Change in the differentiation pattern ofXenopus laevis ectoderm by variation of the incubation time and concentration of vegetalizing factor.

Early amphibian gastrula ectoderm (Xenopus laevis) has been treated with vegetalizing factor using the sandwich technique, varying the period of incubation and the inducer concentration.The pattern of induced tissues depends on three factors: the inducer concentration, the size of inducer pellet and the time of exposure of ectodermal target cells to inducer.Short treatment with inducer will result in the formation of blood cells and heart structures. An increase in incubation time or inducer concentration, or both, will cause the formation of increasing amounts of such dorsal mesodermal structures as pronephros, somites and notochord. Neural structures can only be observed in explants with considerable amounts of somites and notochord.Ectoderm treated with high concentrations of vegetalizing factor for the whole period of competence will differentiate into endoderm.Furthermore, the results show thatX. laevis ectoderm does not show any autoneuralizing tendency under our experimental conditions. It therefore seems to be a suitable tool for the study of primary embryonic induction.