1
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Pinto LM, Pailas A, Bondarchenko M, Sharma AB, Neumann K, Rizzo AJ, Jeanty C, Nicot N, Racca C, Graham MK, Naughton C, Liu Y, Chen CL, Meakin PJ, Gilbert N, Britton S, Meeker AK, Heaphy CM, Larminat F, Van Dyck E. DAXX promotes centromeric stability independently of ATRX by preventing the accumulation of R-loop-induced DNA double-stranded breaks. Nucleic Acids Res 2024; 52:1136-1155. [PMID: 38038252 PMCID: PMC10853780 DOI: 10.1093/nar/gkad1141] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2022] [Revised: 11/08/2023] [Accepted: 11/13/2023] [Indexed: 12/02/2023] Open
Abstract
Maintaining chromatin integrity at the repetitive non-coding DNA sequences underlying centromeres is crucial to prevent replicative stress, DNA breaks and genomic instability. The concerted action of transcriptional repressors, chromatin remodelling complexes and epigenetic factors controls transcription and chromatin structure in these regions. The histone chaperone complex ATRX/DAXX is involved in the establishment and maintenance of centromeric chromatin through the deposition of the histone variant H3.3. ATRX and DAXX have also evolved mutually-independent functions in transcription and chromatin dynamics. Here, using paediatric glioma and pancreatic neuroendocrine tumor cell lines, we identify a novel ATRX-independent function for DAXX in promoting genome stability by preventing transcription-associated R-loop accumulation and DNA double-strand break formation at centromeres. This function of DAXX required its interaction with histone H3.3 but was independent of H3.3 deposition and did not reflect a role in the repression of centromeric transcription. DAXX depletion mobilized BRCA1 at centromeres, in line with BRCA1 role in counteracting centromeric R-loop accumulation. Our results provide novel insights into the mechanisms protecting the human genome from chromosomal instability, as well as potential perspectives in the treatment of cancers with DAXX alterations.
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Affiliation(s)
- Lia M Pinto
- DNA Repair and Chemoresistance Group, Department of Cancer Research, Luxembourg Institute of Health (LIH), L-1210 Luxembourg, Luxembourg
- Faculty of Science, Technology and Communication, University of Luxembourg, L-4365 Esch-sur-Alzette, Luxembourg
- Discovery & Translational Science Department, Leeds Institute of Cardiovascular and Metabolic Medicine, University of Leeds, Leeds LS2 9JT, UK
| | - Alexandros Pailas
- DNA Repair and Chemoresistance Group, Department of Cancer Research, Luxembourg Institute of Health (LIH), L-1210 Luxembourg, Luxembourg
- Faculty of Science, Technology and Communication, University of Luxembourg, L-4365 Esch-sur-Alzette, Luxembourg
| | - Max Bondarchenko
- DNA Repair and Chemoresistance Group, Department of Cancer Research, Luxembourg Institute of Health (LIH), L-1210 Luxembourg, Luxembourg
- Faculty of Science, Technology and Communication, University of Luxembourg, L-4365 Esch-sur-Alzette, Luxembourg
| | - Abhishek Bharadwaj Sharma
- DNA Repair and Chemoresistance Group, Department of Cancer Research, Luxembourg Institute of Health (LIH), L-1210 Luxembourg, Luxembourg
| | - Katrin Neumann
- DNA Repair and Chemoresistance Group, Department of Cancer Research, Luxembourg Institute of Health (LIH), L-1210 Luxembourg, Luxembourg
| | - Anthony J Rizzo
- Department of Pathology, Johns Hopkins University School of Medicine, Baltimore, MD 21231, USA
| | - Céline Jeanty
- DNA Repair and Chemoresistance Group, Department of Cancer Research, Luxembourg Institute of Health (LIH), L-1210 Luxembourg, Luxembourg
| | - Nathalie Nicot
- Translational Medicine Operations Hub, Luxembourg Institute of Health (LIH), Luxembourg, Luxembourg
| | - Carine Racca
