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Fig. 7 Endoderm and anterior mesoderm formation requires non-embryonic sources of nodal-related ligands. (A-H) Pharyngula stage (24 hpf; A,B,E,F, lateral views) and gastrula stage (7 hpf; C,D,G,H, animal pole views) phenotypes of WT and Mndr1 zebrafish embryos after YSL injection of 8 ng Ctrl MO or a combination of 10 ng Ndr2 MO and 10 ng Ndr1 MO. Embryos were fixed and stained with antisense probes against egr2b and desma RNAs (A,B,E,F; see Fig. 6 legend) and against RNA encoding the forkhead box transcription factor Foxa2, which labels gastrula stage endoderm and dorsal mesoderm (C,D,G,H). Black arrowheads indicate heart muscle staining by desma. Red arrowheads indicate dorsal mesoderm; the remaining foxa2 stain, where present, marks endoderm. Arrows indicate the anterior limit of the tail. Fractions indicate the number of equivalent outcomes/number of embryos observed. Siblings of the embryos in E and G are also shown in Fig. 6E and 6F, respectively. Insets in G and H show the distribution of fluorescently labeled MO in representative YSL injections. (I) Model of the developmental requirements for non-embryonic sources of Mxtx2, Ndr2 and Ndr1. The dashed line indicates a Nodal-independent pathway downstream of Mxtx2. Anterior mesoderm refers to the totality of head and trunk mesoderm.