26 research outputs found
ERH proteins: connecting RNA processing to tumorigenesis?
No full textInternational audienceWith the development of -omics approaches, the scientific community is now submerged by a wealth of information that can be used to analyze various parameters: the degree of protein sequence conservation, protein 3D structures as well as RNA and protein expression levels in various benign and tumor tissues, during organism development or upon exposure to chemicals such as endocrine disrupters. However, if such information can be used to identify genes with potentially important biological function, additional studies are needed to deeply characterize their cellular function in model organisms. Here, we discuss the case of such a gene: ERH, encoding a highly conserved homodimeric protein found in unicellular eukaryotes, plants and metazoan, of yet unknown biological function, which might be linked to mRNA metabolism and that is emerging as important for cell migration and metastasis
Long Non-Coding RNAs in the Control of Gametogenesis: Lessons from Fission Yeast
No full textLong non-coding RNAs (lncRNAs) contribute to cell fate decisions by modulating genome expression and stability. In the fission yeast Schizosaccharomyces pombe, the transition from mitosis to meiosis results in a marked remodeling of gene expression profiles, which ultimately ensures gamete production and inheritance of genetic information to the offspring. This key developmental process involves a set of dedicated lncRNAs that shape cell cycle-dependent transcriptomes through a variety of mechanisms, including epigenetic modifications and the modulation of transcription, post-transcriptional and post-translational regulations, and that contribute to meiosis-specific chromosomal events. In this review, we summarize the biology of these lncRNAs, from their identification to mechanism of action, and discuss their regulatory role in the control of gametogenesis
Interactions between transcription, RNA processing and degradation in yeast Saccharomyces cerevisiae
No full textChez la levure Saccharomyces cerevisiae, l exosome est un large complexe possédant une activité exonucléase 3 -5 et participant à de nombreuses réactions de maturation et de dégradation de l ARN. Nous avons montré que plusieurs transcripts dérivant de regions intergéniques sont rapidement degradés dans une souche sauvage par l action combinée de l exosome et d un nouveau complexe appelé TRAMP, dont la sous-unité catalytique est une poly(A) polymérase. Nous avons proposé que la dégradation de ces ARNs, nommés CUTs pour Cryptic Unstable Transcripts, est un mécanisme requis pour limiter la transcription inappropriée ou pour permettre la transcription sans production d ARNs. Nous avons aussi démontré que la terminaison de la transcription des CUTs est induite par des protéines de liaison à l ARN, Nrd1p and Nab3p, qui ciblent les transcripts vers la dégradation par l exosome et TRAMP. Le complexe THO et l ARN hélicase Sub2p sont impliqués dans la biogénèse des ARNms et participent au couplage entre transcription et export. Des mutations dans ces gènes entraînent la dégradation et la rétention d ARNms à proximité du site de transcription par l exosome. Nous avons montré que le complexe TRAMP est impliqué dans la dégradation des transcripts mais pas leur rétention. Par ailleurs, nous avons observé que dans des mutants THO/sub2, un complexe associé à l ADN qui contient des facteurs de polyadénylation et des composants du pore nucléaire ne peut pas être résolu pour les étapes suivantes d export. Le complexe THO et Sub2p seraient ainsi impliqués dans une étape de remodelage requise pour déplacer le complexe de polyadénylation et engager l ARNm dans la voie d export.In budding yeast Saccharomyces cerevisiae, the exosome is a large complex with 3 to 5 exonuclease activity that has been implicated in numerous RNA processing and degradation events. We have shown that several transcripts mapping to intergenic regions are rapidly degraded in a wild type strain by the combined action of the exosome and a novel complex called TRAMP, whose catalytic subunit is a poly(A) polymerase. We proposed that degradation of these RNAs, called CUTs for Cryptic Unstable Transcripts, is a mechanism required to limit inappropriate