| 1. |
- Bergqvist, Cecilia, 1986-
(författare)
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The role of nuclear envelope proteins in chromatin organization, differentiation and disease
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In eukaryotes the genetic material is separated from the cytoplasm by the nuclear envelope (NE), consisting of the outer and inner nuclear membrane, the nuclear lamina and the nuclear pores. The genetic material is highly structured with transcriptionally inactive heterochromatin enriched at the nuclear periphery and transcriptionally active euchromatin in the nuclear interior. Underlying the inner nuclear membrane is the nuclear lamina (nucleoskeleton) that together with several hundred nuclear envelope transmembrane proteins (NETs) connect chromatin to the nuclear periphery. Most NETs are uncharacterized and expressed in a tissue-specific manner. Mutations in NE proteins are linked to distinct degenerative disorders, referred to as envelopathies or laminopathies. The NET primarily studied in this thesis is called Spindle-Associated Membrane Protein 1 (Samp1). We showed that overexpression of Samp1 induced a fast differentiation of human induced pluripotent stem cells and that the binding between two NETs, Samp1 and Emerin, is regulated by RanGTP. Another focus of this thesis was the development and use of a novel method called Fluorescent Ratiometric Imaging of Chromatin (FRIC). FRIC quantitatively monitors the epigenetic state of chromatin in live cells. Using FRIC, we were able to show that Samp1 promotes peripheral heterochromatin organization. FRIC also detected an increased distribution of heterochromatin at the nuclear periphery during neuronal differentiation. In conclusion, FRIC is a useful tool that could serve medical research in elucidating the effects of different chemical agents and the roles of NE proteins in chromatin organization.
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| 2. |
- Bergqvist, Cecilia
(författare)
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The role of nuclear membrane proteins in differentiation and chromatin organization
- 2016
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The nuclear envelope, consisting of an outer and an inner nuclear membrane, surrounds the genomic material. The genomic material (chromatin) is highly structured with (transcriptionally inactive) heterochromatin mostly found in the nuclear periphery and (transcriptionally active) euchromatin mostly found in the nuclear interior. Underlying the nuclear envelope is the nuclear lamina that consists of lamin proteins and nuclear envelope transmembrane proteins (NETs), which organize chromatin in the nuclear periphery. There are several hundred uncharacterized tissue-specific NETs, with only a few linked to cellular differentiation. Induced pluripotent stem cells (iPSCs) enable studies of early differentiation and are a promising tool for cell replacement therapies.In this licentiate thesis, we have focused on investigating the role of the inner nuclear membrane protein Samp1 in chromatin organization and cell differentiation. Overexpression of Samp1 induced a fast differentiation of iPSCs, suggesting that Samp1 may be involved in the differentiation process. We have also developed a novel image analysis method to be able to monitor chromatin organization in live cells. Depletion of Samp1 affected chromatin distribution and resulted in increased formation of peripheral heterochromatin, contradictory to what is expected of other characterized NETs. It is possible that Samp1 might have a role in both differentiation and chromatin organization and that future studies might link these two processes together.
