Figure 4.

Overexpression of bon mRNA rescues endoderm formation in bon mutants. Embryos were injected with 100 pg of β-galactosidase (lacZ) or bon mRNA at the 1–4 cell stage (A–F). Gut tube formation was assessed by analyzing fkd7 expression in 24 hpf embryos (E,F). (A–D) Dorsal views. lacZ overexpression does not affect sox17 expression in bon^m425 (A) or bon^s9 (B) mutants. The number of sox17-expressing endodermal precursors is significantly increased in bon^m425 (C) and bon^s9 mutants (D) following bon overexpression. An enlargement of the most vegetal sox17-expressing population of cells is also seen in both alleles following bon overexpression (arrows in C and D). (E,F) Lateral views, anterior to the left and dorsal to the top. fkd7 expression in the gut tube, which is absent in lacZ-injected bon^s9 mutants (arrow in E), is restored following bon overexpression (arrow in F).