Harrisson F, Callebaut M, Vakaet L
Department of Anatomy and Embryology, State University Centre, Antwerp, Belgium.
Anat Rec. 1991 Mar;229(3):369-83. doi: 10.1002/ar.1092290310.
The de-epithelialization of cells of the upper layer during the phenomena of polyingression and primitive streak ingression was studied by analyzing, from the time of laying to the end of gastrulation, the ultrastructure of the basal lamina underlying the upper layer. The electron density of the basal lamina and associated extracellular materials was enhanced by addition of tannic acid to the fixative. Special attention was also paid to the spatial and temporal distribution of blebs at the basal surface of the upper layer, and to the contribution of the de-epithelialized cells to the formation of the deep layer. The results indicate that a nascent basal lamina is already present at the time of laying, especially beneath regions of the area pellucida where polyingression is not apparent. From the onset of incubation, the basal lamina rapidly develops, and it is interrupted by a large number of blebs. However, during the first 6-8 h of incubation, i.e., stages 1-2 of Vakaet (Arch. Biol. (Liège) 81:387-426, 1970), a downward movement of de-epithelialized cells that insert into the deep layer and form the endophyll persists cranially. This phenomenon of polyingression, which starts during the intrauterine period, probably extends from caudal to cranial and comes to an end by stage 3. During these first three stages, the number of blebs progressively decreases, especially in the cranial part of the area pellucida, and a thicker, continuous basal lamina associated with numerous interstitial bodies is laid down. The caudal part of the upper layer is still actively blebbing at that time. Due to the convergence of this area toward the axis of the blastoderm, which leads to ingression at and elongation of the primitive streak up to and including stage 6, the number of blebs at the basal surface of the upper layer progressively decreases. From stage 7 on, blebs are virtually absent; shortening of the primitive streak and formation of the head process begin. At the level of the head process, primitive streak ingression has ceased and a novel basal lamina is progressively deposited beneath the upper layer. By stage 9, a thick, smooth basal lamina physically separates the upper layer from the head mesenchyme. Summarizing, at the time of gastrulation, the presence of blebs that perforate the basal lamina is correlated with the de-epithelialization of cells. Before incubation, however, de-epithelialization of upper-layer cells occurs before the assembly of the basal lamina.(ABSTRACT TRUNCATED AT 400 WORDS)
通过分析从产卵时到原肠胚形成结束时上层下方基膜的超微结构，研究了多内陷和原条内陷现象期间上层细胞的去上皮化过程。在固定剂中添加单宁酸可增强基膜及相关细胞外物质的电子密度。还特别关注了上层基底面泡状突起的时空分布，以及去上皮化细胞对深层形成的贡献。结果表明，在产卵时就已存在新生的基膜，尤其是在明区中多内陷不明显的区域下方。从孵化开始，基膜迅速发育，并被大量泡状突起中断。然而，在孵化的前6 - 8小时，即瓦凯特（Vakaet）分期的第1 - 2阶段（《生物学杂志（列日）》81:387 - 426，1970年），去上皮化细胞向下移动并插入深层形成内胚叶的过程在头部持续存在。这种多内陷现象始于子宫内期，可能从尾端向头端延伸，并在第3阶段结束。在这前三个阶段，泡状突起的数量逐渐减少，尤其是在明区的头部区域，同时形成了与大量间质小体相关的更厚、连续的基膜。此时上层的尾端部分仍在活跃地形成泡状突起。由于该区域向胚盘轴汇聚，导致原条在第6阶段及之前包括第6阶段处内陷并伸长，上层基底面的泡状突起数量逐渐减少。从第7阶段开始，几乎没有泡状突起；原条缩短，头部突开始形成。在头部突水平，原条内陷停止，新的基膜逐渐沉积在上层下方。到第9阶段，一层厚而光滑的基膜将上层与头部间充质物理分隔开。总之，在原肠胚形成时，穿透基膜的泡状突起的存在与细胞的去上皮化相关。然而，在孵化前，上层细胞的去上皮化发生在基膜组装之前。（摘要截取自400字）
