Cellular Mechanisms of Matching Between Fast and Slow Motoneurons and Myotubes

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An important aspect of normal neuromuscular development is the matching of fast and slow motoneurons with appropriate muscle fiber types, but the mechanisms responsible for this matching are presently not understood. Embryonic chick is a suitable system for the study of this problem, as the tissues involved are easily manipulated. The time course of appropriate innervation will be determined during embryonic development of chick hindlimb muscle. This will determine if specificity occurs with initial innervation, or if appropriate matching is produced by a rearrangement of neuromuscular connections. The molecular mechanisms involved in the matching of neurons to specific muscle fiber types will be investigated. An in-vitro model will be used to test the preference of fast or slow motoneurons for outgrowth on substrates containing fast or slow myotube membrane components. Also, since antigenic differences between fast and slow myotube membranes may be surface components that are recognized by motoneurons during innervation, polyclonal and monoclonal antibodies will be raised against slow and fast muscle surface membrance components. These antibodies can then be used to characterize molecular differences between fast and slow muscle, and to interfere with the recognition process during development in ovo. These studies will provide a fuller understanding of the cellular and molecular events during normal selective synaptogenesis.