- Institut de Pharmacologie et Biologie Structurale (IPBS), Université de Toulouse, CNRS, Université Toulouse III - Paul Sabatier (UT3), 31077 Toulouse Cedex 4, France
| | - Mindy K Graham
- Department of Pathology, Johns Hopkins University School of Medicine, Baltimore, MD 21231, USA
| | - Catherine Naughton
- Medical Research Council Human Genetics Unit, Institute of Genetics and Molecular Medicine, The University of Edinburgh, Edinburgh EH4 1QY, UK
| | - Yaqun Liu
- Institut Curie, PSL Research University, CNRS UMR3244, Dynamics of Genetic Information, Sorbonne Université, 75248 Paris Cedex 05, France
| | - Chun-Long Chen
- Institut Curie, PSL Research University, CNRS UMR3244, Dynamics of Genetic Information, Sorbonne Université, 75248 Paris Cedex 05, France
| | - Paul J Meakin
- Discovery & Translational Science Department, Leeds Institute of Cardiovascular and Metabolic Medicine, University of Leeds, Leeds LS2 9JT, UK
| | - Nick Gilbert
- Medical Research Council Human Genetics Unit, Institute of Genetics and Molecular Medicine, The University of Edinburgh, Edinburgh EH4 1QY, UK
| | - Sébastien Britton
- Institut de Pharmacologie et Biologie Structurale (IPBS), Université de Toulouse, CNRS, Université Toulouse III - Paul Sabatier (UT3), 31077 Toulouse Cedex 4, France
| | - Alan K Meeker
- Department of Pathology, Johns Hopkins University School of Medicine, Baltimore, MD 21231, USA
| | - Christopher M Heaphy
- Department of Medicine, Boston University School of Medicine, Boston, MA 02118, USA
| | - Florence Larminat
- Institut de Pharmacologie et Biologie Structurale (IPBS), Université de Toulouse, CNRS, Université Toulouse III - Paul Sabatier (UT3), 31077 Toulouse Cedex 4, France
| | - Eric Van Dyck
- DNA Repair and Chemoresistance Group, Department of Cancer Research, Luxembourg Institute of Health (LIH), L-1210 Luxembourg, Luxembourg
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Sharma AB, Ramlee MK, Kosmin J, Higgs MR, Wolstenholme A, Ronson GE, Jones D, Ebner D, Shamkhi N, Sims D, Wijnhoven PWG, Forment JV, Gibbs-Seymour I, Lakin ND. Author Correction: C16orf72/HAPSTR1/TAPR1 functions with BRCA1/Senataxin to modulate replication-associated R-loops and confer resistance to PARP disruption. Nat Commun 2023; 14:7784. [PMID: 38012134 PMCID: PMC10682469 DOI: 10.1038/s41467-023-43353-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2023] Open
Affiliation(s)
| | | | - Joel Kosmin
- Department of Biochemistry, University of Oxford, South Parks Road, Oxford, UK
| | - Martin R Higgs
- Institute of Cancer and Genomic Sciences, University of Birmingham, Edgbaston, Birmingham, UK
| | - Amy Wolstenholme
- Department of Biochemistry, University of Oxford, South Parks Road, Oxford, UK
| | - George E Ronson
- Department of Biochemistry, University of Oxford, South Parks Road, Oxford, UK
- Institute of Cancer and Genomic Sciences, University of Birmingham, Edgbaston, Birmingham, UK
| | - Dylan Jones
- Target Discovery Institute, Nuffield Department of Medicine, University of Oxford, Oxford, UK
| | - Daniel Ebner
- Target Discovery Institute, Nuffield Department of Medicine, University of Oxford, Oxford, UK
| | - Noor Shamkhi
- Department of Biochemistry, University of Oxford, South Parks Road, Oxford, UK
| | - David Sims
- Weatherall Institute of Molecular Medicine, University of Oxford, John Radcliffe Hospital, Oxford, UK
| | - Paul W G Wijnhoven
- Early Oncology R&D, AstraZeneca, 1 Francis Crick Avenue, Cambridge Biomedical Campus, Cambridge, CB2 0AA, UK
| | - Josep V Forment
- Early Oncology R&D, AstraZeneca, 1 Francis Crick Avenue, Cambridge Biomedical Campus, Cambridge, CB2 0AA, UK
| | - Ian Gibbs-Seymour
- Department of Biochemistry, University of Oxford, South Parks Road, Oxford, UK
| | - Nicholas D Lakin
- Department of Biochemistry, University of Oxford, South Parks Road, Oxford, UK.
