Asymmetry in Myogenesis

The de novo growth and morphogenesis of tissue and organs occurs only during the embryonic phase of development. The first skeletal muscle tissues to develop begin in the embryonic somites, epithelial segments of the paraxial mesoderm. The primary myotome consists of segmental sheets of differentiated, mononuclear myocytes arranged in parallel arrays. Recent studies demonstrate that the organization of each myotome segment results from the sequential, asymmetric birth of myoblast cells, followed by morphogenetic cell movements leading to terminal differentiation. The progressive growth of the myotome is driven by stem cell activity that is asymmetrically located in the dorsomedial lip (DML) of the overlying dermomyotome epithelium. Symmetric cell division within the DML simultaneously produce new epithelial dermomyotome cells that will subsequently form later generations of muscle and connective tissue, such as the dermis. The analysis of development of the primary myotome using experimental embryology, cell biology and molecular approaches provide unique opportunities for understanding the role of progenitor stem cells in tissue growth and morphogenesis. Supported by research grants from the US National Institutes of Health and the Muscular Dystrophy Association of America.