衣藻、纤毛与“纤毛相关疾病”

纤毛或鞭毛（两个名称在本文互为通用）是以细胞微管为核心而组装形成的一种细胞器官．运动纤毛在细胞运动中起的作用是显而易见的,比如精子的运动：近年来发现,曾被认为是退化器官的不动原生纤毛在动物发育和各种生理器官的正常生理活动中起着重要作用．原生纤毛具有调控细胞分裂,Hedgehog信号通路,非经典Wnt信号通路及钙信号传导等的作用．纤毛及其附属结构在结构或功能上的缺陷会导致多种多样的疾病,总称为“纤毛相关疾病”,包括男性不育症、呼吸道疾病（如不动纤毛综合征、肾囊肿、失明、多指（趾）症、内脏转位、肥胖症、高血压乃至精神发育迟滞等．纤毛在结构和功能上是非常保守的,我们目前对纤毛的结构与功能的认识和对“纤毛相关疾病”发生机理的了解主要来自于对各种模式生物的研究,其中包括具有研究优势的模式生物——雷氏衣藻（Chlamydomonas reinhardtii,一种单细胞绿萍）．对纤毛的进一步研究将深化人们对“纤毛相关疾病”的认识、促进对它的诊断、预防和治疗．本文对衣藻、纤毛及“纤毛相关疾病”的研究进展作一简短概述．     

初级纤毛与Wnt信号通路相关性研究进展

初级纤毛是一类以微管为基础结构的细胞器,其来源于细胞的母中心粒,锚定在细胞膜并如“天线”般突出细胞表面。作为细胞感受器,初级纤毛从环境中接受各种信号,传导至细胞内引起细胞反应。近期的研究表明,初级纤毛对与胚胎发育密切相关的Wnt信号通路的传导起重要作用。纤毛的损害可造成Wnt信号通路的异常,并引起胚胎中多类脏器一系列的病理改变,导致初级纤毛相关疾病的发生。文章主要阐述了初级纤毛与Wnt/β-catenin、Wnt/PCP通路及初级纤毛相关疾病之间的关系,并对初级纤毛相关疾病的治疗进行了初步探讨。对初级纤毛与Wnt信号通路关系的深入研究将有助于人们对该类疾病的进一步诊断和治疗。     

纤毛、纤毛发生与Wnt/PCP信号通路

纤毛是以微管为核心组分、突出于细胞表面且高度保守的细胞器,具有运动、摄食、感知并传递外界信号等功能。纤毛发生是纤毛在细胞膜表面定位并装配的过程。多年来,对纤毛发生过程及其调控机制的探索始终是亚细胞结构与功能研究的热点之一。Wnt/PCP信号通路是参与胚胎及器官发育的主要信号转导途径之一。近年来大量研究显示,Wnt/PCP信号通路和纤毛发生密切相关。纤毛结构与功能的异常可造成Wnt/PCP信号通路异常,导致纤毛相关疾病的发生;同时,Wnt/PCP信号通路又决定着纤毛的形态和极性。因此,深入研究纤毛与Wnt/PCP信号通路的关系将有助于从细胞与分子生物学水平揭示纤毛发生的调控机制。     

神经细胞初级纤毛在中枢神经系统疾病中作用的研究进展

初级纤毛广泛存在于哺乳动物中枢神经系统中,是神经细胞重要的胞外细胞器。初级纤毛中含有多种离子通道、G蛋白耦联受体、激酶等,提示初级纤毛可感受胞外信号并将信号转导至细胞内,从而引起细胞对外界刺激信号产生应答反应。近年来大量研究表明调控纤毛结构及功能的基因发生突变后,会导致许多单基因的遗传性疾病。当神经细胞初级纤毛中激酶、G蛋白耦联受体以及离子通道的功能异常后,往往会引起一系列的神经精神疾病、神经系统发育异常等神经系统疾病。本文就初级纤毛在神经系统疾病中作用的研究进展进行综述。     

多纤毛细胞纤毛精确组装的调控机制

高等动物体内气管、脑室管膜及输卵管等上皮组织具有一类富含运动纤毛的多纤毛细胞,通过其细胞表面运动纤毛的周期性摆动可以清洁气管、驱动脑脊液流动和受精卵运动。运动纤毛发生或功能的异常则可导致气管炎、脑积水、不孕不育等多种遗传疾病。然而,在多纤毛细胞分化过程中关于如何精确组装运动性纤毛复杂结构的分子机制仍不清楚。该研究运用蛋白组学、超高分辨率显微成像和电镜等多种技术,发现多纤毛细胞特有的亚细胞结构–纤维状颗粒物是由中心体周围基质蛋白Pcm1相分离形成的具有液体特征的无膜细胞器,不仅参与调控多纤毛细胞摇篮体的组装和空间分布,而且在其多孔状结构中大量富集了特定的基体和纤毛的结构蛋白质,并精确调控这些组分在运动纤毛发生的不同阶段定位到基体和纤毛中,阐明了纤维状颗粒物作为组织者精确调控运动纤毛组装的分子机制。     

