Fig. 7. In vivo analysis of essential NCE elements. (A-C) The activity of the NCE carrying mutations in the Krox20 binding sites alone (A,B; Fig. 3, construct #18) or both the Krox20 binding site mutations and a 15 nt deletion to inactivate the putative HMG box binding sites (C; Fig. 3, construct #23), were analysed by chick electroporation (A,C) or by mouse transgenesis (B). ß-galactosidase activity was dramatically reduced (A,B) or eliminated (C) as compared to the wild-type construct (#11, see Fig. 4B-D). (D,E) A 41 bp sequence encompassing the putative HMG box binding sites (Fig. 5) was multimerised, linked to the reporter (Fig. 3, construct #24) and analysed by chick electroporation (D) and mouse transgenesis (E). Weak ß-galactosidase activity is observed throughout the cranial neural crest. Embryos are whole mounts with anterior to the right. NC, neural crest.

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