Tissue-specific changes in nuclear RNA content during early development of Triturus vulgaris

During early development of Triturus vulgaris, as a measure for nuclear activity in neuroectoderm, mesoderm and endoderm, nuclear RNA content was determined by cytochemical methods. In the first stages of gastrulation, that is to say during the early phase of neural induction, the RNA content of the inducing system is considerably higher than in the reacting system. Then, with a phase-shift of about 10 h, the RNA content of the neuroectoderm increases quickly also. In the following stages the nuclear RNA content of both regions is reduced. A second continuous increase in the RNA amount coincides with the formation of the neural tube. In the mesoderm, enhancement of RNA content correlates with cytodifferentiation of the chorda. In all stages the RNA content of the endoderm is higher than in the other tissues and it becomes successively diminished from the early gastrula to the tailbud stage.