Xenopus importin beta validates human importin beta as a cell cycle negative regulator

Delmar, Valerie A.; Chan, Rene C.; Forbes, Douglass J.

doi:10.1186/1471-2121-9-14

Cited by 13 publications

(34 citation statements)

References 89 publications

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“…These data imply that the recruitment of certain nucleoporins is regulated by transportin and importin beta (through direct or indirect interactions), but that the recruitment of other Nups is not. When tested, RanGTP reversed the binding of transportin to key Nup subunits (Figures 3, A and B, and 6), consistent with the model that RanGTP promotes pore assembly by releasing nucleoporins from karyopherin sequestration (Harel et al, 2003a;Hetzer et al, 2005;Antonin et al, 2008;Delmar et al, 2008;Lim et al, 2008).We provide evidence for the first time that both transportin and importin beta can negatively regulate the earliest known step in the initiation of pore assembly, the recruitment to chromatin of the pore-targeting protein ELYS/ MEL-28 (Figures 4 and 5). We further find that transportin and importin beta can bind directly to the extreme C-terminus of ELYS in a chromatin-binding region that contains an NLS-like region, but not the ELYS AT-hook ( Figure 6A, CBD2).…”

supporting

confidence: 79%

“…Mitotic Xenopus egg extracts can successfully recapitulate spindle assembly (see below). Similarly, interphase egg extracts have provided a powerful way to observe and manipulate nuclear assembly (Lohka and Masui, 1984;Newport, 1987;Smythe and Newport, 1991;Powers et al, 1995;Ullman and Forbes, 1995;Macaulay and Forbes, 1996;Goldberg et al, 1997;Hetzer et al, 2001; Harel et al, 2003a,b; Walther et al, 2003a,b;Chan and Forbes, 2006;Clarke and Zhang, 2008;Delmar et al, 2008). For nuclear assembly, fractionated Xenopus egg cytosol is combined with Xenopus egg membranes, sperm chromatin, and an energy-regenerating system.…”

Section: Introductionmentioning

confidence: 99%

“…This inhibition of fusion can be counteracted by the inclusion of increased RanGTP (Harel et al, 2003a;Walther et al, 2003b;. If excess importin beta is added to membrane-Molecular Biology of the Cell 4044 enclosed nuclear intermediates, it separately blocks nuclear pore assembly (Harel et al, 2003a;Walther et al, 2003b;Delmar et al, 2008). RanGTP reverses the inhibition of nuclear pore assembly, but only when untagged importin beta is used as the negative regulator .…”

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confidence: 99%

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Transportin Regulates Major Mitotic Assembly Events: From Spindle to Nuclear Pore Assembly

Lau

Delmar

Chan

et al. 2009

MBoC

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Mitosis in higher eukaryotes is marked by the sequential assembly of two massive structures: the mitotic spindle and the nucleus. Nuclear assembly itself requires the precise formation of both nuclear membranes and nuclear pore complexes. Previously, importin alpha/beta and RanGTP were shown to act as dueling regulators to ensure that these assembly processes occur only in the vicinity of the mitotic chromosomes. We now find that the distantly related karyopherin, transportin, negatively regulates nuclear envelope fusion and nuclear pore assembly in Xenopus egg extracts. We show that transportin-and importin beta-initiate their regulation as early as the first known step of nuclear pore assembly: recruitment of the critical pore-targeting nucleoporin ELYS/MEL-28 to chromatin. Indeed, each karyopherin can interact directly with ELYS. We further define the nucleoporin subunit targets for transportin and importin beta and find them to be largely the same: ELYS, the Nup107/160 complex, Nup53, and the FG nucleoporins. Equally importantly, we find that transportin negatively regulates mitotic spindle assembly. These negative regulatory events are counteracted by RanGTP. We conclude that the interplay of the two negative regulators, transportin and importin beta, along with the positive regulator RanGTP, allows precise choreography of multiple cell cycle assembly events. INTRODUCTIONDuring mitosis, the intracellular architecture of the higher eukaryotic cell undergoes constant and dramatic change. The chromosomes condense, the nuclear envelope breaks down, a mitotic spindle forms and separates the chromosomes, and finally a nuclear envelope is reassembled around each set of daughter chromosomes. The movement of the cell cycle from one stage of mitosis to the next involves the coordinated action of multiple kinases and phosphatases. Recently, however, new regulators have been identified that contribute not to the timing but to the spatial control of assembly of both the mitotic spindle and the nucleus: karyopherins and RanGTP.Karyopherins are most well known for their function in interphase as the transport receptors for nuclear import and export (reviewed in Tran and Wente, 2006;Stewart, 2007). Nuclear proteins larger than ϳ20 -40 kDa are actively imported, whereas snRNAs, tRNAs, and other cargoes are exported through the nuclear pores by karyopherins.Karyopherins consist of a large family of importins (import receptors) and exportins (export receptors; reviewed in Weis, 2003;Pemberton and Paschal, 2005). The first and most studied import receptor of the karyopherin family was importin beta (Adam and Adam, 1994;Chi et al., 1995;Gorlich et al., 1995;Imamoto et al., 1995;Radu et al., 1995;Floer et al., 1997). Importin beta mediates the nuclear import of many proteins through the use of a specific adaptor, such as importin alpha (reviewed in Cook et al., 2007). Importin alpha recognizes cargoes containing classical or bipartite nuclear localization signals (NLSs), which are composed largely of basic amino acids (reviewed ...

