Human T-cell leukemia virus type 1 (HTLV-1) is the etiological agent of adult T-cell leukemia/lymphoma (ATLL), an aggressive malignant proliferation of activated CD4+ T lymphocytes. The viral Tax oncoprotein is critically involved in both HTLV-1-replication and T-cell proliferation, a prerequisite to the development of ATLL. In this study, we investigated the in vivo contribution of the Tax PDZ domain-binding motif (PBM) to the lymphoproliferative process. To that aim, we examined T-cell proliferation in humanized mice (hu-mice) carrying a human hemato-lymphoid system infected with either a wild type (WT) or a Tax PBM-deleted (ΔPBM) provirus. We observed that the frequency of CD4+ activated T-cells in the peripheral blood and in the spleen was significantly higher in WT than in ΔPBM hu-mice. Likewise, human T-cells collected from WT hu-mice and cultivated in vitro in presence of interleukin-2 were proliferating at a higher level than those from ΔPBM animals. We next examined the association of Tax with the Scribble PDZ protein, a prominent regulator of T-cell polarity, in human T-cells analyzed either after ex vivo isolation or after in vitro culture. We confirmed the interaction of Tax with Scribble only in T-cells from the WT hu-mice. This association correlated with the presence of both proteins in aggregates at the leading edge of the cells and with the formation of long actin filopods. Finally, data from a comparative genome-wide transcriptomic analysis suggested that the PBM-PDZ association is implicated in the expression of genes regulating proliferation, apoptosis and cytoskeletal organization. Collectively, our findings suggest that the Tax PBM is an auxiliary motif that contributes to the sustained growth of HTLV-1 infected T-cells in vivo and in vitro and is essential to T-cell immortalization.
Abstract Embryonic stem cell (ESC) fate decisions are regulated by a complex molecular circuitry that requires tight and coordinated gene expression regulations at multiple levels from chromatin organization to mRNA processing. Recently, ribosome biogenesis and translation have emerged as key pathways that efficiently control stem cell homeostasis. However, the molecular mechanisms underlying the regulation of these pathways remain largely unknown to date. Here, we analyzed the expression, in mouse ESCs, of over 300 genes involved in ribosome biogenesis and we identified RSL24D1 as the most differentially expressed between self-renewing and differentiated ESCs. RSL24D1 is highly expressed in multiple mouse pluripotent stem cell models and its expression profile is conserved in human ESCs. RSL24D1 is associated with nuclear pre-ribosomes and is required for the maturation and the synthesis of 60S subunits in mouse ESCs. Interestingly, RSL24D1 depletion significantly impairs global translation, particularly of key pluripotency factors, including POU5F1 and NANOG, as well as components of the polycomb repressive complex 2 (PRC2). Consistently, RSL24D1 is required for mouse ESC self-renewal and proliferation. Taken together, we show that RSL24D1-dependant ribosome biogenesis is required to both sustain the expression of pluripotent transcriptional programs and silence developmental programs, which concertedly dictate ESC homeostasis.
Abstract Embryonic stem cell (ESC) fate decisions are regulated by a complex circuitry that coordinates gene expression at multiple levels from chromatin to mRNA processing. Recently, ribosome biogenesis and translation have emerged as key pathways that efficiently control stem cell homeostasis, yet the underlying molecular mechanisms remain largely unknown. Here, we identified RSL24D1 as highly expressed in both mouse and human pluripotent stem cells. RSL24D1 is associated with nuclear pre-ribosomes and is required for the biogenesis of 60S subunits in mouse ESCs. Interestingly, RSL24D1 depletion significantly impairs global translation, particularly of key pluripotency factors and of components from the Polycomb Repressive Complex 2 (PRC2). While having a moderate impact on differentiation, RSL24D1 depletion significantly alters ESC self-renewal and lineage commitment choices. Altogether, these results demonstrate that RSL24D1-dependant ribosome biogenesis is both required to sustain the expression of pluripotent transcriptional programs and to silence PRC2-regulated developmental programs, which concertedly dictate ESC homeostasis.
