Reima I, Lehtonen E, Virtanen I, Fléchon J E
Department of Pathology, University of Helsinki, Finland.
Differentiation. 1993 Aug;54(1):35-45. doi: 10.1111/j.1432-0436.1993.tb00657.x.
The organization of the cytoskeleton during early pig embryogenesis was investigated by using fluorescence and electron microscopy. The early morphogenesis of the pig embryo differed from that of the mouse, the standard model of the early mammalian development. In the pig, both compaction and polarization were gradual, and definitive polarization of cell surface microville occurred first shortly before blastocyst formation; the compaction and polarization of the mouse embryo are completed as early as at the 8 cell stage. Furthermore, the pig morula undergoes cycles of compaction and decompaction throughout its development. Distinct changes in the distribution of actin and the actin-associated proteins alpha-fodrin, vinculin and E-cadherin coincided with these events. In the pig, all these molecules were evenly distributed at all aspects of the blastomeres during early cleavage and then gradually accumulated in regions of intercellular contacts toward the blastocyst stage; microfilaments in trophectoderm cells formed a cortical meshwork associated with apical microvilli and adherent junctions (zonula adherens). In the mouse, the corresponding changes occur earlier, at the 8 cell stage. Microtubules formed a network-like cortical layer beneath the microvilli at the free outer surfaces of pig blastomeres. Cytokeratin bundles were not observed until the early blastocyst, where they characteristically associated with newly formed desmosomes. In both species a close correlation between morphologically defined developmental stages and the organization of the cytoskeleton: actin and actin-associated proteins are involved in polarization and compaction, whereas the appearance of intermediate filament bundles coincides with the building of the first epithelium, the trophectoderm; it is in the timing of events that a contrast between species is observed.
利用荧光显微镜和电子显微镜对猪早期胚胎发育过程中细胞骨架的组织情况进行了研究。猪胚胎的早期形态发生与早期哺乳动物发育的标准模型小鼠不同。在猪中，致密化和极化都是渐进的，细胞表面微绒毛的最终极化最早在囊胚形成前不久发生；而小鼠胚胎的致密化和极化早在8细胞阶段就已完成。此外，猪桑椹胚在其整个发育过程中经历致密化和解致密化循环。肌动蛋白以及与肌动蛋白相关的蛋白α- fodrin、纽蛋白和E-钙黏蛋白分布的明显变化与这些事件同时发生。在猪中，在早期卵裂期间，所有这些分子在卵裂球的各个方面均匀分布，然后在向囊胚阶段发育的过程中逐渐在细胞间接触区域积累；滋养外胚层细胞中的微丝形成了与顶端微绒毛和黏着连接（黏着带）相关的皮质网络。在小鼠中，相应的变化发生得更早，在8细胞阶段。微管在猪卵裂球自由外表面的微绒毛下方形成了网络状皮质层。直到早期囊胚阶段才观察到细胞角蛋白束，它们在那里典型地与新形成的桥粒相关联。在这两个物种中，形态学定义的发育阶段与细胞骨架的组织之间都存在密切相关性：肌动蛋白和与肌动蛋白相关的蛋白参与极化和致密化，而中间丝束的出现与第一个上皮即滋养外胚层的形成同时发生；正是在事件发生的时间上观察到了物种之间的差异。
