Fig. 8. Transplantation experiments demonstrate that the neural crest defect in the Hoxa1-/-/Hoxb1 3'RARE-/- mutants is cell-autonomous. Diagrammatic representation (a,b) of the experimental procedure and the results (c,d). DiI-labelled wild-type r4 cells were transplanted in the r4 of wild-type (a,c) or rx ofHoxa1-/- /Hoxb1 3'RARE-/- (b,d) recipient embryos at the five-somite stage. The embryos were cultured for 24 hours and then observed under fluorescence for migration patterns. The wild-type cells are able to migrate correctly into the second pharyngeal arch (pa2) of both wild-type (c) and Hoxa1-/- /Hoxb1 3'RARE-/- (d) embryos, demonstrating that the ncc defect in the latter is cell-autonomous. os, otic sulcus; pos, preotic sulcus.