transcription or to allow the occurrence of transcription without RNA production. We have also demonstrated that transcription termination of CUTs is triggered by specific RNA-binding proteins, Nrd1p and Nab3p, which direct nascent transcripts to exosome/TRAMP-mediated degradation. The THO complex and its associated RNA helicase Sub2p are involved in mRNA biogenesis and couple transcription to mRNA export. Mutations in any of these genes lead to exosome-dependent degradation and retention of mRNAs at or near the transcription site. We have shown that the TRAMP complex is involved in mRNA degradation but not in retention. Furthermore, we observed that, in THO/sub2 mutants, a DNA-interacting complex containing polyadenylation factors and components of the Nuclear Pore Complex cannot be resolved for further mRNA export. Accordingly, the THO/Sub2p complex would be involved in a remodeling step required to displace the polyadenylation complex and to engage productively the mRNA in the export pathway.ORSAY-PARIS 11-BU Sciences (914712101) / SudocSudocFranceF
Author response: Ubiquitination-dependent control of sexual differentiation in fission yeast
No full textUbiquitination-dependent control of sexual differentiation in fission yeast
No full textInternational audienc
Formation of S. pombe Erh1 homodimer mediates gametogenic gene silencing and meiosis progression
No full textTimely and accurate expression of the genetic information relies on the integration of environmental cues and the activation of regulatory networks involving transcriptional and post-transcriptional mechanisms. In fission yeast, meiosis-specific transcripts are selectively targeted for degradation during mitosis by the EMC complex, composed of Erh1, the ortholog of human ERH, and the YTH family RNA-binding protein Mmi1. Here, we present the crystal structure of Erh1 and show that it assembles as a homodimer. Mutations of amino acid residues to disrupt Erh1 homodimer formation result in loss-of-function phenotypes, similar to erh1∆ cells: expression of meiotic genes is derepressed in mitotic cells and meiosis progression is severely compromised. Interestingly, formation of Erh1 homodimer is dispensable for interaction with Mmi1, suggesting that only fully assembled EMC complexes consisting of two Mmi1 molecules bridged by an Erh1 dimer are functionally competent. We also show that Erh1 does not contribute to Mmi1-dependent down-regulation of the meiosis regulator Mei2, supporting the notion that Mmi1 performs additional functions beyond EMC. Overall, our results provide a structural basis for the assembly of the EMC complex and highlight its biological relevance in gametogenic gene silencing and meiosis progression
Etude des mécanismes de la différenciation sexuelle chez la levure fissipare Schizosaccharomyces pombe
No full textChez la levure fissipare Schizosaccharomyces pombe, un sous-ensemble de gènes méiotiques est transcrit de manière constitutive au cours de la mitose. Afin d’éviter l'expression prématurée du programme méiotique et l'initiation de la différenciation sexuelle, les cellules ont développé un système de dégradation de l'ARN qui élimine sélectivement les transcrits méiotiques correspondants. Ce processus nécessite la protéine de liaison à l'ARN Mmi1 (à domaine YTH), qui reconnaît en cis les molécules d'ARN (motifs UNAAAC) et les cible pour la dégradation par l'exosome nucléaire. Au début de la méiose, Mmi1 est séquestrée au sein d’une particule ribonucléoprotéique composée de la protéine de liaison à l'ARN Mei2 et du long ARN non-codant (lncRNA) meiRNA, permettant ainsi l'expression des gènes méiotiques et le déroulement de la méiose. Mon travail de thèse a consisté à étudier les mécanismes par lesquels Mmi1 assure la dégradation des transcrits méiotiques et qui régulent son activité au cours des cycles mitotiques et méiotiques. Pendant la croissance végétative, Mmi1 s'associe étroitement à la protéine conservée Erh1 pour former le complexe hétérotétramérique Erh1-Mmi1 (EMC) qui est essentiel pour la dégradation des transcrits méiotiques. Par des approches de biologie structurale et de biochimie, nous avons montré qu'Erh1 s'assemble en homodimère in vitro et in vivo, en accord avec des analyses récentes. Des mutations qui empêchent l'homodimérisation d'Erh1 mais