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Juan Ausió - One of the best experts on this subject based on the ideXlab platform.
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Basic surface features of nuclear FKBPs facilitate chromatin binding.
Scientific Reports, 2017Co-Authors: Andrew Leung, Geoff Gudavicius, Cameron D Mackereth, Francy-pesek Jardim, Neda Savic, Yoan Monneau, Rodrigo González-romero, Jose M Eirin-lopez, Till Bartke, Juan AusióAbstract:The Nucleoplasmin family of histone chaperones is identified by a pentamer-forming domain and multiple acidic tracts that mediate histone binding and chaperone activity. Within this family, a novel domain organization was recently discovered that consists of an N-terminal Nucleoplasmin-like (NPL) domain and a C-terminal FKBP peptidyl-proline isomerase domain. Saccharomyces cerevisiae Fpr4 is one such protein. Here we report that in addition to its known histone prolyl isomerase activities, the Fpr4 FKBP domain binds to nucleosomes and nucleosome arrays in vitro. This ability is mediated by a collection of basic patches that enable the enzyme to stably associate with linker DNA. The interaction of the Fpr4 FKBP with recombinant chromatin complexes condenses nucleosome arrays independently of its catalytic activity. Based on phylogenetic comparisons we propose that the chromatin binding ability of 'basic' FKBPs is shared amongst related orthologues present in fungi, plants, and insects. Thus, a subclass of FKBP prolyl isomerase enzymes is recruited to linker regions of chromatin.
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expression and purification of the full murine npm2 and study of its interaction with protamines and histones
Biochemistry and biophysics reports, 2016Co-Authors: Katherine Ellard, Jason J Serpa, Evgeniy V Petrotchenko, Christoph H Borchers, Juan AusióAbstract:Mouse Nucleoplasmin M.NPM2 was recombinantly expressed and the protein consisting of the complete sequence was purified and characterized. Similar to its Xenopus laevis X.NPM2 counterpart, the protein forms stable pentameric complexes and exhibits an almost undistinguishable hydrodynamic ionic strength-dependent unfolding behavior. The interaction of N.PM2 with histones and mouse P1/P2 protamines revealed that these chromosomal proteins bind preferentially to the distal part of the Nucleoplasmin pentamer. Moreover, the present work highlights the critical role played by histones H2B and H4 in the association of the histone H2A-H2B dimers and histone octamer with Nucleoplasmin.
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new insights into the nucleophosmin Nucleoplasmin family of nuclear chaperones
BioEssays, 2007Co-Authors: Lindsay J Frehlick, Jose M Eirinlopez, Juan AusióAbstract:Basic proteins and nucleic acids are assembled into complexes in a reaction that must be facilitated by nuclear chaperones in order to prevent protein aggregation and formation of non-specific nucleoprotein complexes. The nucleophosmin/Nucleoplasmin (NPM) family of chaperones [NPM1 (nucleophosmin), NPM2 (Nucleoplasmin) and NPM3] have diverse functions in the cell and are ubiquitously represented throughout the animal kingdom. The importance of this family in cellular processes such as chromatin remodeling, genome stability, ribosome biogenesis, DNA duplication and transcriptional regulation has led to the rapid growth of information available on their structure and function. The present review covers different aspects related to the structure, evolution and function of the NPM family. Emphasis is placed on the long-term evolutionary mechanisms leading to the functional diversification of the family members, their role as chaperones (particularly as it pertains to their ability to aid in the reprogramming of chromatin), and the importance of NPM2 as an essential component of the amphibian chromatin remodeling machinery during fertilization and early embryonic development. BioEssays 29: 49–59, 2007. © 2006 Wiley Periodicals, Inc.
