The kinetically dominant assembly pathway for centrosomal asters in Caenorhabditis elegans is gamma-tubulin dependent.
gamma-Tubulin-containing complexes are thought to nucleate and anchor centrosomal microtubules (MTs). Surprisingly, a recent study (Strome, S., J. Powers, M. Dunn, K. Reese, C.J. Malone, J. White, G. Seydoux, and W. Saxton. Mol. Biol. Cell. 12:1751-1764) showed that centrosomal asters form in Caenorhabditis elegans embryos depleted of gamma-tubulin by RNA-mediated interference (RNAi). Here, we investigate the nucleation and organization of centrosomal MT asters in C. elegans embryos severely compromised for gamma-tubulin function. We characterize embryos depleted of approximately 98% centrosomal gamma-tubulin by RNAi, embryos expressing a mutant form of gamma-tubulin, and embryos depleted of a gamma-tubulin-associated protein, CeGrip-1. In all cases, centrosomal asters fail to form during interphase but assemble as embryos enter mitosis. The formation of these mitotic asters does not require ZYG-9, a centrosomal MT-associated protein, or cytoplasmic dynein, a minus end-directed motor that contributes to self-organization of mitotic asters in other organisms. By kinetically monitoring MT regrowth from cold-treated mitotic centrosomes in vivo, we show that centrosomal nucleating activity is severely compromised by gamma-tubulin depletion. Thus, although unknown mechanisms can support partial assembly of mitotic centrosomal asters, gamma-tubulin is the kinetically dominant centrosomal MT nucleator.
Hannak
Eva
E
Max Planck Institute of Molecular Cell Biology and Genetics, 01307 Dresden, Germany.
Oegema
Karen
K
Kirkham
Matthew
M
Gönczy
Pierre
P
Habermann
Bianca
B
Hyman
Anthony A
AA
D000818:Animals; D017173:Caenorhabditis elegans / Q000235:genetics* / Q000378:metabolism; D029742:Caenorhabditis elegans Proteins / Q000235:genetics / Q000378:metabolism; D018385:Centrosome / Q000378:metabolism*; D015536:Down-Regulation / Q000502:physiology; D004398:Dyneins / Q000235:genetics / Q000378:metabolism; D005455:Fluorescent Antibody Technique; D015801:Helminth Proteins / Q000235:genetics / Q000378:metabolism; D007700:Kinetics; D008869:Microtubule-Associated Proteins / Q000235:genetics / Q000378:metabolism; D008870:Microtubules / Q000235:genetics / Q000378:metabolism*; D008938:Mitosis / Q000502:physiology*; D008969:Molecular Sequence Data; D009154:Mutation / Q000502:physiology*; D010641:Phenotype; D010802:Phylogeny; D017354:Point Mutation / Q000235:genetics; D012313:RNA / Q000235:genetics; D017386:Sequence Homology, Amino Acid; D015398:Signal Transduction / Q000235:genetics; D008941:Spindle Apparatus / Q000235:genetics / Q000378:metabolism*; D014404:Tubulin / Q000172:deficiency* / Q000235:genetics
D029742:Caenorhabditis elegans Proteins; C456608:Grip-1 protein, C elegans; D015801:Helminth Proteins; D008869:Microtubule-Associated Proteins; D014404:Tubulin; C112750:ZYG-9 protein, C elegans; D012313:RNA; D004398:Dyneins