Kubo Akiharu, Yuba-Kubo Akiko, Tsukita Sachiko, Tsukita Shoichiro, Amagai Masayuki
Department of Dermatology, Keio University School of Medicine, Tokyo 160-8582, Japan.
Mol Biol Cell. 2008 Dec;19(12):5338-46. doi: 10.1091/mbc.e08-07-0691. Epub 2008 Oct 1.
Human respiratory and oviductal cilia have specific apical structures characterized by a narrowed distal portion and a ciliary crown. These structures are conserved among vertebrates that have air respiration systems; however, the molecular components of these structures have not been defined, and their functions are unknown. To identify the molecular component(s) of the cilia apical structure, we screened EST libraries to identify gene(s) that are exclusively expressed in ciliated tissues, are transcriptionally up-regulated during in vitro ciliogenesis, and are not expressed in testis (because sperm flagella have no such apical structures). One of the identified gene products, named sentan, was localized to the distal tip region of motile cilia. Using anti-sentan polyclonal antibodies and electron microscopy, sentan was shown to localize exclusively to the bridging structure between the cell membrane and peripheral singlet microtubules, which specifically exists in the narrowed distal portion of cilia. Exogenously expressed sentan showed affinity for the membrane protrusions, and a protein-lipid binding assay revealed that sentan bound to phosphatidylserine. These findings suggest that sentan is the first molecular component of the ciliary tip to bridge the cell membrane and peripheral singlet microtubules, making the distal portion of the cilia narrow and stiff to allow for better airway clearance or ovum transport.
人类呼吸道和输卵管纤毛具有特定的顶端结构，其特征为远端变窄部分和纤毛冠。这些结构在具有空气呼吸系统的脊椎动物中是保守的；然而，这些结构的分子成分尚未明确，其功能也未知。为了鉴定纤毛顶端结构的分子成分，我们筛选了EST文库，以鉴定在纤毛组织中特异性表达、在体外纤毛发生过程中转录上调且在睾丸中不表达的基因（因为精子鞭毛没有这种顶端结构）。其中一个鉴定出的基因产物名为“仙潭”，定位于运动纤毛的远端尖端区域。使用抗仙潭多克隆抗体和电子显微镜观察发现，仙潭仅定位于细胞膜和外周单微管之间的桥接结构，该结构特异性存在于纤毛变窄的远端部分。外源表达的仙潭对膜突起具有亲和力，蛋白质-脂质结合试验表明仙潭与磷脂酰丝氨酸结合。这些发现表明，仙潭是纤毛尖端连接细胞膜和外周单微管的首个分子成分，使纤毛远端变窄且变硬，以实现更好的气道清理或卵子运输。
