Further Development 17.5: Formation of the Dorsal Aorta

Paraxial Mesoderm: The Somites and Their Derivatives

Most of the circulatory system of an early-stage amniote embryo is directed outside the embryo, its job being to obtain nutrients from the yolk or placenta. The intraembryonic circulatory system begins with the formation of the dorsal aorta. The dorsal aorta is composed of two cell layers: an internal lining of endothelial cells that is surrounded concentrically by a layer of smooth muscle cells. Elsewhere in the body, these two layers of blood vessels are usually derived from the lateral plate mesoderm, as we will detail in Chapter 18. The endotome of the posterior sclerotome, however, provides the endothelial cells and smooth muscle cells for the dorsal aorta and intervertebral blood vessels (see Figure 17.2E and F; Pardanaud et al. 1996; Wiegreffe et al. 2007; Nguyen et al. 2014). The presumptive endothelial cells are induced by Notch signaling in an ephrin B2-dependent manner. These sclerotomal cells are instructed to migrate ventrally by a presumed chemoattractant made by the primary dorsal aorta, a transitory structure made by the lateral plate mesoderm. Eventually, the endothelial cells from the sclerotome replace the cells of the primary dorsal aorta, which will become part of the blood stem cell population (Pouget et al. 2008; Sato et al. 2008; Ohata et al. 2009).

Literature Cited

Nguyen, P. D. and 14 others. 2014. Haematopoietic stem cell induction by somite-derived endothelial cells controlled by meox1. Nature 512: 314–318.
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Ohata, E., R. Tadokoro, Y. Sato, D. Saito and Y. Takahashi. 2009. Notch signal is sufficient to direct an endothelial conversion from non-endothelial somitic cells conveyed to the aortic region by CXCR4. Dev. Biol. 335: 33–42.
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Pardanaud, L., D. Luon, M. Prigent, L.-M., Bourcheix, M. Catala and F. Dieterlen-Lievre 1996. Two distinct endothelial lineages in ontogeny, one of them related to hemopoiesis. Development 122: 1363–1371.
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Pouget, C., K. Pottin and T. Jaffredo. 2008. Sclerotomal origin of vascular smooth muscle cells and pericytes in the embryo. Dev. Biol. 315: 437–447.
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Sato, Y., T. Watanabe, D. Saito, T. Takahashi, S. Yoshida, J. Kohyama, E. Ohata, H. Okano and Y. Takahashi. 2008. Notch mediates the segmental specification of angioblasts in somites and their directed migration toward the dorsal aorta in avian embryos. Dev. Cell 14: 890–901.
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Wiegreffe, C., B. Christ, R. Huang and M. Scaal. 2007. Sclerotomal origin of smooth muscle cells in the wall of the avian dorsal aorta. Dev. Dyn. 236: 2578–2585.
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