1
|
Wu J, Wang P, Li L, You C, Wang Y. Cytotoxic and mutagenic properties of minor-groove O2-alkylthymidine lesions in human cells. J Biol Chem 2018; 293:8638-8644. [PMID: 29685891 DOI: 10.1074/jbc.ra118.003133] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2018] [Revised: 04/11/2018] [Indexed: 12/17/2022] Open
Abstract
Endogenous metabolism, environmental exposure, and cancer chemotherapy can lead to alkylation of DNA. It has been well documented that, among the different DNA alkylation products, minor-groove O2-alkylthymidine (O2-alkyldT) lesions are inefficiently repaired. In the present study, we examined how seven O2-alkyldT lesions, with the alkyl group being a Me, Et, nPr, iPr, nBu, iBu, or sBu, are recognized by the DNA replication machinery in human cells. We found that the replication bypass efficiencies of these lesions decrease with increasing length of the alkyl chain, and that these lesions induce substantial frequencies of T→A and T→G mutations. Replication experiments using isogenic cells deficient in specific translesion synthesis (TLS) DNA polymerases revealed that the absence of polymerase η or polymerase ζ, but not polymerase κ or polymerase ι, significantly decreased both the bypass efficiencies and the mutation frequencies for those O2-alkyldT lesions carrying a straight-chain alkyl group. Moreover, the mutagenic properties of the O2-alkyldT lesions were influenced by the length and topology of the alkyl chain and by TLS polymerases. Together, our results provide important new knowledge about the cytotoxic and mutagenic properties of O2-alkyldT lesions, and illustrate the roles of TLS polymerases in replicative bypass of these lesions in human cells.
Collapse
Affiliation(s)
- Jun Wu
- From the Department of Chemistry and
| | - Pengcheng Wang
- Environmental Toxicology Graduate Program, University of California, Riverside, California 92521-0403
| | - Lin Li
- From the Department of Chemistry and
| | | | - Yinsheng Wang
- From the Department of Chemistry and .,Environmental Toxicology Graduate Program, University of California, Riverside, California 92521-0403
| |
Collapse
|
2
|
Raspelli E, Falbo L, Costanzo V. Xenopus egg extract to study regulation of genome-wide and locus-specific DNA replication. Genesis 2017; 55. [PMID: 28095613 DOI: 10.1002/dvg.22996] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2016] [Revised: 11/10/2016] [Accepted: 11/10/2016] [Indexed: 11/10/2022]
Abstract
Faithful DNA replication, coupled with accurate repair of DNA damage, is essential to maintain genome stability and relies on different DNA metabolism genes. Many of these genes are involved in the assembly of replication origins, in the coordination of DNA repair to protect replication forks progression in the presence of DNA damage and in the replication of repetitive chromatin regions. Some DNA metabolism genes are essential in higher eukaryotes, suggesting the existence of specialized mechanisms of repair and replication in organisms with complex genomes. The impact on cell survival of many of these genes has so far precluded in depth molecular analysis of their function. The cell-free Xenopus laevis egg extract represents an ideal system to overcome survival issues and to facilitate the biochemical study of replication-associated functions of essential proteins in vertebrate organisms. Here, we will discuss how Xenopus egg extracts have been used to study cellular and molecular processes, such as DNA replication and DNA repair. In particular, we will focus on innovative imaging and proteomic-based experimental approaches to characterize the molecular function of a number of essential DNA metabolism factors involved in the duplication of complex vertebrate genomes.
