Figure 9. In situ hybridization of selected genes of the nodal pathway that are involved in endoderm development. Embryos injected at the 1-cell stage with 1 pmol of control MOmis or MOex5, were fixed at the indicated times that correspond in MOmis-injected control embryos to the following developmental stages: dome (41/3 hpf), germ-ring (52/3 hpf), and shield (6 hpf). In situ hybridization was performed using antisense oep (nodal co-receptor), sox32 (downstream of oep) and sox17 (activated by sox32 and required for endoderm specification) RNA probes. In map9 morphants, expression of sox32 and sox17 was restricted to a portion of the blastoderm margin at the shield stage (arrowheads, B8, C8).