Extracellular matrix and integrins influence in the regulation of myogenic precursor cells behaviour

Tese de mestrado, Biologia (Biologia Molecular Humana), 2009, Universidade de Lisboa, Faculdade de CiênciasMyogenesis is the process by which undifferentiated dermomyotomal cells are specified for myogenesis, move towards the myotome where they differentiate into skeletal muscle cells that fuse into myotubes and later in development form myofibers which will constitute the skeletal muscles of the adult. The muscle precursor cells arise from the dermomyotome, an epithelial-like structure that is the source for skeletal muscle and dorsal dermis cells. Some cells, called satellite cells, go throughout part of this differentiation process but remain in a quiescent undifferentiated state (although committed to skeletal muscle fate). These cells are activated in the adult in case of muscle injury or enhanced exercise, for example. In this work we used a satellite cell-derived cell line, C2C12, and the mouse embryo to study the extracellular matrix (ECM) and integrins influence in myogenic determination and differentiation. Integrins are heterodimeric ECM receptors constituted by an α and a ß subunit that can induce, for example, migration or differentiation. The integrin ligand specificity is acquired by the combination of both subunits. Our studies have addressed that laminin-α6ß1 integrin interaction may be coordinating with Notch signaling the maintenance of undifferentiated dermomyotomal cells. By inhibiting Notch signaling, we observed precocious myogenic differentiation of dermomyotomal cells (by Myf5 expression) and the assembly of a laminin matrix around these cells. This result suggests that Myf5 induces laminin assembly. In vitro, fibronectin enhances C2C12 myoblasts alignment and migration. When we observed the myotubes of cells grown on fibronectin, we believe that the enhanced cell alignment imposed by fibronectin-α5ß1 integrin interaction will facilitate cell fusion. In vivo, we found that fibronectin is important for dermomyotome epithelial-integrity, especially through the polarization of N-cadherin, and that α5ß1 integrin signaling may also contribute to myogenic repression in the dermomyotome. These observations show that the ECM and integrins are of paramount importance in myoblast cell behaviour.Resumo alargado em português disponível no document

Dial M(RF) for myogenesis

The transcriptional regulatory network that controls the determination and differentiation of skeletal muscle cells in the embryo has at its core the four myogenic regulatory factors (MRFs) Myf5, MyoD, Mrf4 and MyoG. These basic helix–loop–helix transcription factors act by binding, as obligate heterodimers with the ubiquitously expressed E proteins, to the E-box sequence CANNTG. While all skeletal muscle cells have the same underlying function their progenitors arise at many sites in the embryo and it has become apparent that the upstream activators of the cascade differ in these various populations so that it can be switched on by a variety of inductive signals, some of which act by initiating transcription, some by maintaining it. The application of genome-wide approaches has provided important new information as to how the MRFs function to activate the terminal differentiation programme and some of these data provide significant mechanistic insights into questions which have exercised the field for many years. We also consider the emerging roles played by micro-RNAs in the regulation of both upstream activators and terminal differentiation genes.Peer reviewe

MyoD-expressing progenitors are essential for skeletal myogenesis and satellite cell development

AbstractSkeletal myogenesis in the embryo is regulated by the coordinated expression of the MyoD family of muscle regulatory factors (MRFs). MyoD and Myf-5, which are the primary muscle lineage-determining factors, function in a partially redundant manner to establish muscle progenitor cell identity. Previous diphtheria toxin (DTA)-mediated ablation studies showed that MyoD+ progenitors rescue myogenesis in embryos in which Myf-5-expressing cells were targeted for ablation, raising the possibility that the regulative behavior of distinct, MRF-expressing populations explains the functional compensatory activities of these MRFs. Using MyoDiCre mice, we show that DTA-mediated ablation of MyoD-expressing cells results in the cessation of myogenesis by embryonic day 12.5 (E12.5), as assayed by myosin heavy chain (MyHC) and Myogenin staining. Importantly, MyoDiCre/+;R26DTA/+ embryos exhibited a concomitant loss of Myf-5+ progenitors, indicating that the vast majority of Myf-5+ progenitors express MyoD, a conclusion consistent with immunofluorescence analysis of Myf-5 protein expression in MyoDiCre lineage-labeled embryos. Surprisingly, staining for the paired box transcription factor, Pax7, which functions genetically upstream of MyoD in the trunk and is a marker for fetal myoblasts and satellite cell progenitors, was also lost by E12.5. Specific ablation of differentiating skeletal muscle in ACTA1Cre;R26DTA/+ embryos resulted in comparatively minor effects on MyoD+, Myf-5+ and Pax7+ progenitors, indicating that cell non-autonomous effects are unlikely to explain the rapid loss of myogenic progenitors in MyoDiCre/+;R26DTA/+ embryos. We conclude that the vast majority of myogenic cells transit through a MyoD+ state, and that MyoD+ progenitors are essential for myogenesis and stem cell development

