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Abu-Daya A, Godwin A. CRISPR/Cas9 Gene Disruption Studies in F 0 Xenopus Tadpoles: Understanding Development and Disease in the Frog. Methods Mol Biol 2023; 2633:111-130. [PMID: 36853461 DOI: 10.1007/978-1-0716-3004-4_10] [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] [Indexed: 03/01/2023]
Abstract
CRISPR/Cas9 has become the favorite method for gene knockouts in a range of vertebrate model organisms due to its ease of use and versatility. Gene-specific guide RNAs can be designed to a unique genomic sequence and used to target the Cas9 endonuclease, which causes a double-stranded break at the desired locus. Repair of the breaks through non-homologous end joining often results in the deletion or insertion of several nucleotides, which frequently result in nonsense mutations. Xenopus frogs have long been an excellent model organism in which to study gene function, and they have proven to be useful in gene-editing experiments, especially the diploid species, X. tropicalis. In this chapter, we present our protocols for gene disruption in Xenopus, which we regularly use to investigate developmental processes and model human genetic disease.
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Affiliation(s)
- Anita Abu-Daya
- European Xenopus Resource Centre, University of Portsmouth, Portsmouth, UK.
| | - Annie Godwin
- European Xenopus Resource Centre, University of Portsmouth, Portsmouth, UK.
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2
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Godden AM, Antonaci M, Ward NJ, van der Lee M, Abu-Daya A, Guille M, Wheeler GN. An efficient miRNA knockout approach using CRISPR-Cas9 in Xenopus. Dev Biol 2022; 483:66-75. [PMID: 34968443 PMCID: PMC8865746 DOI: 10.1016/j.ydbio.2021.12.015] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2021] [Revised: 12/15/2021] [Accepted: 12/23/2021] [Indexed: 12/14/2022]
Abstract
In recent years CRISPR-Cas9 knockouts (KO) have become increasingly ultilised to study gene function. MicroRNAs (miRNAs) are short non-coding RNAs, 20-22 nucleotides long, which affect gene expression through post-transcriptional repression. We previously identified miRNAs-196a and -219 as implicated in the development of Xenopus neural crest (NC). The NC is a multipotent stem-cell population, specified during early neurulation. Following EMT, NC cells migrate to various points in the developing embryo where they give rise to a number of tissues including parts of the peripheral nervous system, pigment cells and craniofacial skeleton. Dysregulation of NC development results in many diseases grouped under the term neurocristopathies. As miRNAs are so small, it is difficult to design CRISPR sgRNAs that reproducibly lead to a KO. We have therefore designed a novel approach using two guide RNAs to effectively 'drop out' a miRNA. We have knocked out miR-196a and miR-219 and compared the results to morpholino knockdowns (KD) of the same miRNAs. Validation of efficient CRISPR miRNA KO and phenotype analysis included use of whole-mount in situ hybridization of key NC and neural plate border markers such as Pax3, Xhe2, Sox10 and Snail2, q-RT-PCR and Sanger sequencing. To show specificity we have also rescued the knockout phenotype using miRNA mimics. MiRNA-219 and miR-196a KO's both show loss of NC, altered neural plate and hatching gland phenotypes. Tadpoles show gross craniofacial and pigment phenotypes.
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Affiliation(s)
- Alice M Godden
- School of Biological Sciences, University of East Anglia, Norwich Research Park, Norwich, NR4 7TJ, United Kingdom
| | - Marco Antonaci
- School of Biological Sciences, University of East Anglia, Norwich Research Park, Norwich, NR4 7TJ, United Kingdom
| | - Nicole J Ward
- School of Biological Sciences, University of East Anglia, Norwich Research Park, Norwich, NR4 7TJ, United Kingdom
| | - Michael van der Lee
- School of Biological Sciences, University of East Anglia, Norwich Research Park, Norwich, NR4 7TJ, United Kingdom
| | - Anita Abu-Daya
- King Henry Building, King Henry I St, Portsmouth, PO1 2DY, United Kingdom
| | - Matthew Guille
- King Henry Building, King Henry I St, Portsmouth, PO1 2DY, United Kingdom
| | - Grant N Wheeler
- School of Biological Sciences, University of East Anglia, Norwich Research Park, Norwich, NR4 7TJ, United Kingdom.
