Fig. 4. Transient Nodal signalling autonomously commits cells to an endodermal fate. One single activated cell (white arrowhead) transplanted to the animal pole of a blastula host (A) expresses sox17 during gastrulation (arrowhead in B) and become endodermal derivatives at 24 hpf (arrow in C). Co-injection of Tar* and FAST^SID at the 2-cell stage (D) results in the cells that were transplanted to the animal pole being incorporated into the eye and the brain (E). By contrast, delayed injection of FAST^SID (F) results in cells grafted to the animal pole adopting an endodermal fate (G).