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Sharma AB, Ramlee MK, Kosmin J, Higgs MR, Wolstenholme A, Ronson GE, Jones D, Ebner D, Shamkhi N, Sims D, Wijnhoven PWG, Forment JV, Gibbs-Seymour I, Lakin ND. C16orf72/HAPSTR1/TAPR1 functions with BRCA1/Senataxin to modulate replication-associated R-loops and confer resistance to PARP disruption. Nat Commun 2023; 14:5003. [PMID: 37591890 PMCID: PMC10435583 DOI: 10.1038/s41467-023-40779-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2023] [Accepted: 08/10/2023] [Indexed: 08/19/2023] Open
Abstract
While the toxicity of PARP inhibitors to cells with defects in homologous recombination (HR) is well established, other synthetic lethal interactions with PARP1/PARP2 disruption are poorly defined. To inform on these mechanisms we conducted a genome-wide screen for genes that are synthetic lethal with PARP1/2 gene disruption and identified C16orf72/HAPSTR1/TAPR1 as a novel modulator of replication-associated R-loops. C16orf72 is critical to facilitate replication fork restart, suppress DNA damage and maintain genome stability in response to replication stress. Importantly, C16orf72 and PARP1/2 function in parallel pathways to suppress DNA:RNA hybrids that accumulate at stalled replication forks. Mechanistically, this is achieved through an interaction of C16orf72 with BRCA1 and the RNA/DNA helicase Senataxin to facilitate their recruitment to RNA:DNA hybrids and confer resistance to PARP inhibitors. Together, this identifies a C16orf72/Senataxin/BRCA1-dependent pathway to suppress replication-associated R-loop accumulation, maintain genome stability and confer resistance to PARP inhibitors.
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Affiliation(s)
| | | | - Joel Kosmin
- Department of Biochemistry, University of Oxford, South Parks Road, Oxford, UK
| | - Martin R Higgs
- Institute of Cancer and Genomic Sciences, University of Birmingham, Edgbaston, Birmingham, UK
| | - Amy Wolstenholme
- Department of Biochemistry, University of Oxford, South Parks Road, Oxford, UK
| | - George E Ronson
- Department of Biochemistry, University of Oxford, South Parks Road, Oxford, UK
- Institute of Cancer and Genomic Sciences, University of Birmingham, Edgbaston, Birmingham, UK
| | - Dylan Jones
- Target Discovery Institute, Nuffield Department of Medicine, University of Oxford, Oxford, UK
| | - Daniel Ebner
- Target Discovery Institute, Nuffield Department of Medicine, University of Oxford, Oxford, UK
| | - Noor Shamkhi
- Department of Biochemistry, University of Oxford, South Parks Road, Oxford, UK
| | - David Sims
- Weatherall Institute of Molecular Medicine, University of Oxford, John Radcliffe Hospital, Oxford, UK
| | - Paul W G Wijnhoven
- Early Oncology R&D, AstraZeneca, 1 Francis Crick Avenue, Cambridge Biomedical Campus, Cambridge, CB2 0AA, UK
| | - Josep V Forment
- Early Oncology R&D, AstraZeneca, 1 Francis Crick Avenue, Cambridge Biomedical Campus, Cambridge, CB2 0AA, UK
| | - Ian Gibbs-Seymour
- Department of Biochemistry, University of Oxford, South Parks Road, Oxford, UK
| | - Nicholas D Lakin
- Department of Biochemistry, University of Oxford, South Parks Road, Oxford, UK.