Abstract The regulators that stall ribosome translocation are poorly understood. We find that polyglutamine-expanded mutant Huntingtin (mHtt), the Huntington’s disease (HD) causing protein, promotes ribosome stalling and physiologically suppresses protein synthesis. A comprehensive, genome-wide analysis of ribosome footprint profiling (Ribo-Seq) revealed widespread ribosome stalling on mRNA transcripts and a shift in the distribution of ribosomes toward the 5’ end, with single-codon unique pauses on selected mRNAs in HD cells. In Ribo-Seq, we found fragile X mental retardation protein (FMRP), a known regulator of ribosome stalling, translationally upregulated and it co-immunoprecipitated with mHtt in HD cells and postmortem brain. Depletion of FMRP gene, Fmr1 , however, did not affect the mHtt-mediated suppression of protein synthesis or ribosome stalling in HD cells. Consistent with this, heterozygous deletion of Fmr1 in Q175FDN-Het mouse model, Q175FDN-Het; Fmr1 +/– , showed no discernable phenotype, but a subtle deficit in motor skill learning. On the other hand, depletion of mHtt, which binds directly to ribosomes in an RNase-sensitive manner, enhanced global protein synthesis, increased ribosome translocation and decreased stalling. This mechanistic knowledge advances our understanding of the inhibitory role of mHtt in ribosome translocation and may lead to novel target(s) identification and therapeutic approaches that modulate ribosome stalling in HD. One Sentence Summary Huntington’s disease (HD) protein, mHtt, binds to ribosomes and affects their translocation and promotes stalling independent of the fragile X mental retardation protein.
La regulation dynamique de la synthese des proteines en fonction des besoins de la cellule facilite son adaptation face aux fluctuations de l’environnement. Malgre l’importance de la regulation de la traduction au cours du processus d’expression des genes, l’impact de ce mecanisme sur des processus biologiques fondamentaux, comme la mise en place d’une reponse immunitaire, reste mal compris. Grâce au developpement de nouvelles technologies basees sur l’utilisation du sequencage a haut debit, comme le ribosome profiling, il est desormais possible d’etudier en details la facon dont la synthese des proteines est controlee. Le monosome vs polysome footprinting est une nouvelle methode qui permet d’etudier la traduction des ARN messagers (ARNm) selon leur association avec un seul ribosome (monosome) ou avec plusieurs ribosomes (polysomes). Au cours de ma these, j’ai identifie les parametres essentiels pour la mise en place d’une experience de monosome vs polysome footprinting donnant des resultats fiables en utilisant des macrophages primaires derives de la moelle osseuse de souris. Je me suis interessee a ce type de cellules immunitaires particulier car elles presentent une grande capacite a detecter des modifications dans leur environnement et a modifier leur taux d’expression de proteines en fonction des signaux recus. Leur grande plasticite est notamment essentielle pour assurer leurs diverses fonctions de protection de l’organisme, comme le declenchement et la resolution de la reponse inflammatoire. La methode de monosome vs polysome footprinting ayant ete initialement developpee chez la levure, son utilisation avec un modele d’etude different a necessite de nombreuses modifications du protocole. Suite a cette phase de developpement technologique, j’ai pu confirmer que les monosomes, une population de ribosomes historiquement consideres comme inactifs, sont activement impliques dans le processus de traduction dans les macrophages primaires de souris. Les donnees obtenues ont egalement permis d’identifier des caracteristiques communes entre les ARNm enrichis dans les monosomes chez la levure et dans les macrophages murins. La regulation de la synthese des proteines via l’association a des monosomes ou a des polysomes pourrait donc etre un mecanisme conserve chez les organismes eucaryotes. Enfin, le travail d’optimisation realise dans les macrophages primaires murins ouvre la possibilite d’etudier l’effet de la regulation de la traduction sur la mise en place et la resolution de la reponse inflammatoire de facon tres detaillee.
