Regulatory factors working in the downstream pathway of the neural inducer Chordin

在对神经诱导剂下游基因的差异筛选中，我们发现了两个极早期的神经基因：ZIC相关的L(ZIC-R1)，一个与果蝇配对规则基因奇数配对相关的锌指因子ZIC-L(ZIC-R1)；以及SOX-2，一个与Sry相关的HMG因子。这两个基因首先在原肠发育初期的未来神经外胚层中广泛检测到表达，之后是Chordin的表达，并先于神经原蛋白(Xngnr-1)的表达。ZIC-R1mRNA注射激活原神经基因XngnR-1，并在分离的动物和体内启动神经和神经元的分化。相反，SOX-2单独不足以引起神经分化，但可以与成纤维细胞生长因子信号协同作用，启动神经诱导。因此，Zic-R1在连接神经诱导剂和下游原神经基因的途径中发挥作用，而SOX-2使外胚层对细胞外信号做出反应，这表明神经诱导的早期阶段涉及多种功能的同时激活。我们还鉴定了其他几个由Chordin诱导的神经特异性分子，其中一些在早期外胚层上具有神经化或模式形成活性。因此，我根据早期的神经模式阐明了包括Zic和Sox在内的这些分子的作用。此外，我还分离到了一种在Chordin下游工作的新转录因子，即SOX-D。

n a differential screen for downstream genes of the neural inducers, we identified two extremely early neural genes induced by the neural inducer Chordin and suppressed by BMP-4 in a primary response fashion : Zic-related-l (Zic-r1), a zinc finger factor related to the Drosophila pair-rule gene odd-paired, and Sox-2, a Sry-related HMG factor.Expression of the two genes are first detected widely in the prospective neuroectoderm at the beginning of gastrulation, following the onset of Chordin expression and preceding that of Neurogenin(Xngnr-1). Zic-r1 mRNA injection activates the proneural gene Xngnr-1, and initiates neural and neuronal differentiation in isolated animal caps and in vivo. In contrast Sox-2 alone is not sufficient to cause neural differentiation but can work synergistically with FGF signaling to initiate neural induction. Thus, Zic-r1 acts in the pathway bridging the neural inducer with the downstream proneural genes while Sox-2 makes the ectoderm responsive to extracellular signals, demonstrating that the early phase of neural induction involves simultaneous activation of multiple functions.We are also characterizing several other neural-specific molecules induced by chordin, some of which have neuralizing or patterning activities on early ectoderm. I thus elucidated the roles of these molecules including Zic and Sox in the light of early neural patterning. In addition, I have isolated a new transcription factor working in the downstream of Chordin, namely SOX-D.