A complex of NuMA and cytoplasmic dynein is essential for mitotic spindle assembly.
NuMA is a nuclear protein during interphase but redistributes to the spindle poles early in mitosis. To investigate its role during spindle formation, we tested spindle assembly in frog egg extracts from which NuMA was immunodepleted. Immunodepletion revealed that NuMA forms a complex with cytoplasmic dynein and dynactin. The depleted extracts failed to assemble normal mitotic spindles, producing, instead, chromatin-associated irregular arrays of microtubules lacking characteristic spindle poles. A subdomain of the NuMA tail was shown to induce microtubule aster formation by mediating microtubule bundling. Our findings suggest that NuMA forms bifunctional complexes with cytoplasmic dynein and dynactin that can tether microtubules at the spindle poles and that are essential for mitotic spindle pole assembly and stabilization.
Ludwig Institute for Cancer Research, University of California at San Diego, La Jolla 92093-0660, USA.
A
A
Merdes
K
K
Ramyar
J D
JD
Vechio
D W
DW
Cleveland
D000595:Amino Acid Sequence; D000818:Animals; D034961:Antigens, Nuclear; D018797:Cell Cycle Proteins; D016764:Cell Polarity; D000072159:Dynactin Complex; D004398:Dyneins / Q000502:physiology*; D006801:Humans; D046911:Macromolecular Substances; D008868:Microtubule Proteins / Q000502:physiology; D008869:Microtubule-Associated Proteins; D008870:Microtubules / Q000648:ultrastructure; D008938:Mitosis / Q000502:physiology*; D008969:Molecular Sequence Data; D034521:Nuclear Matrix-Associated Proteins; D009687:Nuclear Proteins / Q000502:physiology*; D009865:Oocytes; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D008941:Spindle Apparatus / Q000502:physiology* / Q000648:ultrastructure; D014404:Tubulin / Q000378:metabolism; D029867:Xenopus Proteins; D014982:Xenopus laevis
D034961:Antigens, Nuclear; D018797:Cell Cycle Proteins; D000072159:Dynactin Complex; D046911:Macromolecular Substances; D008868:Microtubule Proteins; D008869:Microtubule-Associated Proteins; C489079:NUMA1 protein, Xenopus; C050045:NUMA1 protein, human; D034521:Nuclear Matrix-Associated Proteins; D009687:Nuclear Proteins; D014404:Tubulin; D029867:Xenopus Proteins; D004398:Dyneins