The overall aim of our research is to understand how the growth of neurons is modulated by interaction with extracellular matrix molecules. This proposal centers upon understanding how the extracellular matrix molecule tenascin-C regulates neuronal growth. Tenascin-C is not a single molecule, but is instead a family of alternatively spliced variants containing different combinations of fibronectin type III domains. We have found that the region of tenascin-C containing only the alternately spliced fibronectin type III domains, called fnA-D, when used by itself, dramatically increases neurite outgrowth in culture. In fact, this molecule is the most potent growth promoter we have identified in our tests in culture. The alternatively spliced region also provides directional cues to growing neurites, which we define as neurite guidance. Neurites demonstrate a strong preference for fbA-D when they are given a choice at an interface. FnA-D even influences extension into normally repulsive chondroitin sulfate proteoglycans, the major inhibitory molecules in the glial scar. We have associated these features with different domains of the fnA-D molecule: promotion of neurite outgrowth with fnD (the seventh fibronectin type III domain), and neurite guidance with fnC (the sixth domain). More specifically we further localized the outgrowth activity to the 8 amino acids 29-36 within fnD which we call the """"""""outgrowth promoting motif"""""""" (OPM). We have also determined that an antibody directed against the OPM can reduce neurite outgrowth by tenascin-C, thus demonstrating that this region is functional within the intact molecule. Our initial goal is thus to explore the hypothesis that neurite outgrowth and neurite guidance mediated by fnA-D are distinct processes, each of which can be manipulated independently to encourage directed neuronal regrowth. In addition, we will explore the hypothesis that these domains of tenascin-C may have properties as soluble chemoattractant molecules.
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