EMBO Workshop Report: Molecular genetics of muscle development and neuromuscular diseases Kloster Irsee, Germany, September 26-October 1, 1999

Developing a novel serum-free cell culture model of skeletal muscle differentiation by systematically studying the role of different growth factors in myotube formation

This work describes the step-by-step development of a novel, serum-free, in vitro cell culture system resulting in the formation of robust, contracting, multinucleate myotubes from dissociated skeletal muscle cells obtained from the hind limbs of fetal rats. This defined system consisted of a serum-free medium formulation developed by the systematic addition of different growth factors as well as a nonbiological cell growth promoting substrate, N-1[3-(trimethoxysilyl) propyl] diethylenetriamine. Each growth factor in the medium was experimentally evaluated for its effect on myotube formation. The resulting myotubes were evaluated immunocytochemically using embryonic skeletal muscle, specifically the myosin heavy chain antibody. Based upon this analysis, we propose a new skeletal muscle differentiation protocol that reflects the roles of the various growth factors which promote robust myotube formation. Further observation noted that the proposed skeletal muscle differentiation technique also supported muscle-nerve coculture. Immunocytochemical evidence of nerve-muscle coculture has also been documented. Applications for this novel culture system include biocompatibility and skeletal muscle differentiation studies, understanding myopathies, neuromuscular disorders, and skeletal muscle tissue engineering.

Engineering of muscle tissue

The loss or failure of an organ or tissue is one of the most frequent, devastating, and costly problems in health care. Tissue engineering and regenerative medicine is an emerging interdisciplinary field that applies the principles of biology and engineering to the development of viable substitutes that restore, maintain, or improve the function of human tissues and organs. Tissue engineering science has provided critical new knowledge that will deepen our understanding of the phenotype of an important category of cell types-the muscle cells-and this knowledge may enable meaningful advances in musculoskeletal tissue engineering. There are two principle strategies for the replacement of impaired muscle tissues. One approach uses the application of isolated and differentiated cells (in vivo tissue engineering), using a transport matrix for the cell delivery; the other uses in vitro-designed and pre-fabricated tissue equivalents (in vitro tissue engineering). Future developments and the decision regarding which approach is more promising depend on the elucidation of the relationships among cell growth and differentiation, the three-dimensional environment, the architecture of the cells, and gene expression of the developmental process and the survival of the cells and integration in the host in in vivo experiments. As the techniques of tissue engineering become more sophisticated and as issues such as vascularization and innervation are addressed, the usefulness of these methods for reconstructive surgery may grow significantly.

Muscle development genes: their relevance in neuromuscular disorders

Myogenesis is a complex cascade of events that involves the specification and differentiation of muscle precursor cells or myoblasts, their fusion to form primary and secondary myotubes and subsequent maturation into muscle fibres. In addition, the development of axial muscle requires the migration of muscle precursor cells. These events are under strict genetic control. The contribution of individual genes to this process has been highlighted both by the phenotype of mice with targeted inactivation of individual myogenic regulatory factors and by rare human disorders in which the involvement of these genes has been demonstrated. The inactivation of known myogenic regulatory genes is associated with abnormal regulation of skeletal muscle differentiation and has an effect on regeneration but does not cause progressive muscle weakness or wasting. This review summarises recent developments in this field and will be of particular relevance to those interested in neuromuscular disorders. We also examine the possibility that some rare human conditions associated with abnormal muscle formation may be due to genetic defects in one of the myogenic regulatory genes.