Part of the Bodega Marine Laboratory Marine Science Series book series (BMSS)
Mesoderm Formation in the Chick Embryo, Revisited
At the time of egg laying, the chick blastoderm consists of a disc, some 2mm in diameter, comprising an inner, translucent area pellucida and an outer, more opaque area opaca (Figures 1, 2). The latter region contributes only to extraembryonic structures. The first layer of cells to be present as such is the epiblast, which is continuous over both areae opaca and pellucida. It is a one-cell thick epithelium which soon becomes pseudostratified and columnar, the apices of the cells facing the albumen. From the center of this initial layer arises a second layer of cells, the primary hypoblast, consisting of several unconnected islands of 5–20 cells (for more detailed explanation of the terminology see Stern 1990 and Figures 1 and 2). Subsequently, more cells are added to the primary hypoblast, and by 6 hr of incubation it becomes a loose but continuous epithelium, the secondary hypoblast. The source of these new hypoblast cells is the deep (endodermal) portion of a crescent-shaped region, the marginal zone (Figure 2), which separates areae pellucida and opaca at the future posterior (caudal) end of the embryo.
KeywordsChick Embryo Marginal Zone Neural Crest Cell Neural Cell Adhesion Molecule Primitive Streak
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© Plenum Press, New York 1991