Department of Life Sciences and Institute of Genome Sciences, National Yang-Ming University, Taipei 112, Taiwan.
Exp Cell Res. 2012 Sep 10;318(15):1877-88. doi: 10.1016/j.yexcr.2012.05.005. Epub 2012 May 30.
Tight regulation of cell numbers by controlling cell proliferation and apoptosis is important during development. Recently, the Hippo pathway has been shown to regulate tissue growth and organ size in Drosophila. In mammalian cells, it also affects cell proliferation and differentiation in various tissues, including the nervous system. Interplay of several signaling cascades, such as Notch, Wnt, and Sonic Hedgehog (Shh) pathways, control cell proliferation during neuronal differentiation. However, it remains unclear whether the Hippo pathway coordinates with other signaling cascades in regulating neuronal differentiation. Here, we used P19 cells, a mouse embryonic carcinoma cell line, as a model to study roles of YAP, a core component of the Hippo pathway, in neuronal differentiation. P19 cells can be induced to differentiate into neurons by expressing a neural bHLH transcription factor gene Ascl1. Our results showed that YAP promoted cell proliferation and inhibited neuronal differentiation. Expression of Yap activated Shh but not Wnt or Notch signaling activity during neuronal differentiation. Furthermore, expression of Yap increased the expression of Patched homolog 1 (Ptch1), a downstream target of the Shh signaling. Knockdown of Gli2, a transcription factor of the Shh pathway, promoted neuronal differentiation even when Yap was over-expressed. We further demonstrated that over-expression of Yap inhibited neuronal differentiation in primary mouse cortical progenitors and Gli2 knockdown rescued the differentiation defect in Yap over-expressing cells. In conclusion, our study reveals that Shh signaling acts downstream of YAP in regulating neuronal differentiation.
细胞数量的严格调控通过控制细胞增殖和凋亡在发育过程中非常重要。最近，Hippo 途径已被证明可调节果蝇中的组织生长和器官大小。在哺乳动物细胞中，它还影响包括神经系统在内的各种组织中的细胞增殖和分化。几个信号级联的相互作用，如 Notch、Wnt 和 Sonic Hedgehog (Shh) 途径，在神经元分化过程中控制细胞增殖。然而，Hippo 途径是否与其他信号级联在调节神经元分化中协同作用仍不清楚。在这里，我们使用 P19 细胞，一种小鼠胚胎癌细胞系，作为研究 Hippo 途径核心组成部分 YAP 在神经元分化中的作用的模型。通过表达神经 bHLH 转录因子基因 Ascl1，P19 细胞可以被诱导分化为神经元。我们的结果表明 YAP 促进细胞增殖并抑制神经元分化。在神经元分化过程中，Yap 的表达激活了 Shh，但不激活 Wnt 或 Notch 信号活性。此外，Yap 的表达增加了 Shh 信号下游靶基因 Patched 同源物 1 (Ptch1) 的表达。Gli2（Shh 途径的转录因子）的敲低即使在 Yap 过表达时也促进了神经元分化。我们进一步证明，在 Yap 过表达的细胞中，过表达 Yap 抑制了原代小鼠皮质祖细胞的神经元分化，而 Gli2 的敲低挽救了 Yap 过表达细胞的分化缺陷。总之，我们的研究表明 Shh 信号在调节神经元分化中作为 YAP 的下游发挥作用。
