We are using a monoclonal antibody, QH-1, as a label for angioblasts in quail embryos to study vascular development. Our previous experiments showed that major embryonic blood vessels, such as the dorsal aortae and posterior cardinal veins, develop from angioblasts of mesodermal origin that appear in the body of the embryo proper (Coffin and Poole: Development, 102:735-748, '88). We theorized that there are two separate processes for blood vessel development that occur in quail embryos. One mechanism termed "vasculogenesis" forms blood vessels in place by the aggregation of angioblasts into a cord. The other mechanism, termed "angiogenesis," is the formation of new vessels by sprouting of capillaries from existing vessels. Here we report the results of microsurgical transplantation experiments designed to determine the extent of cell migration taking place during blood vessel formation. Comparison of the chimeras to normal embryos suggests that the vascular pattern develops, in part, from the normally restricted points of entry of angioblasts into the head from the ventral and dorsal aortae. Transplantations of quail mesoderm (1-15 somite stage) into the head of 5-15 somite chick hosts resulted in extensive sprouting and in migration of single and small groups of angioblasts away from the graft sites. Transplantations into the trunk resulted in incorporation of the graft into the normal vascular pattern of the host. Lateral plate mesoderm was incorporated into the dorsal aortae and individual sprouts grew between somites and along the neural tube to contribute to the intersomitic and vertebral arteries, respectively.
We describe a new method for analyzing embryonic events dependent on a specific peptide recognition signal. A short, specific amino acid sequence in fibronectin has been implicated as a recognition site in fibronectin-mediated interactions. Fibroblast adhesion to fibronectin is competitively inhibited by certain synthetic peptides, including the decapeptide Arg-Gly-Asp-Ser-Pro-Ala-Ser-Ser-Lys-Pro, which appears to contain the cell recognition sequence. We found that this peptide inhibited both amphibian gastrulation and avian neural crest cell migration in vivo, as well as the attachment and migration of neural crest cells in vitro. These processes are major cell migratory events previously suggested to involve fibronectin. Negative controls included another conserved fibronectin peptide from the collagenbinding region containing the sequence Cys-GIn-Asp-Ser-Glu-Thr-Arg-Thr-Phe-Tyr and another peptide. Our results demonstrate the feasibility of using synthetic peptides directed at recognition sites in extracellular proteins as probes of morphogenetic processes, and they provide further support for the hypothesis that fibronectin is involved in gastrulation and neural crest cell migration.
The embryonic vasculature forms by the segregation, migration, and assembly of angioblasts from mesoderm, a process termed vasculogenesis. The initial role of fibroblast growth factor 2 (FGF-2) in vascular development appears to be in the induction of endothelial precursors, angioblasts. Quail somites transplanted into chick embryos will give rise to angioblasts of quail origin. The number of angioblasts present within the chimera is dependent on the host environment. Angioblast induction can be demonstrated in vitro by the addition of FGF-2 to cultures of dissociated somitic mesoderm, as assessed by QH-1 epitope expression. Manipulation of FGF-2 concentration in the quail/chick chimeras by FGF-2 peptide or neutralizing antibody injections increases or decreases angioblast induction in the predicted manner. To better control growth factor release in vivo we have implanted beads that release FGF-2 into the embryonic environment. FGF-2 beads implanted into the somite induce angioblast differentiation in the epithelial somite; whereas, beads lateral to the somitic mesoderm induce the formation of ectopic vessels. These studies suggest that FGF-2 is important for both the induction of angioblasts and the assembly of angioblasts into the initial vasculature pattern.
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