Collapse
Affiliation(s)
- Erica Raspelli
- DNA metabolism laboratory, IFOM, The FIRC institute for Molecular Oncology, Milan, Italy
| | - Lucia Falbo
- DNA metabolism laboratory, IFOM, The FIRC institute for Molecular Oncology, Milan, Italy
| | - Vincenzo Costanzo
- DNA metabolism laboratory, IFOM, The FIRC institute for Molecular Oncology, Milan, Italy
| |
Collapse
|
3
|
Dai X, You C, Wang Y. The Functions of Serine 687 Phosphorylation of Human DNA Polymerase η in UV Damage Tolerance. Mol Cell Proteomics 2016; 15:1913-20. [PMID: 26988343 DOI: 10.1074/mcp.m115.052167] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2015] [Indexed: 01/11/2023] Open
Abstract
DNA polymerase η (polη) is a Y-family translesion synthesis polymerase that plays a key role in the cellular tolerance toward UV irradiation-induced DNA damage. Here, we identified, for the first time, the phosphorylation of serine 687 (Ser(687)), which is located in the highly conserved nuclear localization signal (NLS) region of human polη and is mediated by cyclin-dependent kinase 2 (CDK2). We also showed that this phosphorylation is stimulated in human cells upon UV light exposure and results in diminished interaction of polη with proliferating cell nuclear antigen (PCNA). Furthermore, we demonstrated that the phosphorylation of Ser(687) in polη confers cellular protection from UV irradiation and increases the efficiency in replication across a site-specifically incorporated cyclobutane pyrimidine dimer in human cells. Based on these results, we proposed a mechanistic model where Ser(687) phosphorylation functions in the reverse polymerase switching step of translesion synthesis: The phosphorylation brings negative charges to the NLS of polη, which facilitates its departure from PCNA, thereby resetting the replication fork for highly accurate and processive DNA replication. Thus, our study, together with previous findings, supported that the posttranslational modifications of NLS of polη played a dual role in polymerase switching, where Lys(682) deubiquitination promotes the recruitment of polη to PCNA immediately prior to lesion bypass and Ser(687) phosphorylation stimulates its departure from the replication fork immediately after lesion bypass.
Collapse
Affiliation(s)
- Xiaoxia Dai
- From the §Department of Chemistry, University of California, Riverside, California 92521-0403
| | - Changjun You
- From the §Department of Chemistry, University of California, Riverside, California 92521-0403
| | - Yinsheng Wang
- From the §Department of Chemistry, University of California, Riverside, California 92521-0403
| |
Collapse
|
4
|
Liang Q, Dexheimer TS, Zhang P, Rosenthal AS, Villamil MA, You C, Zhang Q, Chen J, Ott CA, Sun H, Luci DK, Yuan B, Simeonov A, Jadhav A, Xiao H, Wang Y, Maloney DJ, Zhuang Z. A selective USP1-UAF1 inhibitor links deubiquitination to DNA damage responses. Nat Chem Biol 2014; 10:298-304. [PMID: 24531842 DOI: 10.1038/nchembio.1455] [Citation(s) in RCA: 186] [Impact Index Per Article: 18.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2013] [Accepted: 12/11/2013] [Indexed: 12/31/2022]
Abstract
Protein ubiquitination and deubiquitination are central to the control of a large number of cellular pathways and signaling networks in eukaryotes. Although the essential roles of ubiquitination have been established in the eukaryotic DNA damage response, the deubiquitination process remains poorly defined. Chemical probes that perturb the activity of deubiquitinases (DUBs) are needed to characterize the cellular function of deubiquitination. Here we report ML323 (2), a highly potent inhibitor of the USP1-UAF1 deubiquitinase complex with excellent selectivity against human DUBs, deSUMOylase, deneddylase and unrelated proteases. Using ML323, we interrogated deubiquitination in the cellular response to UV- and cisplatin-induced DNA damage and revealed new insights into the requirement of deubiquitination in the DNA translesion synthesis and Fanconi anemia pathways. Moreover, ML323 potentiates cisplatin cytotoxicity in non-small cell lung cancer and osteosarcoma cells. Our findings point to USP1-UAF1 as a key regulator of the DNA damage response and a target for overcoming resistance to the platinum-based anticancer drugs.
