Fauny Jean-Daniel, Thisse Bernard, Thisse Christine
Université de Strasbourg, Illkirch Cedex, France.
Development. 2009 Nov;136(22):3811-9. doi: 10.1242/dev.039693.
Formation of the vertebrate embryo is known to depend on the activity of organizing centers. The dorsal Spemann organizer is the source of growth factor antagonists that participate in the creation of signaling gradients. In various species, the existence of head, trunk and trunk-tail inducers has been proposed to explain the formation of different parts of the embryo along the anteroposterior (A/P) axis. In zebrafish, two organizing centers have been described, the dorsal and tail organizers, located at the dorsal and ventral gastrula margins, respectively. Here, we report that organizer functions are executed not only by the dorsal and ventral margins, but also by all parts of the blastula-gastrula margin. The position of different marginal territories along the dorsoventral axis defines the A/P nature of the structures they are able to organize. At the molecular level, we show that this organizing activity results from the simultaneous activation of BMP and Nodal signaling pathways. Furthermore, the A/P character of the organized structures is not defined by absolute levels but instead by the ratio of BMP and Nodal activities. Rather than resulting from the activity of discrete centers, organization of the zebrafish embryo depends on the activity of the entire margin acting as a continuous and global organizer that is established by a gradual ventral-to-dorsal modulation of the ratio of marginal BMP to Nodal activity.
脊椎动物胚胎的形成依赖于组织中心的活性。背侧的施佩曼组织者是生长因子拮抗剂的来源，这些拮抗剂参与信号梯度的建立。在不同物种中，人们提出存在头部、躯干和躯干-尾部诱导物来解释胚胎沿前后（A/P）轴不同部分的形成。在斑马鱼中，已经描述了两个组织中心，即背侧组织者和尾部组织者，分别位于原肠胚的背侧和腹侧边缘。在此，我们报告组织功能不仅由背侧和腹侧边缘执行，而且由囊胚-原肠胚边缘的所有部分执行。沿背腹轴不同边缘区域的位置决定了它们能够组织的结构的A/P性质。在分子水平上，我们表明这种组织活性是由BMP和Nodal信号通路的同时激活导致的。此外，所组织结构的A/P特征不是由绝对水平定义的，而是由BMP和Nodal活性的比率定义的。斑马鱼胚胎的组织并非源于离散中心的活性，而是依赖于整个边缘的活性，该边缘作为一个连续的全局组织者起作用，它是通过边缘BMP与Nodal活性比率从腹侧到背侧的逐渐调节而建立的。