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Richards F, Llorca-Cardenosa MJ, Langton J, Buch-Larsen SC, Shamkhi NF, Sharma AB, Nielsen ML, Lakin ND. Regulation of Rad52-dependent replication fork recovery through serine ADP-ribosylation of PolD3. Nat Commun 2023; 14:4310. [PMID: 37463936 DOI: 10.1038/s41467-023-40071-w] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2022] [Accepted: 07/06/2023] [Indexed: 07/20/2023] Open
Abstract
Although Poly(ADP-ribose)-polymerases (PARPs) are key regulators of genome stability, how site-specific ADP-ribosylation regulates DNA repair is unclear. Here, we describe a novel role for PARP1 and PARP2 in regulating Rad52-dependent replication fork repair to maintain cell viability when homologous recombination is dysfunctional, suppress replication-associated DNA damage, and maintain genome stability. Mechanistically, Mre11 and ATM are required for induction of PARP activity in response to replication stress that in turn promotes break-induced replication (BIR) through assembly of Rad52 at stalled/damaged replication forks. Further, by mapping ADP-ribosylation sites induced upon replication stress, we identify that PolD3 is a target for PARP1/PARP2 and that its site-specific ADP-ribosylation is required for BIR activity, replication fork recovery and genome stability. Overall, these data identify a critical role for Mre11-dependent PARP activation and site-specific ADP-ribosylation in regulating BIR to maintain genome integrity during DNA synthesis.
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Affiliation(s)
- Frederick Richards
- Department of Biochemistry, University of Oxford, South Parks Road, Oxford, UK
| | | | - Jamie Langton
- Department of Biochemistry, University of Oxford, South Parks Road, Oxford, UK
| | - Sara C Buch-Larsen
- Novo Nordisk Foundation Centre for Protein Research, Faculty of Health and Medical Sciences, University of Copenhagen, Blegdamsvej 3B, 2200, Copenhagen, Denmark
| | - Noor F Shamkhi
- Department of Biochemistry, University of Oxford, South Parks Road, Oxford, UK
| | | | - Michael L Nielsen
- Novo Nordisk Foundation Centre for Protein Research, Faculty of Health and Medical Sciences, University of Copenhagen, Blegdamsvej 3B, 2200, Copenhagen, Denmark
| | - Nicholas D Lakin
- Department of Biochemistry, University of Oxford, South Parks Road, Oxford, UK.
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5
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Sharma AB, Erasimus H, Pinto L, Caron MC, Gopaul D, Peterlini T, Neumann K, Nazarov PV, Fritah S, Klink B, Herold-Mende CC, Niclou SP, Pasero P, Calsou P, Masson JY, Britton S, Van Dyck E. XAB2 promotes Ku eviction from single-ended DNA double-strand breaks independently of the ATM kinase. Nucleic Acids Res 2021; 49:9906-9925. [PMID: 34500463 PMCID: PMC8464071 DOI: 10.1093/nar/gkab785] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2021] [Revised: 08/16/2021] [Accepted: 09/01/2021] [Indexed: 12/18/2022] Open
Abstract
Replication-associated single-ended DNA double-strand breaks (seDSBs) are repaired predominantly through RAD51-mediated homologous recombination (HR). Removal of the non-homologous end-joining (NHEJ) factor Ku from resected seDSB ends is crucial for HR. The coordinated actions of MRE11-CtIP nuclease activities orchestrated by ATM define one pathway for Ku eviction. Here, we identify the pre-mRNA splicing protein XAB2 as a factor required for resistance to seDSBs induced by the chemotherapeutic alkylator temozolomide. Moreover, we show that XAB2 prevents Ku retention and abortive HR at seDSBs induced by temozolomide and camptothecin, via a pathway that operates in parallel to the ATM-CtIP-MRE11 axis. Although XAB2 depletion preserved RAD51 focus formation, the resulting RAD51-ssDNA associations were unproductive, leading to increased NHEJ engagement in S/G2 and genetic instability. Overexpression of RAD51 or RAD52 rescued the XAB2 defects and XAB2 loss was synthetically lethal with RAD52 inhibition, providing potential perspectives in cancer therapy.
