WNT信号通路抑制星形胶质细胞生成的分子机制研究

During the development of central nervous system (CNS), neural stem cells in the ventricular zone firstly give rise to various types of neurons, followed by astrocytes and oligodendrocytes. What signals or factors control the developmental switch from neurogenesis to gliogenesis remains one of the fundamental questions in developmental neurobiology. Our recent study showed that activation of WNT signaling inhibits the generation of oligodendrocyte progenitor cells, and astrocyte precursors as well. We thus hypothesize that WNT signaling may play important roles in the inhibition of gliogenesis. Consistent with this hypothesis, our preliminary experiments showed that the inhibition of gliogenesis by WNT signaling is probably mediated by the up-regulation of Ngn2. In this proposal, we will use various mutant mice to study the functions of WNT signaling during the neuron-to-glia switch, and trace the fate of neural stem cells after modifying the WNT signaling. We will also screen the target genes of WNT signaling, and examine their functions in gliogenesis using in ovo electroporation assays. This study will provide important insights into the molecular mechanisms underlying the switch from neurogenesis to gliogenesis, and facilitate the design of molecular strategies to promote neural regeneration in injured or diseased neural tissues.

在中枢神经系统的发育过程中，室区的神经干细胞先生成不同种类的神经元，再生成星形胶质细胞和少突胶质细胞。发育神经生物学的一个基本问题是：究竟有什么信号或因子控制着神经干细胞的神经元生成向胶质细胞生成的转变。我们已发表的研究表明WNT信号通路被激活后，少突胶质细胞的生成被抑制，而星形胶质细胞的生成也可能减少。我们因此推测WNT可能是重要的胶质细胞生成抑制信号。由此开展的前期试验表明WNT信号通路可能通过促进Ngn2的表达抑制胶质细胞生成。我们拟先通过体内基因突变小鼠分析WNT信号通路在胶质细胞生成中的功能，并追踪神经干细胞的命运。接着筛选WNT信号通路的靶基因，并通过鸡胚电转实验验证靶基因在胶质细胞生成的功能。本项目的完成，能够使我们深入了解神经元生成向胶质细胞生成的转变机制，为神经元的再生研究提供一定的基础。

在中枢神经系统发育过程中，神经干细胞依次分化成神经元和胶质细胞。WNT/β-catenin信号通路是神经干细胞的增殖和神经元生成过程中维持平衡的关键调控信号之一。但是WNT信号通路在胶质细胞生成时期对神经干细胞的调控功能未知。通过激活或敲除β-catenin，我们发现激活WNT信号通路使脊髓中神经干细胞不能转变为星形胶质细胞；与此相应的，敲除β-catenin后导致脊髓中的星形胶质细胞提前产生。进一步的分析发现激活WNT信号通路能够显著增加Neurogenin 2（Ngn2）基因的表达，而RNA干扰Ngn2的表达之后，WNT信号通路激活的神经干细胞则能恢复向星形胶质细胞分化。此外，实验表明Ngn2能直接结合到多个星形胶质细胞特异性基因的启动子上并抑制其转录。综上所述，我们的研究首次提供了证据表明WNT信号通路能够通过调控Ngn2的表达来抑制星形胶质细胞生成，其中Ngn2起到直接结合星形胶质细胞特异性基因启动子并抑制其转录的功能。