MRNA length and 3’UTR structure govern the translation selectivity in RPS14-haploinsufficient erythroblasts [transcriptome]
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ABSTRACT: 5q- syndrome is a somatic ribosomopathy linked to the monoallelic deletion of the RPS14 gene and characterized by a proeminent erythroid phenotype. The mechanism of anemia involves an impaired differentiation and increased apoptosis of erythroblasts. Here we show that GATA1 protein expression is low in line with a defect in the representation of its mRNA at the ribosome. A global analysis of transcripts on polysomes indicates that translation is selective with a decreased representation of the transcripts with a short coding sequence and UTRs and a highly structured 3’UTR, a subset of transcripts that includes GATA1. Our whole proteome analysis confirms that post-transcriptionally downregulated proteins were encoded by transcripts with a short length and structured 3’UTR. We identified a subset of post-translationally downregulated proteins including ribosomal proteins and translation elongation factors encoded by 5’TOP mRNAs that were enriched on the ribosome. Our results indicate that the thermodynamic characteristics of 3’UTR and in a lesser extend 5’UTR and the transcript length are the determinants of translation selectivity under RPS14 haploinsufficiency conditions and that a post-translational regulation of ribosomal proteins accounts for their decreased content in the cell. We performed transcriptome and translatome expression profiling of cells infected with shRPS14 or shSCR
Project description:5q- syndrome is a somatic ribosomopathy linked to the monoallelic deletion of the RPS14 gene and characterized by a proeminent erythroid phenotype. The mechanism of anemia involves an impaired differentiation and increased apoptosis of erythroblasts. We have analyzed total cell extracts from UT7 cells with or without a decrease of RPS14 proteins induced by shRNAs. Our data show that GATA1 protein expression is low in line with a defect in the representation of its mRNA at the ribosome. A global analysis of transcripts on polysomes indicates that translation is selective with a decreased representation of the transcripts with a short coding sequence and UTRs and a highly structured 3’UTR, a subset of transcripts that includes GATA1. Our whole proteome analysis confirms that post-transcriptionally downregulated proteins were encoded by transcripts with a short length and structured 3’UTR. We identified a subset of post-translationally downregulated proteins including ribosomal proteins and translation elongation factors encoded by 5’TOP mRNAs that were enriched on the ribosome. Our results indicate that the thermodynamic characteristics of 3’UTR and in a lesser extend 5’UTR and the transcript length are the determinants of translation selectivity under RPS14 haploinsufficiency conditions and that a post-translational regulation of ribosomal proteins accounts for their decreased content in the cell.
Project description:5q- syndrome is a somatic ribosomopathy linked to the monoallelic deletion of the RPS14 gene and characterized by a proeminent erythroid phenotype. The mechanism of anemia involves an impaired differentiation and increased apoptosis of erythroblasts. Here we show that GATA1 protein expression is low in line with a defect in the representation of its mRNA at the ribosome. A global analysis of transcripts on polysomes indicates that translation is selective with a decreased representation of the transcripts with a short coding sequence and UTRs and a highly structured 3’UTR, a subset of transcripts that includes GATA1. Our whole proteome analysis confirms that post-transcriptionally downregulated proteins were encoded by transcripts with a short length and structured 3’UTR. We identified a subset of post-translationally downregulated proteins including ribosomal proteins and translation elongation factors encoded by 5’TOP mRNAs that were enriched on the ribosome. Our results indicate that the thermodynamic characteristics of 3’UTR and in a lesser extend 5’UTR and the transcript length are the determinants of translation selectivity under RPS14 haploinsufficiency conditions and that a post-translational regulation of ribosomal proteins accounts for their decreased content in the cell. We performed transcriptome and translatome expression profiling of cells infected with shRPS14 or shSCR
