Fig. 1. Comparison of reporter gene expression in Krox20 heterozygous embryos. Reporter gene expression was assayed by X-gal staining in Krox20^lacZ/+ (A,C,E,G) and Krox20^Cre/+ R26R (B,D,F) embryos, and by AP staining in Krox20^Cre/+ Z/AP embryos (H-J). Embryos shown in I,J were processed for Krox20 ISH (brown) after AP staining. (A-H) Hindbrains of whole-mounted embryos with rostral towards the left. (I,J) Flat-mounted hindbrains with rostral towards the top. From the 14-15 s stage onward, neural crest cells exiting r5 are positive for the reporter gene only in the Krox20^lacZ/+ embryo (arrowhead in C). Derivatives of the r5 neural crest are labelled in the Krox20^Cre/+ R26R embryo at 9.5 dpc in the third branchial arch (BA3) (arrowheads in F), and at 10.5 dpc in BA3 and in the superior ganglion of the glossopharyngeal nerve (IX) (arrow in H). At 10.5 dpc, in the Krox20^lacZ/+ embryo (G), lacZ expression is detected in the boundary cap cells of the trigeminal (Vbc) and facial (VIIbc) nerves (arrow in G).

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