Glycogenome expression dynamics during mouse C2C12 myoblast differentiation suggests a sequential reorganization of membrane glycoconjugates

<p>Abstract</p> <p>Background</p> <p>Several global transcriptomic and proteomic approaches have been applied in order to obtain new molecular insights on skeletal myogenesis, but none has generated any specific data on glycogenome expression, and thus on the role of glycan structures in this process, despite the involvement of glycoconjugates in various biological events including differentiation and development. In the present study, a quantitative real-time RT-PCR technology was used to profile the dynamic expression of 375 glycogenes during the differentiation of C2C12 myoblasts into myotubes.</p> <p>Results</p> <p>Of the 276 genes expressed, 95 exhibited altered mRNA expression when C2C12 cells differentiated and 37 displayed more than 4-fold up- or down-regulations. Principal Component Analysis and Hierarchical Component Analysis of the expression dynamics identified three groups of coordinately and sequentially regulated genes. The first group included 12 down-regulated genes, the second group four genes with an expression peak at 24 h of differentiation, and the last 21 up-regulated genes. These genes mainly encode cell adhesion molecules and key enzymes involved in the biosynthesis of glycosaminoglycans and glycolipids (neolactoseries, lactoseries and ganglioseries), providing a clearer indication of how the plasma membrane and extracellular matrix may be modified prior to cell fusion. In particular, an increase in the quantity of ganglioside G_M3at the cell surface of myoblasts is suggestive of its potential role during the initial steps of myogenic differentiation.</p> <p>Conclusion</p> <p>For the first time, these results provide a broad description of the expression dynamics of glycogenes during C2C12 differentiation. Among the 37 highly deregulated glycogenes, 29 had never been associated with myogenesis. Their biological functions suggest new roles for glycans in skeletal myogenesis.</p

Positive Regulation of Myogenic bHLH Factors and Skeletal Muscle Development by the Cell Surface Receptor CDO

AbstractSkeletal myogenesis is controlled by bHLH transcription factors of the MyoD family that, along with MEF-2 factors, comprise a positive feedback network that maintains the myogenic transcriptional program. Cell-cell contact between muscle precursors promotes myogenesis, but little is known of the underlying mechanisms. CDO, an Ig superfamily member, is a component of a cell surface receptor complex found at sites of cell-cell contact that positively regulates myogenesis in vitro. We report here that mice lacking CDO display delayed skeletal muscle development. Additionally, satellite cells from these mice differentiate defectively in vitro. CDO functions to activate myogenic bHLH factors via enhanced heterodimer formation, most likely by inducing hyperphosphorylation of E proteins. The Cdo gene is, in turn, a target of MyoD. The promyogenic effect of cell-cell contact is therefore linked to the activity of myogenic bHLH factors. Furthermore, the myogenic positive feedback network extends from the cell surface to the nucleus

Histone Chaperones Regulate Mammalian Gene Expression

Histone chaperones are fundamental molecules that aid in the synthesis, translocation, and exchange of histones across the barrier of cytoplasm to nucleus. Regulation in repair, replication, and nucleosome assembly constitute the widely associated functions of histone chaperones. Recently, they have been associated with transcriptional regulation. Different stages of mammalian development have been correlated to the expression of histone chaperones. From oocyte and sperm till the formation and development of zygote, different histone chaperones demonstrated distinct regulatory roles. Efficient models of studying mammalian development include differentiation of embryonic stem cells (ESCs) to different lineages. Both in vitro and in vivo differentiation of mammalian cells exhibit regulation by different subtypes of histone chaperones. Due to the ethical issues concerning the use of embryos for the derivation of ESCs, induced pluripotent stem cells (iPSCs) were derived from pre-existing differentiated cells by a phenomenon called cellular reprogramming. Cellular reprogramming is characterized by erasure of pre-existing epigenetic signature to a new modulated epigenome. Histone chaperones serve as either facilitator or barrier to reprogramming. Here, we will discuss how histone chaperones could regulate the gene expression pattern by regulating epigenetic modification during the complex process of mammalian development and reprogramming

Heartbreak hotel: a convergence in cardiac regeneration

In February 2016, the Company of Biologists hosted an intimate gathering of leading international researchers at the forefront of experimental cardiovascular regeneration, with its emphasis on ‘Transdifferentiation and Tissue Plasticity in Cardiovascular Rejuvenation’. As I review here, participants at the workshop revealed how understanding cardiac growth and lineage decisions at their most fundamental level has transformed the strategies in hand that presently energize the prospects for human heart repair

Analysis of Protein Arginine Methyltransferase Function during Myogenic Gene Transcription: A Dissertation