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Nucleoplasmin mediated unfolding of chromatin involves the displacement of linker associated chromatin proteins
Biochemistry, 2005Co-Authors: Isbaal Ramos, Adelina Prado, Ron M Finn, And Arturo Muga, Juan AusióAbstract:We have previously characterized the interaction of Nucleoplasmin with core histones and studied the possible involvement of this chaperone molecule in transcription. Here we study the interaction of Nucleoplasmin with chromatin. We show that highly phosphorylated Xenopus laevis egg Nucleoplasmin can unfold sperm and somatic chromatin in a way that involves the removal of chromosomal proteins from linker DNA regions without a stable interaction with the nucleosome. The complexes between egg Nucleoplasmin and both somatic and sperm-specific linker proteins have been hydrodynamically characterized using sedimentation equilibrium in the analytical ultracentrifuge. The results are discussed within the context of the possible implication of Nucleoplasmin in processes such as transcription and replication licensing which take place after egg fertilization at the onset of development.
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analysis of the stability and function of Nucleoplasmin through cysteine mutants
Archives of Biochemistry and Biophysics, 2005Co-Authors: Carme Arnan, Juan A. Subirana, Manel Chiva, Juan Ausió, Celia Prieto, Lara Salvany, Núria SaperasAbstract:Xenopus laevis Nucleoplasmin is a pentameric nuclear chaperone. The relation between the structure and the multifunctional aspects of the molecule has not yet been clearly established. In the course of analysing a C-terminally His-tagged recombinant version of the region equivalent to the trypsin resistant core (r-NP142) of the molecule, we found that this domain exhibited a substantially decreased oligomerization potential. To better understand the role of the three cysteines of Nucleoplasmin on its pentameric functional structure, we have selectively mutated these residues to serine and generated three mutants (C15S, C35S, and C45S) both for the complete recombinant Nucleoplasmin (r-NP) and the truncated r-NP142 non-tagged forms. We demonstrate that there are no disulphide bridges stabilizing either the monomer or the pentamer. Neither C15S nor C35S has any structural effects, while the mutation C45S abolishes the ability of r-NP142 to pentamerize. This structural impairment suggests that hydrophobic interactions of Cys 45 are critical for the stability of the protein. Our studies allow to analyse for the first time the structural and functional properties of Nucleoplasmin in its monomeric form.
Chiaki Katagiri - One of the best experts on this subject based on the ideXlab platform.
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physicochemical and functional comparison of xenopus laevis Nucleoplasmin obtained from oocytes and from overexpression in bacteria
Archives of Biochemistry and Biophysics, 1999Co-Authors: Núria Saperas, Juan A. Subirana, Manel Chiva, Rosa Aligue, Chiaki Katagiri, Toru Itoh, Juan AusióAbstract:We compare the physicochemical and functional characteristics of Nucleoplasmin obtained from Xenopus laevis oocytes and by bacterial overexpression of a plasmid containing the Nucleoplasmin gene. The comparison shows that, while the secondary structure of the protein is not affected by the method used to obtain this protein, the bacterial expressed form exhibits a marked tendency to form large aggregates and an impaired ability to displace protamines from sperm nuclei. These results add a word of caution to the indiscriminate use, in functional or structural (crystallographic) studies, of bacterially overproduced proteins that have been end-terminally tagged with polyhistidine.
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the histone binding protein Nucleoplasmin does not facilitate binding of transcription factor iiia to nucleosomal xenopus laevis 5s rrna genes
Biochemistry, 1998Co-Authors: Leann Howe, Toru Itoh, Chiaki Katagiri, Juan AusióAbstract:In an attempt to understand the mechanism by which transcription factors compete with histone octamers for cognate binding sites in chromatin, the effect of the histone binding protein Nucleoplasmin on the binding of TFIIIA to nucleosomal 5S rRNA genes was tested. In this study, it was shown that, despite the previously reported nucleosome remodeling ability of Nucleoplasmin, the binding of TFIIIA to nucleosomal DNA cannot be facilitated by this protein. Furthermore, it was demonstrated that Nucleoplasmin cannot overcome nucleosome mediated repression of transcription of reconstituted 5S rRNA genes. In contrast to earlier work, this study used a homologous system composed of the 5S rRNA gene, Nucleoplasmin, and TFIIIA from Xenopus laevis.
