Nuclear reformation after mitosis requires downregulation of the Ran GTPase effector RanBP1 in mammalian cells
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The GTPase Ran regulates nucleocytoplasmic transport in interphase and spindle organisation in mitosis via effectors of the importin beta superfamily. Ran-binding protein 1 (RanBP1) regulates guanine nucleotide turnover on Ran, as well as its interactions with effectors. Unlike other Ran network members that are steadily expressed, RanBP1 abundance is modulated during the mammalian cell cycle, peaking in mitosis and declining at mitotic exit. Here, we show that RanBP1 downregulation takes place in mid to late telophase, concomitant with the reformation of nuclei. Mild RanBP1 overexpression in murine cells causes RanBP1 to persist in late mitosis and hinders a set of events underlying the telophase to interphase transition, including chromatin decondensation, nuclear expansion and nuclear lamina reorganisation. Moreover, the reorganisation of nuclear pores fails associated with defective nuclear relocalisation of NLS cargoes. Co-expression of importin beta, together with RanBP1, however mitigates these defects. Thus, RanBP1 downregulation is required for nuclear reorganisation pathways operated by importin beta after mitosis.
KeywordsNuclear Envelope NIH3T3 Cell Ethylene Glycol Tetraacetic Acid Ethylene Glycol Tetraacetic Acid Mitotic Exit
We are extremely grateful to Antonio Tedeschi (IMP, Vienna) for contributing to early stages of this work and to Giulia Guarguaglini (IBPM, Rome) for insightful comments on this manuscript. This work was supported by MIUR - Italian Ministry of University and Research (FIRB grant RBIN04T7MT and PRIN grant 200879X9N9-004), Associazione Italiana per la Ricerca sul Cancro (AIRC) and by funds from Assicurazioni Generali and Fondazione Roma Terzo Settore.
In vivo recording of an NIH3T3 cell co-transfected with H2B-GFP and RanBP1-RFP. Images were taken every 2 min for 3 h (IF images every 30 min), and the movie runs at four frames per second (MOV 397 kb)
In vivo recording of stable L929-centrin1-GFP cells transfected with RanBP1-RFP. Images were taken every 10 min for 36 h (IF images after 6 h, thereafter every 12 h), and the movie runs at seven frames per second. Note that the RanBP1-transfected cell (red) divides once and does not divide again for the remainder of the recording time. (MOV 885 kb)
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