细胞纤毛在信号转导与器官发育中的作用与机制

纤毛(cilia)是细胞表面的突起状细胞器,几乎存在于所有细胞表面,且广泛分布于组织和器官的上皮.纤毛由外部的纤毛膜和内部的轴丝组成,结构在进化上十分保守.根据微管组成和排列方式的不同,纤毛可分为9+2型运动纤毛与9+0型基本纤毛或非运动纤毛.作为一种特殊的感受器,纤毛通过影响细胞信号通路参与胚胎形成、心脏等内脏器官发育及人体重要生理活动.本课题组在国际上首次把前列腺素信号通路与纤毛生长及心脏发育相联系.研究发现,ABCC4/LKT前列腺素转运蛋白从细胞内运输前列腺素E2(PGE2)至细胞外,并通过结合位于纤毛膜上的G蛋白偶联受体EP4影响细胞内c AMP浓度,调节纤毛内运输蛋白的正向速率,进而调控纤毛生长与心脏等器官的左右不对称性发育.纤毛生长或功能缺陷会引发先天性心脏病、多囊肾、视网膜变性等多种疾病.本文主要介绍纤毛参与调控细胞内信号转导与器官发育及相关纤毛疾病.     

初级纤毛的研究进展

初级纤毛是以中心体作为基体并突出于细胞膜表面的一种特化的细胞结构,存在于绝大多数休眠期以及已分化的哺乳动物细胞,介导多种细胞信号通路的转导,因此初级纤毛功能的异常会导致一系列人类疾病。该文主要总结了初级纤毛的结构、起始生长与解聚过程及中心体/纤毛蛋白降解途径等方面的最新研究进展,讨论了初级纤毛异常与纤毛疾病的关系,为纤毛疾病的诊断与治疗提供了参考。     

原纤毛－多囊蛋白复合物在肾和骨组织中的类似作用

纤毛－多囊蛋白复合物的功能或者结构异常,是导致常染色体显性多囊肾病的主要原因.该复合物除了被认为在正常的肾上皮细胞上起着机械和化学感受器的作用,可能在骨细胞中也有类似的作用.本文总结了多囊蛋白和纤毛的结构、分布特点以及在肾发育过程中所发挥的作用;着重综述了纤毛 多囊蛋白复合物在肾上皮细胞上作为机械和化学感受器,通过影响细胞内一系列的信号途径,调控细胞的基因转录和蛋白合成的最新研究进展,包括与细胞内钙离子变化有关的钙调神经磷酸酶－NFAT途径和PI3K－Atk途径,调控细胞周期的JAK－STAT途径,及维持正常肾结构的Wnt/β连环蛋白信号途径等;还将通过比较在肾上皮细胞上纤毛 多囊蛋白复合物所激活的信号传导途径和在骨细胞中传导机械刺激的信号转导途径的类同,提示在骨细胞中,纤毛 多囊蛋白复合物可能起着在肾上皮细胞上类似的机械感受器作用,为系统性阐明多囊肾病的发病机制,以及揭示失重或负重状态下骨细胞机械感受的分子机制提供了一个新思路.     

BBS8蛋白参与衣藻鞭毛膜蛋白的运输

真核细胞的纤毛(也称鞭毛)是一种突出于细胞表面的极性细胞器,纤毛不仅参与细胞运动,还参与信号传导等过程,其结构或功能异常引发的一系列人类疾病称为"纤毛相关性疾病"。纤毛相关性疾病巴德-毕德氏综合征(Bardet-Biedl syndrome,简称BBS)由BBS相关基因缺陷导致,为了研究致病基因BBS8的生理作用和功能,构建模式生物莱茵衣藻BBS8基因缺陷突变体,利用性状观测和生化分析检测突变体的表现型和生理功能。免疫荧光表明BBS8蛋白是一种鞭毛蛋白且在基体有特异性定位;bbs8突变体感光极性运动消失,并在解聚诱导实验中鞭毛解聚缓慢;鞭毛的银染和质谱结果表明突变体的鞭毛膜蛋白在鞭毛内异常积累。文中通过实验证据说明BBS8蛋白在参与鞭毛内膜蛋白运输中起到重要作用,并极可能通过介导膜蛋白反向运输发挥生理功能。     

