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)

Abstract

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. Copyright © 1994, Wiley Blackwell. All rights reserved