Somitic wnt16-deltaC/deltaD signaling required for HSC specification is abrogated in ptc1;ptc2 mutants. Zebrafish flat mounts are shown with anterior to the left and posterior to the right. (A-B) Somitic wnt16 expression is strongly down-regulated in ptc1;ptc2 embryos at 10 somites (B black arrowheads), and this down-regulation persisted at the 15-second stage (C-D black arrowheads). (E-F) Expression of deltaC was absent from the somitic mesoderm (SM) of ptc1;ptc2 embryos (F black arrowheads) but was present within the presomitic mesoderm (PSM; F gray arrowheads). (G-H) deltaD expression was strongly down-regulated within the SM (H black arrowheads) and PSM (H gray arrowheads) of ptc1;ptc2 embryos.