The neural tube, the embryonic precursor to the brain and spinal cord, begins as a flat sheet of epithelial cells, divided into non-neural and neural ectoderm. Proper neural tube closure requires that the edges of the neural ectoderm, the neural folds, to elevate upwards and fuse along the dorsal midline of the embryo. We have previously shown that members of the claudin protein family are required for the early phases of chick neural tube closure. Claudins are transmembrane proteins, localized in apical tight junctions within epithelial cells where they are essential for regulation of paracellular permeability, strongly involved in apical-basal polarity, cell-cell adhesion, and bridging the tight junction to cytoplasmic proteins. Here we explored the role of Claudin-3 (Cldn3), which is specifically expressed in the non-neural ectoderm. We discovered that depletion of Cldn3 causes folic acid-insensitive primarily spinal neural tube defects due to a failure in neural fold fusion. Apical cell surface morphology of Cldn3-depleted non-neural ectodermal cells exhibited increased membrane blebbing and smaller apical surfaces. Although apical-basal polarity was retained, we observed altered Par3 and Pals1 protein localization patterns within the apical domain of the non-neural ectodermal cells in Cldn3-depleted embryos. Furthermore, F-actin signal was reduced at apical junctions. Our data presents a model of spina bifida, and the role that Cldn3 is playing in regulating essential apical cell processes in the non-neural ectoderm required for neural fold fusion.

神经管是大脑和脊髓的胚胎前身，最初是一层扁平的上皮细胞，分为非神经外胚层和神经外胚层。正确的神经管闭合需要神经外胚层、神经皱襞的边缘向上抬升并沿着胚胎的背侧中线融合。我们之前已经表明，紧密蛋白家族的成员对于小鸡神经管闭合的早期阶段是必需的。密蛋白是跨膜蛋白，位于上皮细胞内的顶端紧密连接中，对于细胞旁通透性的调节至关重要，强烈参与顶端-基底极性、细胞-细胞粘附以及桥接紧密连接与细胞质蛋白。在这里，我们探讨了 Claudin-3 (Cldn3) 的作用，它在非神经外胚层中特异性表达。我们发现 Cldn3 的耗竭会导致对叶酸不敏感的主要脊髓神经管缺陷，这是由于神经褶融合失败所致。 Cldn3 耗尽的非神经外胚层细胞的顶端细胞表面形态表现出膜起泡增加和顶端表面变小。尽管顶端-基底极性得以保留，但我们观察到 Cldn3 缺失胚胎中非神经外胚层细胞顶端域内 Par3 和 Pals1 蛋白定位模式的改变。此外，顶端连接处的 F-肌动蛋白信号减少。我们的数据展示了脊柱裂模型，以及 Cldn3 在调节神经折叠融合所需的非神经外胚层中重要的顶端细胞过程中所发挥的作用。