Inner/Outer Nuclear Membrane Fusion in Nuclear Pore Assembly

Fichtman, Boris; Ramos, Corinne; Rasala, Beth A.; Harel, Amnon; Forbes, Douglass J.

doi:10.1091/mbc.e10-04-0309

Cited by 42 publications

(36 citation statements)

References 137 publications

(186 reference statements)

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“…9 Several groups recently reported the importance of Pom121 for the recruitment of the Nup107-160 complex into new assembly sites of NPC on closed nuclear envelopes. [11][12][13] These observations agree closely with live-cell imaging of NPC formation. 14 Downregulation of Pom121 by Cdkinhibition could be a reason to suppress of Nup107 or Nup133 that was fluorescently labeled and how much excess YFPNup107 or Nup133-YFP was expressed are also critical issues, because they have important implications in the interpretation of the data.…”

Section: Novel Approaches For Investigating Nuclear Growth and Npc Fosupporting

confidence: 82%

Nuclear size, nuclear pore number and cell cycle

Maeshima

Iino

Hihara

et al. 2011

Nucleus

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In eukaryotic cells, the nucleus is a complex and sophisticated organelle containing genomic DNA and supports essential cellular activities. Its surface contains many nuclear pore complexes (NPCs), channels for macromolecular transport between the cytoplasm and nucleus. It has been observed that the nuclear volume and the number of NPCs almost doubles during interphase in dividing cells, but the coordination of these events with the cell cycle was poorly understood, particularly in mammalian cells. Recently, we demonstrated that cyclin-dependent protein kinases (Cdks) control interphase NPC formation in dividing human cells. Cdks drive the very early step of NPC formation because Cdk inhibition suppressed the generation of "nascent pores," which are considered to be immature NPCs, and disturbed expression and localization of some nucleoporins. Cdk inhibition did not affect nuclear volume, suggesting that these two processes have distinct regulatory mechanisms in the cell cycle. The details of our experimental systems and finding are discussed in more depth. With new findings recently reported, we also discuss possible molecular mechanisms of interphase NPC formation.

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Section: Novel Approaches For Investigating Nuclear Growth and Npc Fosupporting

confidence: 82%

Nuclear size, nuclear pore number and cell cycle

Maeshima

Iino

Hihara

et al. 2011

Nucleus

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“…9B). The interaction of POM121 with Nup160 (Mitchell et al, 2010), is likely to represent a subsequent step in the assembly process, which might be required to induce fusion of the inner and outer nuclear membrane and the formation of an initial pore channel (Fichtman et al, 2010).…”

Section: Discussionmentioning

confidence: 99%

“…In addition, these membrane nucleoporins have been suggested to play specific roles in NPC assembly, such as recruiting soluble Nups to the initial assembly sites and triggering fusion of the inner and outer nuclear membrane (Antonin et al, 2005;Drummond and Wilson, 2002;Fichtman et al, 2010;Macaulay and Forbes, 1996;Mitchell et al, 2010;Stavru et al, 2006b). A persistent problem has been the lack of overall phylogenetic conservation in sequence and topology of the integral membrane Nups.…”

Section: Introductionmentioning

confidence: 99%

A dominant-negative form of POM121 binds chromatin and disrupts the two separate modes of nuclear pore assembly

Shaulov

Gruber

Cohen

et al. 2011

Journal of Cell Science

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SummaryNuclear pore complexes (NPCs) are formed during two separate stages of the metazoan cell cycle. They are assembled into the reforming nuclear envelope (NE) at the exit from mitosis and into an intact, expanding NE during interphase. Here, we show that a soluble internal fragment of the membrane nucleoporin POM121 has a dominant-negative effect on both modes of assembly in a cell-free reconstitution system. The soluble POM121 fragment binds chromatin at sites that are distinct from ELYS-Nup107-160 'seeding' sites and prevents membrane enclosure and NPC formation. Importin-b negatively regulates chromatin binding by the POM121 fragment through a conserved NLS motif and is also shown to affect the recruitment of the endogenous membrane protein to chromatin in the full assembly system. When an intact NE is present before the addition of the dominant-negative fragment, NPCs are inserted into the NE but membrane expansion is inhibited. This results in densely packed NPCs with no intervening membrane patches, as visualized by scanning electron microscopy. We conclude that POM121 plays an important role in both modes of assembly and links nuclear membrane formation and expansion to nuclear pore biogenesis.

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“…Along with NE disassembly in mitosis, NPCs depolymerize into nucleoporins and disperse into the cytoplasm. At the end of mitosis, NE reforms around each of the two segregated daughter chromosome masses, and NPCs reassemble either on the chromatin as NE forms or NPC inserts into the NE [2][3][4]. The mechanism for NE assembly is still poorly understood, but can be studied in vitro using Xenopus egg extracts as well as in intact cells.…”

Section: Introductionmentioning

confidence: 99%

Chromatin-bound NLS proteins recruit membrane vesicles and nucleoporins for nuclear envelope assembly via importin-α/β

Liu

et al. 2012

Cell Res

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The mechanism for nuclear envelope (NE) assembly is not fully understood. Importin-β and the small GTPase Ran have been implicated in the spatial regulation of NE assembly process. Here we report that chromatin-bound NLS (nuclear localization sequence) proteins provide docking sites for the NE precursor membrane vesicles and nucleoporins via importin-α and -β during NE assembly in Xenopus egg extracts. We show that along with the fast recruitment of the abundant NLS proteins such as nucleoplasmin and histones to the demembranated sperm chromatin in the extracts, importin-α binds the chromatin NLS proteins rapidly. Meanwhile, importin-β binds cytoplasmic NE precursor membrane vesicles and nucleoporins. Through interacting with importin-α on the chromatin NLS proteins, importin-β targets the membrane vesicles and nucleoporins to the chromatin surface. Once encountering Ran-GTP on the chromatin generated by RCC1, importin-β preferentially binds Ran-GTP and releases the membrane vesicles and nucleoporins for NE assembly. NE assembly is disrupted by blocking the interaction between importin-α and NLS proteins with excess soluble NLS proteins or by depletion of importin-β from the extract. Our findings reveal a novel molecular mechanism for NE assembly in Xenopus egg extracts.

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Inner/Outer Nuclear Membrane Fusion in Nuclear Pore Assembly

Cited by 42 publications

References 137 publications

Nuclear size, nuclear pore number and cell cycle

Nuclear size, nuclear pore number and cell cycle

A dominant-negative form of POM121 binds chromatin and disrupts the two separate modes of nuclear pore assembly

Chromatin-bound NLS proteins recruit membrane vesicles and nucleoporins for nuclear envelope assembly via importin-α/β

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