Bld10p constitutes the cartwheel-spoke tip and stabilizes the 9-fold symmetry of the centriole

Curr Biol. 2007 Oct 23;17(20):1778-83. doi: 10.1016/j.cub.2007.09.021. Epub 2007 Sep 27.

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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Algal Proteins / genetics
  • Algal Proteins / metabolism*
  • Animals
  • Centrioles / metabolism*
  • Centrioles / ultrastructure*
  • Chlamydomonas / genetics
  • Chlamydomonas / metabolism*
  • Chlamydomonas / ultrastructure*
  • Flagella / metabolism
  • Flagella / ultrastructure
  • Genes, Protozoan
  • Microscopy, Immunoelectron
  • Mutation
  • Protozoan Proteins / genetics
  • Protozoan Proteins / metabolism*

Substances

  • Algal Proteins
  • Protozoan Proteins