Figure 2.

Endoderm development is defective in bon mutants. Wild-type (A,C,E) and bon mutant (B,D,F) embryos were examined for expression of sox17 at 90% epiboly (A,B), fkd7 at the 10-somite stage (C,D), and shh at 36 hpf (E,F). (A,B) During gastrulation sox17 is expressed in the endodermal precursors throughout the hypoblast as well as in the forerunner cells (arrowhead in A). Endodermal sox17 expression is greatly reduced in bon mutants (B), whereas sox17 expression in the forerunner cells is normal (arrowhead in B). (C,D) During mid-somitogenesis fkd7 is expressed in the endoderm (arrow in C) as well as in the floor plate and hypochord. In bon mutants (D), there are only a few fkd7-expressing endodermal cells (arrow in D), whereas expression in the floor plate and hypochord is normal. (E,F) Similarly, in 36 hpf wild-type embryos, shh is expressed throughout the endoderm (arrowheads in E); bon mutants exhibit small patches of shh-expressing endoderm (arrowheads in F). shh is also expressed in the floor plate, forebrain, and fin buds. All panels show dorsal views, with anterior to the top, except E and F, where anterior is to the left.