Activin-like factor from a Xenopus laevis cell line responsible for mesoderm induction

INDUCTION of mesoderm during early amphibian embryogenesis can be mimicked in vitro by adding growth factors, including heparin-binding and type-beta transforming growth factors (TGF-β), to isolated ectoderm expiants from Xenopus laevis embryos 1–5 . Although the mesoderm-inducing factor (MIF) from X. laevis XTC cells (XTC-MIF) 6,7 has properties similar to TGF-β, this factor is still unidentified. Recently, we obtained a number of homogeneous cell lines from the heterogeneous XTC population, which differ in their MIF production 8 . Only one, XTC-GTX-11, produced MIF, although it was similar to the rest of the clones in its production of known growth factors, including TGF-β activity 8 . This observation, together with the identification of activin A as a potent MIF (ref. 9) led us to study the parallel activities of MIF and activin. Here we report an analysis of activin-like activity from XTC cells and some of the XTC clones, including XTC-GTX-11. There is a clear consistent correlation between MIF activity and presence of activin activity, indicating that XTC-MIF is the Xenopus homologue of mammalian activin.