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Fig. 4
Tg(wnt8aPAC:EGFP) expression depends on Nodal. A–J: In situ hybridizations in control (A,C,E,G,I) or SB-431542 treated embryos (B,D,F,H,J). A–F: Shield stage, animal pole views, dorsal right. A,B: wnt8a levels in the ventrolateral margin are reduced when Nodal signaling is inhibited, and the dorsal clearing is expanded (arrows). C,D: Tg(wnt8aPAC:EGFP) expression responds in an identical way to wnt8a. E,F: In situ hybridization for ntl to confirm effectiveness of SB-431542 treatment. Note dorsal clearing of ntl (arrows), corresponding to the loss of dorsal mesoderm; this phenotype resembles the cyc;sqt double mutant (compare to fig. 6U in Dougan et al., 2003). G–J: Late bud stage, posterior views. G,H: wnt8a expression persists in the tailbud of SB-431542-treated embryos but is not detected in the prospective pronephros. Arrows indicate prospective pronephros expression domain. I,J: Tg(wnt8aPAC:EGFP) expression responds identically to wnt8a. Persistent transcripts are observed in the tail paraxial mesoderm (asterisks). Note that no EGFP transcripts are detected in the position of the prospective pronephros, lateral to the presomitic mesoderm domain (arrow). K–P: The EGFP+ lineage forms tail mesoderm in SB-431542-treated embryos. K,L: Control Tg(wnt8aPAC:EGFP) 24-hpf embryo. Note strong expression in trunk and tail mesoderm. M,N: 24-hpf SB-431542-treated Tg(wnt8aPAC:EGFP) embryos. Note that developing tail mesoderm expresses EGFP. O: EGFP transcripts in a control Tg(wnt8aPAC:EGFP) embryo. Note expression in tailbud (arrow) but not in trunk or tail somitic mesoderm. P: EGFP transcripts are also detected in the tailbud of SB-431542-treated Tg(wnt8aPAC:EGFP) embryos (arrow).