Division of Pathogenetic Signaling, Department of Biochemistry and Molecular Biology, Kobe University Graduate School of Medicine, Kobe, Hyogo, Japan ; Division of Molecular and Cellular Biology, Department of Biochemistry and Molecular Biology, Kobe University Graduate School of Medicine, Kobe, Hyogo, Japan ; CREST, Japan Science and Technology Agency, Kawaguchi, Saitama, Japan.
PLoS One. 2013 Nov 13;8(11):e80356. doi: 10.1371/journal.pone.0080356. eCollection 2013.
Adherens junctions (AJs) play a role in mechanically connecting adjacent cells to maintain tissue structure, particularly in epithelial cells. The major cell-cell adhesion molecules at AJs are cadherins and nectins. Afadin binds to both nectins and α-catenin and recruits the cadherin-β-catenin complex to the nectin-based cell-cell adhesion site to form AJs. To explore the role of afadin in radial glial and ependymal cells in the brain, we generated mice carrying a nestin-Cre-mediated conditional knockout (cKO) of the afadin gene. Newborn afadin-cKO mice developed hydrocephalus and died neonatally. The afadin-cKO brain displayed enlarged lateral ventricles and cerebral aqueduct, resulting from stenosis of the caudal end of the cerebral aqueduct and obliteration of the ventral part of the third ventricle. Afadin deficiency further caused the loss of ependymal cells from the ventricular and aqueductal surfaces. During development, radial glial cells, which terminally differentiate into ependymal cells, scattered from the ventricular zone and were replaced by neurons that eventually covered the ventricular and aqueductal surfaces of the afadin-cKO midbrain. Moreover, the denuded ependymal cells were only occasionally observed in the third ventricle and the cerebral aqueduct of the afadin-cKO midbrain. Afadin was co-localized with nectin-1 and N-cadherin at AJs of radial glial and ependymal cells in the control midbrain, but these proteins were not concentrated at AJs in the afadin-cKO midbrain. Thus, the defects in the afadin-cKO midbrain most likely resulted from the destruction of AJs, because AJs in the midbrain were already established before afadin was genetically deleted. These results indicate that afadin is essential for the maintenance of AJs in radial glial and ependymal cells in the midbrain and is required for normal morphogenesis of the cerebral aqueduct and ventral third ventricle in the midbrain.
黏着连接（AJs）在机械连接相邻细胞以维持组织结构方面发挥作用，尤其是在上皮细胞中。AJs 中的主要细胞-细胞粘附分子是钙黏蛋白和 nectin。Afadin 与 nectin 和 α-连环蛋白结合，并将钙黏蛋白-β-连环蛋白复合物募集到基于 nectin 的细胞-细胞粘附位点，形成 AJs。为了探讨 afadin 在脑的放射状胶质细胞和室管膜细胞中的作用，我们生成了 nestin-Cre 介导的 afadin 基因条件敲除（cKO）的小鼠。新生的 afadin-cKO 小鼠发生脑积水并在新生时死亡。afadin-cKO 大脑显示出侧脑室和脑导水管扩大，这是由于脑导水管尾部狭窄和第三脑室腹侧部分闭塞所致。Afadin 缺乏进一步导致脑室和导水管表面的室管膜细胞丢失。在发育过程中，终末分化为室管膜细胞的放射状胶质细胞从脑室区散布，并被最终覆盖 afadin-cKO 中脑脑室和导水管表面的神经元取代。此外，在 afadin-cKO 中脑的第三脑室和脑导水管中仅偶尔观察到裸露的室管膜细胞。Afadin 在对照中脑中的放射状胶质细胞和室管膜细胞的 AJs 中与 nectin-1 和 N-钙黏蛋白共定位，但这些蛋白在 afadin-cKO 中脑中没有集中在 AJs 上。因此，afadin-cKO 中脑的缺陷很可能是由于 AJs 的破坏所致，因为在 afadin 基因缺失之前，中脑中的 AJs 已经建立。这些结果表明，afadin 对于维持中脑中的放射状胶质细胞和室管膜细胞的 AJs 是必需的，并且对于中脑脑导水管和腹侧第三脑室的正常形态发生是必需的。
