RESTRICTING OXYGEN-SUPPLY TO THE PROSPECTIVE DORSAL SIDE DOES NOT REVERSE AXIS POLARITY IN EMBRYOS OF XENOPUS-LAEVIS

During the first cell cycle, the prospective dorsal side of the embryo of Xenopus laevis becomes enriched in mitochondria relative to the ve ntral side. This differential distribution of mitochondria persists th rough-out early development, but it is not known if it is of functiona l significance, since there do not appear to be dorsal-ventral differe nces in metabolic rate. However, the unilateral anaerobiosis experimen ts of Landstrom and Lovtrup do suggest a role for energy metabolism in determining axis polarity. These experiments apparently show that res tricting oxygen supply to the prospective dorsal side causes a reversa l of dorsal-ventral axis polarity. We have reinvestigated this point u sing cell-marking techniques. We find that although gastrulation is in itiated at the open end of the tube, the polarity of neural plate deve lopment is unaffected. Thus, definitive dorsal-ventral polarity is not affected by the experimental treatment, and it is unlikely that gradi ents of energy metabolism have a role in specifying axis polarity in X . laevis.