Nakagawa S, Takeichi M
Department of Biophysics, Faculty of Science, Kyoto University, Kitashirakawa, Sakyo-ku, Kyoto 606-8502, Japan.
Development. 1998 Aug;125(15):2963-71. doi: 10.1242/dev.125.15.2963.
During the emergence of neural crest cells from the neural tube, the expression of cadherins dynamically changes. In the chicken embryo, the early neural tube expresses two cadherins, N-cadherin and cadherin-6B (cad6B), in the dorsal-most region where neural crest cells are generated. The expression of these two cadherins is, however, downregulated in the neural crest cells migrating from the neural tube; they instead begin expressing cadherin-7 (cad7). As an attempt to investigate the role of these changes in cadherin expression, we overexpressed various cadherin constructs, including N-cadherin, cad7, and a dominant negative N-cadherin (cN390 ), in neural crest-generating cells. This was achieved by injecting adenoviral expression vectors encoding these molecules into the lumen of the closing neural tube of chicken embryos at stage 14. In neural tubes injected with the viruses, efficient infection was observed at the neural crest-forming area, resulting in the ectopic cadherin expression also in migrating neural crest cells. Notably, the distribution of neural crest cells with the ectopic cadherins changed depending on which constructs were expressed. Many crest cells failed to escape from the neural tube when N-cadherin or cad7 was overexpressed. Moreover, none of the cells with these ectopic cadherins migrated along the dorsolateral (melanocyte) pathway. When these samples were stained for Mitf, an early melanocyte marker, positive cells were found accumulated within the neural tube, suggesting that the failure of their migration was not due to differentiation defects. In contrast to these phenomena, cells expressing non-functional cadherins exhibited a normal migration pattern. Thus, the overexpression of a neuroepithelial cadherin (N-cadherin) and a crest cadherin (cad7) resulted in the same blocking effect on neural crest segregation from neuroepithelial cells, especially for melanocyte precursors. These findings suggest that the regulation of cadherin expression or its activity at the neural crest-forming area plays a critical role in neural crest emigration from the neural tube.
在神经嵴细胞从神经管中产生的过程中，钙黏蛋白的表达会动态变化。在鸡胚中，早期神经管在产生神经嵴细胞的最背侧区域表达两种钙黏蛋白，即N-钙黏蛋白和钙黏蛋白-6B（cad6B）。然而，这两种钙黏蛋白在从神经管迁移的神经嵴细胞中的表达会下调；取而代之的是，它们开始表达钙黏蛋白-7（cad7）。为了研究这些钙黏蛋白表达变化的作用，我们在产生神经嵴的细胞中过表达了各种钙黏蛋白构建体，包括N-钙黏蛋白、cad7和一种显性负性N-钙黏蛋白（cN390）。这是通过在第14阶段将编码这些分子的腺病毒表达载体注射到鸡胚正在闭合的神经管腔中来实现的。在注射了病毒的神经管中，在神经嵴形成区域观察到了高效感染，导致迁移的神经嵴细胞中也出现了异位钙黏蛋白表达。值得注意的是，带有异位钙黏蛋白的神经嵴细胞的分布会根据所表达的构建体而改变。当N-钙黏蛋白或cad7过表达时，许多嵴细胞无法从神经管中逸出。此外，带有这些异位钙黏蛋白的细胞中没有一个沿着背外侧（黑素细胞）途径迁移。当对这些样本进行早期黑素细胞标志物Mitf染色时，发现阳性细胞聚集在神经管内，这表明它们迁移失败并非由于分化缺陷。与这些现象相反，表达无功能钙黏蛋白的细胞表现出正常的迁移模式。因此，神经上皮钙黏蛋白（N-钙黏蛋白）和嵴钙黏蛋白（cad7）的过表达对神经嵴与神经上皮细胞的分离产生了相同的阻断作用，尤其是对黑素细胞前体。这些发现表明，在神经嵴形成区域对钙黏蛋白表达或其活性的调节在神经嵴从神经管的迁出中起着关键作用。