Skeletal muscle differentiation requires synergy between tissue-specific transcription factors, chromatin remodeling enzymes and the general transcription machinery. Here we demonstrate that two distinct protein arginine methyltransferases are required to complete the differentiation program. Prmt5 is a type II methyltransferase, symmetrically dimethylates histones H3 and H4 and has been shown to play a role in transcriptional repression. An additional member of the Prmt family, Carm1 is a type I methyltransferase, and asymmetrically methylates histone H3 and its substrate proteins. MyoD regulates the activation of the early class of skeletal muscle genes, which includes myogenin. Prmt5 was bound to and dimethylates H3R8 at the myogenin promoter in a differentiation-dependent fashion. When proteins levels of Prmt5 were reduced by antisense, disappearance of H3R8 dimethylation and Prmt5 binding was observed. Furthermore, binding of Brg1 to regulatory sequences of the myogenin promoter was abolished. All subsequent events relying on Brg1 function, such as chromatin remodeling and stable binding by muscle specific transcription factors such as MyoD, were eliminated. Robust association of Prmt5 and dimethylation of H3R8 at myogenin promoter sequences was observed in mouse satellite cells, the precursors of mature myofibers. Prmt5 binding and histone modification were observed to a lesser degree in mature myofibers. Therefore, these results indicate that Prmt5 is required for dimethylating histone at the myogenin locus during skeletal muscle differentiation in order to facilitate the binding of Brg1, the ATPase subunit of the chromatin remodeling complex SWI/SNF. Further exploration of the role of Prmt5 during the activation of the late class of muscle genes revealed that though Prmt5 is associated with and dimethylates histones at the regulatory elements of late muscle genes in tissue and in culture, it was dispensable for late gene activation. Previous reports had indicated that Carm1 was involved during late gene activation. We observed that Carm1 was bound to and responsible for dimethylating histones at late muscle gene promoters in tissue and in culture. In contrast to Prmt5, a complete knockout of Carm1 resulted in abrogation of late muscle gene activation. Furthermore, loss of Carm1 binding and dimethylated histones resulted in a disappearance of Brg1 binding and chromatin remodeling at late muscle gene loci. Time course chromatin immunoprecipitations revealed that Carm1 binding and histone dimethylation occurred concurrently with the onset of late gene activation. In vitro binding assays revealed that an interaction between Carm1, myogenin and Mef2D exists. These results demonstrate that Carm1 is recruited to the regulatory sequences of late muscle genes via its interaction with either myogenin or Mef2D and is responsible for dimethylates histones in order to facilitate the binding of Brg1. Therefore, these results indicate that during skeletal muscle differentiation, distinct roles exist for these Prmts such that Prmt5 is required for activation of early genes while Carm1 is essential for late gene induction

Intracellular rols7 mRNA localization and the importance of Barren for mitosis in the embryonic myogenesis of Drosophila melanogaster

The body wall musculature of the D. melanogaster larva is a highly ordered assembly of striated myotubes that are formed by fusion of myoblasts, much like the skeletal muscle fibres of vertebrates. In this study, the embryonic development of this musculature is used as a genetic model system for myogenesis, muscle regeneration and related processes. Rols7 is a crucial protein in the signal transduction chain that controls the Actin filament branching necessary for myoblast fusion. In somatic muscle founder cells, the rols7 mRNA shows intracellular localization into one or more patches near the cell surface. This thesis demonstrates that the rols7 transcript’s 3’ untranslated region is necessary for its localization. A reporter mRNA with this trailer region as well as the 5’ untranslated region gets intracellularly localized in a way seemingly identical to the wild type pattern, even in the absence of native rols transcripts. The rols7 mRNA is shown to be intracellularly localized in the circular and longitudinal visceral muscle founder cells as well; in the latter it forms spots close to the tips of the spindle-shaped cells, near the expected sites of cell-cell fusion. At least for this latter cell type it can be suspected that rols7 mRNA localisation facilitates protein localisation and eventually myoblast fusion by preforming the Rols7 protein’s distribution pattern. In search of previously unknown factors involved in myogenesis, the muscle phenotype of the EMS-induced mutant line E831 is analyzed. As the cause for the disturbed arrangement of the embryonic body wall musculature a nonsense mutation of the Condensin subunit barren is identified. Cap-G, another Condensin subunit, is found to show a phenotype very similar to that of barren. While in a barren mutant both muscle founder cells and fusion competent myoblasts seem to get specified, muscle identity genes are expressed irregularly in a manner that corresponds to the perturbation of the muscle pattern. In every cell, the Condensin complex fulfills a variety of essential functions. To help clarify whether the muscle phenotype is connected to Condensin’s regulatory role during interphase or its function in chromosome segregation during mitosis, the time point at which Barren is needed in the musculature has to be identified. To this end, the Gal4-UAS system is used to express a barren rescue construct. Gal4 drivers are found to rescue the phenotype only if they express Barren considerably before the final cell division that gives rise to the muscle founder cells. This finding suggests that the muscle phenotype is caused by a mitotic defect. The mechanism behind the loss of muscle identity appears to be a phenomenon related to the genomic instability of cancer cell lines