Murine tenascin-W: a novel mammalian tenascin expressed in kidney and at sites of bone and smooth muscle development.

We cloned and characterized a novel member of the tenascin family of extracellular matrix proteins--the murine orthologue of zebrafish tenascin-W. Full-length recombinant tenascin-W was expressed and purified from mammalian cell cultures. Rotary shadowing followed by electron microscopy showed that tenascin-W forms hexabrachions. We studied its expression during development and in the adult by immunohistochemistry, in situ hybridization and immunoblotting. Tenascin-W is expressed during palate formation, osteogenesis and smooth muscle development. In the adult, tenascin-W is found in the kidney, cardiac semilunar valves, corneal limbus and periosteum. Tenascin-W and tenascin-C expression overlap in many of these areas. Bone-morphogenic-protein-2 treated C2C12 cells secrete tenascin-W and are able to adhere to and to extend actin-rich processes on a tenascin-W substratum. In vitro, cells bind to tenascin-W in an RGD-dependent manner. This adhesion is increased by transfection of alpha8 integrin, which localizes with tenascin-W in the periosteum and kidney.

Tenascin-N: characterization of a novel member of the tenascin family that mediates neurite repulsion from hippocampal explants.

Tenascin-N, a novel member of the tenascin family, was identified and shown to encode characteristic structural motifs of a cysteine-rich stretch, 3.5 epidermal growth factor-like repeats, 12 fibronectin type III homologous domains, and a fibrinogen-like domain. The third fibronectin type III homologous domain is altered by RNA splicing. Characterization of the expression of tenascin-N by in situ hybridization analysis assigned transcripts to many types of neurons in the central nervous system, to the medullary region in the kidney, and to resident macrophages of the T-cell zone in the splenic white pulp. By immunohistochemistry, tenascin-N expression is detectable in all brain regions, with a characteristic staining pattern in the hippocampus demarcating the CA3 region. Recombinantly expressed protein fragments of the alternatively spliced isoforms were presented in choice assays on patterned substrates to neurites and migrating neurons from hippocampal CA3 region explant cultures. The smaller splice variant inhibited neurite outgrowth or cell migration, whereas the longer splice form did not inhibit these functions. These observations suggest that the novel tenascin family member mediates specific repulsive properties on neurites and neurons by generating splice isoforms.