Collapse
Affiliation(s)
- Qin Liang
- Department of Chemistry and Biochemistry, University of Delaware, Newark, Delaware, USA
| | - Thomas S Dexheimer
- National Center for Advancing Translational Sciences, National Institutes of Health, Bethesda, Maryland, USA
| | - Ping Zhang
- Department of Chemistry and Biochemistry, University of Delaware, Newark, Delaware, USA
| | - Andrew S Rosenthal
- National Center for Advancing Translational Sciences, National Institutes of Health, Bethesda, Maryland, USA
| | - Mark A Villamil
- Department of Chemistry and Biochemistry, University of Delaware, Newark, Delaware, USA
| | - Changjun You
- Department of Chemistry, University of California-Riverside, Riverside, California, USA
| | - Qiuting Zhang
- State Key Laboratory of Food Science and Technology, Nanchang University, Nanchang, Jiangxi, China
| | - Junjun Chen
- Department of Chemistry and Biochemistry, University of Delaware, Newark, Delaware, USA
| | - Christine A Ott
- Department of Chemistry and Biochemistry, University of Delaware, Newark, Delaware, USA
| | - Hongmao Sun
- National Center for Advancing Translational Sciences, National Institutes of Health, Bethesda, Maryland, USA
| | - Diane K Luci
- National Center for Advancing Translational Sciences, National Institutes of Health, Bethesda, Maryland, USA
| | - Bifeng Yuan
- Department of Chemistry, University of California-Riverside, Riverside, California, USA
| | - Anton Simeonov
- National Center for Advancing Translational Sciences, National Institutes of Health, Bethesda, Maryland, USA
| | - Ajit Jadhav
- National Center for Advancing Translational Sciences, National Institutes of Health, Bethesda, Maryland, USA
| | - Hui Xiao
- Laboratory of Macromolecular Analysis and Proteomics, Albert Einstein College of Medicine, Bronx, New York, USA
| | - Yinsheng Wang
- Department of Chemistry, University of California-Riverside, Riverside, California, USA
| | - David J Maloney
- National Center for Advancing Translational Sciences, National Institutes of Health, Bethesda, Maryland, USA
| | - Zhihao Zhuang
- Department of Chemistry and Biochemistry, University of Delaware, Newark, Delaware, USA
| |
Collapse
|
5
|
You C, Swanson AL, Dai X, Yuan B, Wang J, Wang Y. Translesion synthesis of 8,5'-cyclopurine-2'-deoxynucleosides by DNA polymerases η, ι, and ζ. J Biol Chem 2013; 288:28548-56. [PMID: 23965998 DOI: 10.1074/jbc.m113.480459] [Citation(s) in RCA: 57] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023] Open
Abstract
Reactive oxygen species can give rise to a battery of DNA damage products including the 8,5'-cyclo-2'-deoxyadenosine (cdA) and 8,5'-cyclo-2'-deoxyguanosine (cdG) tandem lesions. The 8,5'-cyclopurine-2'-deoxynucleosides are quite stable lesions and are valid and reliable markers of oxidative DNA damage. However, it remains unclear how these lesions compromise DNA replication in mammalian cells. Previous in vitro biochemical assays have suggested a role for human polymerase (Pol) η in the insertion step of translesion synthesis (TLS) across the (5'S) diastereomers of cdA and cdG. Using in vitro steady-state kinetic assay, herein we showed that human Pol ι and a two-subunit yeast Pol ζ complex (REV3/REV7) could function efficiently in the insertion and extension steps, respectively, of TLS across S-cdA and S-cdG; human Pol κ and Pol η could also extend past these lesions, albeit much less efficiently. Results from a quantitative TLS assay showed that, in human cells, S-cdA and S-cdG inhibited strongly DNA replication and induced substantial frequencies of mutations at the lesion sites. Additionally, Pol η, Pol ι, and Pol ζ, but not Pol κ, had important roles in promoting replication through S-cdA and S-cdG in human cells. Based on these results, we propose a model for TLS across S-cdA and S-cdG in human cells, where Pol η and/or Pol ι carries out nucleotide insertion opposite the lesion, whereas Pol ζ executes the extension step.
