The perennial organelle: assembly and disassembly of the primary cilium

Abstract

SummaryPrimary 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.

NudC regulates actin dynamics and ciliogenesis by stabilizing cofilin 1

“…In consistence with the results above, knockdown of NudC in HEK293T cells also substantially induced primary cilia assembly (Supplementary information, Figure S5). Given that ciliation is associated with cell cycle regulation [1,21,22], we determined whether NudC depletion influences cell cycle. Flow cytometry showed that there was no significant difference between the control and NudC-depleted RPE-1 cells during cell cycle progression under our conditions ( Figure 2G and 2H).…”

Tubal transport of gametes and embryos: a review of physiology and pathophysiology

“…It is noteworthy that the 9+2 arrangement in ciliated epithelial cells is in contrast with the 9+0 arrangement of the single primary cilium that may be observed on the apical surface of secretory cells. These primary immotile cilia do not have dynein arms or nexin links and lack the central two single microtubules [24][25][26][27].…”

CYLD mediates ciliogenesis in multiple organs by deubiquitinating Cep70 and inactivating HDAC6

“…The primary cilium is an immotile, solitary structure that emanates from the surfaces of most mammalian cell types and can sense various extracellular signals [1,2]. By contrast, motile cilia are typically found in large numbers on differentiated epithelial cells, such as those in the trachea, brain ventricle, and oviduct; ciliary motility is critical for the flow of mucus and cerebrospinal fluid and the movement of eggs [3].…”