Fig. 4. Localisation of the mouse and chick NCE. Genomic fragments were fused to the ß-globin/lacZ promoter/reporter and analysed for ß-galactosidase activity by electroporation in the chick neural tube (B,C,E,G,H) or by transgenesis in the mouse at 9.5 dpc (A,D,F). (A,B) Mouse sequences between -31 kb and -23.5 kb relative to Krox20 (Fig. 3, construct #6S). (C,D) Sequences between -26.5 kb and -25.5 kb (Fig. 3, construct #11). (E-G) A 247 bp subfragment of this region either alone (E,F; Fig. 3, construct #17) or co-electroporated with a Krox20 expression construct (G; Fig. 3, construct #17+). (H) A 1.7 kb chick sequence with homology to mouse fragment #17. All embryos are whole mounts with anterior to the right. r3, r5 and neural crest (NC) are indicated by arrowheads. ^*, occasional ectopic expression.