Collapse
|
6
|
Burns JA, Dreij K, Cartularo L, Scicchitano DA. O6-methylguanine induces altered proteins at the level of transcription in human cells. Nucleic Acids Res 2010; 38:8178-87. [PMID: 20702424 PMCID: PMC3001077 DOI: 10.1093/nar/gkq706] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2010] [Revised: 07/20/2010] [Accepted: 07/27/2010] [Indexed: 11/14/2022] Open
Abstract
O(6)-Methylguanine (O(6)-meG), which is produced in DNA following exposure to methylating agents, instructs human RNA polymerase II to mis-insert bases opposite the lesion during transcription. In this study, we examined the effect of O(6)-meG on transcription in human cells and investigated the subsequent effects on protein function following translation of the resulting mRNA. In HEK293 cells, O(6)-meG induced incorporation of uridine or cytidine in nascent RNA opposite the adduct. In cells containing active O(6)-alkylguanine-DNA alkyltransferase (AGT), which repairs O(6)-meG, 3% misincorporation of uridine was observed opposite the lesion. In cells where AGT function was compromised by addition of the AGT inhibitor O(6)-benzylguanine, ∼ 58% of the transcripts contained a uridine misincorporation opposite the lesion. Furthermore, the altered mRNA induced changes to protein function as demonstrated through recovery of functional red fluorescent protein (RFP) from DNA coding for a non-fluorescent variant of RFP. These data show that O(6)-meG is highly mutagenic at the level of transcription in human cells, leading to an altered protein load, especially when AGT is inhibited.
Collapse
Affiliation(s)
| | | | | | - David A. Scicchitano
- Department of Biology, New York University, 1009 Silver Center, 100 Washington Square East, New York, NY 10003, USA
| |
Collapse
|
7
|
Francis NJ, Follmer NE, Simon MD, Aghia G, Butler JD. Polycomb proteins remain bound to chromatin and DNA during DNA replication in vitro. Cell 2009; 137:110-22. [PMID: 19303136 PMCID: PMC2667909 DOI: 10.1016/j.cell.2009.02.017] [Citation(s) in RCA: 134] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2008] [Revised: 10/22/2008] [Accepted: 02/02/2009] [Indexed: 01/11/2023]
Abstract
The transcriptional status of a gene can be maintained through multiple rounds of cell division during development. This epigenetic effect is believed to reflect heritable changes in chromatin folding and histone modifications or variants at target genes, but little is known about how these chromatin features are inherited through cell division. A particular challenge for maintaining transcription states is DNA replication, which disrupts or dilutes chromatin-associated proteins and histone modifications. PRC1-class Polycomb group protein complexes are essential for development and are thought to heritably silence transcription by altering chromatin folding and histone modifications. It is not known whether these complexes and their effects are maintained during DNA replication or subsequently re-established. We find that when PRC1-class Polycomb complex-bound chromatin or DNA is replicated in vitro, Polycomb complexes remain bound to replicated templates. Retention of Polycomb proteins through DNA replication may contribute to maintenance of transcriptional silencing through cell division.
Collapse
Affiliation(s)
- Nicole J Francis
- Department of Molecular and Cellular Biology, Harvard University, 7 Divinity Avenue, Cambridge, MA 02138, USA.
| | | | | | | | | |
Collapse
|
8
|
Wood RJ, Maynard-Smith MD, Robinson VL, Oyston PC, Titball RW, Roach PL. Kinetic analysis of Yersinia pestis DNA adenine methyltransferase activity using a hemimethylated molecular break light oligonucleotide. PLoS One 2007; 2:e801. [PMID: 17726531 PMCID: PMC1949145 DOI: 10.1371/journal.pone.0000801] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2007] [Accepted: 08/05/2007] [Indexed: 11/19/2022] Open
Abstract
Background DNA adenine methylation plays an important role in several critical bacterial processes including mismatch repair, the timing of DNA replication and the transcriptional control of gene expression. The dependence of bacterial virulence on DNA adenine methyltransferase (Dam) has led to the proposal that selective Dam inhibitors might function as broad spectrum antibiotics. Methodology/Principal Findings Herein we report the expression and purification of Yersinia pestis Dam and the development of a continuous fluorescence based assay for DNA adenine methyltransferase activity that is suitable for determining the kinetic parameters of the enzyme and for high throughput screening against potential Dam inhibitors. The assay utilised a hemimethylated break light oligonucleotide substrate containing a GATC methylation site. When this substrate was fully methylated by Dam, it became a substrate for the restriction enzyme DpnI, resulting in separation of fluorophore (fluorescein) and quencher (dabcyl) and therefore an increase in fluorescence. The assays were monitored in real time using a fluorescence microplate reader in 96 well format and were used for the kinetic characterisation of Yersinia pestis Dam, its substrates and the known Dam inhibitor, S-adenosylhomocysteine. The assay has been validated for high throughput screening, giving a Z-factor of 0.71±0.07 indicating that it is a sensitive assay for the identification of inhibitors. Conclusions/Significance The assay is therefore suitable for high throughput screening for inhibitors of DNA adenine methyltransferases and the kinetic characterisation of the inhibition.