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| 3. |
- Buch, Charlotta
(författare)
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Dynamic protein trafficking of the nuclear membrane and in peroxisomes
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The cell nucleus is enclosed by the nuclear envelope (NE), a double lipid membrane separating the nucleoplasm from the cytoplasm. Transport of macromolecules between the nucleus and the cytoplasm takes places through nuclear pore complexes (NPCs) in a selective and energy dependent manner. The inner nuclear membrane (INM) contains transmembrane proteins that interact with the nuclear lamina and chromatin. In addition to being a barrier between the nucleoplasm and cytoplasm, an emerging view is that the NE has an active role in chromatin organization and gene regulation.In order to study structural and functional organization of the NE in live cells, we have used green fluorescent protein (GFP)-labeled proteins and laser scanning confocal microscopy (LSCM). In order to investigate dynamic properties of specific proteins or protein complexes we have used photobleaching techniques. In order to understand the organization of the NPC it is essential to study components necessary for NPC biogenesis and maintenance. We have investigated the possible alterations in the NPC in cells naturally lacking one of the integral membrane proteins of the NPC, gp210. Despite the lack of gp210, we observed no difference in distribution or density of pores. Neither did cell cycle progression nor generation time differ between cells having or lacking gp210. In addition, targeting or dynamic properties of the NPC proteins POM121, Nup107 or Nup153 were unaltered in the absence of gp210. We conclude that gp210 can not be essential for NPC biogenesis or maintaining stability of the NPC.The steps involved in onset of nuclear apoptosis are unclear. We studied nuclear alterations during apoptosis. We show that the nucleocytoplasmic barrier is disrupted early in apoptosis at the same time as chromatin collapses against the nuclear periphery but prior to nucleosomal DNA fragmentation. In addition, the disruption of nucleocytoplasmic transport correlates with caspase-3 dependent cleavage of POM121 at aspartate-531.The INM is estimated to contain ~70 uncharacterized transmembrane proteins. We characterized a novel putative mammalian NE protein that we termed Samp1. We show that Samp1 is an integral membrane protein specifically localized to the inner nuclear membrane during interphase. Interestingly, during mitosis a sub fraction of Samp1 distributed in the polar region of the mitotic spindle, colocalizing with tubulin and a lipid marker. However, another inner nuclear membrane protein, emerin, was excluded from this area. Thus Samp1 appears to define a specific membrane domain associated with the mitotic machinery.The distribution of peroxisomal fatty acid metabolizing enzymes have been reported to vary in different tissues. We investigated whether photobleaching techniques could be used to study the distribution of peroxisomal matrix proteins. We used GFP-labeled peroxisomal proteins and fluorescence recovery after photobleaching to show that peroxisomal matrix proteins become “trapped” inside peroxisomes after import. Thus we conclude that fluorescence loss in photobleaching can be used to distinguish between a strictly cytoplasmic localization and a dual localization when a protein is present both in the cytoplasm and in peroxisomes. Using this technique we determined that GFP-BAAT (bile acid-CoA:amino acid N-acyltransferase) is exclusively localized to the cytoplasm in HeLa cells.
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| 4. |
- Figueroa, Ricardo A., 1979-
(författare)
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The functional organization of nuclear membrane proteins and development of new technology for studies of cell signaling
- 2011
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The eukaryotic cell is defined by the nucleus, which is delimited by a double membrane structure termed the nuclear envelope (NE). The NE is implicated in a multitude of different processes, for example chromatin organization. During mitosis in higher eukaryotes the nucleus is disassembled to allow the formation of the mitotic spindle, which segregates the duplicated chromosomes between daughter cells. We have characterized a novel transmembrane protein of the inner nuclear membrane. Because of its distribution along spindle microtubule during mitosis, we termed the protein Samp1 (Spindle associated membrane protein 1). Samp1 is the founding member of transmembrane proteins that define a novel membrane domain that we have termed the SE (spindle endomembrane). Furthermore, we have shown that in interphase Samp1 specifically interacts with the centrosome and A-type lamina network proteins. Moreover, Samp1 contains an evolutionary highly conserved N-terminal tail containing two putative zinc fingers. Recent studies indicate local caspase activity in dendrites or axons during development and in neurodegenerative disorders. Here I present the development of a novel and unique system to monitor protease activity at sub-cellular resolution in live cells. This system relies on a cleavable FRET sensor that is anchored to the cytoskeleton. Using this system we demonstrate local caspase activation of the soma in neuronaly differentiated cells. We also used the anchored FRET sensors to monitor caspase activation after treatment with the Alzheimer’s decease related amyloid-β peptide. Moreover we have improved a NF-ĸB decoy delivery system. The system consists of a cell penetrating peptide, transportan-10, covalently linked to a peptide nucleic acid sequence that hybridizes with a nonanucleotide sequence in the decoy. We show that this system effectively delivered the decoy and inhibited an inflammatory response in primary rat glial cells.
