Ran induces spindle assembly by reversing the inhibitory effect of importin alpha on TPX2 activity.
The small GTPase Ran, bound to GTP, is required for the induction of spindle formation by chromosomes in M phase. High concentrations of Ran.GTP are proposed to surround M phase chromatin. We show that the action of Ran.GTP in spindle formation requires TPX2, a microtubule-associated protein previously known to target a motor protein, Xklp2, to microtubules. TPX2 is normally inactivated by binding to the nuclear import factor, importin alpha, and is displaced from importin alpha by the action of Ran.GTP. TPX2 is required for Ran.GTP and chromatin-induced microtubule assembly in M phase extracts and mediates spontaneous microtubule assembly when present in excess over free importin alpha. Thus, components of the nuclear transport machinery serve to regulate spindle formation in M phase.
Gruss
O J
OJ
European Molecular Biology Laboratory, Meyerhofstrasse 1, D-69117 Heidelberg, Germany.
Carazo-Salas
R E
RE
Schatz
C A
CA
Guarguaglini
G
G
Kast
J
J
Wilm
M
M
Le Bot
N
N
Vernos
I
I
Karsenti
E
E
Mattaj
I W
IW
D000818:Animals; D018797:Cell Cycle Proteins; D002843:Chromatin / Q000378:metabolism; D003001:Cloning, Molecular; D005260:Female; D020558:GTP Phosphohydrolases / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D015870:Gene Expression / Q000502:physiology; D006367:HeLa Cells; D006801:Humans; D028884:Karyopherins; D008869:Microtubule-Associated Proteins / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D008870:Microtubules / Q000378:metabolism; D008938:Mitosis / Q000502:physiology*; D009363:Neoplasm Proteins; D009687:Nuclear Proteins / Q000378:metabolism*; D009865:Oocytes / Q000166:cytology / Q000378:metabolism; D010750:Phosphoproteins; D008941:Spindle Apparatus / Q000378:metabolism*; D029867:Xenopus Proteins; D014982:Xenopus laevis; D020931:ran GTP-Binding Protein / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*
D018797:Cell Cycle Proteins; D002843:Chromatin; D028884:Karyopherins; D008869:Microtubule-Associated Proteins; D009363:Neoplasm Proteins; D009687:Nuclear Proteins; D010750:Phosphoproteins; C486551:TPX2 protein, Xenopus; C122167:TPX2 protein, human; D029867:Xenopus Proteins; D020558:GTP Phosphohydrolases; D020931:ran GTP-Binding Protein