Differentiation of the Yolk Sac of the Chick Studied by Electron Microscopy

作者：Ruth Bellairs · 发表于：Development · 年份：1963 · DOI：10.1242/dev.11.1.201 · 被引用次数：107 · 研究领域：Caveolin-1 and cellular processes、Glycosylation and Glycoproteins Research、Proteoglycans and glycosaminoglycans research

ABSTRACT The marginal cells of the area opaca and early yolk sac are extended distally into long processes which may measure up to 500μ in length by as little as μ in depth. In whole mounts of blastoderms, examined by fight microscopy, these processes can be seen forming a clear rim to the blastoderm. They possess cytoplasmic granules, but no mitochondria or endoplasmic reticulum. It is suggested that these processes enable the blastoderm to migrate under the vitelline membrane. The endoderm of the region lying immediately proximal to the edge has been found to be composed of cells and not of a syncytium as is generally supposed. These cells are frequently separated by patches of modified yolk, consisting of a meshwork of membranes. These membranes possess a fine structure similar to that of myelin figures and it is suggested that they are formed by hydration of yolk lipids by water drawn through the vitelline membrane from the egg white. This meshwork corresponds with the region known at this stage as the periblast by some light microscopists. No evidence about the nature of the periblast in early cleavage is presented. The incidence of desmosomes in the area opaca appears to increase between 1 and 2 days of incubation. It is shown that each cell membrane retains its anatomical identity throughout the desmosome. Structural changes begin to take place in the intracellular yolk drops of the area vasculosa just before the establishment of the yolk sac circulation. These changes...