The Golgi apparatus as an initiator of ciliogenesis

细胞感知和响应环境的能力在生命的所有阶段都是至关重要的。这在发育过程中可能是最重要的，因为细胞分化成特定的组织类型。人体内的大多数细胞延伸出初级纤毛，作为感知细胞外环境并对其做出反应的天线。初级纤毛是正常发育信号所必需的，细胞形成纤毛能力的任何缺陷都会导致严重的发育缺陷。这些疾病统称为纤毛疾病，包括特定的综合征，如Meckel-Gruber和Bardet-Biedel综合征，以及多囊肾病和短肋骨多指。通过定义单基因的致病突变，我们开始了解这些疾病的原因。要做到这一点，关键是要确保我们充分了解这些初级纤毛是如何构建和维持的。纤毛是一组称为轴丝的特殊微管细丝的延伸，轴丝被高度特化的膜包围。这一过程需要两个关键的细胞元素--细胞骨架和膜--的密切合作。我们已经确定了驱动纤毛形成的初始膜的来源。多年来，我们一直致力于细胞膜和蛋白质在细胞中的运输，最近，这让我们偶然发现，我们研究了多年的关键蛋白质之一，Giantin，实际上是细胞产生纤毛所必需的。我们已经确定了一种发生这种情况的机制，它将高尔基体的一种膜蛋白giantin与驱动纤毛内运输的两种主要马达蛋白之一dynein-2联系起来。高尔基体是所有哺乳动物细胞分泌途径的中心细胞器，它负责修饰和分类所有主要细胞细胞器的蛋白质。因此，它也直接位于微管轴丝延伸出的中心体附近。已知Dynein-2是纤毛功能所必需的，在体外和患者中，该复合体的突变会导致各种纤毛相关的疾病。我们认为Giantin通过dynein-2来控制纤毛组装的最早阶段。现在，我们希望利用我们在膜和微管动力学方面的丰富经验，特别是活细胞成像，来详细定义这一角色。我们已经与英国、美国和法国的关键实验室建立了合作关系，这意味着我们处于有利地位，可以推动这项工作向前发展。我们的实验将研究关键成分对新出现的纤毛的输送以及微管轴丝周围膜的组织。我们希望这些实验能够确定高尔基体在纤毛形成中的作用，并在调节纤毛功能的途径方面带来新的研究途径，以及识别可能导致尚未确定遗传缺陷的纤毛疾病的候选基因。

The ability of cells to sense and respond to the environment is critical at all stages of life. This is perhaps most important during development as cells differentiate into specific tissue types. Most cells in the human body extend a primary cilium that acts as an antenna to sense and respond to the extracellular environment. Primary cilia are required for proper developmental signalling and any defect in a cells ability to form a cilium causes serious developmental defects. These diseases, collectively known as the ciliopathies, include specific syndromes such as Meckel-Gruber and Bardet-Biedel Syndrome as well as polycystic kidney disease and short rib polydactyly. We are beginning to understand the causes of these diseases by defining the causative mutations in single genes. A key to this is to ensure that we fully understand the way in which these primary cilia are built and maintained. Cilia are extensions of a specialised set of microtubule filaments called the axoneme that are surrounded by a high specialised membrane. This process requires a close cooperation of two key cellular elements - the cytoskeleton and the membranes. We have identified a source of the initial membrane that drives the formation of the cilium. For many years we have worked on transport of membranes and proteins through the cell and recently this has led us serendipitously to discover that one of the key proteins that we have studies for many years, giantin, is in fact required for cells to make cilia. We have identified a mechanism by which this occurs which links giantin, a membrane protein of the Golgi apparatus, to dynein-2, one of two of the main motor proteins that drives transport within the cilium. The Golgi is the central organelle of the secretory pathway in all mammalian cells and it is responsible for the modification and sorting of proteins destined for all major cellular organelles. As such it also lies directly adjacent to the centrosome from which the microtubule axoneme extends. Dynein-2 is known to be required for cilium function and mutations in this complex cause a variety of cilia-related disorders in vitro and in patients. We propose that giantin acts through dynein-2 to control the earliest stages of assembly of cilia. Now we wish to use our extensive experience of membrane and microtubule dynamics, in particular live cell imaging, to define this role in detail. We have established collaborations with key labs in the UK, USA, and France that mean we are well placed to drive this work forwards. Our experiments will study the delivery of key components to the newly emerging cilium as well as the organization of membranes around the microtubule axoneme. We expect these experiments to define the role of the Golgi in forming the cilium and lead to new avenues of research in terms of pathways that one might approach to modulate ciliary function as well as identifying candidate genes that might underlie those ciliopathies for which a genetic defect is not yet defined.