Department of Molecular and Cellular Physiology, Stanford University, Stanford, 94305 CA, USA.
J Cell Sci. 2010 Feb 15;123(Pt 4):511-8. doi: 10.1242/jcs.061093.
Primary cilia contain signaling receptors of diverse classes, and ciliary dysfunction results in a variety of developmental defects. Thus, primary cilia are thought to have an important role in sensing and transducing cellular signals. Although there is clear evidence demonstrating that these organelles are assembled and disassembled dynamically as cells progress through the cell cycle, the mechanisms by which the cell cycle controls the assembly and disassembly of the primary cilium remain poorly understood. In this Commentary, we review the basic cellular mechanisms that underlie the early stages of cilium assembly and discuss how the cell cycle communicates with the ciliation program. A commonly held view is that ciliation occurs exclusively in cells that have exited the cell cycle and entered quiescence or differentiation. However, this concept is at odds with the finding that, during development, many actively proliferating cells require cilia-mediated signaling pathways to instruct their developmental fate. Here, we reassess the quiescence-centric view of ciliation by reviewing historic and current literature. We discuss ample evidence that cilia are in fact present on many proliferating cells, and that a transient peak of ciliation before the G1-S transition might be tightly coupled to entry into the DNA replication phase. Finally, we touch on the relationship between the ciliation and cell-division cycles and the tissue distribution of primary cilia in order to highlight potential roles for the primary cilium in restraining cells from the hyperproliferative state that contributes to cancer.
初级纤毛含有多种信号受体,纤毛功能障碍会导致多种发育缺陷。因此,初级纤毛被认为在感知和转导细胞信号方面具有重要作用。尽管有明确的证据表明,这些细胞器在细胞周期中随着细胞的进展而动态地组装和拆卸,但细胞周期控制初级纤毛组装和拆卸的机制仍知之甚少。在这篇评论中,我们回顾了构成纤毛组装早期阶段的基本细胞机制,并讨论了细胞周期如何与纤毛形成程序进行通讯。一个普遍的观点是,纤毛形成仅发生在已退出细胞周期并进入静止或分化状态的细胞中。然而,这一概念与以下发现相矛盾,即在发育过程中,许多活跃增殖的细胞需要纤毛介导的信号通路来指导其发育命运。在这里,我们通过回顾历史和当前的文献,重新评估以静止为中心的纤毛形成观点。我们讨论了充分的证据,证明实际上许多增殖细胞都存在纤毛,并且在 G1-S 转换之前的短暂纤毛峰可能与进入 DNA 复制阶段紧密相关。最后,我们还探讨了纤毛和细胞分裂周期之间的关系以及初级纤毛在组织中的分布,以突出初级纤毛在抑制细胞进入导致癌症的过度增殖状态方面的潜在作用。