BAKER P C
J Cell Biol. 1965 Jan;24(1):95-116. doi: 10.1083/jcb.24.1.95.
The blastoporal groove of the early gastrula of the treefrog, Hyla regilla, was examined with the electron microscope. The innermost extension of the groove is lined with invaginating flask- and wedge-shaped cells of entoderm and mesoderm. The distal surfaces of these cells bear microvilli which are underlain with an electron-opaque layer composed of fine granular material and fibrils. The dense layer and masses of vesicles proximal to it fill the necks of the cells. In flask cells bordering the forming archenteron the vesicles are replaced by large vacuoles surrounded by layers of membranes. The cells lining the groove are tightly joined at their distal ends in the region of the dense layer. Proximally, the cell bodies are separated by wide intercellular spaces. The cell body, which is migrating toward the interior of the gastrula, contains the nucleus plus other organalles and inclusions common to amphibian gastrular cells. A dense layer of granular material, vesicles, and membranes lies beneath the surface of the cell body and extends into pseudopodium-like processes and surface undulations which cross the intercellular spaces. A special mesodermal cell observed in the dorsal lining of the groove is smaller and denser than the surrounding presumptive chordamesodermal cells. A long finger of cytoplasm, filled with a dense layer, vesicles and membranes, extends from its distal surface along the edge of the groove, ending in a tight interlocking with another mesodermal cell. Some correlations between fine structure and the mechanics of gastrulation are discussed, and a theory of invagination is proposed, based on contraction and expansion of the dense layer and the tight junctions at distal cell surfaces.
用电子显微镜对雨蛙（Hyla regilla）原肠胚早期的胚孔沟进行了检查。沟的最内层延伸部分内衬着内胚层和中胚层的内陷烧瓶状和楔形细胞。这些细胞的远端表面有微绒毛，其下方是由细颗粒物质和纤维组成的电子不透明层。致密层及其近端的大量小泡充满了细胞的颈部。在与形成的原肠相邻的烧瓶状细胞中，小泡被由膜层包围的大液泡所取代。沟内衬的细胞在致密层区域的远端紧密相连。近端，细胞体被宽阔的细胞间隙隔开。向原肠内部迁移的细胞体包含细胞核以及两栖类原肠胚细胞常见的其他细胞器和内含物。一层由颗粒物质、小泡和膜组成的致密层位于细胞体表面下方，并延伸到穿过细胞间隙的伪足状突起和表面起伏中。在沟的背侧内衬中观察到的一种特殊中胚层细胞比周围假定的脊索中胚层细胞更小且更致密。一条充满致密层、小泡和膜的细胞质长指从其远端表面沿着沟的边缘延伸，最终与另一个中胚层细胞紧密联锁。讨论了精细结构与原肠形成机制之间的一些相关性，并基于致密层的收缩和扩张以及远端细胞表面的紧密连接提出了一种内陷理论。