磷酸化调控纤毛的解聚

<正>纤毛(也称鞭毛)是突出于真核细胞表面的一类在进化上很保守的细胞器,由纤毛膜、轴丝及其底部的基体组成.纤毛广泛分布于原生动物及脊椎动物细胞表面,负责感受内外环境信号以及驱动细胞运动.在哺乳动物特别是人类中,纤毛结构和功能的异常能导致多囊肾,神经系统发育缺陷,听觉、嗅觉和视觉的衰退,呼吸道疾病和不育症等,这些疾病统称为纤毛病,其发病率在1/1000左右.目前还没有治疗     

Scoring a backstage pass: mechanisms of ciliogenesis and ciliary access

Cilia are conserved, microtubule-based cell surface projections that emanate from basal bodies, membrane-docked centrioles. The beating of motile cilia and flagella enables cells to swim and epithelia to displace fluids. In contrast, most primary cilia do not beat but instead detect environmental or intercellular stimuli. Inborn defects in both kinds of cilia cause human ciliopathies, diseases with diverse manifestations such as heterotaxia and kidney cysts. These diseases are caused by defects in ciliogenesis or ciliary function. The signaling functions of cilia require regulation of ciliary composition, which depends on the control of protein traffic into and out of cilia.     

Cilia-related diseases

More and more attention is paid to diseases such as internal transfer and brain malformation which are caused by the abnormal morphogenesis of cilia. These cilia-related diseases are divided into two categories: ciliopathy resulting from defects of primary cilia and primary ciliary dyskinesia (PCD) caused by functional dysregulation of motile cilia. Cilia are widely distributed, and their related diseases can cover many human organs and tissues. Recent studies prove that primary cilia play a key role in maintaining homeostasis in the cardiovascular system. However, molecular mechanisms of cilia-related diseases remain elusive. Here, we reviewed recent research progresses on characteristics, molecular mechanisms and treatment methods of ciliopathy and PCD. Our review is beneficial to the further research on the pathogenesis and treatment strategies of cilia-related diseases.     

Ins and outs of GPCR signaling in primary cilia

Primary cilia are specialized microtubule‐based signaling organelles that convey extracellular signals into a cellular response in most vertebrate cell types. The physiological significance of primary cilia is underscored by the fact that defects in assembly or function of these organelles lead to a range of severe diseases and developmental disorders. In most cell types of the human body, signaling by primary cilia involves different G protein‐coupled receptors (GPCRs), which transmit specific signals to the cell through G proteins to regulate diverse cellular and physiological events. Here, we provide an overview of GPCR signaling in primary cilia, with main focus on the rhodopsin‐like (class A) and the smoothened/frizzled (class F) GPCRs. We describe how such receptors dynamically traffic into and out of the ciliary compartment and how they interact with other classes of ciliary GPCRs, such as class B receptors, to control ciliary function and various physiological and behavioral processes. Finally, we discuss future avenues for developing GPCR‐targeted drug strategies for the treatment of ciliopathies.     

Differential Roles of Tubby Family Proteins in Ciliary Formation and Trafficking

Cilia are highly specialized organelles that extend from the cell membrane and function as cellular signaling hubs. Thus, cilia formation and the trafficking of signaling molecules into cilia are essential cellular processes. TULP3 and Tubby (TUB) are members of the tubby-like protein (TULP) family that regulate the ciliary trafficking of G-protein coupled receptors, but the functions of the remaining TULPs (i.e., TULP1 and TULP2) remain unclear. Herein, we explore whether these four structurally similar TULPs share a molecular function in ciliary protein trafficking. We found that TULP3 and TUB, but not TULP1 or TULP2, can rescue the defective cilia formation observed in TULP3-knockout (KO) hTERT RPE-1 cells. TULP3 and TUB also fully rescue the defective ciliary localization of ARL13B, INPP5E, and GPR161 in TULP3 KO RPE-1 cells, while TULP1 and TULP2 only mediate partial rescues. Furthermore, loss of TULP3 results in abnormal IFT140 localization, which can be fully rescued by TUB and partially rescued by TULP1 and TULP2. TUB’s capacity for binding IFT-A is essential for its role in cilia formation and ciliary protein trafficking in RPE-1 cells, whereas its capacity for PIP₂ binding is required for proper cilia length and IFT140 localization. Finally, chimeric TULP1 containing the IFT-A binding domain of TULP3 fully rescues ciliary protein trafficking, but not cilia formation. Together, these two TULP domains play distinct roles in ciliary protein trafficking but are insufficient for cilia formation in RPE-1 cells. In addition, TULP1 and TULP2 play other unknown molecular roles that should be addressed in the future.     

