Augmin: a protein complex required for centrosome-independent microtubule generation within the spindle.
Since the discovery of gamma-tubulin, attention has focused on its involvement as a microtubule nucleator at the centrosome. However, mislocalization of gamma-tubulin away from the centrosome does not inhibit mitotic spindle formation in Drosophila melanogaster, suggesting that a critical function for gamma-tubulin might reside elsewhere. A previous RNA interference (RNAi) screen identified five genes (Dgt2-6) required for localizing gamma-tubulin to spindle microtubules. We show that the Dgt proteins interact, forming a stable complex. We find that spindle microtubule generation is substantially reduced after knockdown of each Dgt protein by RNAi. Thus, the Dgt complex that we name "augmin" functions to increase microtubule number. Reduced spindle microtubule generation after augmin RNAi, particularly in the absence of functional centrosomes, has dramatic consequences on mitotic spindle formation and function, leading to reduced kinetochore fiber formation, chromosome misalignment, and spindle bipolarity defects. We also identify a functional human homologue of Dgt6. Our results suggest that an important mitotic function for gamma-tubulin may lie within the spindle, where augmin and gamma-tubulin function cooperatively to amplify the number of microtubules.
Goshima
Gohta
G
Institute for Advanced Research, Nagoya University, Chikusa-ku, Nagoya 464-8601, Japan. goshima@iar.nagoya-u.ac.jp
Mayer
Mirjam
M
Zhang
Nan
N
Stuurman
Nico
N
Vale
Ronald D
RD
D000595:Amino Acid Sequence; D000818:Animals; D002460:Cell Line; D018385:Centrosome / Q000378:metabolism*; D020090:Chromosome Segregation; D029721:Drosophila Proteins / Q000235:genetics / Q000378:metabolism*; D004331:Drosophila melanogaster / Q000166:cytology*; D006367:HeLa Cells; D018398:Homeodomain Proteins / Q000235:genetics / Q000378:metabolism; D006801:Humans; D008869:Microtubule-Associated Proteins / Q000235:genetics / Q000378:metabolism*; D008870:Microtubules / Q000378:metabolism*; D008969:Molecular Sequence Data; D046912:Multiprotein Complexes / Q000235:genetics / Q000378:metabolism*; D021122:Protein Subunits / Q000235:genetics / Q000378:metabolism; D034622:RNA Interference; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D016415:Sequence Alignment; D008941:Spindle Apparatus / Q000378:metabolism* / Q000648:ultrastructure; D014404:Tubulin / Q000235:genetics / Q000378:metabolism*
D029721:Drosophila Proteins; D018398:Homeodomain Proteins; D008869:Microtubule-Associated Proteins; D046912:Multiprotein Complexes; D021122:Protein Subunits; D011993:Recombinant Fusion Proteins; D014404:Tubulin; C098130:cnn protein, Drosophila