HsSAS-6-dependent cartwheel assembly ensures stabilization of centriole intermediates

Abstract

At the onset of procentriole formation, a structure called the cartwheel is formed adjacent to the pre-existing centriole. SAS-6 proteins are thought to constitute the hub of the cartwheel structure. However, the exact function of the cartwheel in the process of centriole formation has not been well characterized. In this study, we focused on the functions of human SAS-6 (HsSAS-6, also known as SASS6). By using an in vitro reconstitution system with recombinant HsSAS-6, we first observed its conserved molecular property of forming the central part of the cartwheel structure. Furthermore, we uncovered critical functions of HsSAS-6 by using a combination of an auxin-inducible HsSAS-6-degron (AID) system and super-resolution microscopy in human cells. Our results demonstrate that the HsSAS-6 is required not only for the initiation of centriole formation, but also for the stabilization of centriole intermediates. Moreover, after procentriole formation, HsSAS-6 is necessary for limiting Plk4 accumulation at the centrioles and thereby suppressing the formation of initiation sites that would otherwise promote the development of extra procentrioles. Overall, these findings illustrate the conserved and fundamental functions of the cartwheel in centriole duplication.

Nu MA assemblies organize microtubule asters to establish spindle bipolarity in acentrosomal human cells

“…Thus, we examined whether the observed structure of NuMA could be attributed to the inhibition of PLK4 or to the low microtubule density induced by the removal of centrosomes. Monopolar‐ and bundle‐like NuMA structures were similarly observed in centrosome‐eliminated cells after Sas6 depletion using the AID system (Appendix Fig S2E; Yoshiba et al , ), suggesting that the aforementioned phenotype was not the result of PLK4 inhibition. We further confirmed that the microtubule density in the acentrosomal spindle was higher than that in the centrosomal spindle (Appendix Fig S2F).…”

ATAD5 suppresses centrosome over-duplication by regulating UAF1 and ID1

“…However, in the absence of ATAD5, ID1 is released from UAF1, thereby free ID1 accumulates at centrosome, leading to centrosome defects. [45]. Recruitment of Sas-6 to the centrioles is promoted by Polo-like kinase 4 (Plk4) and SCL/ TAL1 interrupting locus (STIL) [46].…”

A first-takes-all model of centriole copy number control

“…pool is integrated into cartwheels. Along this line of thought, a recent paper could not detect cenriole assembly defects in a SAS-6 degradation system despite a significant reduction in its levels [14]. [14,26].…”

“…Along this line of thought, a recent paper could not detect cenriole assembly defects in a SAS-6 degradation system despite a significant reduction in its levels [14]. [14,26]. Second, a specialised atomic-force microscopy protocol has enabled cartwheel ring assembly to be imaged live [27].…”

“…Depletion of either one efficiently abrogates centriole duplication and their overexpression triggers the production of random supernumerary centrioles in a dose-dependent manner [8][9][10][11]. Quantitative proteomics revealed that Plk4, STIL, and SAS-6 are relatively low-abundance proteins at physiological conditions [12] although centriole duplication proceeds efficiently at a relatively broad range of their concentrations [13,14]. Although active degradation of Plk4, STIL, and SAS-6 via the cell cycle machinery and/or their own activity [15][16][17] may allow their levels to be kept within a given range, quasi-deterministic centriole duplication requires mechanisms that buffer stochasticity in Plk4, STIL, and SAS-6 levels.…”