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Fig. 5. Endoderm is required for endothelial tube formation. (A) Wild-type stage-37 embryo showing posterior cardinal vein (closed arrowhead), intersomitic vessels (open arrowhead) and a prominent vascular plexus. (B,C) Stage-37 embryos deprived of endoderm at stage 10 contain thick assemblages of angioblasts (closed arrowheads), but do not contain endothelial tubes. (D) Stage-37 embryo deprived of endoderm at stage 10 and rescued by the addition of a vegetal plug of endoderm from a sibling embryo. Note the presence of posterior cardinal veins (closed arrowhead) and intersomitic vessels (open arrowhead). (E) Cross-section through a wild-type stage-37 embryo showing posterior cardinal vein (closed arrowhead) and dorsal aorta (open arrowhead). (F) Cross-section through a stage-37 endodermless embryo showing presence of angioblasts (closed arrowhead) but no assembly into endothelial tubes. All embryos were assayed by in situ hybridization with the vascular marker X-msr. e, endoderm; n, notochord; nt, neural tube. |
