Purification, partial characterization and biological effects of the XTC mesoderm-inducing factor Available to Purchase

The mesoderm of Xenopus laevis is formed through an inductive interaction in which a signal from the vegetal hemisphere of the blastula acts on overlying animal pole cells. We have recently reported that the Xenopus XTC cell line secretes a mesoderm-inducing factor (MIF) which may resemble the natural signal. In this paper, we describe the purification and biological effects of XTC-MIF. XTC-MIF is a hydrophobic protein with an isoelectric point of 7·8 and an apparent relative molecular mass (M_r) of 23500. On reduction, XTC-MIF loses its biological activity and the protein dissociates into two inactive subunits with apparent M_r of about 15 000. These properties closely resemble those of transforming growth factor type β (TGF-β2), and it is interesting that TGF-)32 has recently been shown to have mesoderm-inducing activity.

The biological response to XTC-MIF is graded. After exposure to 0·2 – 1·0 ng ml⁻¹ XTC-MIF, stage-8 animal pole explants form mesenchyme and mesothelium. At higher concentrations, up to about 5 ng ml⁻¹, muscle is formed, occasionally with neural tissue. In response to concentrations of XTC-MIF greater than 5·10 ng ml⁻¹, notochord and neural tissue are usually formed. The formation of notochord and neural tissue in response to XTC-MIF represents a qualitative difference between this inducing factor and the other known group of MIFs, the heparin-binding growth factors.