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Published online April 28, 2008
doi:10.1083/jcb.200711053
The Journal of Cell Biology, Vol. 181, No. 3, 421-429
The Rockefeller University Press, 0021-9525 $30.00
© 2008 Goshima et al.
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 Augmin: a protein complex required for centrosome-independent microtubule generation within the spindle

Gohta Goshima1,2, Mirjam Mayer2,3, Nan Zhang4, Nico Stuurman2,4, and Ronald D. Vale2,4

1 Institute for Advanced Research, Nagoya University, Chikusa-ku, Nagoya 464-8601, Japan
2 Physiology Course 2007, Marine Biological Laboratory, Woods Hole, MA 02543
3 Max Planck Institute for Molecular Cell Biology and Genetics Dresden, 01307 Dresden, Germany
4 The Howard Hughes Medical Institute and the Department of Cellular and Molecular Pharmacology, University of California, San Francisco, San Francisco, CA 94158

Correspondence to Gohta Goshima: goshima{at}iar.nagoya-u.ac.jp

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.

Abbreviations used in this paper: {gamma}-TuRC, {gamma}-tubulin ring complex; {gamma}-TuSC, {gamma}-tubulin small complex; kMT, kinetochore MT; MT, microtubule; NEBD, nuclear envelope breakdown.


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