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Abstract
The cryopreservation of Xenopus sperm allows for a significant reduction of the number of animals that must be kept, more efficient archiving of genetically altered (GA) lines, and easy exchange of lines with other laboratories, leading to improvements in animal welfare and cost efficiency. In this protocol, sperm from Xenopus laevis or Xenopus tropicalis are frozen using straightforward techniques and standard laboratory equipment. Testes are macerated in Leibovitz's L-15 medium, mixed with a simple cryoprotectant made from egg yolk and sucrose, and frozen slowly overnight in a polystyrene box at -80°C. Unlike mouse sperm, Xenopus sperm can be stored at -80°C rather than in liquid nitrogen, further reducing costs. The frozen sperm are then used for in vitro fertilization.
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Affiliation(s)
- Anna Noble
- European Xenopus Research Center (EXRC), School of Biological Sciences, University of Portsmouth, Portsmouth PO1 2UP, United Kingdom
| | - Anita Abu-Daya
- European Xenopus Research Center (EXRC), School of Biological Sciences, University of Portsmouth, Portsmouth PO1 2UP, United Kingdom
| | - Matt Guille
- European Xenopus Research Center (EXRC), School of Biological Sciences, University of Portsmouth, Portsmouth PO1 2UP, United Kingdom
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Horb M, Wlizla M, Abu-Daya A, McNamara S, Gajdasik D, Igawa T, Suzuki A, Ogino H, Noble A, Robert J, James-Zorn C, Guille M. Xenopus Resources: Transgenic, Inbred and Mutant Animals, Training Opportunities, and Web-Based Support. Front Physiol 2019; 10:387. [PMID: 31073289 PMCID: PMC6497014 DOI: 10.3389/fphys.2019.00387] [Citation(s) in RCA: 33] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2019] [Accepted: 03/21/2019] [Indexed: 02/06/2023] Open
Abstract
Two species of the clawed frog family, Xenopus laevis and X. tropicalis, are widely used as tools to investigate both normal and disease-state biochemistry, genetics, cell biology, and developmental biology. To support both frog specialist and non-specialist scientists needing access to these models for their research, a number of centralized resources exist around the world. These include centers that hold live and frozen stocks of transgenic, inbred and mutant animals and centers that hold molecular resources. This infrastructure is supported by a model organism database. Here, we describe much of this infrastructure and encourage the community to make the best use of it and to guide the resource centers in developing new lines and libraries.
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Affiliation(s)
- Marko Horb
- National Xenopus Resource, Marine Biological Laboratory, Woods Hole, MA, United States
| | - Marcin Wlizla
- National Xenopus Resource, Marine Biological Laboratory, Woods Hole, MA, United States
| | - Anita Abu-Daya
- European Xenopus Resource Centre, Portsmouth, United Kingdom
| | - Sean McNamara
- National Xenopus Resource, Marine Biological Laboratory, Woods Hole, MA, United States
| | - Dominika Gajdasik
- School of Biological Sciences, King Henry Building, Portsmouth, United Kingdom
| | - Takeshi Igawa
- Amphibian Research Center, Hiroshima University, Higashihiroshima, Japan
| | - Atsushi Suzuki
- Amphibian Research Center, Hiroshima University, Higashihiroshima, Japan
| | - Hajime Ogino
- Amphibian Research Center, Hiroshima University, Higashihiroshima, Japan
| | - Anna Noble
- European Xenopus Resource Centre, Portsmouth, United Kingdom
| | | | - Jacques Robert
- Department of Microbiology and Immunology, University of Rochester Medical Center, Rochester, NY, United States
| | - Christina James-Zorn
- Xenbase, Division of Developmental Biology, Cincinnati Children's Research Foundation, Cincinnati, OH, United States
| | - Matthew Guille
- European Xenopus Resource Centre, Portsmouth, United Kingdom.,School of Biological Sciences, King Henry Building, Portsmouth, United Kingdom
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Abu-Daya A, Khokha MK, Zimmerman LB. The hitchhiker's guide to Xenopus genetics. Genesis 2012; 50:164-75. [PMID: 22344745 DOI: 10.1002/dvg.22007] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2011] [Revised: 12/19/2011] [Accepted: 12/23/2011] [Indexed: 01/12/2023]
Abstract
A decade after the human genome sequence, most vertebrate gene functions remain poorly understood, limiting benefits to human health from rapidly advancing genomic technologies. Systematic in vivo functional analysis is ideally suited to the experimentally accessible Xenopus embryo, which combines embryological accessibility with a broad range of transgenic, biochemical, and gain-of-function assays. The diploid X. tropicalis adds loss-of-function genetics and enhanced genomics to this repertoire. In the last decade, diverse phenotypes have been recovered from genetic screens, mutations have been cloned, and reverse genetics in the form of TILLING and targeted gene editing have been established. Simple haploid genetics and gynogenesis and the very large number of embryos produced streamline screening and mapping. Improved genomic resources and the revolution in high-throughput sequencing are transforming mutation cloning and reverse genetic approaches. The combination of loss-of-function mutant backgrounds with the diverse array of conventional Xenopus assays offers a uniquely flexible platform for analysis of gene function in vertebrate development.
