RT Journal Article SR Electronic T1 The Structure of Cilium Inner Junctions Revealed by Electron Cryo-tomography JF bioRxiv FD Cold Spring Harbor Laboratory SP 2024.09.09.612100 DO 10.1101/2024.09.09.612100 A1 Li, Sam A1 Fernandez, Jose-Jesus A1 Ruehle, Marisa D. A1 Howard-Till, Rachel A. A1 Fabritius, Amy A1 Pearson, Chad G. A1 Agard, David A. A1 Winey, Mark E. YR 2024 UL http://biorxiv.org/content/early/2024/09/09/2024.09.09.612100.abstract AB The cilium is a microtubule-based organelle critical for many cellular functions. Its assembly initiates at a basal body and continues as an axoneme that projects out of the cell to form a functional cilium. This assembly process is tightly regulated. However, our knowledge of the molecular architecture and the mechanism of assembly is limited. By applying electron cryo-tomography and subtomogram averaging, we obtained subnanometer resolution structures of the inner junction in three distinct regions of the cilium: the proximal region of the basal body, the central core of the basal body, and the flagellar axoneme. The structures allowed us to identify several basal body and axoneme components. While a few proteins are distributed throughout the entire length of the organelle, many are restricted to particular regions of the cilium, forming intricate local interaction networks and bolstering local structural stability. Finally, by knocking out a critical basal body inner junction component Poc1, we found the triplet MT was destabilized, resulting in a defective structure. Surprisingly, several axoneme-specific components were found to “infiltrate” into the mutant basal body. Our findings provide molecular insight into cilium assembly at its inner junctions, underscoring its precise spatial regulation.Competing Interest StatementThe authors have declared no competing interest.BBbasal bodyTMTtriplet microtubuleDMTdoublet microtubule