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Fig. 3 The DN-RARα2a acts in a dominant negative fashion. (A) DN-RARα2a is able to block induction of an RA-responsive luciferase reporter gene (tk-[βRARE]2-luc). Co-injection of DN-RARα2a RNA completely abolishes the response of the reporter gene to RA. Graph shows fold-induction relative to reporter alone; six embryos were used for each experimental condition and assays were carried out in duplicate and averaged. (B-E) hoxa4a expression, 10 hpf, lateral view. (B) Normal embryo. (C) hoxa4a expression is upregulated and extended towards the anterior after 1 hour treatment with RA. (D) DN-RAR mRNA injection blocks hoxa4a expression. (E) DN-RAR blocks the ability of RA to activate hoxa4a expression.