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confidence: 79%

Section: Introductionmentioning

confidence: 99%

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confidence: 99%

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Transportin Regulates Major Mitotic Assembly Events: From Spindle to Nuclear Pore Assembly

Lau

Delmar

Chan

et al. 2009

MBoC

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“…Importin-b, a component of nuclear protein import, is associated with the nuclear pore complexes (NPCs; Stewart, 2007;Villányi et al, 2008). Besides the regular faint spots, which denote the NPCs, a few bright speckles -most likely annulate lamellae (Delmar et al, 2008;Lau et al, 2009) -appear in the nuclear envelope (Fig. 1A).…”

Section: Resultsmentioning

confidence: 99%

‘Poking’ microtubules bring about nuclear wriggling to position nuclei

Szikora

Gáspár

Szabad

2013

Journal of Cell Science

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SummaryNuclei wriggle in the cells of the follicle epithelium of the Drosophila pre-vitellogenic egg primordia. Although similar phenomena have been reported for a number of cultured cell types and some neurons in the zebrafish embryo, the mechanism and importance of the process have remained unexplained. Wriggling involves successive sudden and random minor turns of the nuclei, approximately three twists per minute with roughly 12˚per twist, one of which lasts typically for 14 seconds. Wriggling is generated by the growing microtubules seeded throughout the cell cortex, which, while poking the nuclei, buckle and exert 5-40 piconewtons over ,16 seconds. While wriggling, the nuclei drift ,5 mm in a day in the immensely growing follicle cells along the apical-basal axis from the apical to the basal cell region. A .2-fold excess of the microtubules nucleated in the apical cell region, as compared with those seeded in the basal cell cortex, makes the nuclei drift along the apical-basal axis. Nuclear wriggling and positioning appear to be tightly related processes: they cease simultaneously when the nuclei become anchored by the actin cytoskeleton; moreover, colchicine or taxol treatment eliminates both nuclear wriggling and positioning. We propose that the wriggling nuclei reveal a thus far undescribed nuclear positioning mechanism.

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“…Importin-β, a component of nuclear protein import, is associated with the nuclear pore complexes (NPCs; Stewart 2007;Villanyi et al 2008). Besides the regular faint spots, which denote the NPCs, a few bright speckles -most likely annulate lamellae (Delmar et al, 2008;Lau et al, 2009) -appear in the nuclear envelope (Fig. 2).…”

Section: Importin-β-gfp Speckles Wriggle In the Nuclear Envelope Of Tmentioning

confidence: 99%

‘Poking’ microtubules bring about nuclear wriggling to position nuclei

Szikora¹,

Gáspár²,

Szabad³

2013

Development

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Xenopus importin beta validates human importin beta as a cell cycle negative regulator

Cited by 13 publications

References 89 publications

Transportin Regulates Major Mitotic Assembly Events: From Spindle to Nuclear Pore Assembly

Transportin Regulates Major Mitotic Assembly Events: From Spindle to Nuclear Pore Assembly

‘Poking’ microtubules bring about nuclear wriggling to position nuclei

‘Poking’ microtubules bring about nuclear wriggling to position nuclei

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