A novel Cre‐inducible knock‐in ARL13B‐tRFP fusion cilium reporter

Cilia play a major role in the regulation of numerous signaling pathways and are essential for embryonic development. Mutations in genes affecting ciliary function can cause a variety of diseases in humans summarized as ciliopathies. To facilitate the detection and visualization of cilia in a temporal and spatial manner in mouse tissues, we generated a Cre‐inducible cilium‐specific reporter mouse line expressing an ARL13B‐tRFP fusion protein driven by a CMV enhancer/chicken β actin promotor (pCAG) from the Hprt locus. We detected bright and specific ciliary signals by immunostainings of various mono‐ and multiciliated tissues and by time‐lapse live‐cell analysis of cultured embryos and organ explant cultures. Additionally, we monitored cilium assembly and disassembly in embryonic fibroblast cells using live‐cell imaging. Thus, the ARL13B‐tRFP reporter mouse strain is a valuable tool for the investigation of ciliary structure and function in a tissue‐specific manner to understand processes, such as ciliary protein trafficking or cilium‐dependent signaling in vitro and in vivo.     

Structure and function of mammalian cilia

In the past half century, beginning with electron microscopic studies of 9 + 2 motile and 9 + 0 primary cilia, novel insights have been obtained regarding the structure and function of mammalian cilia. All cilia can now be viewed as sensory cellular antennae that coordinate a large number of cellular signaling pathways, sometimes coupling the signaling to ciliary motility or alternatively to cell division and differentiation. This view has had unanticipated consequences for our understanding of developmental processes and human disease.     

Cilia‐localized LKB1 regulates chemokine signaling,macrophage recruitment,and tissue homeostasis in the kidney

Polycystic kidney disease (PKD) and other renal ciliopathies are characterized by cysts, inflammation, and fibrosis. Cilia function as signaling centers, but a molecular link to inflammation in the kidney has not been established. Here, we show that cilia in renal epithelia activate chemokine signaling to recruit inflammatory cells. We identify a complex of the ciliary kinase LKB1 and several ciliopathy‐related proteins including NPHP1 and PKD1. At homeostasis, this ciliary module suppresses expression of the chemokine CCL2 in tubular epithelial cells. Deletion of LKB1 or PKD1 in mouse renal tubules elevates CCL2 expression in a cell‐autonomous manner and results in peritubular accumulation of CCR2⁺ mononuclear phagocytes, promoting a ciliopathy phenotype. Our findings establish an epithelial organelle, the cilium, as a gatekeeper of tissue immune cell numbers. This represents an unexpected disease mechanism for renal ciliopathies and establishes a new model for how epithelial cells regulate immune cells to affect tissue homeostasis.     

纤毛疾病和与之相关的基因

近年来,研究发现纤毛在生成或者形态的缺陷均能导致新生儿遗传性疾病。与其他细胞器不同的是,纤毛这一小的毛发状细胞器能在几乎所有的极性细胞表面上生成,而且功能非常多样化。纤毛在调节脊椎动物的发育和内环境的平衡起着相当重要的作用,而与纤毛相关基因的缺失则与一系列疾病相关,包括:Nephronophthisis、Joubert综合症、Meckel-Gruber综合症和BardetBiedl综合症等。结合最近的研究,本文主要对四类主纤毛相关疾病的基因进行归类总结。     

Cilia and polycystic kidney disease,kith and kin

In the past decade, cilia have been found to play important roles in renal cystogenesis. Many genes, such as PKD1 and PKD2 which, when mutated, cause autosomal dominant polycystic kidney disease (ADPKD), have been found to localize to primary cilia. The cilium functions as a sensor to transmit extracellular signals into the cell. Abnormal cilia structure and function are associated with the development of polyscystic kidney disease (PKD). Cilia assembly includes centriole migration to the apical surface of the cell, ciliary vesicle docking and fusion with the cell membrane at the intended site of cilium outgrowth, and microtubule growth from the basal body. This review summarizes the most recent advances in cilia and PKD research, with special emphasis on the mechanisms of cytoplasmic and intraciliary protein transport during ciliogenesis. Birth Defects Research (Part C) 102:174–185, 2014 . © 2014 Wiley Periodicals, Inc .