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Affiliation(s)
- Abhishek Bharadwaj Sharma
- DNA Repair and Chemoresistance Group, Department of Oncology, Luxembourg Institute of Health (LIH), Luxembourg, Luxembourg
| | - Hélène Erasimus
- DNA Repair and Chemoresistance Group, Department of Oncology, Luxembourg Institute of Health (LIH), Luxembourg, Luxembourg.,Faculty of Science, Technology and Communication, University of Luxembourg, Esch-sur-Alzette, Luxembourg
| | - Lia Pinto
- DNA Repair and Chemoresistance Group, Department of Oncology, Luxembourg Institute of Health (LIH), Luxembourg, Luxembourg.,Faculty of Science, Technology and Communication, University of Luxembourg, Esch-sur-Alzette, Luxembourg
| | - Marie-Christine Caron
- CHU de Québec Research Center, Oncology Division, Québec City, Canada.,Department of Molecular Biology, Medical Biochemistry and Pathology, Laval University Cancer Research Center, Québec City, Canada
| | - Diyavarshini Gopaul
- Institut de Génétique Humaine, CNRS et Université de Montpellier, Equipe Labellisée Ligue Contre le Cancer, Montpellier, France
| | - Thibaut Peterlini
- CHU de Québec Research Center, Oncology Division, Québec City, Canada.,Department of Molecular Biology, Medical Biochemistry and Pathology, Laval University Cancer Research Center, Québec City, Canada
| | - Katrin Neumann
- DNA Repair and Chemoresistance Group, Department of Oncology, Luxembourg Institute of Health (LIH), Luxembourg, Luxembourg
| | - Petr V Nazarov
- Quantitative Biology Unit, Multiomics Data Science Group, LIH, Luxembourg
| | - Sabrina Fritah
- NorLux Neuro-Oncology Laboratory, Department of Oncology, LIH, Luxembourg
| | - Barbara Klink
- National Center of Genetics, Laboratoire National de Santé, Dudelange, Luxembourg.,Functional Tumour Genetics Group, Department of Oncology, LIH, Luxembourg
| | | | - Simone P Niclou
- NorLux Neuro-Oncology Laboratory, Department of Oncology, LIH, Luxembourg.,Department of Biomedicine, University of Bergen, Norway
| | - Philippe Pasero
- Institut de Génétique Humaine, CNRS et Université de Montpellier, Equipe Labellisée Ligue Contre le Cancer, Montpellier, France
| | - Patrick Calsou
- Institut de Pharmacologie et de Biologie Structurale, Université de Toulouse, CNRS, UPS, Toulouse, France, Equipe Labellisée Ligue Nationale Contre le Cancer 2018
| | - Jean-Yves Masson
- CHU de Québec Research Center, Oncology Division, Québec City, Canada.,Department of Molecular Biology, Medical Biochemistry and Pathology, Laval University Cancer Research Center, Québec City, Canada
| | - Sébastien Britton
- Institut de Pharmacologie et de Biologie Structurale, Université de Toulouse, CNRS, UPS, Toulouse, France, Equipe Labellisée Ligue Nationale Contre le Cancer 2018
| | - Eric Van Dyck
- DNA Repair and Chemoresistance Group, Department of Oncology, Luxembourg Institute of Health (LIH), Luxembourg, Luxembourg
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Sharma AB, Dimitrov S, Hamiche A, Van Dyck E. Centromeric and ectopic assembly of CENP-A chromatin in health and cancer: old marks and new tracks. Nucleic Acids Res 2019; 47:1051-1069. [PMID: 30590707 PMCID: PMC6379705 DOI: 10.1093/nar/gky1298] [Citation(s) in RCA: 40] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2018] [Revised: 12/13/2018] [Accepted: 12/18/2018] [Indexed: 12/20/2022] Open
