Yasui Kinya
Department of Anthropology, National Museum of Nature and Science, Amakubo, Tsukuba, Ibaraki, Japan.
Int J Dev Biol. 2017;61(10-11-12):591-600. doi: 10.1387/ijdb.170118ky.
Comparison of early development is a powerful approach to understand how spherical embryos set up the basis for body patterning. Localization of the germ plasm likely couples with the site of gastrulation in many animals including cnidarians. A center of single or complex Wnt signaling pathway(s) is also co-localized with germ plasm and plays a role primarily in antero-posterior patterning in most animals. In addition, a Nodal signaling center appears in deuterostomes perpendicular to Wnt signaling and governs dorso-ventral patterning. Wnt and Nodal signaling pathways function as orthogonal coordinates to pattern embryos in three-dimensions. Amphioxus early embryos establish similar coordinates, but the location of Wnt signaling along the equator might modify the function of the Nodal signaling center to specify the chordate basic body pattern inverting dorso-ventral polarity, which is thought to have occurred during the evolution of deuterostomes. Surprising similarities in early developmental processes found in cnidarians and deuterostomes, and divergences of cnidarians-bilaterians, deuterostomes-protostomes, and ambulacrarians-chordates occurred one after another possibly within a geologically short period may link molecular mechanisms that gave rise to bilaterians, deuterostomes, and chordates.
早期发育的比较是理解球形胚胎如何建立身体模式基础的有力方法。在包括刺胞动物在内的许多动物中，生殖质的定位可能与原肠胚形成的位置相关联。单一或复杂的Wnt信号通路中心也与生殖质共定位，并且在大多数动物的前后模式形成中主要发挥作用。此外，在后口动物中出现了一个与Wnt信号垂直的Nodal信号中心，它控制背腹模式形成。Wnt和Nodal信号通路作为正交坐标在三维空间中对胚胎进行模式化。文昌鱼早期胚胎建立了类似的坐标，但沿赤道的Wnt信号位置可能会改变Nodal信号中心的功能，从而指定脊索动物的基本身体模式，使背腹极性反转，这被认为发生在后口动物的进化过程中。刺胞动物和后口动物在早期发育过程中惊人的相似之处，以及刺胞动物 - 两侧对称动物、后口动物 - 原口动物和步带动物 - 脊索动物之间可能在地质上较短的时期内相继发生的分歧，可能将产生两侧对称动物、后口动物和脊索动物的分子机制联系起来。
