1Thomas J. Poole and 2Eric B. Finkelstein
1SUNY Upstate Medical University, Syracuse, New York 2Schepens Eye Research Institute and Harvard Medical School, Boston, Massachusetts
Vascular endothelial growth factor (VEGF) expression and its regulation are critical for normal vascular development. Gene knockout studies in mice resulted in embryonic lethality from a failure of endothelial cell specification and blood vessel formation. Such studies have revealed an essential role for VEGF in vascular development. Animals heterozygous or homozygous for the VEGF-null mutation are embryonic lethal, demonstrating a critical role for dose regulation of VEGF during vascular morphogenesis. Additional studies in which mice were engineered to overexpress VEGF  or downregulate VEGF specifically in yolk sac endoderm  also lead to disruption of vascular patterns, a further demonstration that precise control of VEGF levels is critical for normal vascular development. Studies in the quail embryo, zebrafish, and frog have led to similar conclusions. Such studies have utilized delivery of soluble growth factor (quail, frog), delivery of soluble inhibitors (quail), and genetic knockdown with antisense or morpholi-nos (zebrafish, frog). All studies have demonstrated that increased or decreased VEGF levels result in abnormal vascular patterns.
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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.