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conformation of Nucleoplasmin and its interaction with dna protamine complex as a simple model of fish sperm nuclei
International Journal of Biological Macromolecules, 1997Co-Authors: Kazumichi Iwata, Chiaki Katagiri, Kentaro Hozumi, Nobuo Sakairi, Toru Itoh, Seiichi Tokura, Norio NishiAbstract:Nucleoplasmin was isolated from Xenopus laevis eggs and purified by an improved method using an open column. Its conformation was investigated spectrophotometrically by UV, CD and fluorescence. It was shown that alpha-helix content of Nucleoplasmin was 30-40%, and one of the two tryptophan residues in Nucleoplasmin located in the hydrophobic surroundings and the other in the relatively hydrophilic surroundings. The isolated Nucleoplasmin was found to decondense sperm nuclei of salmon also, suggesting a possibility of the existence of Nucleoplasmin-like protein in fish as well. Collapse of the protamine (salmine)-DNA complex as a simple model for fish sperm nuclei by Nucleoplasmin was directly observed by measuring OD320 of aqueous protamine-DNA mixtures. This is a molecular level observation for the removal of protamine from DNA-protamine complex.
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Nucleoplasmin mediated decondensation of mytilus sperm chromatin identification and partial characterization of a Nucleoplasmin like protein with sperm nuclei decondensing activity in mytilus californianus
Biochemistry, 1995Co-Authors: Philip Rice, Toru Itoh, Chiaki Katagiri, Rafael A Garduno, Juan AusióAbstract:We have been able to induce sperm nuclear decondensation in the mussel Mytilus californianus (mollusc) using either egg extracts or pure Nucleoplasmin from Xenopus (amphibian). The nuclear decondensation involves removal of the sperm nuclear basic proteins (SNBPs) which bind to Nucleoplasmin. An attempt has been made to isolate an ooplasmic factor from Mytilus with a similar sperm-chromatin decondensing activity. An acidic, thermostable protein with a molecular mass of 58,000 has been purified and partially characterized.
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dependence of removal of sperm specific proteins from xenopus sperm nuclei on the phosphorylation state of Nucleoplasmin
Development Growth & Differentiation, 1995Co-Authors: Keita Ohsumi, Arata Shimada, Eiichi Okumura, Takeo Kishimoto, Chiaki KatagiriAbstract:In Xenopus laevis, Nucleoplasmin from fully grown oocytes is not highly phosphorylated, but is more extensively phosphorylated during oocyte maturation to retain this state until mid-blastula transition. Incubation of demembranated sperm with Nucleoplasmin from oocytes or mature eggs revealed that egg Nucleoplasmin is twice as potent as oocyte Nucleoplasmin in removing sperm-specific basic proteins from chromatin (protamine-removing activity: PRA). Dephosphorylation of egg Nucleoplasmin by alkaline phosphatase induced a remarkable decline of PRA in Nucleoplasmin. Treatment of oocyte Nucleoplasmin with cdc2 protein kinase induced an increase of the extent of phosphorylation, but to a level lower than that exhibited by egg Nucleoplasmin, suggesting the involvement of other unspecified kinase(s) in phosphorylating Nucleoplasmin during oocyte maturation. Incubation of sperm with cdc2 kinase induced selective phosphorylation of sperm-specific basic proteins, accompanied by their enhanced removal from sperm chromatin upon exposure to high-salt solutions. These results suggest that removal of sperm-specific basic proteins from sperm chromatin in fertilized eggs is facilitated by phosphorylation of both Nucleoplasmin and sperm-specific basic proteins.
David Shechter - One of the best experts on this subject based on the ideXlab platform.
