REGIONALIZATION OF TENASCIN EXPRESSION AS A RESPONSE TO MESODERMAL INDUCERS

Tenascin (TN) is an extracellular matrix (ECM) glycoprotein which poss esses antiadhesive properties and thus is able to modulate cell intera ctions with molecules of the ECM. In Xenopus embryos, TN is expressed dorsally in a very restricted pattern. We have studied the distributio n of TN mRNA in tailbud-stage embryos by in situ hybridization. We sho w that TN transcripts are principally expressed in myotome cells. No T N mRNA could be detected in lateral plate mesoderm. This had led us to study TN expression in response to mesodermal inducers. Analysis of t he distribution of TN after mesodermal induction of blastula animal ca ps with activin A and bFGF or after ectopic expression of XBra shows t hat TN expression is elicited when dorsal or posterior structures are formed. Our results show that TN regionalization in Xenopus embryos de pends on mesoderm patterning.