Purifying and assaying mesoderm-inducing factors from vertebrate embryos

Abstract

Abstract The first cell-cell interaction in amphibian development is mesoderm induction, when a signal from the vegetal hemisphere of the embryo induces overlying equatorial cells to form mesoderm rather than ectoderm (see Figure 1). The last five years have seen a great increase in our understanding of mesoderm induction, largely due to the discovery of several ‘mesoderm-inducing factors’-molecules which induce prospective ectodermal tissue of the amphibian embryo to differentiate as a variety of mesodermal cell types such as muscle, notochord, mesenchyme, and mesothelium. Most of these inducing factors are members of the transforming growth factor type (TGF ) or fibroblast growth factor (FGF) families (1), and one of the most potent, activin, has been shown to induce expression of mesoderm-specific genes, or of mesodermal cell behaviour, in mouse (2), bird (3), and fish (4), as well as amphibian embryos. This indicates that mesoderm induction occurs in all vertebrates and the process is thus of considerable interest and importance.