Projets
english

Les membres du groupe collaborent à plusieurs projets distincts:

Le maintien des télomères:

La télomérase est une ribonucléoprotéine qui participe à la réplication des extrémitéschromosomiques. Une région de la composante ARN (TER pour TElomerase RNA) de la télomérase est complémentaire aux répétitions télomériques et sert de matrice pour leurs synthèses. La régulation de la fonction télomérique est associée avec une expression génétique altérée, la sénescence cellulaire et le cancer. La télomérase est un intéressant modèle d'étude, non seulement de par son rôle dans la transformation cellulaire et le vieillissement, mais également de par son implication évolutive dans l'origine des répétitions télomériques. Il a été proposé que les télomérases sont les descendantes d'une ARN polymérase ARN-dépendante qui aurait évolué en ADN polymérase dans les cellules modernes. Trois membres du groupe ARN de Sherbrooke (Chabot, Wellinger, et Abou Elela) étudient présentement la structure et la fonction de l'ARN des télomérases et cherchent à réguler sa fonction. Pour des exemples de ces travaux, voir:
  • Patry C, Bouchard L, Labrecque P, Gendron D, Lemieux B, Toutant J, Lapointe E, Wellinger R, Chabot B. Small interfering RNA-mediated reduction in heterogeneous nuclear ribonucleoparticule A1/A2 proteins induces apoptosis in human cancer cells but not in normal mortal cell lines. Cancer Res. 2003 Nov 15;63(22):7679-88.
  • LaBranche H, Dupuis S, Ben-David Y, Bani MR, Wellinger RJ, Chabot B. Telomere elongation by hnRNP A1 and a derivative that interacts with telomeric repeats and telomerase. Nat Genet. 1998 Jun;19(2):199-202.

La maturation des ARN et les ARN catalytiques:

Chez les eucaryotes, les ARN pré-messagers subissent plusieurs modifications dans le but de former des ARN messagers fonctionnels. Ces modifications incluent l'épissage des introns, la formation de la structure coiffe, l'édition et la formation de la queue de poly(A). Ces différentes modifications sont cruciales et contribuent à déterminer le phénotype cellulaire, elles sont également une source importante de variations génétiques. Actuellement, plusieurs membres du groupe ARN s'intéressent aux mécanismes, aux fonctions et aux applications de la maturation des ARN. Ainsi, Wellinger, Chabot, et Abou Elela développent des méthodes d'inhibition de l'épissage dans les cellules de mammifères pour mieux comprendre le mécanisme d'action (voir: Villemaire J, Dion I, Elela SA, Chabot B. Reprogramming alternative pre-messenger RNA splicing through the use of protein-binding antisense oligonucleotides. J Biol Chem. 2003, 278: 50031-9.).

D'autres membres du groupe ARN s'intéressent aux protéines et aux ARN impliqués dans la maturation des ARN. Par exemple, Lafontaine, Abou Elela, et Bisaillon ont récemment unis leurs efforts pour étudier la cinétique de coupure de l'ARN de l'orthologue bactérien de la RNAse III, la protéine Rnt1. Perreault et Bisaillon quant à eux, caractérisent les paramètres thermodynamiques impliqués dans le repliement des molécules d'ARN (par exemple, voir: Reymond C, Bisaillon M, Perreault JP. Monitoring of an RNA multistep folding pathway by isothermal titration calorimetry. Biophys 2009, 96: 132-140). Ces deux chercheurs, utilisent également leurs expertises respectives pour évaluer les déterminants moléculaires de certaines enzymes qui participent à la maturation des ARN messagers (par exemple, voir: Soulière M, Perreault JP, Bisaillon M. Magnesuim-biding studies reveal fundamental differences between closely related RNA triphosphotoses. Nucleic Acid Res 2008, 36: 451-461). Finalement, les travaux de Massé et Lafontaine visent à caractériser les riboswitches, ces ARN qui ont la capacité de lier divers ligands et d'affecter l'expression génétique.


L'épissage alternatif:

Les ARN pré-messagers sont exprimés et modifiés dans le noyau cellulaire. Les évidences récentes démontrent un lien étroit entre la transcription des ARN et leur maturation. Chez les eucaryotes, les gènes sont constitués d'une suite d'exons et d'introns alternés. Lors de la transcription, les ARN pré-messagers sont épissés afin de former des ARN messagers matures. L'épissage consiste en l'excision des introns et en la ligature des exons. L 'ARNm mature, constitué des seuls exons, est alors exporté vers le cytoplasme pour être traduit en protéine. Chez la levure, de nombreux gènes ne contiennent pas d'introns. Deux sentiers d'exportation des ARN messagers existent donc: un sentier intron-dépendant et un sentier intron-indépendant. Certains membres du groupe ARN de Sherbrooke cherchent à élucider les mécanismes impliqués dans ces sentiers en inhibant spécifiquement certains événement d'épissage spécifique ou encore en éliminant certains introns et en observant les effets cellulaires.






