The Xenopus Eomesodermin promoter and its concentration-dependent responseto activin

Eomesodermin is an essential early gene in Xenopus mesoderm formation and s hows a morphogen-like response to activin. Here we define the regions of th e Eomesodermin promoter required for mesodermal expression and for concentr ation-dependent response to activin. We find an activin response element (A RE) located between -5.6 and -5.0 kb which contains two critical FAST2 bind ing sites. The ARE alone is necessary and sufficient for concentration-depe ndent response to activin. A 5.6 kb promoter recapitulates Eomes expression in normal mesoderm cells. A repressor element extinguishes Eomes expressio n in the endoderm. We relate our results to mesoderm patterning in early Xe nopus development and to a mechanism of morphogen gradient response. (C) 20 00 Elsevier Science Ireland Ltd. All rights reserved.