Fates of Animal-Dorsal Blastomeres of Eight-Cell Stage Xenopus Embryos Vary according to the Specific Patterns of the Third Cleavage Plane

The third cleavage plane in typical Xenopus embryos is horizontal. However, there are numbers of cases in which the third cleavage plane slants and yet the embryo develops normally. Pairs of animal-dorsal (AD) blastomeres of eight-cell stage Xenopus embryos with horizontal or oblique third cleavage plane were marked by intracellular injection of fluorescein dextran amine in order to locate their progeny. In neurulae, progeny of AD blastomeres was found mainly along the dorsal midline forming longitudinal clonal bands along the midline in the neural plate and the mesoderm underneath. AD blastomeres with oblique third cleavage plane further yielded the ventral endo-mesoderm in the head. On the other hand, they formed narrower clonal bands in the anterior ectoderm compared with AD blastomeres with horizontal third cleavage plane. Thus the fates of animal-dorsal brastomeres of eight-cell stage Xenopus embryos vary according to the specific patterns of the third cleavage plane. This indicates that the third cleavage in the Xenopus embryo does not affect the normal fate of each region of the embryo presumed at the eight-cell stage.