Origins of the Embryonic Vascular Pattern

Vascular development is studied in several model vertebrate embryos, with different species having distinct advantages for understanding various aspects of vascular morphogenesis. Avian embryos of the chicken and Japanese quail have the advantage of accessibility in the egg or whole embryo culture, quail/chick chimeras, and a monoclonal antibody (QH-1) that labels quail angioblasts and endothelial cells. Mouse embryos from a variety of transgenic and knockout lines have been examined for vascular patterning defects, leading to the discovery of unexpected roles for several genes. Frog embryos have the advantage of ease of injection of DNA constructs for overexpression and classic tissue transplantation studies. Zebrafish embryos are nearly transparent, allowing for easy observation of the developing vasculature, and large-scale genetic screens have identified mutants with vascular pattern formation defects.

The formation of embryonic blood vessels occurs through a series of events (Figure 1). First, angioblasts (endothelial cell precursors) are induced from the embryonic mesoderm (Figure 1A), which at this stage is an epithelial cell sheet. The new angioblast initially undergoes an epithelial to mesenchymal transformation (EMT; Figure 1B), and the new mesenchymal cell migrates (Figure 1C) and coheres to other angioblasts, forming an initial solid cord of cells (Figure 1D) at sites of vessel formation (vas-culogenesis). This solid cord further differentiates through unclear mechanisms to form a lumen in which a blood vessel tube is lined with endothelial cells (Figure 1E). In the case of the dorsal aorta, the first major vessel formed in the developing embryo, angioblasts originate from mesoderm directly adjacent to where they assemble in a process called vasculogenesis type I. In contrast, angioblasts that form the endocardium and cardinal veins migrate as individual cells or clusters that assemble at a distance from sites of angioblast origin in a process called vasculogenesis type II. Angiogenesis is the sprouting of new vessels from preexisting vessels. The first example of angiogenesis in the embryo

Figure 1 Initial Steps in Dorsal Aorta Morphogenesis. Embryonic blood vessels form from angioblasts that originate from the embryonic mesoderm by epithelial to mesenchymal transformation (EMT). (A) Two cells in a simple cuboidal epithelium acquire gene expression changes (shaded) that distinguish them as angioblasts. (B) These two angioblasts undergo EMT. (C) The angioblasts migrate and cohere to one another. (D) Two angioblasts have formed a portion of a solid cord. In the case of the dorsal aorta, a thin cord runs in the cranial-to-caudal direction. (E) A lumen is formed between two endothelial cells that continue to adhere at their junctions. (F) A sprout has formed off the vessel with the formed lumen.

Figure 1 Initial Steps in Dorsal Aorta Morphogenesis. Embryonic blood vessels form from angioblasts that originate from the embryonic mesoderm by epithelial to mesenchymal transformation (EMT). (A) Two cells in a simple cuboidal epithelium acquire gene expression changes (shaded) that distinguish them as angioblasts. (B) These two angioblasts undergo EMT. (C) The angioblasts migrate and cohere to one another. (D) Two angioblasts have formed a portion of a solid cord. In the case of the dorsal aorta, a thin cord runs in the cranial-to-caudal direction. (E) A lumen is formed between two endothelial cells that continue to adhere at their junctions. (F) A sprout has formed off the vessel with the formed lumen.

is morphogenesis of the intersomitic arteries that sprout from the dorsal aorta (Figure 1F) after a lumen has formed.

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Blood Pressure Health

Your heart pumps blood throughout your body using a network of tubing called arteries and capillaries which return the blood back to your heart via your veins. Blood pressure is the force of the blood pushing against the walls of your arteries as your heart beats.Learn more...

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