Abstract
The histone H3 variant CENP-A confers epigenetic identity to the centromere and plays crucial roles in the assembly and function of the kinetochore, thus ensuring proper segregation of our chromosomes. CENP-A containing nucleosomes exhibit unique structural specificities and lack the complex profile of gene expression-associated histone posttranslational modifications found in canonical histone H3 and the H3.3 variant. CENP-A mislocalization into noncentromeric regions resulting from its overexpression leads to chromosomal segregation aberrations and genome instability. Overexpression of CENP-A is a feature of many cancers and is associated with malignant progression and poor outcome. The recent years have seen impressive progress in our understanding of the mechanisms that orchestrate CENP-A deposition at native centromeres and ectopic loci. They have witnessed the description of novel, heterotypic CENP-A/H3.3 nucleosome particles and the exploration of the phenotypes associated with the deregulation of CENP-A and its chaperones in tumor cells. Here, we review the structural specificities of CENP-A nucleosomes, the epigenetic features that characterize the centrochromatin and the mechanisms and factors that orchestrate CENP-A deposition at centromeres. We then review our knowledge of CENP-A ectopic distribution, highlighting experimental strategies that have enabled key discoveries. Finally, we discuss the implications of deregulated CENP-A in cancer.
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Affiliation(s)
- Abhishek Bharadwaj Sharma
- NORLUX Neuro-Oncology Laboratory, Department of Oncology, Luxembourg Institute of Health (LIH), 84 Val Fleuri, L-1526 Luxembourg, Luxembourg
| | - Stefan Dimitrov
- Université Grenoble Alpes, CNRS UMR 5309, INSERM U1209, Institute for Advanced Biosciences (IAB), Site Santé-Allée des Alpes, 38700 La Tronche, France.,Izmir Biomedicine and Genome Center, İzmir, Turkey
| | - Ali Hamiche
- Département de Génomique Fonctionnelle et Cancer, Institut de Génétique et Biologie Moléculaire et Cellulaire (IGBMC), Université de Strasbourg, CNRS, INSERM, 67404 Illkirch Cedex, France
| | - Eric Van Dyck
- NORLUX Neuro-Oncology Laboratory, Department of Oncology, Luxembourg Institute of Health (LIH), 84 Val Fleuri, L-1526 Luxembourg, Luxembourg
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Sharma AB, Sharma SK, Sharma M, Pandey RK, Reddy DS. Structural and optical investigation of semiconductor CdSe/CdS core-shell quantum dot thin films. Spectrochim Acta A Mol Biomol Spectrosc 2009; 72:285-290. [PMID: 19038577 DOI: 10.1016/j.saa.2008.09.031] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/28/2008] [Revised: 09/02/2008] [Accepted: 09/26/2008] [Indexed: 05/27/2023]
Abstract
Highly luminescent CdSe/CdS core-shell nanocrystals have been assembled on indium tin oxide (ITO) coated glass substrates using a wet synthesis route. The physical properties of the quantum dots (QD) have been investigated using X-ray diffraction, transmission electron microscopy and optical absorption spectroscopy techniques. These quantum dots showed a strong enhancement in the near band edge absorption. The in situ luminescence behavior has been interpreted in the light of the quantum confinement effect and induced strain in the core-shell structure.
