60 abundantly co-fractionate in organelles involved in EV biogenesis and in EVs. Cellular activation led to an increase in Y RNA concentration at EV biogenesis sites and this correlated with increased EV-associated levels of Y RNA and Ro60. These results suggest that Y RNA incorporation into EVs may be controlled by local intracellular changes in the concentration of Y RNA and their protein binding partners.

RNY3 modulates cell proliferation and IL13 mRNA levels in a T lymphocyte model: a possible new epigenetic mechanism of IL-13 regulation

Allergic asthma is the most common type of asthma. It is characterized by T_H2 cell-driven inflammation in which interleukin-13 (IL-13) plays a pivotal role. Cytoplasmic RNAs (Y-RNAs), a variety of non-coding RNAs that are dysregulated in many cancer types, are also differentially expressed in patients with allergic asthma. Their function in the development of the disease is still unknown. We investigated the potential role of RNY3 RNA (hY3) in the T_H2 cell inflammatory response using the Jurkat cell line as a model. hY3 expression levels were modulated to mimic the upregulation effect in allergic disease. We evaluated the effect of hY3 over cell stimulation and the expression of the T_H2 cytokine IL13. Total RNA was isolated and retrotranscribed, and RNA levels were assessed by qPCR. In Jurkat cells, hY3 levels increased upon stimulation with phorbol 12-myristate 13-acetate (PMA) and ionomycin. When transfecting with high levels of hY3 mimic molecules, cell proliferation rate decreased while IL13 mRNA levels increased upon stimulation compared to stimulated control cells. Our results show the effect of increased hY3 levels on cell proliferation and the levels of IL13 mRNA in Jurkat cells. Also, we showed that hY3 could act over other cells via exosomes. This study opens up new ways to study the potential regulatory function of hY3 over IL-13 production and its implications for asthma development.

53BP1-ACLY-SLBP-coordinated activation of replication-dependent histone biogenesis maintains genomic integrity

p53-binding protein 1 (53BP1) regulates the DNA double-strand break (DSB) repair pathway and maintains genomic integrity. Here we found that 53BP1 functions as a molecular scaffold for the nucleoside diphosphate kinase-mediated phosphorylation of ATP-citrate lyase (ACLY) which enhances the ACLY activity. This functional association is critical for promoting global histone acetylation and subsequent transcriptome-wide alterations in gene expression. Specifically, expression of a replication-dependent histone biogenesis factor, stem-loop binding protein (SLBP), is dependent upon 53BP1-ACLY-controlled acetylation at the SLBP promoter. This chain of regulation events carried out by 53BP1, ACLY, and SLBP is crucial for both quantitative and qualitative histone biogenesis as well as for the preservation of genomic integrity. Collectively, our findings reveal a previously unknown role for 53BP1 in coordinating replication-dependent histone biogenesis and highlight a DNA repair-independent function in the maintenance of genomic stability through a regulatory network that includes ACLY and SLBP.

Hidden Role of Gut Microbiome Dysbiosis in Schizophrenia: Antipsychotics or Psychobiotics as Therapeutics?

Schizophrenia is a chronic, heterogeneous neurodevelopmental disorder that has complex symptoms and uncertain etiology. Mounting evidence indicates the involvement of genetics and epigenetic disturbances, alteration in gut microbiome, immune system abnormalities, and environmental influence in the disease, but a single root cause and mechanism involved has yet to be conclusively determined. Consequently, the identification of diagnostic markers and the development of psychotic drugs for the treatment of schizophrenia faces a high failure rate. This article surveys the etiology of schizophrenia with a particular focus on gut microbiota regulation and the microbial signaling system that correlates with the brain through the vagus nerve, enteric nervous system, immune system, and production of postbiotics. Gut microbially produced molecules may lay the groundwork for further investigations into the role of gut microbiota dysbiosis and the pathophysiology of schizophrenia. Current treatment of schizophrenia is limited to psychotherapy and antipsychotic drugs that have significant side effects. Therefore, alternative therapeutic options merit exploration. The use of psychobiotics alone or in combination with antipsychotics may promote the development of novel therapeutic strategies. In view of the individual gut microbiome structure and personalized response to antipsychotic drugs, a tailored and targeted manipulation of gut microbial diversity naturally by novel prebiotics (non-digestible fiber) may be a successful alternative therapeutic for the treatment of schizophrenia patients.