Collapse
Affiliation(s)
- Robert J. Wood
- School of Chemistry, University of Southampton, Southampton, United Kingdom
- * To whom correspondence should be addressed. E-mail: (RW); (PR)
| | | | - Victoria L. Robinson
- Chemical and Biological Sciences, Defence Science and Technology Laboratory, Salisbury, United Kingdom
| | - Petra C.F. Oyston
- Chemical and Biological Sciences, Defence Science and Technology Laboratory, Salisbury, United Kingdom
| | - Rick W. Titball
- Chemical and Biological Sciences, Defence Science and Technology Laboratory, Salisbury, United Kingdom
| | - Peter L. Roach
- School of Chemistry, University of Southampton, Southampton, United Kingdom
- * To whom correspondence should be addressed. E-mail: (RW); (PR)
| |
Collapse
|
9
|
Abstract
When tethered in cis to DNA, the transcriptional corepressor mSin3B inhibits polyomavirus (Py) ori-dependent DNA replication in vivo. Histone deacetylases (HDACs) appear not to be involved, since tethering class I and class II HDACs in cis does not inhibit replication and treating the cells with trichostatin A does not specifically relieve inhibition by mSin3B. However, the mSin3B L59P mutation that impairs mSin3B interaction with N-CoR/SMRT abrogates inhibition of replication, suggesting the involvement of N-CoR/SMRT. Py large T antigen interacts with mSin3B, suggesting an HDAC-independent mechanism by which mSin3B inhibits DNA replication.
Collapse
Affiliation(s)
- An-Yong Xie
- Department of Biochemistry, University of Missouri-Columbia, Columbia, Missouri 65211, USA
| | | |
Collapse
|
10
|
Xie AY, Bermudez VP, Folk WR. Stimulation of DNA replication from the polyomavirus origin by PCAF and GCN5 acetyltransferases: acetylation of large T antigen. Mol Cell Biol 2002; 22:7907-18. [PMID: 12391158 PMCID: PMC134729 DOI: 10.1128/mcb.22.22.7907-7918.2002] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The PCAF and GCN5 acetyltransferases, but not p300 or CBP, stimulate DNA replication when tethered near the polyomavirus origin. Replication stimulation by PCAF and GCN5 is blocked by mutational inactivation of their acetyltransferase domains but not by deletion of sequences that bind p300 or CBP. Acetylation of histones near the polyomavirus origin assembled into chromatin in vivo is not detectably altered by expression of these acetyltransferases. PCAF and GCN5 interact with polyomavirus large T antigen in vivo, PCAF acetylates large T antigen in vitro, and large T-antigen acetylation in vivo is dependent upon the integrity of the PCAF acetyltransferase domain. These data suggest replication stimulation occurs through recruitment of large T antigen to the origin and acetylation by PCAF or GCN5.
Collapse
Affiliation(s)
- An-Yong Xie
- Department of Biochemistry, University of Missouri-Columbia, Columbia, Missouri 65211, USA
| | | | | |
Collapse
|
11
|
Neuber E, Havari E, Aquiles Sanchez J, Powers RD, Wangh LJ. Efficient human sperm pronucleus formation and replication in Xenopus egg extracts. Biol Reprod 1999; 61:912-20. [PMID: 10491624 DOI: 10.1095/biolreprod61.4.912] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/01/2022] Open
Abstract
We have achieved efficient in vitro reactivation and replication of human sperm nuclei in frog egg extracts by constructing a 4-step protocol that mimics the events of fertilization and pronucleus formation in mammalian eggs. With use of this protocol, 78-97% of human sperm nuclei from fertile donors synchronously swelled and completed full genome replication in about 2 h. We document the changes in nuclear structure that accompany efficient DNA synthesis and discuss future research and potential clinical implications of this new system.
