Momoi Akihiro, Yoda Hiroki, Steinbeisser Herbert, Fagotto Francois, Kondoh Hisato, Kudo Akira, Driever Wolfgang, Furutani-Seiki Makoto
Abteilung für Entwicklungsbiologie, Institut für Biologie I, Universität Freiburg, D-79104 Freiburg, Germany.
Mech Dev. 2003 Apr;120(4):477-89. doi: 10.1016/s0925-4773(03)00003-0.
The dorsal ectoderm of vertebrate gastrula is first specified into anterior fate by an activation signal and posteriorized by a graded transforming signal, leading to the formation of forebrain, midbrain, hindbrain and spinal cord along the anteroposterior (A-P) axis. Transplanted non-axial mesoderm rather than axial mesoderm has an ability to transform prospective anterior neural tissue into more posterior fates in zebrafish. Wnt8 is a secreted factor that is expressed in non-axial mesoderm. To investigate whether Wnt8 is the neural posteriorizing factor that acts upon neuroectoderm, we first assigned Frizzled 8c and Frizzled 9 to be functional receptors for Wnt8. We then, transplanted non-axial mesoderm into the embryos in which Wnt8 signaling is cell-autonomously blocked by the dominant-negative form of Wnt8 receptors. Non-axial mesodermal transplants in embryos in which Wnt8 signaling is cell-autonomously blocked induced the posterior neural markers as efficiently as in wild-type embryos, suggesting that Wnt8 signaling is not required in neuroectoderm for posteriorization by non-axial mesoderm. Furthermore, Wnt8 signaling, detected by nuclear localization of beta-catenin, was not activated in the posterior neuroectoderm but confined in marginal non-axial mesoderm. Finally, ubiquitous over-expression of Wnt8 does not expand neural ectoderm of posterior character in the absence of mesoderm or Nodal-dependent co-factors. We thus conclude that other factors from non-axial mesoderm may be required for patterning neuroectoderm along the A-P axis.
脊椎动物原肠胚的背侧外胚层首先通过激活信号被指定为前部命运，并通过梯度转化信号被指定为后部命运，从而沿着前后（A-P）轴形成前脑、中脑、后脑和脊髓。在斑马鱼中，移植非轴向中胚层而非轴向中胚层具有将预期的前部神经组织转化为更后部命运的能力。Wnt8是一种在非轴向中胚层中表达的分泌因子。为了研究Wnt8是否是作用于神经外胚层的神经后部化因子，我们首先确定卷曲蛋白8c和卷曲蛋白9是Wnt8的功能性受体。然后，我们将非轴向中胚层移植到胚胎中，在这些胚胎中，Wnt8信号通过Wnt8受体的显性负性形式被细胞自主阻断。在Wnt8信号被细胞自主阻断的胚胎中进行的非轴向中胚层移植诱导后部神经标记物的效率与野生型胚胎一样高，这表明在神经外胚层中，非轴向中胚层进行后部化不需要Wnt8信号。此外，通过β-连环蛋白的核定位检测到的Wnt8信号在后部神经外胚层中未被激活，而是局限于边缘非轴向中胚层。最后，在没有中胚层或Nodal依赖性辅助因子的情况下，Wnt8的普遍过表达不会扩大具有后部特征的神经外胚层。因此，我们得出结论，非轴向中胚层的其他因子可能是沿A-P轴对神经外胚层进行模式化所必需的。