Hidden Role of Gut Microbiome Dysbiosis in Schizophrenia: Antipsychotics or Psychobiotics as Therapeutics?

Schizophrenia is a chronic, heterogeneous neurodevelopmental disorder that has complex symptoms and uncertain etiology. Mounting evidence indicates the involvement of genetics and epigenetic disturbances, alteration in gut microbiome, immune system abnormalities, and environmental influence in the disease, but a single root cause and mechanism involved has yet to be conclusively determined. Consequently, the identification of diagnostic markers and the development of psychotic drugs for the treatment of schizophrenia faces a high failure rate. This article surveys the etiology of schizophrenia with a particular focus on gut microbiota regulation and the microbial signaling system that correlates with the brain through the vagus nerve, enteric nervous system, immune system, and production of postbiotics. Gut microbially produced molecules may lay the groundwork for further investigations into the role of gut microbiota dysbiosis and the pathophysiology of schizophrenia. Current treatment of schizophrenia is limited to psychotherapy and antipsychotic drugs that have significant side effects. Therefore, alternative therapeutic options merit exploration. The use of psychobiotics alone or in combination with antipsychotics may promote the development of novel therapeutic strategies. In view of the individual gut microbiome structure and personalized response to antipsychotic drugs, a tailored and targeted manipulation of gut microbial diversity naturally by novel prebiotics (non-digestible fiber) may be a successful alternative therapeutic for the treatment of schizophrenia patients.

RNAs as Regulators of Cellular Matchmaking

RNA molecules are increasingly being identified as facilitating or impeding the interaction of proteins and nucleic acids, serving as so-called scaffolds or decoys. Long non-coding RNAs have been commonly implicated in such roles, particularly in the regulation of nuclear processes including chromosome topology, regulation of chromatin state and gene transcription, and assembly of nuclear biomolecular condensates such as paraspeckles. Recently, an increased awareness of cytoplasmic RNA scaffolds and decoys has begun to emerge, including the identification of non-coding regions of mRNAs that can also function in a scaffold-like manner to regulate interactions of nascently translated proteins. Collectively, cytoplasmic RNA scaffolds and decoys are now implicated in processes such as mRNA translation, decay, protein localization, protein degradation and assembly of cytoplasmic biomolecular condensates such as P-bodies. Here, we review examples of RNA scaffolds and decoys in both the nucleus and cytoplasm, illustrating common themes, the suitability of RNA to such roles, and future challenges in identifying and better understanding RNA scaffolding and decoy functions.

Identification and initial characterization of POLIII-driven transcripts by msRNA-sequencing

Non-coding RNAs (ncRNAs) are powerful regulators of gene expression but medium-sized (50–300 nts in length) ncRNAs (msRNAs) are barely picked-up precisely by RNA-sequencing. Here we describe msRNA-sequencing (msRNAseq), a modified protocol that associated with a computational analyses pipeline identified about ~1800 msRNA loci, including over 300 putatively novel msRNAs, in human and murine cells. We focused on the identification and initial characterization of three POLIII-derived transcripts. The validation of these uncharacterized msRNAs identified an ncRNA in antisense orientation from the POLR3E locus transcribed by POLIII. This msRNA, termed POLAR (POLR3E Antisense RNA), has a strikingly short half-life, localizes to paraspeckles (PSPs) and associates with PSP-associated proteins indicating that msRNAseq identifies functional msRNAs. Thus, our analyses will pave the way for analysing the roles of msRNAs in cells, development and diseases.

Studies with recombinant U7 snRNP demonstrate that CPSF73 is both an endonuclease and a 5'-3' exonuclease

