Gene expression of muscle proteins and molecular mechanisms of contractile structure formation

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1. Developmental relationship of myosin binding proteins to myosin during myofibrillogenesis :Immunofluorescence microscopy of embryonic skeletal muscle revealed that myomesin, connectin and C-protein play an important role for assembly and regular alignment of myosin molecules. It has also been suggested that a mechanism works to remore transiently expressed embryonic isoforms (non-muscle actin and cardiac C-protein) from functional structures after they play some unknown role(s) for structure formation.2. Dynamics of actin during myofibrillogenesis :Rhodamine (rh)-labeled actin was microinjected into cultured skeletal muscle cells and stained with anti-nebulin and anti-connectin. It was found that nebulin plays an important role for incorporaton of actin into and exchange of actin in nascent myofibrils, but connectin does not have such a role. This was confirmed by injection of anti-nebulin and anti-connectin to rh-actin injection.3. Dynamics of actin and α-actinin in myofibrils and stress fibers:Co-injection of fluorescently labeled actin and α-actinin into cultured cardiomyocytes revealed difference in exchangeability between both proteins in developing myofibrils. This difference seems to be related to the formation of I-Z-I structure of myofibrils. Exchangeability of bothproteins in stress fibers of fibroblasts was high, and thus myofibrils and stress fibers are different structures although they are similar in appearance and composition.