The long term goals of this study are to understand how the regulation of the neural cell adhesion molecule (NCAM) is muscle changes during development and what cellular mechanisms affect NCAM modification. It is hoped that this knowledge will further our understanding of the molecular mechanism by which NCAM mediates cell adhesion, since at present no precise molecular model exists. These questions will be addressed by two types of studies. First, NCAM biosynthesis will be studied by biosynthetic radiolabelling cultured chick myotubes. Turnover time, rate of polysialation, sulfation and phosphorylation will be examined. A comparison with earlier studies on neural NCAM biosynthesis will establish it the polypeptides are identically modified in the two tissues which could be of functional importance. Second, regulatory factors of three categories will be examined for their ability to regulate NCAM in myotube culture. 1) Conditions that affect muscle functional activity will be tested for their ability to alter total NCAM levels (as determined by ELISA), polypeptide size and polysialation (as determined on SDS- PAGE). Neuronal regulation in vivo down-regulated NCAM polypeptide synthesis and polysialation. Hence myotube culture provides a system where factors can be tested in isolation for their ability to mimic neuronal regulation 2) Regulation of NCAM by steroid hormones will be similarly examined by treating cultures with dexamethasone and a variety of steroids for several days. 3) The involvement of second messengers in the cellular control mechanism mediating NCAM regulation will be explored by studying factors affecting several kinases, such as cyclic nucleotides and diacylglycerol. NCAM will be quantified and polysialation studied after prolonged treatment, while phosphorylation will be studied after shorter treatments. NCAM regulation appears to be important in the development of neuromuscular junction and is altered in adult diseases such as polymyositis, Duchenne and Becker muscular dystrophies, and tascio-scapular and limb girdle dystrophies. Understanding its regulation will assist in developing a precise molecular model of NCAM function which may explain its involvement in degenerative muscle diseases, as well its presumed role in histogenesis.
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