Projects
français

The members of our group are involved in many collaborative projects:

Telomere maintenance:

Telomerase is a ribonucleoprotein particle that serves as a reverse transcriptase capable of replicating the chromosome end. A region in the RNA component (TER for TElomerase RNA) of telomerase is complementary to telomeric repeats and serves as template for their synthesis. The regulation of telomerase function is associated with altered gene expression, cellular senescence, and cancer. Telomerase is an attractive molecule to study, not only because of its involvement in cell transformation and aging, but also as a fossil that may have led to the origin of the telomeric repeats. It was proposed that telomerases are the descendents of an RNA-directed RNA polymerase that evolved into RNA-directed DNA polymerase in modern cells. Three members of the Sherbrooke RNA group (Chabot, Wellinger, and Abou Elela) are currently studying telomerase RNA structure and function and are devising ways to regulate its function at telomeres. For example of this work see:
  • Patry C, Bouchard L, Labrecque P, Gendron D, Lemieux B, Toutant J, Lapointe E, Wellinger R, Chabot B. Small interfering RNA-mediated reduction in heterogeneous nuclear ribonucleoparticule A1/A2 proteins induces apoptosis in human cancer cells but not in normal mortal cell lines. Cancer Res. 2003 Nov 15;63(22):7679-88.
  • LaBranche H, Dupuis S, Ben-David Y, Bani MR, Wellinger RJ, Chabot B. Telomere elongation by hnRNP A1 and a derivative that interacts with telomeric repeats and telomerase. Nat Genet. 1998 Jun;19(2):199-202.

RNA processing, modification, and catalysis:

In eukaryotes, nascent RNA often contains filler sequences that are removed to produce the functional RNA transcript. These fillers exist in the form of spacers between independently functional sequences, as extensions at the periphery of the mature sequence, or as introns that interrupt the coding sequence of a mature RNA. Generally, spacer RNAs are removed by endonucleolytic cleavage leading to the formation of discrete mature RNAs, as is the case during pre-rRNA processing. RNA extensions are often found in stable non-coding RNA transcripts like snRNAs, and they are removed by a combination of endonucleolytic and exonucleolytic cleavages. In contrast, introns are discarded through a splicing reaction that removes them by two specific transesterification reactions to form the mature RNA and the excised intron. These different processing reactions determine the phenotype of the eukaryotic cell and are thought to be the source of the genetic variations that drive evolution. Currently, many questions regarding the evolution, functions, mechanisms, and applications of RNA processing are investigated. Wellinger, Chabot, and Abou Elela are designing ways to inhibit splicing in mammalian cells and understand its basic mechanism of function (see Villemaire J, Dion I, Elela SA, Chabot B. Reprogramming alternative pre-messenger RNA splicing through the use of protein-binding antisense oligonucleotides. J Biol Chem. 2003, 278: 50031-9.).

Various enzymes are involved in the synthesis and maturation of RNA molecules. Members of the Sherbrooke RNA group are studying both the RNA and proteins components involved in these processes. For instance, Lafontaine, Abou Elela, and Bisaillon recently joined efforts to study the kinetics of RNA cleavage in real time using the yeast orthologue of bacterial RNAse III, Rnt1. Perreault and Bisaillon are characterizing the thermodynamic parameters involved in the folding of RNA molecules (for example, see: Reymond C, Bisaillon M, Perreault JP. Monitoring of an RNA multistep folding pathway by isothermal titration calorimetry. Biophys 2009, 96: 132-140). These two researchers are also using their respective expertise to evaluate the molecular determinants of enzymes that are involved in the synthesis and modification of mRNAs (for example, see: Soulière M, Perreault JP, Bisaillon M. Magnesuim-biding studies reveal fundamental differences between closely related RNA triphosphotoses. Nucleic Acid Res 2008, 36: 451-461). Finally, Massé and Lafontaine are currently joining efforts to study riboswitches, molecules that can directly bind a small target molecule, and whose binding of the target affects the gene's activity.


Alternative splicing:

Pre-messenger RNAs are transcribed and processed in the nucleus. Current evidence suggests a link between transcription and processing. Moreover, the nuclear export of intron-containing pre-mRNAs is thought to be linked to RNA splicing and 3' processing. This coupling may be important for the efficiency of transport, but is not strictly required since the transport of pre-mRNA lacking introns are not affected by mutating components of the splicing machinery. In yeast, the intron-dependent and intron-independent pathways of mRNA export appear to require different factors. Although the proportion of yeast genes that lack introns is small, the intron-containing pre-mRNAs encompass close to 30% of the bulk of mRNAs. One possibility is that yeast introns are required to direct a subset of mRNAs to a specific export pathway, which is controlled by specific environmental cues. For example, because the majority of the expressed intron-containing mRNA codes for ribosomal proteins, a lack of nutrients may rapidly block the transport of intron-containing mRNA to prevent ribosome production. Alternatively, introns may be required for the coordination of complex biosynthetic pathways. For example, splicing may help in the coordination of ribosome biogenesis ensuring equal production of ribosomal proteins and RNAs. The group is currently addressing these questions either by inhibiting specific splicing events in mammalian cells and follow its effect on cell functions or by genetically removing introns from specific genes and follow its effect in yeast cells.