Ferrer F, Garcia C, Villar J, Arias M
Departamento de Biologia Celular y Anatomia, Facultad de Veterinaria, Universidad de León, España.
Anat Histol Embryol. 1995 Sep;24(3):191-6. doi: 10.1111/j.1439-0264.1995.tb00034.x.
An ultrastructural study of the different stages of pre-implantation in sheep was carried out, analysing the changes brought about mainly in the morula and blastocyst stages. The analysis of the embryos obtained showed a series of common characteristics in all stages, most noticeable being the presence of a high number of vesicles distributed in a uniform way in the cytoplasm, and also the presence of numerous electron-dense mitochondria in many varied forms. The most important ultrastructural modifications took place at the 16-cell stage and affected, principally, the nucleus, which presented numerous condensations of chromatin distributed along the nucleoplasm. The nucleoli adopted a reticular morphology, abandoning the compact aspects presented in the previous stage. These changes might be involved in the synthesis of embryonic RNA, and, accordingly, in the activation of the genome of this species. These data indicate that this stage is critical to the embryonic development and might be related to the blockage produced in the development of cultivated sheep embryos at the point of transition from 8 to 16 cells. Nevertheless, it should be pointed out that the first signs of modifications in the aspect of the nucleus are observed at the four-cell stage, being characterized by the appearance of vacuolated areas in the nucleolus, indicating the first signs of embryonic nucleic activity, which would anticipate the main change in the control of the protein synthesis.
对绵羊植入前不同阶段进行了超微结构研究，主要分析桑椹胚和囊胚阶段发生的变化。对所获胚胎的分析显示，所有阶段都有一系列共同特征，最明显的是细胞质中均匀分布着大量囊泡，以及存在多种形态的大量电子致密线粒体。最重要的超微结构变化发生在16细胞阶段，主要影响细胞核，细胞核中沿核质分布着大量染色质凝聚物。核仁呈现出网状形态，不再具有前一阶段的致密外观。这些变化可能参与胚胎RNA的合成，进而参与该物种基因组的激活。这些数据表明，这个阶段对胚胎发育至关重要，可能与培养的绵羊胚胎从8细胞向16细胞转变时发育受阻有关。然而，应该指出的是，在四细胞阶段就观察到了细胞核外观变化的最初迹象，其特征是核仁中出现空泡化区域，这表明胚胎核酸活性的最初迹象，预示着蛋白质合成控制的主要变化。
