1. Max Planck Institute of Molecular Cell Biology and Genetics, Pfotenhauerstrasse 108, 01307 Dresden, Germany
2. Boulder Laboratory for 3D Electron Microscopy of Cells, Department of Molecular, Cellular and Developmental Biology, Campus Box 347, University of Colorado, Boulder, Colorado 80309, USA

Correspondence to: Laurence Pelletier¹ Correspondence and requests for materials should be addressed to L.P. (Email: pelletie@mpi-cbg.de).

Abstract

Centrioles are necessary for flagella and cilia formation^{1, 2}, cytokinesis^{3, 4}, cell-cycle control⁵ and centrosome organization/spindle assembly⁶. They duplicate once per cell cycle, but the mechanisms underlying their duplication remain unclear. Here we show using electron tomography of staged C. elegans one-cell embryos that daughter centriole assembly begins with the formation and elongation of a central tube followed by the peripheral assembly of nine singlet microtubules. Tube formation and elongation is dependent on the SAS-5 and SAS-6 proteins, whereas the assembly of singlet microtubules onto the central tube depends on SAS-4. We further show that centriole assembly is triggered by an upstream signal mediated by SPD-2 and ZYG-1. These results define a structural pathway for the assembly of a daughter centriole and should have general relevance for future studies on centriole assembly in other organisms.

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