Nieuwkoop P D
Hubrecht Laboratory, Netherlands Institute for Developmental Biology, Utrecht.
Int J Dev Biol. 1999;43(7):615-23.
This posthumous review of early embryonic inductions concludes: 1) the amphibian egg has only two distinct components, animal and vegetal. Interactions at their mutual boundary forms meso-endoderm. This is "meso-endoderm induction", not just "mesoderm induction". 2) The dorso-ventral polarity of the yolk mass implies a dorsally situated inducing centre. 3) Accumulation of cells into one, two, three or many cell masses [problastopores] along the circumference of the meso-endoderm results in as many axes, implying a self-organizing capacity of meso-endoderm. 4) Induction of the meso-endoderm is slow, spreading cell to cell through the animal moiety from the boundary of the vegetal yolk mass towards the animal pole. 5) Interaction between mesoderm and ectoderm is a separate step leading to cranio-caudal differentiation of the archenteron roof. 6) The initial invaginating endoderm and mesoderm, representing the future pharynx endoderm and prechordal plate mesoderm, first contacts the most posterior presumptive neurectoderm after having passed the still uninvaginated trunk mesoderm. At that moment an antero-posterior level neural induction actually starts. 7) The ectoderm contraction wave coincides spatially and temporally with the induced neural plate. 8) Two successive homoiogenetic waves of inductive activity pass through the presumptive neurectoderm in the anterior direction, the first one, "activation", giving rise to neural differentiation and ultimately forebrain, the second one, "transformation", to more caudal CNS structures. These are separate, successive steps in CNS regional induction. 9) The midbrain represents a secondary formation in the neural plate. 10) The observed changes in morphogenesis may depend upon separate, successive binary decisions via [cell and] nuclear state splitters [involving differentiation waves].
1）两栖类卵子只有两个不同的成分，即动物极和植物极。它们相互边界处的相互作用形成中内胚层。这是“中内胚层诱导”，而不仅仅是“中胚层诱导”。2）卵黄块的背腹极性意味着存在一个位于背部的诱导中心。3）中内胚层圆周上的细胞聚集形成一个、两个、三个或多个细胞团[原胚孔]，从而产生同样数量的轴，这意味着中内胚层具有自我组织能力。4）中内胚层的诱导是缓慢的，通过动物部分从植物极卵黄块的边界向动物极逐细胞扩散。5）中胚层和外胚层之间的相互作用是导致原肠顶颅尾分化的一个单独步骤。6）最初内陷的内胚层和中胚层，代表未来的咽内胚层和前索板中胚层，在经过尚未内陷的躯干中胚层后，首先接触最靠后的预定神经外胚层。此时，前后水平的神经诱导实际上开始。7）外胚层收缩波在空间和时间上与诱导的神经板重合。8）两个连续的同源诱导活性波从前向后穿过预定神经外胚层，第一个“激活”波导致神经分化并最终形成前脑，第二个“转化”波导致更靠后的中枢神经系统结构形成。这些是中枢神经系统区域诱导中单独的、连续的步骤。9）中脑是神经板中的次生结构。10）观察到的形态发生变化可能取决于通过[细胞和]核状态分裂器[涉及分化波]的单独的、连续的二元决定。