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| 5. |
- Jaffer Ali, Mohammed Hakim, 1986-
(författare)
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Multifaceted roles of the transmembrane nuclear envelope protein, Samp1
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The eukaryotic nuclear envelope (NE), separates the nucleoplasm from cytoplasm and is made up of two concentric lipid membranes, the outer and the inner nuclear membranes (ONM and INM), the nuclear pore complexes (NPCs) and an underlying filamentous nuclear lamina. The INM contains hundreds of unique transmembrane proteins of which only a handful have been characterized. In this thesis, I aimed to understand the functional organization of proteins in the nuclear envelope and I focused on investigating the functions of a recently identified INM transmembrane protein, Samp1. We have developed a novel and robust approach, MCLIP, to identify specific protein-protein interactions taking place in live cells. Using MCLIP, we have shown that Samp1 interacts with proteins of the LINC complex, the nuclear lamina and components of the mitotic spindle. Samp1's specific interactions with a variety of binding partners, suggest that Samp1 plays important roles both in interphase and in mitosis. We have also shown that Samp1 can provide a binding site at the INM for the GTPase Ran, a master regulator of protein interactions in interphase and in mitosis. Furthermore, we have also investigated the role of Samp1 in cell differentiation using two independent model systems. In human iPSCs, ectopic expression of Samp1 promoted differentiation despite pluripotent culture conditions. In C2C12 myoblast, depletion of Samp1 completely blocked differentiation into myotubes. The two studies complement each other and suggest that Samp1 has a strong differentiation promoting activity. Taken together, the findings in this thesis, give insights on the unexpected and unforeseen roles played by a transmembrane protein in different fundamental cellular process.
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| 6. |
- Jaffer Ali, Mohammed Hakim
(författare)
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Nuclear envelope protein interaction studies
- 2014
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The nuclear envelope (NE) separating the nucleoplasm from cytoplasm consists of two concentric lipid membranes, the outer (ONM) and inner (INM) nuclear membranes, the nuclear pore complexes (NPCs) and an underlying nuclear lamina network. The INM contains more than 100 unique transmembrane proteins of which only a few have been characterized. This thesis is focused on one of these INM proteins, Samp1 (Spindle associated membrane protein 1)Protein-protein interactions in the NE have been difficult to study due to the resistance of NE proteins to extraction. We have established a reversible in vivo crosslinking immunoprecipitation method called, MCLIP (Membrane protein Cross-Link ImmunoPrecipitation) to overcome this problem. Using MCLIP we were able to show that, Samp1 specifically interacts with Emerin, Lamin B1, Sun1 and the small GTPase Ran. We also showed that, the nucleoplasmic domain of Samp1 and Emerin can interact with each other directly.Furthermore, we investigated the functional role of Samp1 in mitosis. Samp1 depletion gave rise to aneuploid phenotypes and signs of destabilization of the mitotic spindle. Using MCLIP, in mitotic cells, we showed that, Samp1 interacts with Ran and Importin-β, two key players of mitotic spindle assembly. We observed that, Samp1 modulates the level of Importin-β and NuMA in the mitotic spindle, which may explain the mitotic defects and aberrant phenotypes observed in Samp1 depleted cells. These findings show that Samp1 plays an important role in spindle stabilization and chromosome segregation.
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| 7. |
- Larsson, Veronica J., 1980-
(författare)
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Characterization of the inner nuclear membrane protein Samp1, during interphase and mitosis
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The nucleus, a hallmark in eukaryotic cells, contains the genome separating it from molecules in the cytoplasm. The nucleus is surrounded by a nuclear envelope consisting of two concentric membranes, the outer nuclear membrane and the inner nuclear membrane, the nuclear lamina and nuclear pore complexes. The cytoskeleton is physically connected with the nucleoskeleton by the LINC complexes, spanning the nuclear envelope. In this way, the cell surface is linked directly to chromatin. There are hundreds of unique inner nuclear membrane proteins, but today we only know the functions of a handful. The best characterized inner nuclear membrane proteins are involved in chromatin organization and gene regulation.This thesis focuses on Samp1, an integral membrane protein that localizes to the inner nuclear membrane during interphase. During mitosis, a fraction localizes to the mitotic spindle, which is responsible for accurate segregation of chromosomes.It is difficult to investigate inner nuclear membrane protein-protein interactions, because transmembrane proteins are often associated with the “hard-to-solubilize” nuclear lamina. MCLIP was developed as a method to detect interactions between proteins of the nuclear envelope in live cells. MCLIP has been valuable in identifying interaction partners of Samp1. In interphase, Samp1 distributes in distinct micro-domains of the inner nuclear membrane and interacts with the nuclear lamina, emerin and the LINC complex protein SUN1, suggesting that Samp1 might have a functional role associated with both the nucleoskeleton and cytoskeleton.In mitosis Samp1 distributes in filamentous membrane structures partially overlapping with kinetochore microtubules of the mitotic spindle. Samp1 binds directly to γ-tubulin and recruits γ-tubulin and Haus6 to the mitotic spindle and thus contributes to spindle assembly. Samp1 also interacts with Aurora B, a kinase important for k-fiber error correction at the kinetochores. Depletion of Samp1 caused an increased activation and distribution of Aurora B at the metaphase plate, decreased formation of stable k-fibers, metaphase prolongation and increased chromosome mis-segregation. Samp1 is the first transmembrane protein found to be involved in mitotic spindle assembly and stability, important for correct segregation of chromosomes.