Project description:Ribosomopathies are cell-type-specific pathologies related to a ribosomal protein (RP) gene insult. The 5q- syndrome is a somatic ribosomopathy linked to RPS14 gene haploinsufficiency and characterized by a prominent erythroid hypoplasia. Using quantitative proteomic, we show that GATA1 protein expression is low in shRPS14 cells in which ribosome quantities are diminished. Here, we investigated the cause of low GATA1 protein expression in limiting ribosome availability. A global analysis of translation in RPs deficiencies highlights the rules that drive translation selectivity. We demonstrate that in addition of the transcript length, a high codon adaptation index (CAI) and a highly structured 3’UTR are the key characteristics for a selective translation. An integrated analysis of transcriptome and proteome confirms that the post-transcriptional regulations of gene expression are directly linked to the criteria governing the translational selectivity. In particular, these criteria explain GATA1 translation default with unprecedented precision. More generally, the proteins that accumulate along normal erythropoiesis share the determinants of translation selectivity revealed by the conditions of limiting ribosome availability. We performed translatome expression profiling of cells infected with shRPS14 or shSCR
Project description:The 3' untranslated region (3'UTR) of mRNA plays several important roles in post-transcriptional gene regulation. Some of its functions include regulating mRNA stability by polyadenylation and microRNAs. However, the overall function of the Gata1 3’UTR in mammals has not been defined. In this study, we used CRISPR/CAS9 technology to knock out the sequence of the mouse Gata1 3’UTR. We found a defect in erythropoiesis in mutant mice, evidenced by macrocytic anemia at the baseline. Ablation of Gata1 3’UTR also resulted in a reduced number of erythroid precursors that might be associated with the cell cycle, especially G2/M disruption in fetal livers. Mechanistically, deletion of the Gata1 3’UTR destabilizes the Gata1 mRNA and ultimately reduces Gata1 protein levels. The low stability of the Gata1 mRNA is unlikely to be caused by the loss of binding of microRNAs or lack of polyadenylation; rather, in part, by the dissociation of AU-rich elements in the 3’UTR with a trans-activating factor Elavl1. Specifically, we transcribed Gata1 3’UTR in vitro and performed an RNA pulldown assay followed by mass spectrometry to profile the proteins that bind the 3’UTR. Gene Ontology analysis demonstrated that several proteins specifically targeting the 3’UTR were found to potentially bind Gata1 3’UTR, among which Elavl1 was in almost all categories related to mRNA stabilization. Western blotting and RNA immunoprecipitation confirmed the direct interaction of Gata1 3’UTR with Elavl1. Manipulation of Elavl1 activity and protein levels by the small molecule inhibitor Dihydro-tanshinone-I and Elavl1 overexpression in fetal liver erythroblasts confirmed Elavl1 as a stabilizing factor for Gata1 mRNA. Our findings shed light on the functional significance of the 3’UTR of Gata1 mRNA in the context of erythroid development. More importantly, our findings highlight the complexity and diversity of regulatory mechanisms that govern Gata1 mRNA stability and precise expression at the post-transcriptional levels. In addition, our findings prove that miRNAs are not always essential in vivo for controlling transcription factor levels to maintain body homeostasis.
Project description:RNA helicase A (RHA) binds its target transcripts at the post-transcriptional control element (PCE) located in the 5’ untranslated region (UTR). This interaction represents an “RNA switch” that regulates protein synthesis. Down regulation of RHA by siRNAs was used to identify transcripts with RHA-dependent translation. Reduced accumulation of RNA in polysomes was monitored with microarrays. Cytoplasmic lysates of cells treated with RHA targeted or non-silencing control siRNAs were separated by sucrose density gradient centrifugation. Ribosomal RNA profiles were generated, containing heavy polysomes were collected, and RNA was extracted.
Project description:Roquin proteins target specific RNA stem-loop motifs with their unique ROQ domain for mRNA degradation. The cellular levels of mRNAs are controlled by these post-transcriptional cis-regulatory stem-loop elements in the 3'-untranslated region (3'-UTR). Here, we first provide an RBNS (RNA Bind-n-Seq) experiment using pre-structured RNA libraries as input. This sRBNS (structured RBNS) was used to map Roquin's RNA binding preferences at nucleotide resolution, revealing preferences for loop sizes and consensus motifs for CDEs and ADEs.