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Dynamic intramolecular regulation of the histone chaperone Nucleoplasmin controls histone binding and release
Nature Publishing Group, 2017Co-Authors: Christopher Warren, Tsutomu Matsui, Jerome M. Karp, Takashi Onikubo, Sean Cahill, Michael Brenowitz, David Cowburn, Mark Girvin, David ShechterAbstract:The histone chaperone Nucleoplasmin (Npm) stores histones H2A/H2B in the egg and embryo. Here, the authors use NMR to show that Npm’s intrinsically disordered tail domain controls histone binding at an acidic stretch, which is autoregulated through direct competition with its basic C-terminus
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Protein Arginine Methyltransferase Prmt5-Mep50 Methylates Histones H2A and H4 and the Histone Chaperone
2016Co-Authors: David ShechterAbstract:Results: A complex of Prmt5 and Mep50 methylates histones H2A and H4 and the histone chaperone Nucleoplasmin on an arginine in a conserved motif. Conclusion: Arginine methylation is enriched in the egg and targets chromatin-acting proteins. Significance: Histone arginine methylation probably results in specification of the pluripotent developmental program. Histone proteins carry information contained in post-trans-lational modifications. Eukaryotic cells utilize this histone code to regulate the usage of the underlying DNA. In the maturing oocytes and eggs of the frogXenopus laevis, histones are synthe-sized in bulk in preparation for deposition during the rapid early developmental cell cycles. During this key developmental time frame, embryonic pluripotent chromatin is established. In the egg, non-chromatin-bound histones are complexed with stor-age chaperone proteins, including Nucleoplasmin. Here we describe the identification and characterization of a complex of the protein arginine methyltransferase 5 (Prmt5) and th
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developmental regulation of Nucleoplasmin function by phosphorylation glutamylation and methylation
Epigenetics & Chromatin, 2013Co-Authors: Takashi Onikubo, Jeffrey Shabanowitz, Donald F Hunt, Joshua J Nicklav, Weilin Wang, David ShechterAbstract:Nucleoplasms (Npm) is an abundant storage chaperone for histones H2A and H2B in the oocyte, egg and early embryo of Xenopus laevis. Regulation of Nucleoplasmin histone binding and release is critical to its developmental function in establishing zygotic chromatin. To test the function of Nucleoplasmin post-translational modifications in regulation of its function, we determined its full complement of PTMs, characterized their dynamic changes during development, and tested their role in modulating plasmid supercoiling. Here we present the full mass spectrometric analysis of Nucleoplasmin from two oogenic states: the non-activated, oocyte form, and the activated, egg form. We characterize the changes in phosphorylation that occur upon oocyte maturation and also show that nucleoplasms is differentially polyglutamylated between the two states. Specifically, we show an increase in phosphorylation of nucleoplasms from a majority of two within oocytes to a majority of six within eggs. This hyperphosphorylation occurs upon germinal vesicle breakdown induced by progesterone treatment. We demonstrate dynamic post-translational addition of up to five glutamyl groups (glutamylation) to residues within the second acidic stretch of nucleoplasms. Glutamylation is an isopeptide addition of a glutamic acid to the g-carboxyl of a primary chain glutamate residue. We also identify a highly-abundant, C-terminal arginine methylation on arginine 187 within the “GRGR” motif that we previously demonstrated to be catalyzed by the arginine methyltransferase complex PRMT5-MEP50. Npm hyperphosphorylation is present from egg-laying until the mid-blastula transition, concomitant with the period of transcriptional repression, while arginine methylation and glutamylation persist through gastrulation. Finally, we demonstrate that Nucleoplasms phosphorylation negatively regulates its ability to promote supercoiling, indicative of altered histone release. We conclude that developmentally dynamic changes in Nucleoplasms phosphorylation modulate its histone binding and release.
