INHIBITORY INTERACTIONS CONTROLLING ORGANIZER ACTIVITY IN FISH

An experimental system allowing the observation of 2 active organizing centers during zebrafish development is described. It was achieved by injection into a single marginal cell at the 16-cell stage of TARAM-A -D mRNA. TARAM-A-D was previously described as the mutated constitutiv e form of a type I receptor far transforming growth factor beta. In 70 % of the injected embryos, 2 distinct organizers were observed at the onset of gastrulation. At the end of gastrulation, these embryos showe d duplicated axial structures. Nevertheless, only 25% of the injected embryos displayed a recognizable axis duplication after I day of devel opment. This paradox is taken as an evidence for suppressive effects e xerted in a reciprocal manner when more than is present.