Metazoan replication-dependent histone pre-mRNAs are cleaved at the 3' end by U7 snRNP, an RNA-guided endonuclease that contains U7 snRNA, seven proteins of the Sm ring, FLASH, and four polyadenylation factors: symplekin, CPSF73, CPSF100, and CstF64. A fully recombinant U7 snRNP was recently reconstituted from all 13 components for functional and structural studies and shown to accurately cleave histone pre-mRNAs. Here, we analyzed the activity of recombinant U7 snRNP in more detail. We demonstrate that in addition to cleaving histone pre-mRNAs endonucleolytically, reconstituted U7 snRNP acts as a 5'-3' exonuclease that degrades the downstream product generated from histone pre-mRNAs as a result of the endonucleolytic cleavage. Surprisingly, recombinant U7 snRNP also acts as an endonuclease on single-stranded DNA substrates. All these activities depend on the ability of U7 snRNA to base-pair with the substrate and on the presence of the amino-terminal domain (NTD) of symplekin in either cis or trans, and are abolished by mutations within the catalytic center of CPSF73, or by binding of the NTD to the SSU72 phosphatase of RNA polymerase II. Altogether, our results demonstrate that recombinant U7 snRNP functionally mimics its endogenous counterpart and provide evidence that CPSF73 is both an endonuclease and a 5'-3' exonuclease, consistent with the activity of other members of the β-CASP family. Our results also raise the intriguing possibility that CPSF73 may be involved in some aspects of DNA metabolism in vivo.

POLIII-derived non-coding RNAs acting as scaffolds and decoys

A large variety of eukaryotic small structured POLIII-derived non-coding RNAs (ncRNAs) have been described in the past. However, for only few, e.g. 7SL and H1/MRP families, cellular functions are well understood. For the vast majority of these transcripts, cellular functions remain unknown. Recent findings on the role of Y RNAs and other POLIII-derived ncRNAs suggest an evolutionarily conserved function of these ncRNAs in the assembly and function of ribonucleoprotein complexes (RNPs). These RNPs provide cellular `machineries’, which are essential for guiding the fate and function of a variety of RNAs. In this review, we summarize current knowledge on the role of POLIII-derived ncRNAs in the assembly and function of RNPs. We propose that these ncRNAs serve as scaffolding factors that `chaperone’ RNA-binding proteins (RBPs) to form functional RNPs. In addition or associated with this role, some small ncRNAs act as molecular decoys impairing the RBP-guided control of RNA fate by competing with other RNA substrates. This suggests that POLIII-derived ncRNAs serve essential and conserved roles in the assembly of larger RNPs and thus the control of gene expression by indirectly guiding the fate of mRNAs and lncRNAs.

Y RNA: An Overview of Their Role as Potential Biomarkers and Molecular Targets in Human Cancers

Y RNA are a class of small non-coding RNA that are largely conserved. Although their discovery was almost 40 years ago, their function is still under investigation. This is evident in cancer biology, where their role was first studied just a dozen years ago. Since then, only a few contributions were published, mostly scattered across different tumor types and, in some cases, also suffering from methodological limitations. Nonetheless, these sparse data may be used to make some estimations and suggest routes to better understand the role of Y RNA in cancer formation and characterization. Here we summarize the current knowledge about Y RNA in multiple types of cancer, also including a paragraph about tumors that might be included in this list in the future, if more evidence becomes available. The picture arising indicates that Y RNA might be useful in tumor characterization, also relying on non-invasive methods, such as the analysis of the content of extracellular vesicles (EV) that are retrieved from blood plasma and other bodily fluids. Due to the established role of Y RNA in DNA replication, it is possible to hypothesize their therapeutic targeting to inhibit cell proliferation in oncological patients.

CDK11 is required for transcription of replication-dependent histone genes

Replication-dependent histones (RDH) are required for packaging of newly synthetized DNA into nucleosomes during S-phase when their expression is highly upregulated. However, the mechanisms of this upregulation in metazoan cells remain poorly understood. Using iCLIP and ChIP-seq, we found that human cyclin-dependent kinase 11 (CDK11) associates with RNA and chromatin of RDH genes primarily in the S-phase. Moreover, its N-terminal region binds FLASH, RDH-specific 3´end processing factor, which keeps the kinase on the chromatin. CDK11 phosphorylates serine 2 (Ser2) of the C-terminal domain (CTD) of RNA polymerase II (RNAPII), which is initiated at the middle of RDH genes and is required for further RNAPII elongation and 3´end processing. CDK11 depletion leads to decreased number of cells in S-phase, likely due to the function of CDK11 in RDH gene expression. Thus, the reliance of RDH expression on CDK11 could explain why CDK11 is essential for growth of many cancers.

