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Fig. 1. In situ hybridization reveals expression of VEGF in the hypochord and flk-1 in migrating endothelial precursor cells. (A) Section through the posterior trunk of an early tailbud embryo (stage 30) showing VEGF expression in the somites and in the hypochord (arrow). (B) Higher magnification of the hypochord (arrow) stained for VEGF expression. The notochord is indicated (n). (C) Section through the trunk of an early tailbud embryo (stage 28) showing expression of flk-1 in groups of endothelial precursor cells in the mesenchyme of the lateral plate mesoderm. Flk-1 transcripts are located at the position of the developing cardinal veins, prior to blood vessel formation. (D) Section positionally equivalent to C through the trunk of a mid-tailbud embryo (stage 33) showing migrating angioblasts (arrowheads) that express flk-1. Position of the posterior cardinal veins is indicated (arrows). (E) High magnification view of the dorsal aorta (stage 35) stained for flk-1 expression. Hypochord is indicated (arrow). (F) Schematic representation of tissue layers and expression domains of VEGF and flk-1. Note that the hypochord lies immediately dorsal to endodermal tissue and at some distance from lateral plate mesoderm tissue. Bar, 40 μm (A,C,D) and 20 μm (B,E). |
