Striated Muscle-Myoblasts

Myotubes from the mylohyoid muscle of an 11-week old fetus. They have arisen from mesodermal tissue aggregates known as somites. The development of skeletal muscle can be trace d to a tissue in the somite, the myotome.  Expression of the MyoD gene leads to the formation of very actively dividing muscle progenitor cells , which will then differentiate and form myoblasts . Myoblasts do not divide. They fuse with each other and form syncytes with sometimes thousands of nuclei. The number of fusion cycles determines the size of the fully developed muscle. Myoblasts synthesize muscle-specific proteins and myofibrils. The fusion and assembly of myoblasts to cylinder-shape d Myotubes occurs concomitantly in a coordinate d process. The myofibrils cause the longitudinal myotube striation. However, there is no cross-striation yet. The nuclei still reside in the cell center. The number of muscle fibers does not change in vertebrae after birth. The study of the intricate regulation of their number and size during development may also shed light on the etiology of degenerative muscle diseases.

1 Myotubes

2 Mesenchymal connective tissue

Stain: hemalum-eosin; magnification: × 500

References

Kuehnel, W.(2003). Color Atlas of Cytology, Histology, and Microscopic Anatomy. 4^th edition . Institute of Anatomy Universitätzu Luebeck Luebeck, Germany . Thieme Stuttgar t · New York .