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Affiliation(s)
- Anita Abu-Daya
- Division of Developmental Biology, MRC-National Institute for Medical Research, Mill Hill, London, United Kingdom
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Abstract
Xenopus tropicalis combine the advantages of X. laevis, for example using explants and targeted gain of function, with the ability to take classical genetics approaches to answering cell and developmental biology questions making it arguably the most versatile of the model organisms. Against this background, husbandry of X. tropicalis is less well developed than for its larger, more robust relative. Here we describe the methods used to keep and breed these frogs successfully.
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Affiliation(s)
- Alan Jafkins
- European Xenopus Resource Centre, School of Biological Sciences, University of Portsmouth, Portsmouth, England, UK
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Abu-Daya A, Nishimoto S, Fairclough L, Mohun TJ, Logan MPO, Zimmerman LB. The secreted integrin ligand nephronectin is necessary for forelimb formation in Xenopus tropicalis. Dev Biol 2010; 349:204-12. [PMID: 20977901 PMCID: PMC3021715 DOI: 10.1016/j.ydbio.2010.10.015] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2010] [Revised: 09/27/2010] [Accepted: 10/14/2010] [Indexed: 11/21/2022]
Abstract
While limb regeneration has been extensively studied in amphibians, little is known about the initial events in limb formation in metamorphosing anurans. The small secreted integrin ligand nephronectin (npnt) is necessary for development of the metanephros in mouse. Although expressed in many tissues, its role in other developmental processes is not well-studied. Here we show that a transgene insertion that disrupts this gene ablates forelimb formation in Xenopus tropicalis. Our results suggest a novel role for integrin signalling in limb development, and represent the first insertional phenotype to be cloned in amphibians.
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Affiliation(s)
- Anita Abu-Daya
- Division of Developmental Biology, MRC-National Institute for Medical Research, Mill Hill, London, NW7 1AA, UK
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Abu-Daya A, Sater AK, Wells DE, Mohun TJ, Zimmerman LB. Absence of heartbeat in the Xenopus tropicalis mutation muzak is caused by a nonsense mutation in cardiac myosin myh6. Dev Biol 2009; 336:20-9. [PMID: 19769958 PMCID: PMC2786259 DOI: 10.1016/j.ydbio.2009.09.019] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.8] [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: 04/30/2009] [Revised: 08/17/2009] [Accepted: 09/14/2009] [Indexed: 11/25/2022]
Abstract
Mechanisms coupling heart function and cardiac morphogenesis can be
accessed in lower vertebrate embryos that can survive to swimming tadpole stages
on diffused oxygen. Forward genetic screens in Xenopus
tropicalis have identified more than 80 mutations affecting diverse
developmental processes, including cardiac morphogenesis and function. In the
first positional cloning of a mutation in X. tropicalis, we
show that non-contractile hearts in muzak (muz) embryos are
caused by a premature stop codon in the cardiac myosin heavy chain gene
myh6. The mutation deletes the coiled-coil domain
responsible for polymerization into thick filaments, severely disrupting the
cardiomyocyte cytoskeleton. Despite the lack of contractile activity and absence
of a major structural protein, early stages of cardiac morphogenesis including
looping and chamber formation are grossly normal. Muz hearts
subsequently develop dilated chambers with compressed endocardium and fail to
form identifiable cardiac valves and trabeculae.