Collapse
Affiliation(s)
- E Neuber
- Department of Biology, Brandeis University, Waltham, Massachusetts 02454, USA
| | | | | | | | | |
Collapse
|
12
|
Aquiles Sanchez J, Wonsey DR, Harris L, Morales J, Wangh LJ. Efficient plasmid DNA replication in Xenopus egg extracts does not depend on prior chromatin assembly. J Biol Chem 1995; 270:29676-81. [PMID: 8530355 DOI: 10.1074/jbc.270.50.29676] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
Small plasmids replicate efficiently in unfertilized Xenopus eggs provided they are injected before rather than after activation of the cell cycle. Here we use Xenopus egg extracts to test the hypothesis that efficient replication results from chromatin assembly prior to activation giving preloaded plasmids a head start toward the formation of a replicating pseudonucleus (Sanchez, J.A., Marek, D., and Wangh, L.J. (1992) J. Cell Sci. 103, 907-918). As in ovum, plasmid DNA preincubated in unactivated egg cytoplasmcytostatic factor extracts) replicate more efficiently after extract activation than does the same DNA added to the same extract after activation. Unlike in ovum, however, plasmids that replicate efficiently in vitro do not assemble into chromatin during preincubation and become topologically knotted instead. But even DNA knotting does not explain subsequent efficient replication. Also, plasmids preassembled into chromatin in vitro do not replicate efficiently in activated egg cytoplasm unless first preincubated in a CSF extract. We conclude that unactivated eggs contain replication-enhancing activities that can act independently of plasmid chromatin assembly and DNA topology. These postulated "preloading" factor(s) may be related to licensing factor, an activity that controls initiation of DNA replication in eukaryotic cells. The experimental conditions described here will permit characterization of preloading/licensing factor(s) in the context of a small plasmid substrate.
Collapse
Affiliation(s)
- J Aquiles Sanchez
- Department of Biology, Brandeis University, Waltham, Massachusetts 02254, USA
| | | | | | | | | |
Collapse
|
13
|
Wangh LJ, DeGrace D, Sanchez JA, Gold A, Yeghiazarians Y, Wiedemann K, Daniels S. Efficient reactivation of Xenopus erythrocyte nuclei in Xenopus egg extracts. J Cell Sci 1995; 108 ( Pt 6):2187-96. [PMID: 7673338 DOI: 10.1242/jcs.108.6.2187] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Rapid genome replication is one of the hallmarks of the frog embryonic cell cycle. We report here that complete reactivation of quiescent somatic cell nuclei in Xenopus egg extracts depends on prior restructuring of the nuclear substrate and prior preparation of cytoplasmic extract with the highest capacity to initiate and sustain DNA synthesis. Nuclei from mature erythrocytes swell, replicate their DNA efficiently, and enter mitosis in frozen/thawed extracts prepared from activated Xenopus eggs, provided the nuclei are first treated with trypsin, heparin, and an extract prepared from unactivated, meiotically arrested, eggs. Optimal replicating extracts are prepared from large batches of unfertilized eggs that are synchronously activated into the cell cycle for 28 minutes (at 20 degrees C). Because the Xenopus cell cycle progresses so rapidly, extracts prepared just a few minutes before or after this time have substantially lower DNA synthetic capacities. At the optimal time and temperature, eggs have just reached the G1/S boundary of the first cell cycle. This fact was revealed by injecting and replicating an SV40 plasmid in intact unfertilized eggs as described previously. We estimate that under optimal conditions approximately 6.14 × 10(9) base pairs of DNA/per nucleus are synthesized in 30–40 minutes, a rate that rivals that observed in the zygotic nucleus. The findings reported here are one step in our long term effort to develop a new in vitro/in vivo approach to nuclear transplantation. Nuclear transplantation in amphibian embryos has been used to establish that the genomes of many types of differentiated somatic cells are pluripotent. But very few such nuclei have ever developed into advanced tadpoles or adult frogs, probably because somatic nuclei injected directly into activated eggs fail to reactivate quickly enough to avoid being damaged during first mitosis. We have already shown that unfertilized eggs can be injected prior to activation of the first cell cycle. Future experiments will reveal whether in vitro reactivated somatic cell nuclei transplanted into such eggs reliably reach advanced stages of development.
