Fig. 6. Cdx4 and Hoxd11 expression patterns are downregulated in the tail bud of A1^-/- mutants, but are restored in A1^-/--/- mutants. Cdx4 is expressed in a graded anteroposterior manner along the tail bud mesoderm (tb), hindgut (hg) and neuroepithelium (ne) of the wild-type embryo (A). Hoxd11 shows prominent expression in tail bud (tb) mesoderm and neuroepithelium of the wild-type (D) embryo. In A1^-/- mutants (B) Cdx4 expression is downregulated in the tail bud (tb*) mesoderm, neuroepithelium and hindgut (arrowhead indicates posterior neuropore). A1^-/- embryos (E) also show downregulation of Hoxd11 expression in the tail bud (arrowhead indicates last fully formed somite). A1^-/--/- mutants exhibit normal Cdx4 (C) and Hoxd11 (F) expression, although, in comparison with the wild-type embryo (D inset), Hoxd11 transcripts extend more rostrally along the ventral mesoderm (vm) (F, inset).

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