Microtubule-bundling protein Spef1 enables mammalian ciliary central apparatus formation
Microtubule-bundling protein Spef1 enables mammalian ciliary central apparatus formation
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微管成束蛋白 Spef1 促进哺乳动物纤毛中央装置的形成
DOI：
10.1093/jmcb/mjy014
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发表时间：
2019
影响因子：
5.5
通讯作者：
Zhu Xueliang
中科院分区：
文献类型：
--
作者：
Zheng Jianqun;Liu Hao;Zhu Lei;Chen Yawen;Zhao Huijie;Zhang Wei;Li Fan;Xie Lele;Yan Xiumin;Zhu Xueliang
纤毛是含有9个微管（MT）双峰的细胞突起，其功能是通过跳动推动细胞运动或细胞外液体流动，或通过信号转导感知环境刺激。纤毛需要中央对（CP）装置，由两个覆盖着CP蛋白投影的CP mt组成，用于平面描边。然而，这种“9 + 2”纤毛的CP mt是如何构建的尚不清楚。在这里，我们发现Spef1，一种进化上保守的微管捆绑蛋白，是哺乳动物纤毛中核心的CP MT调节因子。Spef1在具有9 + 2纤毛的哺乳动物细胞中选择性表达，并沿CP特异性定位。通过RNAi在多纤毛小鼠室管膜细胞中去除Spef1，完全消除了CP mt，并显著减弱了CP蛋白（如Hydin和Spag6）的纤毛定位，导致室管膜纤毛的旋转跳动。Spef1通过其n端钙钙蛋白同源结构域与mt结合，通过其c端卷曲的线圈区域形成同型二聚体来捆绑和稳定mt。mt结合或二聚化活性的破坏都取消了外源Spef1恢复CP装置结构和功能的能力。我们建议Spef1捆绑和稳定中心mt，以实现CP装置的组装和功能。
Cilia are cellular protrusions containing nine microtubule (MT) doublets and function to propel cell movement or extracellular liquid flow through beating or sense environmental stimuli through signal transductions. Cilia require the central pair (CP) apparatus, consisting of two CP MTs covered with projections of CP proteins, for planar strokes. How the CP MTs of such ‘9 + 2’ cilia are constructed, however, remains unknown. Here we identify Spef1, an evolutionarily conserved microtubule-bundling protein, as a core CP MT regulator in mammalian cilia. Spef1 was selectively expressed in mammalian cells with 9 + 2 cilia and specifically localized along the CP. Its depletion in multiciliated mouse ependymal cells by RNAi completely abolished the CP MTs and markedly attenuated ciliary localizations of CP proteins such as Hydin and Spag6, resulting in rotational beat of the ependymal cilia. Spef1, which binds to MTs through its N-terminal calponin-homologous domain, formed homodimers through its C-terminal coiled coil region to bundle and stabilize MTs. Disruption of either the MT-binding or the dimerization activity abolished the ability of exogenous Spef1 to restore the structure and functions of the CP apparatus. We propose that Spef1 bundles and stabilizes central MTs to enable the assembly and functions of the CP apparatus.