Fig. 2. Slug expression directly or indirectly induces the expression of rhoB and Pax3 in the chick hindbrain. (A, B) Embryo electroporated with chick Slug at stage 9 and analysed 15 hours later (stage 13) by in situ hybridisation with chick Slug (A) and subsequently subjected to HNK-1 immunohistochemistry (B). The electroporated cells on the right hand side of the neural tube express high levels of Slug and more Slug-expressing cells can be observed migrating from the post-otic hindbrain. It is interesting to note that although many Slug-expressing migratory cells are also HNK-1 positive (white arrowheads in A and B), some migrating cells do not show HNK-1 reactivity (black arrowheads in A and B). The dotted line shows the level of the section in Fig. 3A. (C,D) Different embryos subjected to the same electroporation process and hybridised with rhoB or Pax3 at stage 13. Note the ectopic rhoB expression in the premigratory crest of rhombomeres 4 and 5 and a greater area covered by the rhoB-expressing cells emigrating from r4 and r6. This can be better observed in the sections (G,H) taken from this embryo at the levels indicated by the dotted lines in (C). White arrows in H indicate cells migrating out from r5. (D) An increase in the levels of Pax3 expression can be seen all along the AP axis of the hindbrain. (E,F) Another stage 15 embryo illustrating rhoB (E) and HNK-1 expression (F) after Slug electroporation. Note that there is an increase in crest cells migration from the right hand side, which expresses the two markers. Abbreviations as in Fig. 1.
