Fig. 6. Xanf1 regulation byFoxA4a/Pintallavis and Xvent2 is consistent with Nieuwkoop's two-signal model of neural induction. (A) According to the Nieuwkoop model, anterior potentials induced during the first step of the neural induction throughout the neurectoderm are realised only in the anterior part of the neural plate (red) because of suppression by a transforming signal in the posterior part of the plate (grey). (B) Expression of Xanf1 is activated by Otx2, SoxD and possibly other transcription factors throughout the neural plate. However, during normal development the expression of Xanf1 is inhibited in the posterior part of the neural plate because of the inhibitory influence of FoxA4a/Pintallavis, Xvent2 and some as yet unidentified factors.