Y RNAs: Biogenesis, Function and Implications for the Cardiovascular System

In recent years, progress in the field of high-throughput sequencing technology and its application to a wide variety of biological specimens has greatly advanced the discovery and cataloging of a diverse set of non-coding RNAs (ncRNAs) that have been found to have unexpected biological functions. Y RNAs are an emerging class of highly conserved, small ncRNAs. There is a growing number of reports in the literature demonstrating that Y RNAs and their fragments are not just random degradation products but are themselves bioactive molecules. This review will outline what is currently known about Y RNA including biogenesis, structure and functional roles. In addition, we will provide an overview of studies reporting the presence and functions attributed to Y RNAs in the cardiovascular system.

RNY4 in Circulating Exosomes of Patients With Pediatric Anaplastic Large Cell Lymphoma: An Active Player?

Emerging evidence indicates that extracellular vesicles, particularly exosomes, play a role in several biological processes and actively contribute to cancer development and progression, by carrying and delivering proteins, transcripts and small RNAs (sRNAs). There is high interest in studying exosomes of cancer patients both to develop non-invasive liquid biopsy tests for risk stratification and to elucidate their possible involvement in disease mechanisms. We profiled by RNA-seq the sRNA content of circulating exosomes of 20 pediatric patients with Anaplastic Large Cell Lymphoma (ALCL) and five healthy controls. Our analysis disclosed that non-miRNA derived sRNAs constitute the prominent fraction of sRNA loaded in exosomes and identified 180 sRNAs significantly more abundant in exosomes of ALCL patients compared to controls. YRNA fragments, accounting for most of exosomal content and being significantly increased in ALCL patients, were prioritized for further investigation by qRT-PCR. Quantification of RNY4 fragments and full-length sequences disclosed that the latter are massively loaded into exosomes of ALCL patients with more advanced and aggressive disease. These results are discussed in light of recent findings on the role of RNY4 in the modulation of tumor microenvironment.

IGF2BP1 enhances an aggressive tumor cell phenotype by impairing miRNA-directed downregulation of oncogenic factors

The oncofetal IGF2 mRNA binding proteins (IGF2BPs) are upregulated in most cancers but their paralogue-specific roles in tumor cells remain poorly understood. In a panel of five cancer-derived cell lines, IGF2BP1 shows highly conserved oncogenic potential. Consistently, the deletion of IGF2BP1 impairs the growth and metastasis of ovarian cancer-derived cells in nude mice. Gene expression analyses in ovarian cancer-derived cells reveal that the knockdown of IGF2BPs is associated with the downregulation of mRNAs that are prone to miRNA regulation. All three IGF2BPs preferentially associate upstream of miRNA binding sites (MBSs) in the 3′UTR of mRNAs. The downregulation of mRNAs co-regulated by miRNAs and IGF2BP1 is abrogated at low miRNA abundance or when miRNAs are depleted. IGF2BP1 associates with these target mRNAs in RISC-free complexes and its deletion enhances their association with AGO2. The knockdown of most miRNA-regulated target mRNAs of IGF2BP1 impairs tumor cell properties. In four primary cancers, elevated synthesis of these target mRNAs is largely associated with upregulated IGF2BP1 mRNA levels. In ovarian cancer, the enhanced expression of IGF2BP1 and most of its miRNA-controlled target mRNAs is associated with poor prognosis. In conclusion, these findings indicate that IGF2BP1 enhances an aggressive tumor cell phenotype by antagonizing miRNA-impaired gene expression.

Extracellular RNAs: A New Awareness of Old Perspectives

Extracellular RNA (exRNA) has recently expanded as a highly important area of study in biomarker discovery and cancer therapeutics. exRNA consists of diverse RNA subpopulations that are normally protected from degradation by incorporation into membranous vesicles or by lipid/protein association. They are found circulating in biofluids, and have proven highly promising for minimally invasive diagnostic and prognostic purposes, particularly in oncology. Recent work has made progress in our understanding of exRNAs-from their biogenesis, compartmentalization, and vesicle packaging to their various applications as biomarkers and therapeutics, as well as the new challenges that arise in isolation and purification for accurate and reproducible analysis. Here we review the most recent advancements in exRNA research.

