Mitotic control by mRNA splicing regulators ensures primary cilia formation.

The biogenesis of the primary cilium is coordinated with cell cycle exit/re-entry in most types of cells. After serum starvation, the cilia-generating cells enter quiescence and produce the primary cilium; upon re-addition of serum, they re-enter the cell cycle and resorb the cilium. We previously identified novel mechanisms to link cell cycle progression and ciliogenesis by high-content genome-wide RNAi cell-based screening. In the present study, we pay attention to reveal the impact of mRNA splicing on cilia assembly after mitosis of cell cycle. We demonstrate that splicing regulators such as SON and XAB2 play an important role in mitosis exit, and thus affect ciliogenesis in G1/G0 phases. Knockdown of the splicing regulators in hTERT-RPE1 cells caused abnormal G2/M arrest under both serum addition and serum starvation, indicating defects in mitosis exit. Moreover, the knockdown cells failed to assemble the cilia under serum starvation and an inhibition of mRNA splicing using SSA, a spliceosome inhibitor, also revealed ciliogenesis defect. Finally, we show that the SSA-treated zebrafish display abnormal vascular development as a ciliary defect. These findings suggest the pivotal role of mRNA splicing regulators in cilia assembly and underscore the importance of mitotic regulation in ciliogenesis.