Project description:Recent studies have revealed that the mRNA translation is punctuated by ribosomal pauses through the body of transcripts. However, little is known about its physiological significance and regulatory aspects. Here we present a multi-dimensional ribosome profiling approach to quantify the dynamics of initiation and elongation of 80S ribosomes across the entire transcriptome in mammalian cells. We show that a subset of transcripts have a significant pausing of 80S ribosome around the start codon, creating a major barrier to the commitment of translation elongation. Intriguingly, genes encoding ribosome proteins themselves exhibit an exceptionally high initiation pausing on their transcripts. Our studies also reveal that the initiation pausing is dependent on the 5M-bM-^@M-^Y untranslated region (5M-bM-^@M-^Y UTR) of mRNAs and subject to the regulation of mammalian target of rapamycin complex 1 (mTORC1). Thus, the initiation pausing of 80S ribosome represents a novel regulatory step in translational control mediated by nutrient signaling pathway. Monitor the translational status of transcriptome in mammalian cells under different conditions
Project description:RNA helicase A (RHA) binds its target transcripts at the post-transcriptional control element (PCE) located in the 5â?? untranslated region (UTR). This interaction represents an â??RNA switchâ?? that regulates protein synthesis. Down regulation of RHA by siRNAs was used to identify transcripts with RHA-dependent translation. Reduced accumulation of RNA in polysomes was monitored with microarrays. Changes in cytoplasmic RNA steady state abundance was monitored as well. Sixty nine genes exhibit decreased transcript polysome association when subjected to RHA downregulation. A majority of the transcripts that experienced a reduction in the polysome fraction had no significant change in their cytoplasmic abundance (45 genes). Keywords: gene expression array-based Cytoplasmic lysates of cells treated with RHA targeted or non-silencing control siRNAs were separated by sucrose density gradient centrifugation. Ribosomal RNA profiles were generated, fractions containing polysomes were collected, and RNA was extracted.
Project description:Ribosomal protein haploinsufficiency (RPH) underlies diverse human diseases with distinct and specific phenotypes, including Diamond-Blackfan anemia (DBA). Although multiple mechanisms have been proposed for the erythroid-specific hematopoietic defects observed in DBA, only recently has the role of selectively impaired translation been highlighted in these phenotypes. Exactly how and to what extent this impairment of translation occurs is currently unknown. Here, by identifying a novel DBA gene affecting ribosome biogenesis, we show that both RPH and impaired ribosome biogenesis (IRB) limit the availability of actively translating ribosomes, resulting in the hematopoietic and translational defects observed in DBA. Our results show that the selective impairment of translation is due to a quantitative defect, where ribosomes of invariant protein composition have a reduced abundance, rather than a qualitative defect, where a subset of ribosomes lack specific ribosomal proteins (RPs) and thus may have altered translational capacity. In RPH, we find that cellular RP homeostasis is largely maintained through translational co-regulation, and we identify a selective subset of transcripts that have impaired association with the ribosome. Surprisingly, these transcripts have short and unstructured 5’ UTRs and are highly abundant and efficiently translated in healthy human erythroid progenitors, suggesting that the impaired translation of a number of key transcripts, including GATA1, may underlie DBA. Overall, our study identifies mechanisms by which RPH and IRB affect mRNA translation, illuminating how these alterations can result in cell-type specific defects and cause human disease.
Project description:Due to breakthroughs in RNAi and genome editing methods in the past decade, it is now easier than ever to study fine details of protein synthesis in animal models. However, most of our understanding of translation comes from unicellular organisms and cultured mammalian cells. In this study, we demonstrate the feasibility of perturbing protein synthesis in a mouse liver by targeting translation elongation factor 2 (eEF2) with RNAi. We were able to achieve over 90% knockdown efficacy and maintain it for 2 weeks effectively slowing down the rate of translation elongation. As the total protein yield declined, both proteomics and ribosome profiling assays showed robust translational upregulation of ribosomal proteins relative to other proteins. Although all these genes bear the TOP regulatory motif, the branch of the mTOR pathway responsible for translation regulation was not activated. Paradoxically, coordinated translational upregulation of ribosomal proteins only occurred in the liver but not in murine cell culture. Thus, the upregulation of ribosomal transcripts likely occurred via passive mTOR-independent mechanisms. Impaired elongation sequesters ribosomes on mRNA and creates a shortage of free ribosomes. This leads to preferential translation of transcripts with high initiation rates such as ribosomal proteins. Furthermore, severe eEF2 shortage reduces the negative impact of positively charged amino acids frequent in ribosomal proteins on ribosome progression.