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Affiliation(s)
- A B Sharma
- Department of Physics, Barkatullah University, Bhopal, M.P. 462026, India
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Sharma M, Gupta D, Kaushik D, Sharma AB, Pandey RK. Highly luminescent inverted ZnS/CdS core/shell quantum dots. J Nanosci Nanotechnol 2008; 8:3949-3954. [PMID: 19049156 DOI: 10.1166/jnn.2008.195] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
Synthesis of highly luminescent and monochromatic inverted core-shell structures utilizing ZnS/CdS quantum dots (QDs) has been investigated. The core/shell quantum dots have been characterized using grazing angle X-ray diffraction (XRD), Transmission electron microscopy, Optical absorption and luminescence spectroscopy. The results suggested that passivation of surface states along with an increased localization of electron and hole in CdS shell layer, give rise to increased monochromaticity with higher quantum yield. The possibility of using the inverted core-shell structure as an additional parameter for tuning the color of luminescence has also been discussed.
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Abstract
Self-organized cadmium sulfide quantum dots assembled using wet synthesis route on glass/ITO as well as Si(100) substrates have been investigated, using X-ray diffraction and transmission electron microscopy. The quantum dots have been shown to grow with a strong (111) orientation with narrow size distribution. Self-organized growth of the quantum dots was examined by high resolution imaging with an atomic force microscope. It is shown that increased self-organization is obtained on silicon substrate. The role of surfactant in imparting self-organization has been invoked to explain the observed morphological features. The as grown Q-dots exhibited size dependent blue shift in the absorption edge. The luminescence behavior of the quantum dots self-organized on glass/ITO as well as Si(100) substrate has also been examined. It is shown that substantial enhancement in luminescence yield is obtained for quantum dots grown on silicon substrate. A model to explain the observed luminescence enhancement has also been presented.
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Affiliation(s)
- Diksha Kaushik
- Materials Research Lab, Department of Physics, Bhopal University, Bhopal 462026, India
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10
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Abstract
Primary tuberculosis of tongue is very rare with unusual presentation creating a diagnostic dilemma. We report a case of primary tuberculosis of tongue in a 49-year-old female patient. Tuberculosis was not suspected clinically and there was no other focus elsewhere in the body. Fine needle aspiration cytology was attempted but was inconclusive. The diagnosis was made after histopathological examination.
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Affiliation(s)
- A B Sharma
- Department of Pathology, Regional Institute of Medical Sciences, Imphal 795 004, Manipur, India.
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Kaushik D, Singh RR, Sharma AB, Gupta D, Sharma M, Pandey RK. Self-organized ZnSe quantum dots: synthesis and characterization. J Nanosci Nanotechnol 2008; 8:1502-1511. [PMID: 18468182] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
Self-organized ZnSe quantum dots (Q-ZnSe) were grown on indium tin oxide substrate using wet chemical technique without or in presence of copper and manganese dopants. The structural, morphological and luminescence properties of the as grown Q-dot films have been investigated, using X-ray diffraction, transmission electron microscopy, atomic force microscopy and optical and luminescence spectroscopy. Composition of the samples were analyzed using atomic absorption spectroscopy. The quantum dots have been shown to deposit in a compact, uniform and organized array on the indium tin oxide substrate. The size dependent blue shift in the experimentally determined absorption edge has been compared with the theoretical predictions based on the effective mass and tight binding approximations. It is shown that the experimentally determined absorption edges depart significantly from the theoretically calculated values. The photoluminescence properties of the undoped as well as doped Q-ZnSe have also been discussed.