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protein arginine methyltransferase prmt5 mep50 methylates histones h2a and h4 and the histone chaperone Nucleoplasmin in xenopus laevis eggs
Journal of Biological Chemistry, 2011Co-Authors: Carola Wilczek, Raghu K Chitta, Eileen Woo, Jeffrey Shabanowitz, Brian T Chait, Donald F Hunt, David ShechterAbstract:Histone proteins carry information contained in post-translational modifications. Eukaryotic cells utilize this histone code to regulate the usage of the underlying DNA. In the maturing oocytes and eggs of the frog Xenopus laevis, histones are synthesized in bulk in preparation for deposition during the rapid early developmental cell cycles. During this key developmental time frame, embryonic pluripotent chromatin is established. In the egg, non-chromatin-bound histones are complexed with storage chaperone proteins, including Nucleoplasmin. Here we describe the identification and characterization of a complex of the protein arginine methyltransferase 5 (Prmt5) and the methylosome protein 50 (Mep50) isolated from Xenopus eggs that specifically methylates predeposition histones H2A/H2A.X-F and H4 and the histone chaperone Nucleoplasmin on a conserved motif (GRGXK). We demonstrate that Nucleoplasmin (Npm), an exceedingly abundant maternally deposited protein, is a potent substrate for Prmt5-Mep50 and is monomethylated and symmetrically dimethylated at Arg-187. Furthermore, Npm modulates Prmt5-Mep50 activity directed toward histones, consistent with a regulatory role for Npm in vivo. We show that H2A and Nucleoplasmin methylation appears late in oogenesis and is most abundant in the laid egg. We hypothesize that these very abundant arginine methylations are constrained to pre-mid blastula transition events in the embryo and therefore may be involved in the global transcriptional repression found in this developmental time frame.
Toru Itoh - One of the best experts on this subject based on the ideXlab platform.
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physicochemical and functional comparison of xenopus laevis Nucleoplasmin obtained from oocytes and from overexpression in bacteria
Archives of Biochemistry and Biophysics, 1999Co-Authors: Núria Saperas, Juan A. Subirana, Manel Chiva, Rosa Aligue, Chiaki Katagiri, Toru Itoh, Juan AusióAbstract:We compare the physicochemical and functional characteristics of Nucleoplasmin obtained from Xenopus laevis oocytes and by bacterial overexpression of a plasmid containing the Nucleoplasmin gene. The comparison shows that, while the secondary structure of the protein is not affected by the method used to obtain this protein, the bacterial expressed form exhibits a marked tendency to form large aggregates and an impaired ability to displace protamines from sperm nuclei. These results add a word of caution to the indiscriminate use, in functional or structural (crystallographic) studies, of bacterially overproduced proteins that have been end-terminally tagged with polyhistidine.
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the histone binding protein Nucleoplasmin does not facilitate binding of transcription factor iiia to nucleosomal xenopus laevis 5s rrna genes
Biochemistry, 1998Co-Authors: Leann Howe, Toru Itoh, Chiaki Katagiri, Juan AusióAbstract:In an attempt to understand the mechanism by which transcription factors compete with histone octamers for cognate binding sites in chromatin, the effect of the histone binding protein Nucleoplasmin on the binding of TFIIIA to nucleosomal 5S rRNA genes was tested. In this study, it was shown that, despite the previously reported nucleosome remodeling ability of Nucleoplasmin, the binding of TFIIIA to nucleosomal DNA cannot be facilitated by this protein. Furthermore, it was demonstrated that Nucleoplasmin cannot overcome nucleosome mediated repression of transcription of reconstituted 5S rRNA genes. In contrast to earlier work, this study used a homologous system composed of the 5S rRNA gene, Nucleoplasmin, and TFIIIA from Xenopus laevis.
