The structure and function of tenascins in the nervous system

The tenascins are a family of large extracellular matrix glycoproteins that comprise five known members. Three of these, tenascin-C (TN-C) tenascin-R (TN-R) and tenascin-Y (TN-Y) are expressed in specific patterns during nerv ous system development and are down-regulated after maturation. The express ion of TN-C, the best studied member of the family, persists in restricted areas of the nervous system that exhibit neuronal plasticity and is reexpre ssed after lesion. Numerous studies in vitro suggest specific roles for ten ascins in the nervous system involving precursor cell migration, axon growt h and guidance. TN-C has been shown to occur in a large number of isoform v ariants generated by combinatorial variation of alternatively spliced fibro nectin type III (FNIII) repeats. This finding indicates that TN-C might spe cify neural microenvironments, a hypothesis supported by recent analysis of TN-C knockout animals, which has begun to reveal subtle nervous system dys functions. (C) 2001 Elsevier Science B.V./International Society of Matrix B iology. All rights reserved.