Tenascin is a large glycoprotein that forms disulfide-linked hexamers. Tenascin is made up of a series of repeated structural domains including EGF-like repeats, fibronectin type III repeats, and a region homologous to fibrinogen. Splice variants of tenascin differ in their number of fibronectin type III repeats. Tenascin is expressed in distinctive spatial and temporal patterns in most embryonic tissues at sites of tissue remodeling and cell migration. There is little expression of tenascin in adult tissues except, again, at sites of tissue remodeling and cell migration such as surrounding tumors, in healing wounds, and in branching or damaged blood vessels. Tenascin binds to several cell-surface receptors and mediates cell-substrate adhesion. Nevertheless, tenascin is frequently referred to as an anti-adhesion molecule because for a variety of cell types the presence of tenascin inhibits adhesion to other ECM proteins present. This effect occurs because the binding of tenascin to certain receptors inhibits cell spreading and thereby blocks the stabilization of adhesion that results from cell spreading in vitro assays.