Although the role of VEGF in angioblast induction remains unclear, fibroblast growth factor 2 (FGF-2) has been implicated in angioblast induction in the quail embryo . The expression of VEGF receptor 2 (VEGFR2, flk-1) resembles the expression of the quail antibody QH-1, which labels angioblasts as they undergo EMT. VEGFR2 is the first VEGF receptor expressed, suggesting that VEGF is not involved in angioblast induction. The idea that VEGF is not involved with angioblast induction fits with the phenotypes of VEGF and VEGFR2 knockout mice. In receptor knockout mice, endothelial cell precursors formed, but there were no mature endothelial cells, while in the VEGF ligand knockout mice, endothelial cells formed but failed to differentiate into a vascular pattern. Similarly, VEGFR2 mutations in zebrafish suggest a role for VEGF in sprouting and remodeling but not in initial specification of angioblasts .
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This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.