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Affiliation(s)
- Diksha Kaushik
- Department of Physics, Bhopal University, Bhopal 462026, India
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12
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Zhang JG, Picchi G, Sharma AB. Design of efficient all-optical code-division multiplexing systems supporting multiple-bit-rate and equal-bit-rate transmissions. Appl Opt 2000; 39:2264-2277. [PMID: 18345133 DOI: 10.1364/ao.39.002264] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
We present the design of efficient all-optical code-division multiplexing (AOCDM) systems that can transmit multiple-bit-rate (MBR) data signals over a common optical fiber. This is achieved when the proposed strict optical orthogonal code (OOC) of autocorrelation and cross-correlation constraints of 1 are used but without performance degradation compared with the use of conventional OOC. We describe the design of various strict OOC's by employing the useful concept of slot distances, and methods of code construction are also presented. Moreover, we give the principle of MBR data transmissions in an AOCDM system. It is shown that AOCDM systems using the proposed OOC can effectively transmit multiuser MBR and equal-bit-rate (EBR) data with no increase of system complexity. In principle, optimal strict OOC's need the same or a slightly larger system bandwidth compared with optimal conventional OOC's for EBR operation, whereas the former can require a smaller system bandwidth and have a better system performance than the latter for MBR transmissions. A new, to our knowledge, family of strict OOC's is also introduced, whose code words can have nonconstant weights to support multiuser communications with different transmission quality. Furthermore, we design low-cost AOCDM transmitters that are based on an efficient gain-switching scheme that does not require an electro-optic intensity modulator to on-off modulate an optical clock pulse stream at each transmitter. The basic operation principle is also experimentally demonstrated.
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13
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Anthony JP, Foster RD, Sharma AB, Kearns GJ, Hoffman WY, Pogrel MA. Reconstruction of a complex midfacial defect with the folded fibular free flap and osseointegrated implants. Ann Plast Surg 1996; 37:204-10. [PMID: 8863985 DOI: 10.1097/00000637-199608000-00017] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Refinements in microsurgical techniques, plate fixation, and osseointegration have changed the conceptual approach to midface reconstruction. Free tissue transfer has emerged as the ideal method of reconstructing complex midfacial defects. Single-stage bony restoration of the palate and orbital rim using the folded fibular osteocutaneous free flap is described. The fibular free flap is our first choice for reconstructing complex midfacial defects. The thin, soft, pliable tissue is ideal for intraoral and palatal reconstructions. The bone can be tailored precisely to fit any desired shape, and forms a sturdy support for both orbital and dental prostheses. With a single flap, rapid and reliable restoration of midfacial appearance, orbital support, and palatal function can be achieved.
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Affiliation(s)
- J P Anthony
- Division of Plastic and Reconstructive Surgery, University of California at San Francisco 94115-1632, USA
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Debnath K, Singh TD, Sharma AB, Devi SS, Singh AS. Sex cord tumour with annular tubules--a case report. INDIAN J PATHOL MICR 1994; 37:331-3. [PMID: 7814067] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Affiliation(s)
- K Debnath
- Department of Pathology, Regional Medical College, Imphal, Manipur
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Perrott DH, Smith RA, Sharma AB, McArdle L. Maxillary and mandibular reconstruction in preparation for endosseous implants. J Calif Dent Assoc 1993; 21:39-43. [PMID: 7504094] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 05/21/2023]
Abstract
Bony and soft tissue deficiencies can deter esthetic, functional and prosthetic rehabilitation. Modern surgical techniques using bone or composite grafts to reconstruct or augment implant sites are reviewed.
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Affiliation(s)
- D H Perrott
- UCSF School of Dentistry, San Francisco, CA 94143-0440
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Saijonmaa J, Sharma AB, Halme SJ. Selective excitation of parabolic-index optical fibers by Gaussian beams. Appl Opt 1980; 19:2442-2452. [PMID: 20234433 DOI: 10.1364/ao.19.002442] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
Excitation coefficients of the guided modes of a parabolic-index optical fiber by narrow input Gaussian beams are calculated. The effects of beam offset, tilt, width, and wave-front curvature are examined. A wave-optical procedure for optimizing the input Gaussian beamwidth (to excite as few mode groups as possible) as a function of beam offset is presented and shown to be in agreement with a simple Fourier-optics optimization.
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Sharma AB, Halme SJ. Frequency response of optical fibers using a combination time-frequency domain technique. Appl Opt 1979; 18:1877-1879. [PMID: 20212567 DOI: 10.1364/ao.18.001877] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
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