Circulating Y-RNAs in Extracellular Vesicles and Ribonucleoprotein Complexes; Implications for the Immune System

The exchange of extracellular vesicles (EV) between immune cells plays a role in various immune regulatory processes. EV are nano-sized lipid bilayer-enclosed structures that contain a multitude of proteins and small non-coding RNA molecules. Of the various RNA classes present in EV, miRNAs have been most intensively studied because of their known gene-regulatory functions. These miRNAs constitute only a minor part of all EV-enclosed RNA, whereas other 20–200 nt sized non-coding RNAs were shown to be abundantly present in EV. Several of these mid-sized RNAs perform basic functions in cells, but their function in EV remains elusive. One prominent class of mid-sized extracellular RNAs associated with EV are the Y-RNAs. This family of highly conserved non-coding RNAs was initially discovered as RNA component of circulating ribonucleoprotein autoantigens in serum from Systemic Lupus Erythematosus and Sjögren's Syndrome patients. Y-RNA has been implicated in cellular processes such as DNA replication and RNA quality control. In recent years, Y-RNA has been abundantly detected in EV from multiple different cell lines and biofluids, and also in murine and human retroviruses. Accumulating evidence suggests that EV-associated Y-RNA may be involved in a range of immune-related processes, including inflammation, immune suppression, and establishment of the tumor microenvironment. Moreover, changes in plasma levels of extracellular Y-RNA have been associated with various diseases. Recent studies have aimed to address the mechanisms underlying their release and function. We for example showed that the levels of EV-associated Y-RNA released by immune cells can be regulated by Toll-like receptor (TLR) signaling. Combined, these data have triggered increased interest in extracellular Y-RNAs. In this review, we provide an overview of studies reporting the occurrence of extracellular Y-RNAs, as well as signaling properties and immune-related functions attributed to these RNAs. We list RNA-binding proteins currently known to interact with Y-RNAs and evaluate their occurrence in EV. In parallel, we discuss technical challenges in assessing whether extracellular Y-RNAs are contained in ribonucleoprotein complexes or EV. By integrating the current knowledge on extracellular Y-RNA we further reflect on the biomarker potential of Y-RNA and their role in immune cell communication and immunopathology.

The Implication of mRNA Degradation Disorders on Human DISease: Focus on DIS3 and DIS3-Like Enzymes

RNA degradation is considered a critical posttranscriptional regulatory checkpoint, maintaining the correct functioning of organisms. When a specific RNA transcript is no longer required in the cell, it is signaled for degradation through a number of highly regulated steps. Ribonucleases (or simply RNases) are key enzymes involved in the control of RNA stability. These enzymes can perform the RNA degradation alone or cooperate with other proteins in RNA degradation complexes. Important findings over the last years have shed light into eukaryotic RNA degradation by members of the RNase II/RNB family of enzymes. DIS3 enzyme belongs to this family and represents one of the catalytic subunits of the multiprotein complex exosome. This RNase has a diverse range of functions, mainly within nuclear RNA metabolism. Humans encode two other DIS3-like enzymes: DIS3L (DIS3L1) and DIS3L2. DIS3L1 also acts in association with the exosome but is strictly cytoplasmic. In contrast, DIS3L2 acts independently of the exosome and shows a distinctive preference for uridylated RNAs. These enzymes have been shown to be involved in important cellular processes, such as mitotic control, and associated with human disorders like cancer. This review shows how the impairment of function of each of these enzymes is implicated in human disease.

Small non-coding RNA landscape of extracellular vesicles from human stem cells

Extracellular vesicles (EVs) are reported to be involved in stem cell maintenance, self-renewal, and differentiation. Due to their bioactive cargoes influencing cell fate and function, interest in EVs in regenerative medicine has rapidly increased. EV-derived small non-coding RNA mimic the functions of the parent stem cells, regulating the maintenance and differentiation of stem cells, controlling the intercellular regulation of gene expression, and eventually affecting the cell fate. In this study, we used RNA sequencing to provide a comprehensive overview of the expression profiles of small non-coding transcripts carried by the EVs derived from human adipose tissue stromal/stem cells (AT-MSCs) and human pluripotent stem cells (hPSCs), both human embryonic stem cells (hESCs) and human induced pluripotent stem cells (hiPSC). Both hPSCs and AT-MSCs were characterized and their EVs were extracted using standard protocols. Small non-coding RNA sequencing from EVs showed that hPSCs and AT-MSCs showed distinct profiles, unique for each stem cell source. Interestingly, in hPSCs, most abundant miRNAs were from specific miRNA families regulating pluripotency, reprogramming and differentiation (miR-17-92, mir-200, miR-302/367, miR-371/373, CM19 microRNA cluster). For the AT-MSCs, the highly expressed miRNAs were found to be regulating osteogenesis (let-7/98, miR-10/100, miR-125, miR-196, miR-199, miR-615-3p, mir-22-3p, mir-24-3p, mir-27a-3p, mir-193b-5p, mir-195-3p). Additionally, abundant small nuclear and nucleolar RNA were detected in hPSCs, whereas Y- and tRNA were found in AT-MSCs. Identification of EV-miRNA and non-coding RNA signatures released by these stem cells will provide clues towards understanding their role in intracellular communication, and well as their roles in maintaining the stem cell niche.

