Opposing motor activities are required for the organization of the mammalian mitotic spindle pole.
We use both in vitro and in vivo approaches to examine the roles of Eg5 (kinesin-related protein), cytoplasmic dynein, and dynactin in the organization of the microtubules and the localization of NuMA (Nu-clear protein that associates with the Mitotic Apparatus) at the polar ends of the mammalian mitotic spindle. Perturbation of the function of Eg5 through either immunodepletion from a cell free system for assembly of mitotic asters or antibody microinjection into cultured cells leads to organized astral microtubule arrays with expanded polar regions in which the minus ends of the microtubules emanate from a ring-like structure that contains NuMA. Conversely, perturbation of the function of cytoplasmic dynein or dynactin through either specific immunodepletition from the cell free system or expression of a dominant negative subunit of dynactin in cultured cells results in the complete lack of organization of microtubules and the failure to efficiently concentrate the NuMA protein despite its association with the microtubules. Simultaneous immunodepletion of these proteins from the cell free system for mitotic aster assembly indicates that the plus end-directed activity of Eg5 antagonizes the minus end-directed activity of cytoplasmic dynein and a minus end-directed activity associated with NuMA during the organization of the microtubules into a morphologic pole. Taken together, these results demonstrate that the unique organization of the minus ends of microtubules and the localization of NuMA at the polar ends of the mammalian mitotic spindle can be accomplished in a centrosome-independent manner by the opposing activities of plus end- and minus end-directed motors.
Gaglio
T
T
Department of Biochemistry, Dartmouth Medical School, Hanover, New Hampshire 03755, USA.
Saredi
A
A
Bingham
J B
JB
Hasbani
M J
MJ
Gill
S R
SR
Schroer
T A
TA
Compton
D A
DA
D000818:Animals; D000911:Antibodies, Monoclonal; D034961:Antigens, Nuclear; D018797:Cell Cycle Proteins; D002460:Cell Line; D002474:Cell-Free System; D002645:Chickens; D002522:Chlorocebus aethiops; D000072159:Dynactin Complex; D004398:Dyneins / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D016547:Kinesins / Q000378:metabolism*; D008868:Microtubule Proteins / Q000378:metabolism; D008869:Microtubule-Associated Proteins; D008938:Mitosis; D008954:Models, Biological; D034521:Nuclear Matrix-Associated Proteins; D009687:Nuclear Proteins / Q000378:metabolism*; D009697:Nucleolus Organizer Region / Q000502:physiology* / Q000648:ultrastructure; D011994:Recombinant Proteins / Q000378:metabolism; D008941:Spindle Apparatus / Q000502:physiology* / Q000648:ultrastructure; D029867:Xenopus Proteins
D000911:Antibodies, Monoclonal; D034961:Antigens, Nuclear; D018797:Cell Cycle Proteins; D000072159:Dynactin Complex; C088335:KIF11 protein, Xenopus; D008868:Microtubule Proteins; D008869:Microtubule-Associated Proteins; C489079:NUMA1 protein, Xenopus; C050045:NUMA1 protein, human; D034521:Nuclear Matrix-Associated Proteins; D009687:Nuclear Proteins; D011994:Recombinant Proteins; D029867:Xenopus Proteins; D004398:Dyneins; D016547:Kinesins