Surface ectodermal mechanism and maternal intervention of neural tube defects

项目总结/摘要 我们的长期研究目标是揭示哺乳动物细胞和分子机制， 神经管闭合缺陷了解神经管闭合的基本机制， 转化为预防神经管闭合缺陷的应用，包括露脑畸形和无脑畸形 在头部区域和脊柱裂在尾部脊柱区域。颅脊柱裂，最常见但罕见的 在平面细胞的动物模型中发现了神经管闭合缺陷，具有完全开放的脑和脊柱 极性（PCP）信号转导突变体。Wnt/β-catenin信号通路与Wnt/β-catenin信号通路共享几个组分。 PCP信号通路，并在广泛的发育过程中起着至关重要的作用， 紊乱然而，Wnt/β-catenin信号在神经管闭合和相关结构出生中的作用， 缺陷仍然知之甚少。Lrp6是Wnt/β-连环蛋白信号通路中的共受体，并且也是Wnt/β-连环蛋白信号通路中的共受体。 参与PCP信号通路，机制未知。Lrp6的自发点突变 在小鼠模型中，该基因引起颅或脊髓神经管闭合缺陷，并且与 有神经管闭合缺陷的人叶酸补充剂可能无法防止神经管闭合 Lrp6突变体的缺陷。为了阐明Lrp6介导的信号级联在神经管闭合中的作用，我们 已经产生了Lrp6的条件基因靶向小鼠系。使用各种Cre鼠标线，我们有 初步发现Lrp6在神经管闭合中发挥细胞谱系和区域特异性作用。另 另一方面，Lrp6可能与另一个辅助受体Lrp5在介导β-连环蛋白信号传导中具有功能冗余， 神经管闭合我们最近已经证明，条件性切除β-连环蛋白在 神经外胚层谱系细胞引起脊柱裂，与神经外胚层谱系细胞引起的脊柱裂相似，但比神经外胚层谱系细胞引起的脊柱裂更严重。 神经外胚层Lrp6突变体，表明Lrp5可以补偿Lrp6的部分功能丧失， 介导Wnt/β-连环蛋白信号传导。大量的研究集中在神经外胚层或神经上皮 这些细胞可能在神经管闭合过程中的神经板折叠或弯曲中起重要作用。但是，作用 在神经管闭合过程中邻近的非神经表面外胚层细胞仍然知之甚少。基于 根据我们的初步发现，我们认为Lrp5/6介导的Wnt/β-catenin信号调节了一种独特的 非神经表面外胚层细胞中的细胞突起，以沿着整个神经管闭合 喙尾体轴，以及非神经表面Wnt/β-连环蛋白信号级联的破坏 外胚层细胞会引起一系列的所有类型的严重神经管闭合缺陷。我们亦建议 Wnt/β-catenin信号传导的关键下游效应物的遗传激活可以防止神经管闭合 表面外胚层突变体的缺陷。为了解决这些假设，我们将进行条件基因- 目标分析结合各种强大和创新的研究方法， 这些新的突变小鼠模型中神经管闭合缺陷的细胞和分子机制。我们 还将阐述Lrp5/6介导的Wnt/β-连环蛋白的区域特异性和基因剂量依赖性作用 神经管闭合过程中的信号通路。我们将测试神经管闭合缺陷的基因拯救， 关键候选下游效应物的有条件激活。这项研究可能会揭示重要的线索 用于预防叶酸无法治疗的新生儿神经管闭合缺陷。

PROJECT SUMMARY/ABSTRACT The long-term goal of our research is to uncover the cellular and molecular mechanisms of mammalian neural tube closure defects. Understanding the basic mechanisms underlying neural tube closure may translate into applications for preventing neural tube closure defects, including exencephaly and anencephaly at the cranial region and spina bifida at the caudal spinal region. Craniorachischisis, the severest but rare neural tube closure defect with entirely open brain and spine, has been found in the animal model of planar cell polarity (PCP) signaling mutants. The Wnt/ß-catenin signaling pathway shares several components with the PCP signaling pathway, and plays crucial roles in a wide range of developmental processes and related disorders. However, the role of Wnt/ß-catenin signaling in neural tube closure and related structural birth defects remains poorly understood. Lrp6 is a coreceptor in the Wnt/ß-catenin signaling pathway and is also involved in the PCP signaling pathway with unknown mechanisms. Spontaneous point mutations in the Lrp6 gene give rise to either cranial or spinal neural tube closure defects in the mouse model, and are associated with neural tube closure defects in humans. Folate supplementation may not prevent neural tube closure defects in Lrp6 mutants. To address the role of Lrp6-mediated signaling cascades in neural tube closure, we have generated a conditional gene-targeting mouse line of Lrp6. Using various Cre mouse lines, we have preliminarily found that Lrp6 plays cell lineage- and region-specific roles in neural tube closure. On the other hand, Lrp6 may have functional redundancy with another coreceptor, Lrp5, in mediating ß-catenin signaling in neural tube closure. We have recently demonstrated that conditional ablation of ß-catenin in the neuroectodermal lineage cells causes spina bifida that is similar to, but severer than those seen in the neuroectodermal Lrp6 mutants, suggesting that Lrp5 may compensate for a partial loss-of-function of Lrp6 to mediate Wnt/ß-catenin signaling. Numerous studies have been focused on neuroectodermal or neuroepithelial cells that maybe important in neural plate folding or bending during neural tube closure. However, the role of the adjacent non-neural surface ectodermal cells during neural tube closure remains poorly understood. Based on our preliminary findings, we propose that Lrp5/6-mediated Wnt/ß-catenin signaling regulates a unique cellular process in the non-neural surface ectodermal cells to direct neural tube closure along the entire rostrocaudal body axis, and that disruption of the Wnt/ß-catenin signaling cascade in the non-neural surface ectodermal cells will cause a spectrum of all types of severe neural tube closure defects. We also propose that genetic activation of the key downstream effectors of Wnt/ß-catenin signaling can prevent neural tube closure defects in the surface ectodermal mutants. To address these hypotheses, we will conduct conditional gene- targeting analyses in combination with various powerful and innovative research approaches to examine the cellular and molecular mechanisms of neural tube closure defects in these novel mutant mouse models. We will also address the region-specific and gene-dosage-dependent roles of the Lrp5/6-mediated Wnt/ß-catenin signaling pathway during neural tube closure. We will test the genetic rescue of neural tube closure defects by conditional activation of the key candidate downstream effectors. This study may reveal significant clues towards preventing folate-untreatable neural tube closure defects in human newborns.