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conformation of Nucleoplasmin and its interaction with dna protamine complex as a simple model of fish sperm nuclei
International Journal of Biological Macromolecules, 1997Co-Authors: Kazumichi Iwata, Chiaki Katagiri, Kentaro Hozumi, Nobuo Sakairi, Toru Itoh, Seiichi Tokura, Norio NishiAbstract:Nucleoplasmin was isolated from Xenopus laevis eggs and purified by an improved method using an open column. Its conformation was investigated spectrophotometrically by UV, CD and fluorescence. It was shown that alpha-helix content of Nucleoplasmin was 30-40%, and one of the two tryptophan residues in Nucleoplasmin located in the hydrophobic surroundings and the other in the relatively hydrophilic surroundings. The isolated Nucleoplasmin was found to decondense sperm nuclei of salmon also, suggesting a possibility of the existence of Nucleoplasmin-like protein in fish as well. Collapse of the protamine (salmine)-DNA complex as a simple model for fish sperm nuclei by Nucleoplasmin was directly observed by measuring OD320 of aqueous protamine-DNA mixtures. This is a molecular level observation for the removal of protamine from DNA-protamine complex.
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Nucleoplasmin mediated decondensation of mytilus sperm chromatin identification and partial characterization of a Nucleoplasmin like protein with sperm nuclei decondensing activity in mytilus californianus
Biochemistry, 1995Co-Authors: Philip Rice, Toru Itoh, Chiaki Katagiri, Rafael A Garduno, Juan AusióAbstract:We have been able to induce sperm nuclear decondensation in the mussel Mytilus californianus (mollusc) using either egg extracts or pure Nucleoplasmin from Xenopus (amphibian). The nuclear decondensation involves removal of the sperm nuclear basic proteins (SNBPs) which bind to Nucleoplasmin. An attempt has been made to isolate an ooplasmic factor from Mytilus with a similar sperm-chromatin decondensing activity. An acidic, thermostable protein with a molecular mass of 58,000 has been purified and partially characterized.
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remodeling of human sperm chromatin mediated by Nucleoplasmin from amphibian eggs human sperm chromatin remodeling protamine removal Nucleoplasmin
Development Growth & Differentiation, 1993Co-Authors: Toru Itoh, Keita Ohsumi, Chiaki KatagiriAbstract:The molecular events associated with decondensation of human sperm nuclei were analyzed by incubating sperm with egg extracts from an amphibian, Bufo japonicus. Acid-urea-Triton polyacrylamide gel electrophoresis (AUT-PAGE) showed that the nuclear basic proteins of human sperm consist mainly of protamines (HPI, HPII) with minor amounts of nucleosomal histones. On incubation of lysolecithin (LC)- and dithiothreitol (DTT)-treated human sperm with the egg extract, the nuclei lost HPI and HPII within 15 min in association with extensive nuclear decondensation, and the acquirement of a whole set of nucleosomal histones. Incubation of LC-DTT-sperm with Nucleoplasmin purified from Bufo eggs also induced nuclear decondensation and loss of protamines within 30 min. Native-PAGE and Western blot analyses of incubation medium indicated tight association of the released protamines to Nucleoplasmin, strongly suggesting that protamines are removed from sperm nuclei not enzymatically but by their specific binding to Nucleoplasmin. On incubation of LC-DTT-sperm with Nucleoplasmin and exogenous nucleosomal core histones, micrococcal nuclease-protected DNA fragments were released, although their unit repeat length was slightly less than that of somatic nucleosomes. Thus remodeling of human sperm during fertilization can be mimicked under defined conditions with Nucleoplasmin and exogenous histones.
Gregory H. Leno - One of the best experts on this subject based on the ideXlab platform.
