Project description:Increasing evidence suggests that Long non-coding RNAs (LncRNAs) represent a new class of regulators of stem cells. However, the roles of LncRNAs in stem cell maintenance and myogenesis remain largely unexamined. For this study, hundreds of novel intergenic LncRNAs were identified that are expressed in myoblasts and regulated during differentiation. One of these LncRNAs, termed LncMyoD, is encoded next to the Myod gene and is directly activated by MyoD during myoblast differentiation. Knockdown of LncMyoD strongly inhibits terminal muscle differentiation largely due to a failure to exit the cell cycle. LncMyoD directly binds to IGF2-mRNA-binding-protein 2 (IMP2) and negatively regulates IMP2-mediated translation of proliferation genes such as N-Ras and c-Myc. While the RNA sequence of LncMyoD is not well-conserved between human and mouse, its locus, gene structure and function is preserved. The MyoD-LncMyoD-IMP2 pathway elucidates a mechanism as to how MyoD blocks proliferation to create a permissive state for differentiation. In order to perform an unbiased search for downstream signaling pathways perturbed by LncMyodD downregulation, microarrays were performed on myoblasts treated with control vs LncMyoD shRNAs. Total RNA was extracted using the TRIzol reagent (Invitrogen) and purified with Qiagen RNeasy separation columns (Qiagen) from myoblasts treated with control vs. LncMyoD shRNA. First-strand cDNA was synthesized and hybridized to GeneChip Mouse Genome 430 2.0 Array (Affymetrix).
Project description:Increasing evidence suggests that Long non-coding RNAs (LncRNAs) represent a new class of regulators of stem cells. However, the roles of LncRNAs in stem cell maintenance and myogenesis remain largely unexamined. For this study, hundreds of novel intergenic LncRNAs were identified that are expressed in myoblasts and regulated during differentiation. One of these LncRNAs, termed LncMyoD, is encoded next to the Myod gene and is directly activated by MyoD during myoblast differentiation. Knockdown of LncMyoD strongly inhibits terminal muscle differentiation largely due to a failure to exit the cell cycle. LncMyoD directly binds to IGF2-mRNA-binding-protein 2 (IMP2) and negatively regulates IMP2-mediated translation of proliferation genes such as N-Ras and c-Myc. While the RNA sequence of LncMyoD is not well-conserved between human and mouse, its locus, gene structure and function is preserved. The MyoD-LncMyoD-IMP2 pathway elucidates a mechanism as to how MyoD blocks proliferation to create a permissive state for differentiation. In order to perform an unbiased search for downstream signaling pathways perturbed by LncMyodD downregulation, microarrays were performed on myoblasts treated with control vs LncMyoD shRNAs.
Project description:The Igf2 mRNA binding protein2/Imp2 was selectively deleted from adult mouse muscle; two phenotypes were observed: modestly decreased accrual of skeletal muscle mass after weaning and reduced wheel running activity but normal forced treadmill performance. Reduced voluntary activity occurs when fed a high fat diet but is normalized when consuming standard chow. The reduced muscle mass is due to diminished autocrine Igf2 production, reduced Akt1 activation, disinhibition of Gsk3α and reduced protein synthesis, without altered mTOR complex1 activity. The diet-dependent reduction in spontaneous exercise is accompanied by suboptimal muscle fatty acid oxidation, caused by reduced PPARα mRNA and protein, the former an Imp2 client. Nevertheless, in contrast to global Imp2 deficiency, muscle specific Imp2 inactivation does not alter glucose tolerance or the hypoglycemic effect of insulin. Imp2 deficiency in skeletal muscle reduces autocrine production of Igf2 and fiber growth and disorders nutrient metabolism so as to reduce voluntary physical activity.
Project description:Tissue regeneration depends on the timely activation of adult stem cells. In skeletal muscle, the adult stem cells maintain a quiescent state and proliferate upon injury. We show that muscle stem cells (MuSCs) use direct translational repression to maintain the quiescent state. High resolution single molecule and single cell analyses demonstrate that quiescent MuSCs express high levels of Myogenic Differentiation1 (MyoD) transcript in vivo, whereas MyoD protein is absent. RNA pulldowns and co-stainings show that MyoD mRNA interacts with Staufen1, a potent regulator of mRNA localization, translation, and stability. Staufen1 prevents MyoD translation through its interaction with the MyoD 3’UTR. MuSCs from Staufen1 heterozygous (Staufen1+/-) mice have increased MyoD protein expression, exit quiescence, and begin proliferating. Conversely, blocking MyoD translation maintains the quiescent phenotype. Collectively, our data show that MuSCs express MyoD mRNA and actively repress its translation to remain quiescent yet primed for activation.
