Khaner O
Department of Cell and Animal Biology, Hebrew University, Jerusalem, Israel.
Proc Natl Acad Sci U S A. 1995 Nov 7;92(23):10733-7. doi: 10.1073/pnas.92.23.10733.
In the amniotes, two unique layers of cells, the epiblast and the hypoblast, constitute the embryo at the blastula stage. All the tissues of the adult will derive from the epiblast, whereas hypoblast cells will form extraembryonic yolk sac endoderm. During gastrulation, the endoderm and the mesoderm of the embryo arise from the primitive streak, which is an epiblast structure through which cells enter the interior. Previous investigations by others have led to the conclusion that the avian hypoblast, when rotated with regard to the epiblast, has inductive properties that can change the fate of competent cells in the epiblast to form an ectopic embryonic axis. Thus, it has been suggested that the hypoblast normally induces the epiblast to form a primitive streak at a specific locus. In the work reported here, an attempt was made to reexamine the issue of induction. In contrast to previous reports, it was found that the rotated hypoblast of the chicken embryo does not initiate formation of an ectopic axis in the epiblast. The embryonic axis always initiates and develops according to the basic polarity of the epiblast layer. These results provoke a reinterpretation of the issues of mesoderm induction and primitive streak initiation in the avian embryo.
在羊膜动物中，囊胚期的胚胎由两个独特的细胞层，即上胚层和下胚层组成。成体的所有组织都将源自上胚层，而下胚层细胞将形成胚外卵黄囊内胚层。在原肠胚形成过程中，胚胎的内胚层和中胚层起源于原条，原条是上胚层的一种结构，细胞通过它进入内部。其他人先前的研究得出结论，鸡的下胚层相对于上胚层旋转时，具有诱导特性，能够改变上胚层中感受态细胞的命运，从而形成异位胚胎轴。因此，有人提出下胚层通常诱导上胚层在特定位置形成原条。在本文报道的研究中，我们试图重新审视诱导问题。与先前的报道相反，我们发现鸡胚旋转后的下胚层并不会在上胚层中引发异位轴的形成。胚胎轴总是根据上胚层的基本极性开始并发育。这些结果引发了对鸟类胚胎中胚层诱导和原条起始问题的重新解释。
