CONTROL OF SEMITIC EXPRESSION OF TENASCIN IN XENOPUS-EMBRYOS BY MYOGENIC FACTORS AND BRACHYURY

Tenascin is a large glycoprotein which is expressed in a restricted pa ttern in the extracellular matrix (ECM) of vertebrate embryos. Tenasci n interferes with cell-fibronectin interactions in vitro, and may play a role in the control of cell migration and differentiation during de velopment. In Xenopus, tenascin immunoreactivity is first detected at the early tailbud stage in the ECM of the most anterior somite. Therea fter, it is distributed dorsally along neural crest cell migration pat hways. In this paper, we report that tenascin mRNA is most abundant in dorsal mesoderm at the neurula stage and in somites at the early tail bud stage, indicating that the initial accumulation of tenascin in the ECM is due to secretion from paraxial mesoderm. To understand how ten ascin expression in semitic mesoderm is controlled, we have expressed Xbra and the myogenic factors XMyoD and XMyf5 in blastula animal cap t issue. The tenascin gene is activated by all three transcription facto rs. Interestingly, expression of tenascin mRNA, and accumulation of th e protein in the ECM, can occur without formation of muscle. Our resul ts suggest that tenascin regionalization in early Xenopus embryos depe nds on tenascin RNA expression by semitic mesoderm, where it is likely to be activated by myogenic factors. (C) 1994 Wiley-Liss, Inc.