The role of transcription in primary induction

The present study shows that transcription is responsible for primary induction. Areas which have been already induced continue to differentiate and proliferate. From this it is evident that actinomycin D acts on Hensen's node and does not pass into the induced areas. On comparing the initial 17 hours differentiation and the 40 hours development it is evident that induction starts in the middle of the axis when Hensen's node matures, so that the anterior region of the axis. i.e., the brain, is induced both during elongation and regression of the primitive streak. The spinal region is induced only during the regression of the primitive streak.