The expression of tenascin, a constituent of extracellular matrix (ECM), was studied during the embryonic development of the amphibian Pleurodeles waltl. An antiserum to chick fibroblast tenascin was shown to cross-react with the homologous molecule of the amphibian. Immunostaining of embryo sections with anti-tenascin antiserum revealed that tenascin appears just after the completion of neurulation. At the tailbud stage, tenascin is present in the ECM located at sites of directed cell migration (neural crest cell migration pathways, extension of the pronephretic duct) and mesenchyme condensation (endocardium, aortic arches). The accumulation of tenascin immunoreactivity in the embryonic ECM is correlated with the synthesis of the 220×103Mr polypeptide of the molecule. To provide data on the patterning of tenascin, ectoderm and dorsal blastoporal lip isolated at early gastrula stage were cultured for a period of 3 days. Epidermal vesicles differentiating from isolated ectoderm completely lack tenascin. Conversely, axial mesoderm derivatives present in cultured dorsal blastoporal lip were found to produce tenascin. Neural induction of ectoderm isolated at early gastrula stage was performed in vitro with the dorsal blastoporal lip or concanavalin A. The induced neural tissue was found to accumulate tenascin. Spemann experiments confirmed in vivo that tenascin is expressed by ectodermal cells as a response to neural induction.

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