No description available.

Skeletal muscles represent the largest tissue mass within the body and are primarily involved in the generation of force for voluntary movement. Skeletal muscles have a remarkable capacity to repair, due primarily to the actions of muscle stem cells (MuSCs). MuSCs are normally quiescent in adult skeletal muscle; however, in response to myotrauma (trauma to muscle tissue) from muscle injury or exercise, MuSCs become activated, either undergo self-renewal to replenish the quiescent population or commit to the myogenic lineage as myoblasts, proliferate, and differentiate into myotubes in vitro or fuse to existing myofibers in vivo. This process of generating new myofibers from quiescent MuSCs is termed myogenesis and a full understanding of how myogenesis is regulated remains to be understood. Mounting evidence suggests that amino acids, particularly the essential amino acid leucine, play a role in MuSC regulation. Leucine is specifically translocated and sensed by the L-type amino acid transporter 1 (LAT1); which facilitates leucine uptake in mature myofibers. Inside the cell, leucine activates mammalian or mechanistic target of rapamycin complex 1 (mTORC1) to stimulate cell growth, proliferation, and protein synthesis. Whether leucine has direct effects on myoblast function via LAT1 is unknown. Thus, our overall objective was to begin to characterize the role of LAT1 in myogenesis. Our results indicate that myoblasts differentially expressed LAT1 throughout myogenesis with peak protein content occurring during differentiation (p<0.05 vs. early proliferation). Further, our results indicate thatpharmacological LAT1 inhibition reduced myoblast expansion and differentiation in vitro (both p<0.05 vs. control). Interestingly, myoblast LAT1 protein content did not change in response to leucine supplementation in vitro; however, was lower under in vitro atrophic conditions (p<0.05 vs. control). Based on these findings, we conclude that LAT1 plays an important role in regulating myogenesis. As such, we uncover a novel role for LAT1 in regulating muscle mass via contributing to the control of MuSC function.

No description available.

Thesis (M.Sc.)--York University, 2006. Graduate Programme in Kinesiology and Health Science. / Typescript. Includes bibliographical references. Also available on the Internet. MODE OF ACCESS via web browser by entering the following URL: http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&res_dat=xri:pqdiss&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&rft_dat=xri:pqdiss:MR29615

Thesis (M.Sc.)--York University, 2008. Graduate Programme in Kinesiology and Health Science. / Typescript. Includes bibliographical references (leaves 66-90). Also available on the Internet. MODE OF ACCESS via web browser by entering the following URL: http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&res_dat=xri:pqdiss&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&rft_dat=xri:pqdiss:MR38743

No description available.

Muscle tissue is grown and maintained by muscle stem cells termed satellite cells. Activated satellite cells become myoblasts, which must proliferate then differentiate into functional muscle. This process, known as myogenesis, is controlled by a cascade of epigenetic regulatory events. One facet of this regulation is histone acetylation, which can be influenced by the availability of metabolites within a cell. In this study, the ability of glucose, pyruvate, or glutamine to change histone acetylation levels in cultured myoblasts was investigated. Changing concentrations of glucose or pyruvate had no effect but decreasing the availability of glutamine in cell culture from 2mM to 0.2mM resulted in proliferating myoblasts accruing a hyperacetylated histone phenotype. However, when the same concentration of glutamine was used on differentiating myoblasts the hyperacetylated phenotype was lost and no change to differentiation was observed. This study demonstrates the potentials and limitations of altering epigenetic acetylation with metabolic circumstance. -- Le développement du tissu musculaire est soutenu par les cellules souches musculaires, communément appelées cellules satellites. Les cellules satellites activées se transforment en myoblastes qui doivent ensuite proliférer et se différencier en muscle fonctionnel. Ce processus, connu comme myogenèse, est contrôlé par une cascade de régulation épigénétique. Un aspect de ce processus est l’acétylation d’histones, qui peut être influencée par la disponibilité de métabolites dans la cellule. Dans cette étude de cas, la capacité du glucose, pyruvate, ou glutamine à changer les niveaux d’acétylation d’histones a été examinée. Le changement des concentrations de glucose ou de pyruvate n’a généré aucun effet, mais la diminution de la disponibilité de la glutamine dans la culture cellulaire de 2mM à 0.2mM a eu pour résultat une prolifération de myoblastes présentant un phénotype d’histones hyper-acétylées. Pourtant, quand la même concentration de glutamine a été utilisée pour différencier les myoblastes, le phénotype hyper-acétylé n’a pas été observé et aucun changement de différenciation n’a pu être détecté. Cette étude démontre le potentiel et les limites des modifications de l’acétylation épigénétique selon les circonstances métaboliques.

No description available.

Skeletal muscles of the limb are derived from somites and their precursors migrate to the limb prior to muscle formation. Upon migration, a limited number of stem cells multiply and differentiate to give rise to fusion-competent muscle cells, which fuse to form the multinucleated myotubes. During the course of myogenesis there is thus a period of few days when cells at different developmental stages such as migrating, proliferating, differentiating and fully differentiated co-reside within the developing limb bud. Current understanding on how these cells interact and behave during early and later myogenesis in vivo is lacking. The aim of this project was to identify and further classify the mononucleated myogenic cells present within the developing limb muscle and examine their behaviours at different stages of myogenesis. The lack of an appropriate method to extract and visualise cellular constituents of developing muscles has been a major limitation hindering such investigations in vivo. In this project, we first developed a unique cell isolation method to extract mononucleated cells from developing muscles, allowing examination of mononucleated cells in vivo using immunocytochemistry. As Pax3, Pax7 and Myogenic Regulatory Factors (MRFs) are the key players for the muscle formation, they were used to mark the different myogenic sub-populations. The results from chicken and rats clearly demonstrate that three myogenic cell pools, namely Pax3, Pax7 and MRFs positive cells, and 4 sub-populations formed by their overlap, co-exist in specific proportions within the developing limb muscle, and that their proportions undergo dynamic changes during the course of myogenesis. The most striking observation was that the sizes of Pax3 and MRF compartments remain constant while that of Pax7 compartment increases dramatically during myogenesis. Thus each myogenic cell compartment in the developing muscle has different cell kinetics during primary and secondary myogenesis. The dynamic changes in the proportions of these myogenic sub-populations may constitute a dynamically maintained cellular niche, within which the muscle stem cells reside. Our study suggests that the concept of community effect - the interaction between a group of cells and their surrounding cells, originally from invertebrate muscle system, may be conserved in mammalian systems. Furthermore, this study for the first time, reports that the earliest fully differentiate muscle cells in the rat hindlimb are highly elongated mononucleated cells which express Pax3, MyoD, myogenin and myosin but not Myf-5 protein. In summary, this study provides quantitative data to demonstrate dynamic changes in various mononucleated myogenic cell populations during skeletal muscle formation and reveals that Pax7(+ve) population becomes significantly upregulated during secondary myogenesis.

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