Collapse
Affiliation(s)
- L J Wangh
- Department of Biology, Brandeis University, Waltham, MA 02254, USA
| | | | | | | | | | | | | |
Collapse
|
14
|
Gilbert DM, Neilson A, Miyazawa H, DePamphilis ML, Burhans WC. Mimosine arrests DNA synthesis at replication forks by inhibiting deoxyribonucleotide metabolism. J Biol Chem 1995; 270:9597-606. [PMID: 7721891 DOI: 10.1074/jbc.270.16.9597] [Citation(s) in RCA: 94] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
Mimosine has been reported to specifically prevent initiation of DNA replication in the chromosomes of mammalian nuclei. To test this hypothesis, the effects of mimosine were examined in several DNA replication systems and compared with the effects of aphidicolin, a specific inhibitor of replicative DNA polymerases. Our results demonstrated that mimosine inhibits DNA synthesis in mitochondrial, nuclear, and simian virus 40 (SV40) genomes to a similar extent. Furthermore, mimosine and aphidicolin were indistinguishable in their ability to arrest SV40 replication forks and mammalian nuclear chromosomal replication forks. In contrast to aphidicolin, mimosine did not inhibit DNA replication in lysates of mammalian cells supplied with exogenous deoxyribonucleotide triphosphate precursors for DNA synthesis. Mimosine also had no effect on initiation or elongation of DNA replication in Xenopus eggs or egg extracts containing high levels of deoxyribonucleotide triphosphates. In parallel with its inhibitory effect on DNA synthesis in mammalian cells, mimosine altered deoxyribonucleotide triphosphate pools in a manner similar to that reported for another DNA replication inhibitor that affects deoxyribonucleotide metabolism, hydroxyurea. Taken together, these results show that mimosine inhibits DNA synthesis at the level of elongation of nascent chains by altering deoxyribonucleotide metabolism.
Collapse
Affiliation(s)
- D M Gilbert
- Roche Institute of Molecular Biology, Roche Research Center, Nutley, New Jersey 07110, USA
| | | | | | | | | |
Collapse
|
15
|
Affiliation(s)
- M L DePamphilis
- Roche Research Center, Roche Institute of Molecular Biology, Nutley, New Jersey 07110, USA
| |
Collapse
|
16
|
Zannis-Hadjopoulos M, Nielsen TO, Todd A, Price GB. Autonomous replication in vivo and in vitro of clones spanning the region of the DHFR origin of bidirectional replication (ori beta). Gene X 1994; 151:273-7. [PMID: 7828889 DOI: 10.1016/0378-1119(94)90670-x] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
Plasmids containing the origin of bidirectional replication (ori beta) of the Chinese hamster dihydrofolate reductase-encoding gene (DHFR) were tested for autonomous replication in vivo and in vitro. The results show that plasmids pX24 and pneoS13, that contain a 4.8- and a 11.5-kb fragment, respectively, spanning the ori beta region, are able to replicate autonomously in human cells and in a cell-free system that uses human cell extracts. Another plasmid, pX14, containing a 4.8-kb fragment that is immediately adjacent to the ori beta region, also replicated in these two assays.
Collapse
|
17
|
Abstract
This past year has seen a significant increase in our understanding of eukaryotic origins of replication, of the proteins that identify these origins, of DNA sequences that promote their unwinding, and of transcription factors that stimulate origin activity. DNA replication begins at specific sites in both simple and complex genomes, but origins in complex genomes may include nuclear structure as well as DNA sequence.
Collapse
Affiliation(s)
- M L DePamphilis
- Roche Institute of Molecular Biology, Nutley, New Jersey 07110-1199
| |
Collapse
|