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| 8. |
- Larsson, Veronica J.
(författare)
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The roles of inner nuclear membrane proteins during interphase and mitosis
- 2014
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The nuclear envelope (NE) consists of two concentric membranes, the outer nuclear membrane (ONM) and the inner nuclear membrane (INM). The LINC (linker of nucleoskeleton and cytoskeleton) complex spans both the ONM and the INM connecting the cytoskeleton to the nucleoskeleton and chromatin. Only a few of the known INM proteins have been functionally characterized and shown to have important roles in chromatin organisation. Defects in the genes coding for proteins in the INM and the nuclear lamina give rise to serious human diseases, called envelopathies.In 2009 (Buch et al. 2009) our group made two major discoveries. We showed for the first time, that an integral INM protein distributed along the microtubules of the mitotic spindle. This protein was therefore named Samp1, Spindle Associated Membrane Protein 1. The second discovery was that depletion of Samp1 caused detachment of the centrosome from the NE, suggesting that Samp1 is associated with the microtubule cytoskeleton both in interphase and mitosis.In this thesis we continued to investigate Samp1´s role during interphase. We also wanted to investigate the localisation of Samp1 in the mitotic spindle and possible function during mitosis. We show that the expression of Samp1 mutants and depletion of Samp1 affects the distribution and organisation of A-type lamins, the LINC complex protein Sun1 and the LINC complex associated protein emerin. Thus, in interphase Samp1 is functionally connected to the LINC complex and the A-type lamina network. The LINC complex can help explain how the centrosomes detach from the NE in Samp1 depleted cells. In mitotic cells, we found that depletion of Samp1 caused prolonged metaphase and aberrant mitotic phenotypes such as bi-nucleation, enlarged nuclei and micronuclei. We also showed that Samp1 interacts with RanGTPase and importin-β, which are key players in assembling the mitotic spindle. Samp1 also modulates the levels of importin-β and NuMA in the mitotic spindle, which could explain the mitotic phenotypes that we se in Samp1 depleted cells. Here we present evidence showing, for the first time, that an INM protein is present on kinetochore microtubules and have an essential role for correct chromosome segregation and spindle assembly.
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| 9. |
- Niss, Frida, 1991-
(författare)
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Imaging the molecular pathways of neurodegeneration : New pathologies of SCA7
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Spinocerebellar Ataxia type 7 (SCA7) is a genetic neurodegenerative disease with lethal outcome that affects the cerebellum and retina of patients. This thesis focuses on characterising molecular pathological pathways that cause toxicity and cell death in SCA7. Using primarily an inducible cell model and patient fibroblasts I found that the three RNA binding proteins FUS, TDP-43 and TIA1 are co-sequestered into aggregates formed by the SCA7 causing protein, ATXN7. Consequently I investigated the cellular functions in which these proteins have important roles. I found that FUS’ ability to regulate mRNAs is altered due to mislocalisation, DNA damage is increased, and that stress granules (SGs) are induced in a SCA7 cell model and in patient fibroblasts. Surprisingly, I also found that ATXN7 was present within SGs, and that SGs exhibited an altered shape upon induction of mutant ATXN7. I also participated in developing a microscopy-based method for monitoring chromatin organisation in live cells called FRIC. FRIC is able to detect even subtle changes to peripheral chromatin organisation, and since ATXN7 is a subunit of the transcription regulational complex SAGA, we used FRIC to investigate the effect of mutant ATXN7 on peripheral chromatin organisation. While we found no evidence that mutant ATXN7 affected peripheral chromatin organisation, the inner nuclear membrane protein Samp1 was found to be important for normal chromatin organisation in the nuclear periphery. Finally, I characterised the effect of mutant ATXN7 expression on the nuclear lamina, nuclear pore complexes, and nucleocytoplasmic transport. I found that although key transport factors such as Ran and Importin ß intermittently co-localised with ATXN7 aggregates, there were no apparent defects in nucleocytoplasmic protein import or nuclear envelope integrity. In summation, my investigations resulted in new findings that may be built upon to find key targets for treating SCA7 patients.
