3D Architectural Reconstruction of Mammalian Centriole Distal Appendages using Superresolution Microscopy

Abstract

The primary cilium is an essential microdomain of cells grown upon the mother centriole/basal body serving multiple sensory roles (e.g., smell, light, force) and mediating multiple signaling activities (e.g., hedgehog, Wnt, cAMP). Distal appendages (DAPs) are nanoscale, pinwheel-like structures protruding from the distal end of the centriole that mediate membrane docking during ciliogenesis, marking the cilia base around the ciliary gate. Despite their functional importance, the detailed architecture of DAPs remains largely unknown. Here, we determined a superresolved multiplex of 16 centriole-distal-end components. Surprisingly, rather than pinwheels, intact DAPs exhibit a cone-shaped architecture with components filling the space between each pinwheel blade, a new structural element we termed the distal appendage matrix (DAM). Specifically, CEP83, CEP89, SCLT1, and CEP164 form the backbone of pinwheel blades, with CEP83 confined at the root and CEP164 extending to the tip near the membrane-docking site. By contrast, FBF1 marks the distal end of the DAM near the ciliary membrane. Strikingly, unlike CEP164 which is essential for ciliogenesis, FBF1 is required for ciliary gating of transmembrane proteins, revealing DAPs as an essential component of the ciliary gate. Our findings redefine both the structure and function of DAPs. Funding sources: Ministry of Science and Technology, Taiwan (Grant No. 103-2112-M-001-039-MY3), Academia Sinica Career Development Award.