HuD Is a Neural Translation Enhancer Acting on mTORC1-Responsive Genes and Counteracted by the Y3 Small Non-coding RNA

The RNA-binding protein HuD promotes neurogenesis and favors recovery from peripheral axon injury. HuD interacts with many mRNAs, altering both stability and translation efficiency. We generated a nucleotide resolution map of the HuD RNA interactome in motor neuron-like cells, identifying HuD target sites in 1,304 mRNAs, almost exclusively in the 3' UTR. HuD binds many mRNAs encoding mTORC1-responsive ribosomal proteins and translation factors. Altered HuD expression correlates with the translation efficiency of these mRNAs and overall protein synthesis, in a mTORC1-independent fashion. The predominant HuD target is the abundant, small non-coding RNA Y3, amounting to 70% of the HuD interaction signal. Y3 functions as a molecular sponge for HuD, dynamically limiting its recruitment to polysomes and its activity as a translation and neuron differentiation enhancer. These findings uncover an alternative route to the mTORC1 pathway for translational control in motor neurons that is tunable by a small non-coding RNA.

Non-Coding RNA as Novel Players in the Pathophysiology of Schizophrenia

Schizophrenia is associated with diverse changes in the brain's transcriptome and proteome. Underlying these changes is the complex dysregulation of gene expression and protein production that varies both spatially across brain regions and temporally with the progression of the illness. The growing body of literature showing changes in non-coding RNA in individuals with schizophrenia offers new insights into the mechanisms causing this dysregulation. A large number of studies have reported that the expression of microRNA (miRNA) is altered in the brains of individuals with schizophrenia. This evidence is complemented by findings that single nucleotide polymorphisms (SNPs) in miRNA host gene sequences can confer an increased risk of developing the disorder. Additionally, recent evidence suggests the expression of other non-coding RNAs, such as small nucleolar RNA and long non-coding RNA, may also be affected in schizophrenia. Understanding how these changes in non-coding RNAs contribute to the development and progression of schizophrenia offers potential avenues for the better treatment and diagnosis of the disorder. This review will focus on the evidence supporting the involvement of non-coding RNA in schizophrenia and its therapeutic potential.

snoRNAs associate with mRNA 3' processing complex: New wine in old bottles

3' end processing is required for the maturation of all eukaryotic RNAs. Current model suggests that canonical mRNA 3' processing is carried out exclusively within a protein complex termed mRNA 3' processing complex. In a recent study, by using RNA-biotin based pull-down assay and high-throughput sequencing, we reported that a subset of small nucleolar RNAs (snoRNAs) were physically associated with this macromolecular machinery. Through detailed characterization of one of these snoRNAs, SNORD50A, we revealed that non-coding RNA, such as snoRNA, may play a regulatory role in mRNA 3' processing. Our results provided novel insight into both the regulatory mechanism of mRNA 3' processing and the non-canonical functions of snoRNAs.

A snoRNA modulates mRNA 3' end processing and regulates the expression of a subset of mRNAs

mRNA 3′ end processing is an essential step in gene expression. It is well established that canonical eukaryotic pre-mRNA 3′ processing is carried out within a macromolecular machinery consisting of dozens of trans-acting proteins. However, it is unknown whether RNAs play any role in this process. Unexpectedly, we found that a subset of small nucleolar RNAs (snoRNAs) are associated with the mammalian mRNA 3′ processing complex. These snoRNAs primarily interact with Fip1, a component of cleavage and polyadenylation specificity factor (CPSF). We have functionally characterized one of these snoRNAs and our results demonstrated that the U/A-rich SNORD50A inhibits mRNA 3′ processing by blocking the Fip1-poly(A) site (PAS) interaction. Consistently, SNORD50A depletion altered the Fip1–RNA interaction landscape and changed the alternative polyadenylation (APA) profiles and/or transcript levels of a subset of genes. Taken together, our data revealed a novel function for snoRNAs and provided the first evidence that non-coding RNAs may play an important role in regulating mRNA 3′ processing.

