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An electron microscope study of myofibril formation in embryonic rabbit skeletal muscle
Abstract:
Trunk and limb muscles from fetal and newborn rabbits were investigated by means of light and electron microscopes. At 14 days gestation, the presumptive myoblasts migrate away from the myotome to form the anlage of the muscle of the trunk and limb. Among the population of undifferentiated cells, the myoblasts were recognized due to the presence of actin and myosin filaments. The aggregates of thin and thick filaments appear at the periphery of the cells. There is a great variety of filament assembly. The presence of Z band material appears to be essential for sarcomere formation. At 14 days of gestation the myotubes are more numerous in the limb than in the trunk. The presence of unmaturated fibrils with absence of the M line in the sarcomeres was observed. By day 18 of gestation the myotubes are wider and aggregate to form small bundles. The myofibrils were more numerous and the vesicles of the SR precursor, partly incrustated with ribosomes were dispersed among them. At day 22 of gestation the myotubes are thicker because of the myofibrils which are far more numberous. The sarcomeres were more fully developed, with the M line present. At day 28 of gestation and 3 days after delivery the already developed myofibers were present with a well organized SR system and fully developed sarcomeres.
Insights
Muscle development in fetal rabbits shows myoblasts forming myofibrils and sarcomeres. By late gestation, well-organized muscle fibers with complete sarcomeres are evident, crucial for limb and trunk function.
Area of Science:
- Developmental Biology
- Muscle Physiology
- Cell Biology
Background:
- Skeletal muscle development involves myoblast differentiation and myofibril assembly.
- Understanding the temporal sequence of muscle formation is key to developmental biology.
Purpose of the Study:
- To investigate the ultrastructural development of trunk and limb muscles in fetal and newborn rabbits.
- To identify key stages in myoblast differentiation, myofibril formation, and sarcomere organization.
Main Methods:
- Light and electron microscopy were used to examine muscle tissue.
- Fetal and newborn rabbit specimens at various gestational ages (14, 18, 22, 28 days) and postnatal day 3 were analyzed.
Main Results:
- Myoblasts with actin and myosin filaments were identified by 14 days gestation.
- Immature myofibrils and sarcomeres lacking M lines were observed at 14 days.
- By 18 days, myotubes widened, myofibrils increased, and SR precursor vesicles appeared.
- By 22 days, myotubes thickened with more myofibrils and developed sarcomeres including the M line.
- Fully developed myofibers with organized SR and sarcomeres were present by 28 days gestation and 3 days postpartum.
Conclusions:
- Muscle development progresses from myoblast differentiation to organized myofiber formation.
- Sarcomere maturation, including Z band and M line appearance, is a critical indicator of muscle development.
- The study provides a detailed timeline of skeletal muscle ultrastructure development in rabbits.