Bld10p Constitutes the Cartwheel-Spoke Tip and Stabilizes the 9-Fold Symmetry of the Centriole
2007; Elsevier BV; Volume: 17; Issue: 20 Linguagem: Inglês
10.1016/j.cub.2007.09.021
ISSN1879-0445
AutoresMadoka Hiraki, Yuki Nakazawa, Ritsu Kamiya, Masafumi Hirono,
Tópico(s)Chromosomal and Genetic Variations
ResumoCentrioles/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 [1Dutcher S.K. Elucidation of basal body and centriole functions in Chlamydomonas reinhardtii.Traffic. 2003; 4: 443-451Crossref PubMed Scopus (84) Google Scholar, 2Delattre M. Gönczy P. The arithmetic of centrosome biogenesis.J. Cell Sci. 2004; 117: 1619-1630Crossref PubMed Scopus (120) Google Scholar]. 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 [3Matsuura K. Lefebvre P.A. Kamiya R. Hirono M. Bld10p, a novel protein essential for basal body assemly in Chlamydomonas: Localization to the cartwheel, the first ninefold symmetrical structure appearing during assembly.J. Cell Biol. 2004; 165: 663-671Crossref PubMed Scopus (99) Google Scholar]. Here, we report results by using a series of truncated Bld10p constructs introduced into a bld10 null mutant. Remarkably, a transformant (ΔC2) 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 ∼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 ΔC2 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.
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