Iwanaga Toshihiko, Miki Takashi, Takahashi-Iwanaga Hiromi
Laboratory of Histology and Cytology, Hokkaido University Graduate School of Medicine, Sapporo, Japan.
Biomed Res. 2011 Feb;32(1):73-81. doi: 10.2220/biomedres.32.73.
The primary cilium is now considered to function as a fundamental, not rudimentary, structure for mechanical and chemical sensing by individual cells. Primary cilia in neurons express type III adenylyl cyclase (ACIII) and GPCRs for somatostatin (somatostatin receptor 3, SSTR3), serotonin, and melanin-concentrating hormone. The present immunohistochemical and electron microscopic study revealed an abundant occurrence of SSTR3-expressing solitary cilia in insulin- and growth hormone-secreting cells of the mouse. The SSTR3 immunoreactivity was restricted to the plasma membrane of cilia in both cell types, differing from previously reported immunohistochemical localization of SSTRs to cell bodies. The primary cilia in the islet cells were longer than those in the pituitary cells and extended for a long distance in the intercellular canalicules endowed with microvilli. No other endocrine organs were provided with the SSTR3-expressing primary cilia, while the primary cilia in these organs were frequently immunolabeled with ACIII antibody. Since the somatostatin inhibition of both insulin and GH release is regulated mainly by SSTR1 and SSTR5, the primary cilia expressing SSTR3 may be involved in a signaling which differs from that via other SSTR subtypes expressing in cell bodies.
如今，初级纤毛被认为是一种基本结构，而非退化结构，用于单个细胞进行机械和化学传感。神经元中的初级纤毛表达III型腺苷酸环化酶（ACIII）以及生长抑素、5-羟色胺和促黑素聚集激素的G蛋白偶联受体（生长抑素受体3，SSTR3）。目前的免疫组织化学和电子显微镜研究显示，在小鼠胰岛素和生长激素分泌细胞中大量存在表达SSTR3的单个纤毛。在这两种细胞类型中，SSTR3免疫反应性均局限于纤毛的质膜，这与先前报道的SSTR在细胞体中的免疫组织化学定位不同。胰岛细胞中的初级纤毛比垂体细胞中的更长，并在富含微绒毛的细胞间小管中延伸很长一段距离。没有其他内分泌器官具有表达SSTR3的初级纤毛，而这些器官中的初级纤毛经常被ACIII抗体免疫标记。由于生长抑素对胰岛素和生长激素释放的抑制主要由SSTR1和SSTR5调节，表达SSTR3的初级纤毛可能参与了一种与通过细胞体中表达的其他SSTR亚型所介导的信号传导不同的信号传导。