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| 10. |
- Onischenko, Evgeny A.
(författare)
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Disassembly and reassembly of the nuclear pore complex
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The nuclear pore complexes (NPCs) are multiprotein communicative channels spanning the nuclear envelope. In higher eukaryotes NPCs reversibly disassemble during mitosis into distinct nucleoporin subcomplexes. Some cell types (e.g. oocytes and early embryonic cells) also contain mimics of NPCs of unknown function, which are located in cytoplasmic membranes. They are termed annulate lamellae pore complexes (ALPC). This study was aimed at understanding the process of mitotic disassembly and reassembly of the NPC and at elucidating the function of ALPCs. Using syncytial Drosophila embryos as a model we have tested the proposed function of ALPCs as a storage compartment for nucleoporins fueling assembly of new NPCs in rapidly proliferating cells. Surprisingly, we found that ALPCs are not depleted during assembly of new NPCs and that they represent only a minor fraction of the total embryonic nucleoporins while the major fraction is persistently soluble. We conclude that in Drosophila, ALPCs play only a minor role as a storage compartment for nucleoporins. We developed a novel in vivo model system based on syncytial Drosophila embryos to study mitotic disassembly/reassembly of the NPC. We found that the major mitotic kinase Cdk1 is the key regulator of both NPC and ALPC disassembly/reassembly in vivo and that Cdk1 activity is able to phosphorylate and solubilize nucleoporins in vitro. We also found that phosphatase activity, sensitive to okadaic acid (OA), is required for reassembly of both NPCs and ALPCs in vivo. Additionally, we showed that the Ran GTPase system, that drives active nucleocytoplasmic transport during intephase, is selectively required for post-mitotic reassembly of NPCs but not ALPCs in vivo. Our findings suggest that in live cells NPC assembly is regulated by a dynamic equilibrium between kinase (Cdk1) and phospahatase (sensitive to OA) activity and that it is spatially coordinated by the Ran GTPase system. Finally. using the nucleoporin gp210 as a model. we have tested a role of mitotic phosphorylation of nucleoporins in disassembly of the NPC. We present evidence that a single mitotic phosphorylation of gp210 weakens its binding to the NPC and interferes with its postmitotic recruitment to the newly formed NE. These findings represent the first direct evidence that mitotic nucleoporin phosphorylation functions in disassembly of the NPC.
