Gimlich R L
J Embryol Exp Morphol. 1985 Nov;89 Suppl:89-111.
The experiments described here were designed to reveal the distribution in the frog early embryo of components which are sufficient for specification of the dorsal structures of the embryonic body axis. The approach was to allow cleavage planes to divide the embryo into various well-defined regions and to transplant cells from each region into recipient embryos which would otherwise fail to form axial structures. Partial or complete body axis development could then be scored by the use of external criteria or histological methods. Recipients were embryos which had been irradiated before first cleavage with ultraviolet light on the vegetal surface. Irradiated embryos display a well-characterized set of deficiencies in the dorsal structures of the body axis, but their development can be 'rescued' toward normalcy in several ways. In particular, transplantation of certain small groups of blastomeres from the normal 32- to 64-cell embryo into irradiated recipients was sufficient to cause partial or complete axis development. Cell groups which could cause rescue were located in the vegetal and equatorial levels of one quadrant of the normal embryo--the quadrant centered on the future dorsal midline. Clonal marking analysis showed that the vegetal-most cells of this quadrant contribute primarily to endodermal structures in normal development. In rescued recipient embryos, these cells also contributed only to the endoderm; the dorsal mesoderm and central nervous system were formed exclusively by host cells which originated near the transplant. Rescue could also result from transplantation of equatorial cells from the dorsal quadrant of the normal embryo. As in normal development, these cells formed primarily the chordamesoderm of the rescued embryo. Host cells were induced to contribute the somitic mesoderm, central nervous system, and other structures which would have been missing but for the presence of the transplanted cells. The frequency and degree of rescue caused by equatorial and vegetal transplants is variable. This was explained by the discovery that the location of components needed for rescue varies among individual embryos without regard to the positions of cleavage planes. This was true even when donor embryos were selected on the basis of a precisely regular pattern of cleavage. In such selected embryos, particular blastomeres make a predictable contribution of progeny to the body axis. Thus it may be that the positions of components which can cause axis formation vary without exact regard to the fate map of prospective areas. The implications of this for the study of cytoplasmic localization in the early embryo are discussed.(ABSTRACT TRUNCATED AT 400 WORDS)
此处所描述的实验旨在揭示青蛙早期胚胎中足以决定胚胎体轴背侧结构特征的成分的分布情况。实验方法是让卵裂面将胚胎分割成各个界限分明的区域，并将每个区域的细胞移植到受体胚胎中，否则这些受体胚胎将无法形成轴结构。然后可通过外部标准或组织学方法来记录部分或完整的体轴发育情况。受体是在第一次卵裂前用紫外线照射植物极表面的胚胎。经照射的胚胎在体轴背侧结构方面表现出一系列特征明显的缺陷，但其发育可通过多种方式“挽救”至正常状态。特别是，将正常32至64细胞胚胎中的某些小群卵裂球移植到经照射的受体中，足以导致部分或完整的轴发育。能够导致挽救的细胞群位于正常胚胎一个象限的植物极和赤道平面——以未来背中线为中心的象限。克隆标记分析表明，该象限最靠近植物极的细胞在正常发育中主要形成内胚层结构。在挽救后的受体胚胎中，这些细胞也仅形成内胚层；背侧中胚层和中枢神经系统完全由起源于移植部位附近的宿主细胞形成。正常胚胎背侧象限的赤道细胞移植也可导致挽救。与正常发育情况一样，这些细胞主要形成挽救胚胎的脊索中胚层。宿主细胞被诱导形成体节中胚层、中枢神经系统以及其他若没有移植细胞就会缺失的结构。赤道和植物极移植所导致的挽救频率和程度各不相同。这一现象可通过以下发现来解释：挽救所需成分的位置在各个胚胎中有所不同，与卵裂面的位置无关。即使根据精确规则的卵裂模式选择供体胚胎，情况也是如此。在这类经过挑选的胚胎中，特定的卵裂球对体轴的后代贡献是可预测的。因此，可能导致轴形成的成分位置变化并不完全遵循预期区域的命运图。文中讨论了这一现象对早期胚胎细胞质定位研究的意义。（摘要截选至400字）
