Cell cycle regulation through primary cilium: A long-forgotten story

Protruded from cytomembrane, primary cilium is a widespread cell organelle that can be found in almost all cell types in Mammalia. Because of its comprehensive requirement in various cellular activities and various functions in different organs, primary cilium has been a valuable research area of human pathology research since the turn of the millennium. And the potential application of the interaction between primary cilia and cell cycle regulation may be the most promising direction as many primary cilium-caused diseases are found to be caused by cell cycle dysregulation resulted from primary cilia defects. Therefore, a deep understanding of the interaction between primary cilia and the cell cycle is in great need. Hence in this review, we mainly described how the interaction between primary cilia and cell cycle proceeds and demonstrated three hypotheses raised from much different research. These hypotheses include (1) Primary cilium as a cellular signaling hub to regulate the cell cycle, (2) Primary cilium as a reservoir of cell cycle regulation-related factors, and (3) Primary cilium as a cell cycle checkpoint or a brake. Nonetheless, we also call for more attention on research of interaction between cell cycle and primary cilia and tried to point out some possible research directions for those who are interested.