The mechanism of endoplasmic reticulum (ER) morphogenesis is incompletely understood. ER tubules are shaped by the reticulons (RTNs) and DP1/Yop1p family members, but the mechanism of ER sheet formation is much less clear. Here, we characterize TMEM170A, a human transmembrane protein, which localizes in ER and nuclear envelope membranes.
View Article and Find Full Text PDFThe GTP-bound form of the Ran GTPase (RanGTP), produced around chromosomes, drives nuclear envelope and nuclear pore complex (NPC) re-assembly after mitosis. The nucleoporin MEL-28/ELYS binds chromatin in a RanGTP-regulated manner and acts to seed NPC assembly. Here we show that, upon mitotic NPC disassembly, MEL-28 dissociates from chromatin and re-localizes to spindle microtubules and kinetochores.
View Article and Find Full Text PDFBackground: Production of the GTP-bound form of the Ran GTPase (RanGTP) around chromosomes induces spindle assembly by activating nuclear localization signal (NLS)-containing proteins. Several NLS proteins have been identified as spindle assembly factors, but the complexity of the process led us to search for additional proteins with distinct roles in spindle assembly.
Results: We identify a chromatin-remodeling ATPase, CHD4, as a RanGTP-dependent microtubule (MT)-associated protein (MAP).
The division of cellular space into functionally distinct membrane-defined compartments has been one of the major transitions in the history of life. Such compartmentalization has been claimed to occur in members of the Planctomycetes, Verrucomicrobiae, and Chlamydiae bacterial superphylum. Here we have investigated the three-dimensional organization of the complex endomembrane system in the planctomycete bacteria Gemmata obscuriglobus.
View Article and Find Full Text PDFDisassembly of the nuclear lamina is a key step during open mitosis in higher eukaryotes. The activity of several kinases, including CDK1 (cyclin-dependent kinase 1) and protein kinase C (PKC), has been shown to trigger mitotic lamin disassembly, yet their precise contributions are unclear. In this study, we develop a quantitative imaging assay to study mitotic lamin B1 disassembly in living cells.
View Article and Find Full Text PDFMitosis in metazoa requires nuclear envelope (NE) disassembly and reassembly. NE disassembly is driven by multiple phosphorylation events. Mitotic phosphorylation of the protein BAF reduces its affinity for chromatin and the LEM family of inner nuclear membrane proteins; loss of this BAF-mediated chromatin-NE link contributes to NE disassembly.
View Article and Find Full Text PDFThe position of the nucleus is regulated in different developmental stages and cellular events. During polarization, the nucleus moves away from the future leading edge and this movement is required for proper cell migration. Nuclear movement requires the LINC complex components nesprin-2G and SUN2, which form transmembrane actin-associated nuclear (TAN) lines at the nuclear envelope.
View Article and Find Full Text PDFRanGTP mediates nuclear import and mitotic spindle assembly by dissociating import receptors from nuclear localization signal (NLS) bearing proteins. We investigated the interplay between import receptors and the transmembrane nucleoporin Pom121. We found that Pom121 interacts with importin alpha/beta and a group of nucleoporins in an NLS-dependent manner.
View Article and Find Full Text PDFThe development of the endomembrane system was a major step in eukaryotic evolution. Membrane coats, which exhibit a unique arrangement of beta-propeller and alpha-helical repeat domains, play key roles in shaping eukaryotic membranes. Such proteins are likely to have been present in the ancestral eukaryote but cannot be detected in prokaryotes using sequence-only searches.
View Article and Find Full Text PDFProduction of RanGTP around chromosomes induces spindle assembly by activating nuclear localization signal (NLS)-containing factors. Here, we show that the NLS protein ISWI, a known chromatin-remodeling ATPase, is a RanGTP-dependent microtubule (MT)-associated protein. Recombinant ISWI induces MT nucleation, stabilization, and bundling in vitro.
View Article and Find Full Text PDFThe human Nup107-160 nucleoporin complex plays a major role in formation of the nuclear pore complex and is localized to kinetochores in mitosis. Here we report that Seh1, a component of the Nup107-160 complex, functions in chromosome alignment and segregation by regulating the centromeric localization of Aurora B and other chromosome passenger complex proteins. Localization of CENP-E is not affected by Seh1 depletion and analysis by electron microscopy showed that microtubule kinetochore attachments are intact.
View Article and Find Full Text PDFThe nuclear envelope (NE) is a double lipid bilayer that separates nucleus and cytoplasm. In metazoa, NE breakdown (NEBD) occurs during prophase and NE reformation around segregated chromatids occurs at anaphase-telophase. We identified Caenorhabditis elegans Lipin homologue (called Lpin-1) as an essential factor with roles in endoplasmic reticulum (ER) organization and NEBD.
View Article and Find Full Text PDFThe production of RanGTP around chromosomes is crucial for spindle microtubule assembly in mitosis. Previous work has shown that hepatoma up-regulated protein (HURP) is a Ran target, required for microtubule stabilization and spindle organization. Here we report a detailed analysis of HURP function in Xenopus laevis mitotic egg extracts.
View Article and Find Full Text PDFProduction of Ran-guanosine triphosphate (GTP) around chromosomes induces local nucleation and plus end stabilization of microtubules (MTs). The nuclear protein TPX2 is required for RanGTP-dependent MT nucleation. To find the MT stabilizer, we affinity purify nuclear localization signal (NLS)-containing proteins from Xenopus laevis egg extracts.
View Article and Find Full Text PDFTransport across the nuclear envelope (NE) is mediated by nuclear pore complexes (NPCs). These structures are composed of various subcomplexes of proteins that are each present in multiple copies and together establish the eightfold symmetry of the NPC. One evolutionarily conserved subcomplex of the NPC contains the nucleoporins Nup53 and Nup155.
View Article and Find Full Text PDFPHAX (phosphorylated adaptor for RNA export) is the key regulator of U snRNA nuclear export in metazoa. Our previous work revealed that PHAX is phosphorylated in the nucleus and is exported as a component of the U snRNA export complex to the cytoplasm, where it is dephosphorylated (M. Ohno, A.
View Article and Find Full Text PDFPrecursor (pre)-mRNA splicing can impact the efficiency of coupled steps in gene expression. SRm160 (SR-related nuclear matrix protein of 160 kDa), is a splicing coactivator that also functions as a 3'-end cleavage-stimulatory factor. Here, we have identified an evolutionary-conserved SRm160-interacting protein, referred to as hRED120 (for human Arg/Glu/Asp-rich protein of 120 kDa).
View Article and Find Full Text PDFThe nuclear envelope (NE) of the eukaryotic cell provides an essential barrier that separates the nuclear compartment from the cytoplasm. In addition, the NE is involved in essential functions such as nuclear stability, regulation of gene expression, centrosome separation and nuclear migration and positioning. In metazoa the NE breaks down and re-assembles around the segregated chromatids during each cell division.
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