P3.82 Thursday, Jan. 6 Change in orientation of the myofibrils and cytoskeleton in white muscle fibers of large black sea bass, Centropristis striata. PRIESTER, C.*; BRAUDE, J.P.; KINSEY, S.T.; WATANABE, W.O.; DILLAMAN, R.M.; UNC Wilmington email@example.com
During an examination of hypertrophic growth in white muscle of C. striata, a difference was seen in nuclear distribution. In small fish (<1885g) nuclei were almost exclusively subsarcolemmal (SS), whereas in large fish (1885-4840g) the nuclei were both SS and intermyofibrillar (IM). One aspect of this shift in nuclear distribution was that in some fibers (approximately 20%) IM nuclei formed a circular pattern. Examination of this pattern by histology and polarized light microscopy revealed that fibers with the circular pattern had myofibrils that were shifted in orientation, making them roughly perpendicular to the core myofibrils and wrapping around the central fibrils oriented in the long axis of the muscle fiber. Serial sections showed that this pattern appeared in the middle of the fiber. Transmission electron microscopy at the interface between the two fibril orientations revealed that the reoriented myofibrils were within the same cell, sharing the cytoplasm with the core myofibrils. Also, staining of these fibers for &beta-tubulin and nuclei (DAPI) together with DIC microscopy indicated that the IM nuclei, microtubule cytoskeleton and fibrils had all changed orientation. The microtubule cytoskeleton could be seen in all white muscle fibers. Microtubules mostly paralleled the long axis of the fiber but had perpendicular branches, and surrounded the nuclei. Previously a microtubule cytoskeleton in striated muscle had only been reported in cardiac myocytes, developing myotubes or associated with subsarcolemmal nuclei. It is unknown if the shift in the orientation of the microtubules in the fibers with a circular pattern was a cause or result of the shift in nuclei and myofibril orientation.