Coding and noncoding landscape of extracellular RNA released by human glioma stem cells

Tumor-released RNA may mediate intercellular communication and serve as biomarkers. Here we develop a protocol enabling quantitative, minimally biased analysis of extracellular RNAs (exRNAs) associated with microvesicles, exosomes (collectively called EVs), and ribonucleoproteins (RNPs). The exRNA complexes isolated from patient-derived glioma stem-like cultures exhibit distinct compositions, with microvesicles most closely reflecting cellular transcriptome. exRNA is enriched in small ncRNAs, such as miRNAs in exosomes, and precisely processed tRNA and Y RNA fragments in EVs and exRNPs. EV-enclosed mRNAs are mostly fragmented, and UTRs enriched; nevertheless, some full-length mRNAs are present. Overall, there is less than one copy of non-rRNA per EV. Our results suggest that massive EV/exRNA uptake would be required to ensure functional impact of transferred RNA on brain recipient cells and predict the most impactful miRNAs in such conditions. This study also provides a catalog of diverse exRNAs useful for biomarker discovery and validates its feasibility on cerebrospinal fluid.

While circulating DNA has been extensively explored as a potential cancer biomarker, RNA potential has been overlooked so far. Here the authors present a comprehensive analysis of extracellular RNA secreted by glioblastoma cells that could prove a valuable resource for biomarker discovery and a means of intercellular communication.

PARN Modulates Y RNA Stability and Its 3'-End Formation

Loss-of-function mutations in 3'-to-5' exoribonucleases have been implicated in hereditary human diseases. For example, PARN mutations cause a severe form of dyskeratosis congenita (DC), wherein PARN deficiency leads to human telomerase RNA instability. Since the DC phenotype in PARN patients is even more severe than that of loss-of-function alleles in telomerase components, we hypothesized that PARN would also be required for the stability of other RNAs. Here, we show that PARN depletion reduces the levels of abundant human Y RNAs, which might contribute to the severe phenotype of DC observed in patients. Depletion of PAPD5 or the cytoplasmic exonuclease DIS3L rescues the effect of PARN depletion on Y RNA levels, suggesting that PARN stabilizes Y RNAs by removing oligoadenylated tails added by PAPD5, which would otherwise recruit DIS3L for Y RNA degradation. Through deep sequencing of 3' ends, we provide evidence that PARN can also deadenylate the U6 and RMRP RNAs without affecting their levels. Moreover, we observed widespread posttranscriptional oligoadenylation, uridylation, and guanylation of U6 and Y RNA 3' ends, suggesting that in mammalian cells, the formation of a 3' end for noncoding RNAs can be a complex process governed by the activities of various 3'-end polymerases and exonucleases.

Birth and Death of Histone mRNAs

In metazoans, histone mRNAs are not polyadenylated but end in a conserved stem-loop. Stem-loop binding protein (SLBP) binds to the stem-loop and is required for all steps in histone mRNA metabolism. The genes for the five histone proteins are linked. A histone locus body (HLB) forms at each histone gene locus. It contains factors essential for transcription and processing of histone mRNAs, and couples transcription and processing. The active form of U7 snRNP contains the HLB component FLASH (FLICE-associated huge protein), the histone cleavage complex (HCC), and a subset of polyadenylation factors including the endonuclease CPSF73. Histone mRNAs are rapidly degraded when DNA replication is inhibited by a 3' to 5' pathway that requires extensive uridylation of mRNA decay intermediates.

