Bld10p Constitutes the Cartwheel-Spoke Tip and Stabilizes the 9-Fold Symmetry of the Centriole

Abstract

Centrioles/basal bodies have a characteristic cylindrical structure consisting of nine triplet microtubules arranged in a rotational symmetry. How this elaborate structure is formed is a major unanswered question in cell biology [1, 2]. We previously identified a 170 kDa coiled-coil protein essential for the centriole formation in Chlamydomonas. This protein, Bld10p, is the first protein shown to localize to the cartwheel, a 9-fold symmetrical structure possibly functioning as the scaffold for the centriole-microtubule assembly [3]. Here, we report results by using a series of truncated Bld10p constructs introduced into a bld10 null mutant. Remarkably, a transformant (DeltaC2) in which 35% of Bld10p at the C terminus was deleted assembled centrioles with eight symmetrically arranged triplets, in addition to others with the normal nine triplets. The cartwheels in these eight-membered centrioles had spokes approximately 24% shorter than those in the wild-type, suggesting that the eight-triplet centrioles were formed because the cartwheel's smaller diameter. From the morphology of the cartwheel spoke in the DeltaC2 centriole and immunoelectron-microscope localization, we conclude that Bld10p is a major spoke-tip component that extends the cartwheel diameter and attaches triplet microtubules. These results provide the first experimental evidence for the crucial function of the cartwheel in centriolar assembly.

Quantitative analysis of human centrosome architecture by targeted proteomics and fluorescence imaging

“…It is also remarkable that Cep135 is much more abundant at purified centrosomes than either STIL or Sas‐6 (Fig 2C). Although this result may appear surprising when considering the striking association of the Cep135 homolog Bld10 with the centriolar cartwheel in Chlamydomonas (Matsuura et al , 2004; Hiraki et al , 2007), it falls in line with the observation that the bulk of human Cep135 associates with the proximal ends of mother centrioles rather than the cartwheels of daughter centrioles (Sonnen et al , 2012). Finally, and most interestingly, our data predict that Sas‐6 is about twice as abundant as STIL.…”

CYLD mediates ciliogenesis in multiple organs by deubiquitinating Cep70 and inactivating HDAC6

“…The Chlamydomonas homolog of Cep70, CRC70, has been shown to localize preferentially at immature centrioles and promote centriole assembly by recruiting spindle assembly abnormal protein 6 (SAS-6) and Bld10p [18], two cartwheel proteins required for the formation of the microtubule triplets of centrioles and basal bodies [23,24]. It will be interesting to investigate in the future whether CYLD regulates basal body organization by acting on the Cep70/SAS-6/Bld10p axis.…”

DrosophilaBld10 Is a Centriolar Protein That Regulates Centriole, Basal Body, and Motile Cilium Assembly

“…In Chlamydomonas reinhardtii, mutations in the bld10 gene result in complete loss of flagella, giving the cells a "bald" appearance, due to a failure to assemble centrioles (Matsuura et al, 2004;Hiraki et al, 2007). Bld10p functions in the formation of the cartwheel, a ninefold symmetrical scaffold structure essential for an early step of centriole/basal body assembly .…”

“…Additional centriole/ basal body proteins including Spd-2, Drosophila pericentrin-like protein (D-PLP)/CP309, and uncoordinated (UNC) function in pericentriolar material (PCM) recruitment to centrosomes and/or the assembly of cilia and flagella Kawaguchi and Zheng, 2004;Martinez-Campos et al, 2004;Dix and Raff, 2007;Giansanti et al, 2008). Identification of the complete set of centriole components is necessary to define their individual and cooperative roles in the assembly and function of centrioles and cilia.In Chlamydomonas reinhardtii, mutations in the bld10 gene result in complete loss of flagella, giving the cells a "bald" appearance, due to a failure to assemble centrioles (Matsuura et al, 2004;Hiraki et al, 2007). Bld10p functions in the formation of the cartwheel, a ninefold symmetrical scaffold structure essential for an early step of centriole/basal body assembly .…”