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Abstract

During muscle cell (i.e. myocyte )development, organization of actin and myosin into the contractile unit (i.e. sarcomere) is required for proper muscle contraction. By disrupting the processes of muscle cell development, I am able to see which steps play important roles in proper maturation of myocytes. Elucidation of the key pathways in muscle development could lead to a better understanding of human cardiac hypertrophies and muscle myopathies. Since actin filament formation precedes myosin organization, I am using actin assembly inhibitors to determine if actin filaments are a necessary prerequisite for myosin organization. It is hypothesized that disruption of actin will disrupt myosin organization. In these experiments Jasplakinolide (Jasp) is applied to cultured embryonic myocytes during sarcomere assembly. Jasp binds, stabilizes, and induces polymerization of actin filaments (i.e. F-actin) making it a useful compound for determining if actin dynamics or precise thin filament length are necessary for myosin incorporation into the sarcomere. My results indicate that normal actin organization is required for correct sarcomere development. Myosin organization was reduced by more than 90% in all treatment regimes (50, 100, and 500 nanomolar Jasp). Sarcomeres failed to form and myosin appeared diffuse throughout the myocytes. Mv results indicate that intact, precisely regulated thin filaments are a prerequisite for normal myosin assembly. It remains to be determined if this requirement stems from actin-titin interactions, actin-myosin cross-bridge formation, or some other intermolecular interactions. Hopefully a better understanding of how sarcomeres form will provide insight into diseases involving the improper assembly of muscle such as myopathies or hypertrophies.

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