Project description:Long non-coding RNAs (lncRNAs) are important regulators of skeletal muscle physiology, with altered expression noted in several human diseases including type 2 diabetes. Here we report downregulation of TMEM9B-AS1, a previously uncharacterized lncRNA, in skeletal muscle of men with type 2 diabetes. We demonstrate that loss of TMEM9B-AS1 in primary human myotubes leads to reduction in protein synthesis, concomitant with reduced phosphorylation of ribosomal protein S6, downstream of ERK and mTOR pathways. Moreover, we show that TMEM9B-AS1 plays a pivotal role in the regulation of ribosomal biogenesis by facilitating mRNA stabilization of the transcription factor MYC through a direct physical interaction with the RNA-binding protein IGF2BP1. Disrupted ribosomal biogenesis resulting from downregulation of TMEM9B-AS1 links to the decrease in skeletal muscle mass observed in individuals with type 2 diabetes, shedding new light on the molecular mechanisms underlying this metabolic disorder.
Project description:Skeletal muscle contains long multinucleated and contractile structures known as muscle fibers, which arise from the fusion of myoblasts into nucleated myotubes during myogenesis. The myogenic regulatory factor (MRF) MYF5 is the earliest to be expressed during myogenesis and functions as a transcription factor in muscle progenitor cells (satellite cells) and myocytes. In mouse C2C12 myocytes, MYF5 is implicated in the initial steps of myoblast differentiation into myotubes. Ribonucleoprotein immunoprecipitation (RIP) analysis showed that MYF5 bound a subset of myoblast mRNAs; prominent among them was Ccnd1 mRNA, which encodes the key cell cycle regulator CCND1 (Cyclin D1). Biotin-RNA pulldown, UV-crosslinking, and gel shift experiments indicated that MYF5 was capable of binding the 3' untranslated region (UTR) and the coding region (CR) of Ccnd1 mRNA. MYF5 silencing in proliferating growing myoblasts revealed that and MYF5 promoted CCND1 translation, and it also modestly increased transcription of Ccnd1 mRNA. Importantly, silencing MYF5 reduced myoblast growth as well as differentiation of myoblasts into myotubes, while overexpressing MYF5 in C2C12 cells upregulated CCND1 expression. We propose that MYF5 enhances early myogenesis in part by coordinately elevating Ccnd1 transcription and Ccnd1 mRNA translation. Four replicates were utilized from either Control (IgG) or MYF5-immunoprecipitated RNA samples from C2C12 cells growing in either growth medium (GM) or differentiation medium (DM) for a total of sixteen samples.
Project description:Skeletal muscle contains long multinucleated and contractile structures known as muscle fibers, which arise from the fusion of myoblasts into nucleated myotubes during myogenesis. The myogenic regulatory factor (MRF) MYF5 is the earliest to be expressed during myogenesis and functions as a transcription factor in muscle progenitor cells (satellite cells) and myocytes. In mouse C2C12 myocytes, MYF5 is implicated in the initial steps of myoblast differentiation into myotubes. Ribonucleoprotein immunoprecipitation (RIP) analysis showed that MYF5 bound a subset of myoblast mRNAs; prominent among them was Ccnd1 mRNA, which encodes the key cell cycle regulator CCND1 (Cyclin D1). Biotin-RNA pulldown, UV-crosslinking, and gel shift experiments indicated that MYF5 was capable of binding the 3' untranslated region (UTR) and the coding region (CR) of Ccnd1 mRNA. MYF5 silencing in proliferating growing myoblasts revealed that and MYF5 promoted CCND1 translation, and it also modestly increased transcription of Ccnd1 mRNA. Importantly, silencing MYF5 reduced myoblast growth as well as differentiation of myoblasts into myotubes, while overexpressing MYF5 in C2C12 cells upregulated CCND1 expression. We propose that MYF5 enhances early myogenesis in part by coordinately elevating Ccnd1 transcription and Ccnd1 mRNA translation.
Project description:The gene encoding the IGF2 mRNA binding protein-2/IMP2 is amplified and overexpressed in many cancers, accompanied by a poorer prognosis. Mice deficient in IMP2 exhibit a longer lifespan and a reduced tumor burden at old age. Herein we show in a diverse array of cancer cells that IMP2 overexpression stimulates and IMP2 elimination diminishes proliferation by 50-80%. In addition to its known ability to promote IGF2 abundance, we find that IMP2 strongly promotes IGF action, by binding and stabilizing HMGA1 mRNA. The HMGA1 DNA binding protein, a known oncogene, suppresses the abundance of IGFBP2 and Grb14, inhibitors of IGF action. IMP2 stabilization of HMGA1 mRNA plus IMP2 stimulated IGF2 production synergistically drive cancer cell proliferation and account for IMP2’s tumor promoting action. IMP2’s ability to promote proliferation and IGF action requires mTOR-catalyzed IMP2 phosphorylation.