Fig. 4. Wnt1 transcription in the neural tube is modulated by the developing somites. Dissociating somites were unilaterally grafted in the place of the unsegmented mesoderm. (A) There is premature expression of Wnt1 mRNA (arrowheads) in the caudal hemi-tube adjacent to the graft (^*) at the level of the caudal segmental plate (cSP). (B) Opposite the rostral segmental plate (rSP), Wnt1 transcription is apparent in the intact hemi-tube of this embryo at the age of 23 somites. At this level, the graft (^*) resulted in expansion of the Wnt1 expression domain with associated emigration of NC cells that retained Wnt1 expression (arrow). (C) Grafting of a fragment of sclerotomal tissue (Scl) had no effect on Wnt1 transcription or on NC delamination. Scale bar: 25 µm.