Fig. 2. Identification of a neural crest-specific, autoregulatory element controlling Krox20 expression. (A-D) The transgenic line -31/+7 Krox20/lacZ (see Fig. 3, construct #1) was analysed for ß-galactosidase activity in toto at 8.5 dpc (A), 9.0 dpc (C) and 9.5 dpc (D), or by transverse section through rhombomere 5 at 9.0 dpc (B, dorsal to the top). (E,F) The -31/+7 Krox20/lacZ transgene was analysed in a Krox20 mutant background (Krox20^Cre/Cre) at 9.0 dpc (E) and 9.5 dpc (F). Embryos are oriented with anterior to the right (A, C-F). NC, migrating neural crest. wt, wild type. The scale bar in B represents 40 µm.