Shalgi R, Sherman M I
J Exp Zool. 1979 Oct;210(1):69-80. doi: 10.1002/jez.1402100108.
Mouse blastocysts undergo developmental steps in culture analogous to those occurring during implantation in utero. We examined cultured blastocysts by scanning electron microscopy (SEM) as they passed through these stages. From the time of hatching to the acquisition of adhesiveness, most blastocysts were exhanded, with flattened cells possessing relatively small numbers of microvilli, centrally raised areas (presumably reflecting the location of the nuclei) and intercellular ridges often possessing microvilli. At, or shortly before, the trophoblast outgrowth stage, blastocysts appeared to contract; the cells bulged noticeably, microvilli covered the entire surface of most cells and intercellular ridges were no longer observable. Blastocysts removed from uteri on the seventh day of ovariectomy delay possessed a variety of morphologies and shapes. The blastocoel was frequently collapsed and cell outlines were difficult to discern. These blastocysts were initially adhesive in vitro, but subsequently disengaged from the substratum before becoming permanently adherent several hours later. During the initial phase of adhesiveness, blastocysts were elongated and had prominent intercellular ridges, particularly in the equatorial region. Detached blastocysts contained bulging cells with contours which obscured the intercellular ridges. Surface ultrastructure during subsequent phases resembled non-delayed blastocysts during attachment and outgrowth. On the basis of our studies, we propose that intercellular ridges play some role in blastocyst adhesiveness. However, we must conclude that there are other factors involved in the acquisition of adhesiveness by the blastocyst which are at least equally important but of a nature too subtle to be identified by our SEM analyses. Insofar as delayed blastocysts are concerned, we find that, within limits, the surface alterations that take place when blastocysts are activated in culture mirror those observed following reversal of delay in vivo by administration of hormones. Since delayed blastocysts placed in saline also undergo morphological changes resembling those seen at the onset of activation in utero, we suggest that reversal of implantation delay requires initially neither direct contact with steroid or macromolecular inducers nor an exogenous supply of metabolites.
小鼠囊胚在培养过程中经历的发育阶段类似于在子宫内着床时发生的阶段。我们通过扫描电子显微镜（SEM）检查培养的囊胚，观察它们经历这些阶段的过程。从孵化到获得黏附性的这段时间里，大多数囊胚都已伸展，扁平细胞拥有相对较少数量的微绒毛、中央隆起区域（大概反映了细胞核的位置）以及通常带有微绒毛的细胞间嵴。在滋养层生长阶段或该阶段前不久，囊胚似乎会收缩；细胞明显鼓起，微绒毛覆盖了大多数细胞的整个表面，细胞间嵴不再可见。在卵巢切除延迟第7天从子宫中取出的囊胚具有多种形态和形状。囊胚腔常常塌陷，细胞轮廓难以辨别。这些囊胚最初在体外具有黏附性，但随后从基质上脱离，数小时后才变得永久黏附。在黏附的初始阶段，囊胚伸长，细胞间嵴突出，特别是在赤道区域。脱离的囊胚包含鼓起的细胞，其轮廓掩盖了细胞间嵴。后续阶段的表面超微结构类似于未延迟囊胚在附着和生长过程中的结构。基于我们的研究，我们提出细胞间嵴在囊胚黏附性中发挥一定作用。然而，我们必须得出结论，囊胚获得黏附性还涉及其他因素，这些因素至少同样重要，但性质过于微妙，无法通过我们的扫描电子显微镜分析来识别。就延迟囊胚而言，我们发现，在一定范围内，当囊胚在培养中被激活时发生的表面变化反映了通过给予激素在体内逆转延迟后所观察到的变化。由于置于盐溶液中的延迟囊胚也会发生类似于在子宫内激活开始时所见的形态变化，我们认为逆转着床延迟最初既不需要与类固醇或大分子诱导物直接接触，也不需要外源代谢物供应。