Coordinating cell cycle-regulated histone gene expression through assembly and function of the Histone Locus Body

Metazoan replication-dependent (RD) histone genes encode the only known cellular mRNAs that are not polyadenylated. These mRNAs end instead in a conserved stem-loop, which is formed by an endonucleolytic cleavage of the pre-mRNA. The genes for all 5 histone proteins are clustered in all metazoans and coordinately regulated with high levels of expression during S phase. Production of histone mRNAs occurs in a nuclear body called the Histone Locus Body (HLB), a subdomain of the nucleus defined by a concentration of factors necessary for histone gene transcription and pre-mRNA processing. These factors include the scaffolding protein NPAT, essential for histone gene transcription, and FLASH and U7 snRNP, both essential for histone pre-mRNA processing. Histone gene expression is activated by Cyclin E/Cdk2-mediated phosphorylation of NPAT at the G1-S transition. The concentration of factors within the HLB couples transcription with pre-mRNA processing, enhancing the efficiency of histone mRNA biosynthesis.

Perlman syndrome nuclease DIS3L2 controls cytoplasmic non-coding RNAs and provides surveillance pathway for maturing snRNAs

The exosome-independent exoribonuclease DIS3L2 is mutated in Perlman syndrome. Here, we used extensive global transcriptomic and targeted biochemical analyses to identify novel DIS3L2 substrates in human cells. We show that DIS3L2 regulates pol II transcripts, comprising selected canonical and histone-coding mRNAs, and a novel FTL_short RNA from the ferritin mRNA 5' UTR. Importantly, DIS3L2 contributes to surveillance of maturing snRNAs during their cytoplasmic processing. Among pol III transcripts, DIS3L2 particularly targets vault and Y RNAs and an Alu-like element BC200 RNA, but not Alu repeats, which are removed by exosome-associated DIS3. Using 3' RACE-Seq, we demonstrate that all novel DIS3L2 substrates are uridylated in vivo by TUT4/TUT7 poly(U) polymerases. Uridylation-dependent DIS3L2-mediated decay can be recapitulated in vitro, thus reinforcing the tight cooperation between DIS3L2 and TUTases. Together these results indicate that catalytically inactive DIS3L2, characteristic of Perlman syndrome, can lead to deregulation of its target RNAs to disturb transcriptome homeostasis.

A subset of replication-dependent histone mRNAs are expressed as polyadenylated RNAs in terminally differentiated tissues

Histone proteins are synthesized in large amounts during S-phase to package the newly replicated DNA, and are among the most stable proteins in the cell. The replication-dependent (RD)-histone mRNAs expressed during S-phase end in a conserved stem-loop rather than a polyA tail. In addition, there are replication-independent (RI)-histone genes that encode histone variants as polyadenylated mRNAs. Most variants have specific functions in chromatin, but H3.3 also serves as a replacement histone for damaged histones in long-lived terminally differentiated cells. There are no reported replacement histone genes for histones H2A, H2B or H4. We report that a subset of RD-histone genes are expressed in terminally differentiated tissues as polyadenylated mRNAs, likely serving as replacement histone genes in long-lived non-dividing cells. Expression of two genes, HIST2H2AA3 and HIST1H2BC, is conserved in mammals. They are expressed as polyadenylated mRNAs in fibroblasts differentiated in vitro, but not in serum starved fibroblasts, suggesting that their expression is part of the terminal differentiation program. There are two histone H4 genes and an H3 gene that encode mRNAs that are polyadenylated and expressed at 5- to 10-fold lower levels than the mRNAs from H2A and H2B genes, which may be replacement genes for the H3.1 and H4 proteins.

Non-coding RNAs, the cutting edge of histone messages

In metazoan the 3′-end processing of histone mRNAs is a conserved process involving the concerted action of many protein factors and the non-coding U7 snRNA. Recently, we identified that the processing of histone pre-mRNAs is promoted by an additional ncRNA, the Y3-derived Y3** RNA. U7 modulates the association of the U7 snRNP whereas Y3** promotes recruitment of CPSF (cleavage and polyadenylation specific factor) proteins to nascent histone transcripts at histone locus bodies (HLBs) in mammals. This enhances the 3′-end cleavage of nascent histone pre-mRNAs and modulates HLB assembly. Here we discuss new insights in the role of ncRNAs in the spatiotemporal control of histone synthesis. We propose that ncRNAs scaffold the formation of functional protein-RNA complexes and their sequential deposition on nascent histone pre-mRNAs at HLBs. These findings add to the multiple roles of ncRNAs in controlling gene expression and may provide new avenues for targeting histone synthesis in cancer.