Bld10p constitutes the cartwheel-spoke tip and stabilizes the 9-fold symmetry of the centriole.
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.
Hiraki
Madoka
M
Department of Biological Sciences, University of Tokyo, Tokyo 113-0033, Japan.
Nakazawa
Yuki
Y
Kamiya
Ritsu
R
Hirono
Masafumi
M
D020418:Algal Proteins / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D002502:Centrioles / Q000378:metabolism* / Q000648:ultrastructure*; D002696:Chlamydomonas / Q000235:genetics / Q000378:metabolism* / Q000648:ultrastructure*; D005407:Flagella / Q000378:metabolism / Q000648:ultrastructure; D017125:Genes, Protozoan; D016253:Microscopy, Immunoelectron; D009154:Mutation; D015800:Protozoan Proteins / Q000235:genetics / Q000378:metabolism*
D020418:Algal Proteins; D015800:Protozoan Proteins