The induction of mesoderm is an important process in early amphibian development. In recent studies, activin has become an effective candidate for a natural mesoderm-inducing factor. In the present study, we show that follistatin, an activin-binding protein purified from porcine ovary, inhibits the mesoderm-inducing activity of recombinant human activin A (rh activin A), which is identical to the erythroid differentiation factor (EDF). The quantity of follistatin required for effective suppression of activin was more than three-fold that of activin (w:w). Follistatin also inhibited the mesoderm-inducing activity of the vegetalizing factor purified from chick embryos, suggesting that the vegetalizing factor is closely related to activin.
The mc%odcrm and endodcrm inducing vegctalizing fk%Or was partially sequcnecd aftcf BrCN clcavagc_ A scquenn which is highly conserved in activin A near the C-terminal end Was idcntifled. This shows that the Factor belongs to the activin family. The activins arc not confined IO embryos and gonads, but widely distributed in athcr tissues like calf kidney and calf liver. Functional aspxts are discussed.
~mb~anic indu~ion~ V~e~ii2ingfactor, Activin A: Chicken embryo: Calf kidney; Calf liver
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