Fig. 2. Expression pattern of VEGFR and VEGF during perturbed development. (A) Perturbation along the AV axis. Sea urchin embryos were treated with 30 mM LiCl. Detection of VEGF and VEGFR transcripts by WMISH (as in Fig. 1) on gastrula-stage embryos and DIC images of 48-hour-old embryos. Lateral views with the animal pole at the top. (B) Perturbation along the OA axis. Embryos were treated with 0.5 mM NiCl₂. WMISH of early gastrulae-stage embryos and DIC images of 48-hour-old embryos. Lateral views with the animal pole at the top, or ventral views with the oral side to the left when OA polarity is present (vv).