Abstract
In this report the organizer activity of follistatin was examined by transplantation of pieces of the animal cap, isolated from embryos injected with follistatin mRNA, into the blastocoele of an early host blastula (Einsteck explants). Host embryos developed a secondary axis consisting of myotomes, notochord and neural tube of the trunk or tail character. Secondary structures that are characteristic of a head, such as cement glands or brain and eyes, did not develop in these experiments. These findings suggested that follistatin may have the trunk and tail organizer activity, while it was not possible to reconstitute its head organizer activity.