INTERCELLULAR SIGNALING IN MESODERM FORMATION DURING AMPHIBIAN DEVELOPMENT

The mesoderm of amphibian embryos arises through an inductive interact ion in which a signal from the vegetal hemisphere of the blastula-stag e embryo acts on overlying equatorial cells. Strong candidates for end ogenous mesoderm-inducing signals include members of the fibroblast gr owth factor (FGF) and activin families. In this paper we show that cel ls form different mesodermal cell types in response to different conce ntrations of these factors, and that graded distributions of activin a nd FGF can, in principle, provide sufficient positional information to generate the body plan of the Xenopus embryo.