Activation of a neuralizing factor in amphibian ectoderm.

Isolated gastrula ectoderm has no neural-inducing activity and does not differentiate into neural tissues. It has, however, a high neural-inducing capacity, but the inducing factors are present in a masked, inactive form. The inducing factors are partially activated by homogenization and by freezing of the homogenate and are fully activated by treatment with ethanol. The relative distribution of inducing factors in different subcellular fractions changes after treatment with demecolcine and cytochalasin B or after autolytic incubation of the homogenate. The inducing activity of the high-speed supernatant is enhanced under these conditions. The experiments suggest that the activation of neuralizing factor(s) depends on the release from complex structures. Cytoskeletal elements seem to be involved. When early neural plate homogenate was fractionated, the high-speed supernatant showed neural-inducing activity. This is in contrast to the high-speed supernatant from the ectoderm homogenate, which shows no such activity.