Fig. 7. Wild-type activated cells can form endoderm in cas mutants. (A) At the blastula stage, a few wild-type cells expressing Tar* were transplanted to a cas host. (B) Flat-mount of a young gastrula (60% epiboly) showing the expression of sox17 (blue) by activated cells (brown nuclear staining). Notice the absence of endogenous sox17 expression in cas embryos. The inset shows a close-up view of the region containing the grafted cells. (C-K) Expression of nkx2.3, insulin and fkd7 in 24 hpf wild-type (C,F,I), cas (D,G,J) and grafted cas (E,H,K) embryos. (C-E) The pharyngeal expression of nkx2.3 (C) is absent in cas embryos (D). This expression can be restored by the graft of wild-type activated cells (E). (F-H) Pancreatic expression of insulin (arrow in F), which is absent in cas embryos (G), can be restored by the graft (arrow in H). The expression of nkx2.5 (arrowheads) identifies the cardia bifida of cas embryos and was used to genotype them. (I-K) The expression of fkd7 in the gut (I) is lost in cas embryos (J). This expression can be restored by wild-type activated cells (arrows in K). (L,M) Transverse sections through the pancreatic and gut regions of grafted cas embryos showing that the expression of the insulin and fkd7 (blue, arrowhead in M) is restricted to grafted cells (brown nuclear staining). (N-P) Live grafted cas embryos. At 96 hpf, grafted cells (green) differentiate into endodermal derivatives such as pharyngeal epithelium or segments of gut (arrowheads). In O, the yolk (y) appears green because of its autofluorescence. (C-H) Dorsal views, anterior to the left. (I-K,N-P) Lateral views, anterior to the left, dorsal to the top. no, notochord; nt, nerve tube.
