Multiple roles of afadin in the ultrastructural morphogenesis of mouse hippocampal mossy fiber synapses
Multiple roles of afadin in the ultrastructural morphogenesis of mouse hippocampal mossy fiber synapses
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DOI：
10.1002/cne.24238
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发表时间：
2017-08-15
影响因子：
2.5
通讯作者：
Mizoguchi, Akira
中科院分区：
文献类型：
--
作者：
Sai, Kousyoku;Wang, Shujie;Mizoguchi, Akira
海马苔藓纤维突触与学习和记忆有关，其结构复杂，苔藓纤维扣通过附着点连接（paj）附着在树突轴上，并缠绕在多分支脊柱上，形成突触连接。在这里，我们用电子显微镜分析了afadin缺乏小鼠该突触的超微结构。透射电镜分析显示，在对照突触中观察到典型的paj，其质膜呈明显的对称变暗，并覆盖着较厚的丝状细胞骨架，而在afadin缺陷突触中，观察到典型paj，其质膜呈对称变暗，其厚度和暗度远低于对照典型paj。免疫电镜分析显示，nectin-1、nectin-3和N-cadherin定位于对照典型paj，而nectin-1和nectin-3定位于缺乏afadin的非典型paj的程度低于对照突触，N-cadherin定位于它们的非连接侧翼区域。这些结果表明，非典型paj是由独立于afadin和N-cadherin的nectin-1和nectin-3形成的，而典型paj是由afadin和N-cadherin与nectin-1和nectin-3协同形成的。连续块面扫描电镜分析显示，突触后棘和苔藓纤维钮扣的复杂性、棘头数量、突触后密度面积和对接到活动区的突触囊泡密度均降低。这些结果表明，黄芪苷在海马苔藓纤维突触复杂的超微结构形态发生中起着多种作用。
A hippocampal mossy fiber synapse, which is implicated in learning and memory, has a complex structure in which mossy fiber boutons attach to the dendritic shaft by puncta adherentia junctions (PAJs) and wrap around a multiply-branched spine, forming synaptic junctions. Here, we electron microscopically analyzed the ultrastructure of this synapse in afadin-deficient mice. Transmission electron microscopy analysis revealed that typical PAJs with prominent symmetrical plasma membrane darkening undercoated with the thick filamentous cytoskeleton were observed in the control synapse, whereas in the afadin-deficient synapse, atypical PAJs with the symmetrical plasma membrane darkening, which was much less in thickness and darkness than those of the control typical PAJs, were observed. Immunoelectron microscopy analysis revealed that nectin-1, nectin-3, and N-cadherin were localized at the control typical PAJs, whereas nectin-1 and nectin-3 were localized at the afadin-deficient atypical PAJs to extents lower than those in the control synapse and N-cadherin was localized at their nonjunctional flanking regions. These results indicate that the atypical PAJs are formed by nectin-1 and nectin-3 independently of afadin and N-cadherin and that the typical PAJs are formed by afadin and N-cadherin cooperatively with nectin-1 and nectin-3. Serial block face-scanning electron microscopy analysis revealed that the complexity of postsynaptic spines and mossy fiber boutons, the number of spine heads, the area of postsynaptic densities, and the density of synaptic vesicles docked to active zones were decreased in the afadin-deficient synapse. These results indicate that afadin plays multiple roles in the complex ultrastructural morphogenesis of hippocampal mossy fiber synapses.