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| 11. |
- Rustum, Cecilia, 1974-
(författare)
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Dynamic aspects of nucleocytoplasmic trafficking
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Cellular structures and compartmentalization is the result of a dynamic steady state exchange between its components. This thesis is focused in investigations of dynamic properties of green fluorescent protein (GFP)-labeled proteins in live cells using confocal laser microscopy in combination with bleaching techniques such as fluorescence recovery after photobleaching (FRAP) and fluorescence loss in photobleaching (FLIP).Studies of dynamic properties of c-Myc in living cells showed that c-Myc is shuttling between the nucleus and the cytoplasm. c-Myc also enters the nucleoli during certain conditions. Nucleolar c-Myc is dynamically associated to structural component(s) of nucleoli, but can exchange with soluble pools in the nucleoplasm and cytoplasm.Photobleaching experiments showed that a significant fraction of HIV-1 Vpr is dynamically associated with the NE and rapidly exchanges between the nucleoplasm and the cytoplasm. The yeast two-hybrid system, pull-down experiments and co-immunoprecipitating was used to show that Vpr interacts specifically and directly with a domain in the N-terminal portion of the NPC protein hCG1. The results suggest that the specific interaction of HIV-1 Vpr with the nucleoporin hCG1 results in the dynamic retention of Vpr at the nuclear envelope.The distribution and dynamic properties of NPC proteins was investigated in NIH/3T3 cells, lacking the pore membrane protein gp210. Confocal laser scanning microscopy and FRAP experiments showed that the absence of gp210 from nuclear pores of NIH/3T3 cells did neither alter the distribution nor dynamic properties of POM121 and NUP107 (two NPC proteins stably integrated in the NPC).Degradation of the integral nuclear pore membrane protein POM121 during apoptosis was investigated in relation to other apoptotic events. POM121 cleavage, which is the earliest sign of dismantling of the nuclear membrane, is due to caspase-3-dependent cleavage at aspartate-531. Loss of nuclear compartmentalization in live cells undergoing apoptosis was monitored as appearance of GFP-NLS in the cytoplasm. The time of appearance of cytoplasmic GFP-NLS correlated with caspase-3-dependent cleavage of POM121. Both events occured concomitantly with collapsing of chromatin against the nuclear periphery, but preceded the onset of nucleosomal DNA fragmentation.Translocation ability of the cell-penetrating peptide, transportan, into living cells was investigated. Recombinantly expressed GFP was purified and conjugated to chemically synthesized transportan via a disulfide bond and added to tissues culture cells. Transportan was able to internalize a 27 kDa protein such as GFP in a native folded state into living cells.
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| 12. |
- Vijayaraghavan, Balaje
(författare)
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Identification and characterization of nuclear envelope protein interactions
- 2015
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The Nuclear envelope which surrounds the chromatin of eukaryotic cells contains more than a hundred transmembrane proteins. Mutations in some genes encoding nuclear envelope proteins give rise to human diseases including neurological disorders. The function of many nuclear envelope proteins is not well established. This is partly because nuclear envelope proteins and their interactions are difficult to study due to the inherent resistance to extraction of nuclear envelope proteins. We have developed a novel method called MCLIP, to identify interacting partners of nuclear envelope proteins in live cells. Using MCLIP, we found three new binding partners of the inner nuclear membrane protein Samp1: the intermediate filament protein Lamin B1, the LINC complex protein Sun1 and the G-protein Ran. Furthermore, using in vitro studies, we show that Samp1 binds both Emerin and Ran directly. We have also studied the interaction between Samp1 and Ran in detail.
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| 13. |
- Vijayaraghavan, Balaje, 1987-
(författare)
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Identification and characterization of protein-protein interactions in the nuclear envelope
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The nuclear envelope forms the interface between the nucleus and the cytoplasm. The nuclear envelope consists of the two concentric lipid membranes, the nuclear pores and the nuclear lamina. The inner nuclear membrane contains hundreds of unique transmembrane proteins showing high tissue diversity. Mutations of some proteins in the nuclear envelope give rise to a broad spectrum of diseases called envelopathies or laminopathies. In this thesis, I aimed to study the functional organization of the nuclear envelope by identifying and characterizing interactions between the nuclear envelope proteins. For this, we developed a novel method called the Membrane Protein Crosslink Immuno-Precipitation, which enable identification of protein-protein interactions in the nuclear envelope in live cells. We identified several novel interactions of the inner nuclear membrane protein, Samp1, and studied the interaction between the Samp1 and the nuclear GTPase, Ran in detail. Samp1 can bind to Ran and is thus the first known transmembrane Ran binding protein and Samp1 might provide a local binding site for Ran in the inner nuclear membrane. We found that Samp1 also binds to the inner nuclear membrane protein, Emerin and Ran can regulate the Samp1-Emerin interaction in the nuclear envelope. During mitosis, Samp1 distributes in the mitotic spindle. Therefore, we investigated a possible functional role of Samp1 in the mitotic machinery. Samp1 depletion resulted in aneuploid phenotypes, metaphase prolongation and decreased distribution of γ-tubulin and β-tubulin in the mitotic spindle. We found that Samp1 can bind to γ-tubulin, which is essential for the microtubule nucleation and hence for the spindle stability. The new interesting features of Samp1 provide insights on the unforeseen functions of the nuclear envelope proteins.
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| 14. |
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| 15. |
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