Mechanism and gene expression of mesodermal inducing substances on the presumptive ectoderm of early amphibian development.

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Recently the mesoderm-inducing effects of the transforming growth factor beta(TGF-beta) family of proteins of these proteins, porcine inhibin A and activin A (erythroid differentiation factor) were examined. Treatment of explants with activin A led to differentiation of mesodermal derivatives such as mesenchyme, notochord, blood cells and muscle, but inhibin A had a much lesser effect. Activin A reacted on presumptive ectoderm with very low concentration at 10-50 ng/ml. The mesodermal differentiation induced by activin A was also confirmed by analyses using a polyclonal antibody against muscle myosin. By indirect immunofluorescence analysis, the differentiation of muscle blocks was observed in the activin-A-treated explants, whereas no differentiation was observed in inhibin-A-treated and control explants. These findings confirm that this protein of the TGF-beta family has mesoderm-inducing ability. To find out the activin-homology genes were tried. Three kinds of c-DNA were cloned from Xenopus itself. There are named C4, B3,and M4. For further experiments will be needed to detect whether these m-RNA are expressed during the normal embryonic development.