INHIBITION OF MESODERM FORMATION BY FOLLISTATIN

Mesoderm induction requires interaction between cells of the animal an d vegetal hemispheres of the embryo. Several molecules have been propo sed as candidates for mesoderm-inducing signals, with activin a partic ularly strong candidate. However, it has not been possible to inhibit mesoderm formation in vivo by specifically blocking activin action. Fo llistatin is able to inhibit the action of activin but not that of the mature region of Vg1, a member of the transforming growth factor beta family. Follistatin therefore provides a useful tool for distinguishi ng between signalling by these two factors. We have overexpressed Xeno pus follistatin mRNA and analysed the expression of several mesodermal markers. Our results show an inhibition of mesodermal formation by fo llistatin in a concentration-dependent manner, showing the requirement of activin for mesodermal induction.