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Fig. 6. Transverse sections showing complementarity of flk-1 (A, C, E, G) and VEGF (B, D, F, H) expression patterns. Sections A, B, G, and H were photographed at 100X magnification and sections C at 200X. Dorsal is to the right in A and B. Dorsal is up in all other panels. A: Section through the aortic arch progenitor region of a stage 28 embryo stained for flk-1. Endothelial precursor cells are shown in a punctate pattern in the mesoderm which will form the third aortic arch (arrows) and the anterior portion of the endocardium (arrowhead). B: Section equivalent to A showing staining for VEGF throughout the pharyngeal endoderm which underlies both the aortic arch mesoderm (arrows) and the cardiogenic mesoderm (short arrow). C: Section through the heart of a stage 32 embryo showing flk-1 staining in the endocardium (arrowhead), but not the myocardium. Staining is also visible in the ventral aortae (arrows) which lead from the bulbus cordis (anterior to the heart) to the aortic arches. D: Section equivalent to C showing VEGF expression in the pharyngeal endoderm adjacent to the endocardium (short arrow) and adjacent to the ventral aortae (long arrows). E: Section through the developing kidney of a stage 32 embryo, showing flk-1 staining in the region of the blood sinus which surrounds the developing tubules. F: Section equivalent to E showing VEGF expressing in the developing glomus. G: Section through the posterior trunk of a stage 30 embryo showing flk-1 in the lateral plate mesoderm, under the somites. These regions of staining mark the developing posterior cardinal veins which have not yet fused into mature vessels. H: Section equivalent to G showing VEGF in the somites (open arrowheads) and in the hypochord (arrow). |
