Fig. 4. Ectopic LSox5 expression in the cephalic neural tube upregulates the expression of specific neural crest markers. Embryos were electroporated with pCX-LSox5 on the right-hand side of the neural tube, left to develop for 12 (A-D) or 20-24 hours (E-M), and then subjected to in situ hybridisation to visualise the expression of LSox5 and/or FoxD3 or Sox10. (A,C) Dorsal view of the midbrain and anterior hindbrain of two embryos showing an increase in FoxD3- and Sox10-expressing cells on the transfected side. Transverse sections of these embryos (B,D) show the appearance of ectopic premigratory cells expressing these markers. Dorsal (E) or lateral views (F,G) of two treated embryos show the dramatic increase in FoxD3 and Sox10 expression on the transfected side (ep) 20-24 hours after electroporation. The effect is particularly remarkable in transverse sections at the level of the circumpharyngeal crest (J,K). (H,I) Diagrams representing the area covered by FoxD3- or Sox10-expressing cells in 40 µm serial sections through the cephalic region of the same embryos. These data enable us to estimate the number of cells expressing these markers along the anteroposterior axis (in arbitrary units). A larger area of expression is associated with the transfected side (red bars) in most sections. The red lines correspond to the transverse section in B (A), D (C), J (E,H) and K (F,G,I). (L-M) Transverse sections at a mesencephalic level showing transformed neuroepithelial cells that seem to leave the neural tube beyond the dorsal competence domain (arrowheads) and do not express FoxD3 or Sox10. ov, otic vesicle.