préservent son interaction avec Mmi1 entraînent l'accumulation de transcrits méiotiques en raison d'un défaut de liaison de Mmi1 à ses cibles ARN. L'homodimérisation d’Erh1 est également nécessaire pour séquestrer Mmi1 dans le complexe Mei2-meiRNA et assurer la progression de la méiose. Ainsi, l'assemblage d’EMC est essentiel pour la reconnaissance et la dégradation des transcrits méiotiques par Mmi1 dans les cellules mitotiques et contribue à l'inactivation de cette dernière au début de la méiose. Des travaux antérieurs ont montré que, pendant la croissance végétative, Mmi1 recrute le complexe Ccr4-Not pour ubiquitinyler et limiter l’accumulation de son propre inhibiteur Mei2, maintenant ainsi son activité dans la dégradation des ARNs méiotiques. Nous avons identifié un lncRNA, différent de meiRNA et appelé mamRNA (Mmi1- and Mei2-associated RNA), qui sert de plateforme à Mmi1 pour cibler Mei2 vers le complexe Ccr4-Not. Réciproquement, lorsque cette régulation négative de Mei2 est défectueuse, mamRNA est nécessaire pour l'inactivation de Mmi1 par les niveaux élevés de Mei2. Des expériences d’hybridation in situ par fluorescence en molécules uniques (smFISH) ont également montré que mamRNA est localisé dans un corps nucléaire contenant Mmi1, suggérant que le contrôle mutuel de Mmi1 et Mei2 est confiné dans l’espace. mamRNA peut également relayer meiRNA pour inhiber Mmi1 et favoriser la progression de la méiose. mamRNA apparait donc comme un régulateur critique des activités de Mmi1 et Mei2 pour ajuster la dégradation des ARNs méiotiques et modeler la transition de la mitose vers la méiose.In the fission yeast S. pombe, a subset of meiosis-specific genes is constitutively transcribed during the mitotic cell cycle. To prevent untimely expression of the meiotic program and premature initiation of sexual differentiation, cells have evolved an RNA degradation system that selectively eliminates the corresponding meiotic transcripts. This process requires the YTH-family RNA-binding protein Mmi1, which recognizes cis-elements within RNA molecules (UNAAAC motifs) and targets them for degradation by the nuclear exosome. At the onset of meiosis, Mmi1 is sequestered in a ribonucleoparticle composed of the RNA-binding protein Mei2 and the long non-coding RNA (lncRNA) meiRNA, thereby allowing expression of meiotic genes and meiosis progression. My PhD work consisted in studying the mechanisms by which Mmi1 promotes the degradation of meiotic transcripts and how its activity is regulated during both the mitotic and meiotic cell cycles. During vegetative growth, Mmi1 tightly associates with the evolutionarily conserved Erh1 protein to form the heterotetrameric Erh1-Mmi1 complex (EMC) that is essential for the degradation of meiotic transcripts. Using biochemical and structural approaches, we have shown that Erh1 assembles as a homodimer in vitro and in vivo, consistent with recent analyses. Mutations that disrupt Erh1 homodimerization but preserve interaction with Mmi1 result in the accumulation of meiotic transcripts due to inefficient binding of Mmi1 to its RNA targets. Erh1 homodimerization is also required for Mmi1 luring by the Mei2-meiRNA complex and meiosis progression. Thus, EMC assembly is essential for the recognition and degradation of meiotic transcripts by Mmi1 in mitotic cells and contributes to Mmi1 inactivation at meiosis onset. Previous work showed that, during vegetative growth, Mmi1 recruits the conserved Ccr4-Not complex to ubiquitinylate and downregulate a pool of its own inhibitor Mei2, thereby maintaining its activity in meiotic RNA degradation. We have identified a lncRNA, different from meiRNA and termed mamRNA (Mmi1- and Mei2-associated RNA), to which Mmi1 associates to target Mei2 to the Ccr4-Not complex. Conversely, when Mei2 downregulation is impaired, mamRNA is necessary for Mmi1 inactivation by increased Mei2 levels. Single molecule RNA FISH experiments also indicated that mamRNA localizes to a nuclear body enriched in Mmi1, suggesting that the mutual control of Mmi1 and Mei2 is spatially confined. mamRNA can also take over meiRNA to inhibit Mmi1 and promote meiosis progression. Therefore, mamRNA emerges as a critical regulator of Mmi1 and Mei2 activities to fine tune meiotic RNA degradation and shape the mitosis to meiosis transition
