Fig. 3. Whole-mount expression screening to identify potential ß-catenin target genes. (A-H) Whole-mount in situ hybridization with the indicated probes on wild-type embryos at different developmental stages. All embryos are depicted in a lateral view, anterior to the left, except for the 6- to 7-somite stage embryo in H, which is depicted in a ventral view. (A) Grsf1 is strongly expressed in the primitive streak (ps) at neural-plate stage (NP). At 9-somite stage, Grsf1 is restricted to the posterior neurectoderm in the tailbud (tb), and the midbrain (mb; arrow) and hindbrain region (hb; arrow). (B) Scap2 is expressed in the primitive streak at head-fold stage. At the 9-somite stage, mRNA expression is detected in the tailbud region and foregut pocket (arrow). (C) EST6 is expressed (arrows) in the extraembryonic ectoderm at early-streak (ES) and mid-streak (MS) stage. At head-fold stage, EST6 shows expression in a row of cells anterior to the node (arrows). (D) Punc is expressed in the primitive streak at head-fold stage. At the 11-somite stage, expression is seen in the midbrain (mb) and hindbrain (hb), as well as in the somites (so), inflow tract (ift) and posterior neurectoderm. (E) Zic3 is expressed in the primitive streak at head-fold stage. At 11-somite stage, expression is detected in anterior neurectoderm (ne), heart (h), inflow tract, gut (g), somites, midbrain (mb) and hindbrain (hb), and posterior paraxial mesoderm (pm). (F) EST10 is strongly expressed throughout the definitive endoderm at mid-streak, late-streak (LS), late-bud (LB) and head-fold stage. (G) Fragilis2 is first detected in the region where the allantois will form at mid-streak stage (arrow). At head-fold stage, expression is prominent in the primitive streak region and in the lateral-plate mesoderm (arrows). At 10-somite stage, expression is confined to the lateral-plate mesoderm (lpm), paraxial mesoderm and first forming somite (arrow) in the tailbud region. (H) EST16 shows expression in the primitive streak at late head-fold stage. At 6- to 7-somite stage, expression is confined to the posterior neurectoderm.