Dev Growth Differ 1994 Oct 01;365:499-507. doi: 10.1111/j.1440-169X.1994.00499.x.

In Vitro Control of the Embryonic Form of Xenopus laevis by Activin A: Time and Dose-Dependent Inducing Properties of Activin-Treated Ectoderm: (activin/ectoderm/organizer/Xenopus laevis/neural induction).

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The inducing properties of activin-treated ectoderm of Xenopus laevis were examined by the preculture and sandwich culture methods. Presumptive ectodermal sheets of the late blastula were treated with 10-100 ng/ml of activin A and precultured for 0-7 hr in Steinberg's solution. They were then sandwiched between two sheets of ectoderm from other late blastulae. Ectoderm precultured for a short term induced trunk-tail structures, whereas that precultured for a long term induced head structures in addition to trunk-tail structures. These time-dependent changes in inducing properties occurred more rapidly when the concentration of activin A was higher. These results suggest that the activin-treated ectoderm functioned as a "head organizer" or "trunk-tail organizer" depending upon the concentration of activin A and the duration of preculture. To trace the cell lineage of the sandwich explants, activin-treated ectoderm labeled with fluorescein-dextran-amine (FDA) was used in this study. The explants sandwiching the long term-precultured ectoderm formed head structures equipped with non-labeled neural tissues (brain and eye) as well as FDA-labeled mesodermal tissues. These results suggest that the activin-treated ectoderm mainly differentiates into mesodermal tissues and induces neural tissues as the organizer does in normal development.

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Species referenced: Xenopus laevis