Architecture of mammalian centriole distal appendages accommodates distinct blade and matrix functional elements

Abstract

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. 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.

Analysis of LRRC45 indicates cooperative functions of distal appendages at early steps of ciliogenesis

“…Interestingly, using STED super resolution microscopy we were able to resolve Cep123 as two distinct ring-like structures at the mother centriole. This observation is in agreement with a recent report showing that Cep123 forms a layer close to ODF2 and another one closer to FBF1 (Yang et al, 2017). Our data indicate that LRRC45 decorates the space between the two Cep123 rings.…”

“…Recently, distal appendage proteins were proposed to form two spatially distinct domains, named distal appendage blades and matrix. According to this model, Cep83, SCLT1, Cep164 and Cep123 form defined conical-shaped blades while FBF1 makes up the matrix by filling the space between the blades (Yang et al, 2017). Depletion of LRRC45 reduced the levels of FBF1 at appendages, indicating that it is a major determinant of FBF1 centriolar localisation.…”

BBSome trains remove activated GPCRs from cilia by enabling passage through the transition zone

“…10, D and E ). Because QD GPR161 visits its most base-proximal location in SAG-treated cells while residing within the intermediate compartment, these data indicate that the diameter of the intermediate compartment is close to 550 nm, similar to the 450-nm diameter defined by the tip of the transition fibers ( Lau et al, 2012 ; Yang et al, 2015 , 2017 ; Kanie et al, 2017 ). The periciliary barrier thus appears to be located near the point where the transition fibers attach to the ciliary membrane.…”

“…The periciliary barrier is likely to correspond with the recently described distal appendage matrix (DAM) because depletion of the DAM component FBF1 results in the leakage of GPCRs from cilia ( Yang et al, 2017 ). Remarkably, when the receptors for insulin-like growth factor 1 (IGF1) or for transforming growth factor β (TGF-β) undergo signal-dependent exit from cilia, they transiently localize to a zone at the base of cilia that does not overlap with axonemal markers and may correspond to the intermediate compartment.…”

The molecular machines that traffic signaling receptors into and out of cilia

“…A recent preprint has described a membranous region located between the tip of the transition fibers that the Liao lab named distal appendage matrix (DAM) [58]. The dimensional similarities between the DAM and the PCB are striking and the leakage of Smo and Sstr3 out of cilia in cells depleted of the DAM component FBF1 suggests that the PCB may be equivalent to the DAM.…”