Abstract The polyglutamine expansion of huntingtin (mHTT) causes Huntington disease (HD) and neurodegeneration, but the mechanisms remain unclear. Here, we found that mHtt promotes ribosome stalling and suppresses protein synthesis in mouse HD striatal neuronal cells. Depletion of mHtt enhances protein synthesis and increases the speed of ribosomal translocation, while mHtt directly inhibits protein synthesis in vitro. Fmrp, a known regulator of ribosome stalling, is upregulated in HD, but its depletion has no discernible effect on protein synthesis or ribosome stalling in HD cells. We found interactions of ribosomal proteins and translating ribosomes with mHtt. High-resolution global ribosome footprint profiling (Ribo-Seq) and mRNA-Seq indicates a widespread shift in ribosome occupancy toward the 5′ and 3′ end and unique single-codon pauses on selected mRNA targets in HD cells, compared to controls. Thus, mHtt impedes ribosomal translocation during translation elongation, a mechanistic defect that can be exploited for HD therapeutics.
Abstract Embryonic stem cell (ESC) fate decisions are regulated by a complex molecular circuitry that requires tight and coordinated gene expression regulations at multiple levels from chromatin organization to mRNA processing. Recently, ribosome biogenesis and translation have emerged as key regulatory pathways that efficiently control stem cell homeostasis. However, the molecular mechanisms underlying the regulation of these pathways remain largely unknown to date. Here, we analyzed the expression, in mouse ESCs, of over 300 genes involved in ribosome biogenesis and we identified RSL24D1 as the most differentially expressed between self-renewing and differentiated ESCs. RSL24D1 is highly expressed in multiple mouse pluripotent stem cell models and its expression profile is conserved in human ESCs. RSL24D1 is associated with nuclear pre-ribosomes and is required for the maturation and the synthesis of 60S subunits in mouse ESCs. Interestingly, RSL24D1 depletion significantly impairs global translation, particularly of key pluripotency factors, including POU5F1 and NANOG, as well as components of the polycomb repressive complex 2 (PRC2). Consistently, RSL24D1 is required for mouse ESC self-renewal and proliferation. Taken together, we show that RSL24D1-dependant ribosome biogenesis is required to both sustain the expression of pluripotent transcriptional programs and silence developmental programs, which concertedly dictate ESC homeostasis.
Programmable nucleases have enabled rapid and accessible genome engineering in eukaryotic cells and living organisms. However, their delivery into target cells can be technically challenging when working with primary cells or in vivo. Here, we use engineered murine leukemia virus-like particles loaded with Cas9-sgRNA ribonucleoproteins (Nanoblades) to induce efficient genome-editing in cell lines and primary cells including human induced pluripotent stem cells, human hematopoietic stem cells and mouse bone-marrow cells. Transgene-free Nanoblades are also capable of in vivo genome-editing in mouse embryos and in the liver of injected mice. Nanoblades can be complexed with donor DNA for "all-in-one" homology-directed repair or programmed with modified Cas9 variants to mediate transcriptional up-regulation of target genes. Nanoblades preparation process is simple, relatively inexpensive and can be easily implemented in any laboratory equipped for cellular biology.
Abstract Programmable nucleases have enabled rapid and accessible genome engineering in eukaryotic cells and living organisms. However, their delivery into target cells can be technically challenging when working with primary cells or in vivo . Using engineered murine leukemia virus-like particles loaded with Cas9/sgRNA ribonucleoproteins (“Nanoblades”), we were able to induce efficient genome-editing in cell lines and primary cells including human induced pluripotent stem cells, human hematopoietic stem cells and mouse bone-marrow cells. Transgene-free Nanoblades were also capable of in vivo genome-editing in mouse embryos and in the liver of injected mice. Nanoblades can be complexed with donor DNA for “all-in-one” homology-directed repair or programmed with modified Cas9 variants to mediate transcriptional up-regulation of target genes. Nanoblades preparation process is simple, relatively inexpensive and can be easily implemented in any laboratory equipped for cellular biology.