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Hyperphosphorylation of Nucleoplasmin Facilitates Xenopus Sperm Decondensation at Fertilization
The Journal of biological chemistry, 1996Co-Authors: Gregory H. Leno, A.d. Mills, Anna Philpott, Ronald A. LaskeyAbstract:Previous studies showed that the nuclear phosphoprotein Nucleoplasmin performs the first stage of chromatin decondensation of Xenopus sperm at fertilization. It binds and removes sperm basic proteins replacing them with histones. We now show that this activity depends upon the massive hyperphosphorylation of Nucleoplasmin that occurs when oocytes mature into eggs. Egg extracts or purified hyperphosphorylated egg Nucleoplasmin decondense sperm chromatin and remove sperm basic proteins much faster than oocyte extracts or hypophosphorylated oocyte Nucleoplasmin. Furthermore, dephosphorylation of egg Nucleoplasmin slows sperm decondensation and prevents basic protein removal from sperm chromatin. We conclude that hyperphosphorylation of Nucleoplasmin is used to modulate the rapid changes in chromatin structure that accompany early development in Xenopus.
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the role of Nucleoplasmin in chromatin assembly and disassembly
Philosophical Transactions of the Royal Society B, 1993Co-Authors: Ronald A. Laskey, Stephen M Dilworth, Anthony D Mills, Gregory H. Leno, Anna Philpott, Colin DingwallAbstract:Nucleoplasmin is the most abundant nuclear protein in Xenopus oocytes and eggs. The term ‘molecular chaperone’ was coined to describe its role in the assembly of the nucleosome subunits of chromatin. Although histones and DNA can self-assemble into nucleosomes, Nucleoplasmin can facilitate this process in vitro by competing against non-specific charge interactions. In vivo Nucleoplasmin binds histones H2A and H2B and transfers them to DNA. Another acidic nuclear protein, N1, binds and transfers histones H3 and H4. Nucleoplasmin has at least one other role in modulating chromatin structure in Xenopus eggs. It is required for the first stage of sperm chromatin decondensation. It binds and removes sperm basic proteins and replaces them by histones H2A and H2B, again forming nucleosomes, and resulting in decondensation of the compacted sperm chromatin. In addition we propose that the properties of the nuclear localization signal of Nucleoplasmin can be explained by a model in which heat shock cognate protein hsc70 has a chaperone role in signal presentation during nuclear transport.
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Nucleoplasmin remodels sperm chromatin in Xenopus egg extracts
Cell, 1992Co-Authors: Anna Philpott, Gregory H. LenoAbstract:Nucleoplasmin is necessary and sufficient for the initial stage of Xenopus sperm decondensation in egg extracts. In this article we show that sperm decondensation is accompanied by loss of two sperm-specific basic proteins (X and Y) and gain of histones H2A and H2B, resulting in nucleosome formation. Purified Nucleoplasmin alone removes X and Y and assembles purified H2A and H2B on decondensing sperm chromatin, forming nucleosome cores. Immunodepletion of Nucleoplasmin from extract prevents removal of X and Y and addition of H2A and H2B, while adding back Nucleoplasmin restores decondensation and X and Y removal. Thus, Nucleoplasmin acts as both an assembly and a disassembly factor for remodeling sperm chromatin at fertilization.
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sperm decondensation in xenopus egg cytoplasm is mediated by Nucleoplasmin
Cell, 1991Co-Authors: Anna Philpott, Gregory H. Leno, Ronald A. LaskeyAbstract:At fertilization, sperm chromatin decondenses in two stages, which can be mimicked in extracts of Xenopus eggs. Rapid, limited decondensation is followed by slower, membrane-dependent decondensation and swelling. Nucleoplasmin, an acidic nuclear protein, occurs at high concentration in Xenopus eggs and has a histone-binding role in nucleosome assembly. Immunodepleting Nucleoplasmin from egg extracts inhibits the initial rapid stage of sperm decondensation, and also the decondensation of myeloma nuclei, relative to controls of mock depletion and TFIIIA depletion. Readdition of purified Nucleoplasmin recues depleted extracts. A physiological concentration of purified Nucleoplasmin alone decondenses both sperm and myeloma nuclei. We conclude that Nucleoplasmin is both necessary and sufficient for the first stage of sperm decondensation in Xenopus eggs.