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Affiliation(s)
- Anita Abu-Daya
- MRC National Institute for Medical Research, The Ridgeway, Mill Hill, London, NW7 1AA, UK
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Khokha MK, Krylov V, Reilly MJ, Gall JG, Bhattacharya D, Cheung CYJ, Kaufman S, Lam DK, Macha J, Ngo C, Prakash N, Schmidt P, Tlapakova T, Trivedi T, Tumova L, Abu-Daya A, Geach T, Vendrell E, Ironfield H, Sinzelle L, Sater AK, Wells DE, Harland RM, Zimmerman LB. Rapid gynogenetic mapping of Xenopus tropicalis mutations to chromosomes. Dev Dyn 2009; 238:1398-46. [PMID: 19441086 DOI: 10.1002/dvdy.21965] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
Abstract
Pilot forward genetic screens in Xenopus tropicalis have isolated over 60 recessive mutations. Here we present a simple method for mapping mutations to chromosomes using gynogenesis and centromeric markers. When coupled with available genomic resources, gross mapping facilitates evaluation of candidate genes as well as higher resolution linkage studies. Using gynogenesis, we have mapped the genetic locations of the 10 X. tropicalis centromeres, and performed fluorescence in situ hybridization to validate these locations cytologically. We demonstrate the use of this very small set of centromeric markers to map mutations efficiently to specific chromosomes. Developmental Dynamics 238:1398-1406, 2009. (c) 2009 Wiley-Liss, Inc.
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Affiliation(s)
- Mustafa K Khokha
- Department of Pediatrics and Genetics, Yale University School of Medicine, New Haven, Connecticut, USA
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Goda T, Abu-Daya A, Carruthers S, Clark MD, Stemple DL, Zimmerman LB. Genetic screens for mutations affecting development of Xenopus tropicalis. PLoS Genet 2006; 2:e91. [PMID: 16789825 PMCID: PMC1475704 DOI: 10.1371/journal.pgen.0020091] [Citation(s) in RCA: 64] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2005] [Accepted: 04/28/2006] [Indexed: 11/18/2022] Open
Abstract
We present here the results of forward and reverse genetic screens for chemically-induced mutations in Xenopus tropicalis. In our forward genetic screen, we have uncovered 77 candidate phenotypes in diverse organogenesis and differentiation processes. Using a gynogenetic screen design, which minimizes time and husbandry space expenditures, we find that if a phenotype is detected in the gynogenetic F2 of a given F1 female twice, it is highly likely to be a heritable abnormality (29/29 cases). We have also demonstrated the feasibility of reverse genetic approaches for obtaining carriers of mutations in specific genes, and have directly determined an induced mutation rate by sequencing specific exons from a mutagenized population. The Xenopus system, with its well-understood embryology, fate map, and gain-of-function approaches, can now be coupled with efficient loss-of-function genetic strategies for vertebrate functional genomics and developmental genetics.
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Affiliation(s)
- Tadahiro Goda
- Division of Developmental Biology, National Institute for Medical Research, The Ridgeway, Mill Hill, London, United Kingdom
| | - Anita Abu-Daya
- Division of Developmental Biology, National Institute for Medical Research, The Ridgeway, Mill Hill, London, United Kingdom
| | - Samantha Carruthers
- Vertebrate Development and Genetics, Wellcome Trust Sanger Institute, Wellcome Trust Genome Campus, Hinxton, Cambridge, United Kingdom
| | - Matthew D Clark
- Vertebrate Development and Genetics, Wellcome Trust Sanger Institute, Wellcome Trust Genome Campus, Hinxton, Cambridge, United Kingdom
| | - Derek L Stemple
- Vertebrate Development and Genetics, Wellcome Trust Sanger Institute, Wellcome Trust Genome Campus, Hinxton, Cambridge, United Kingdom
- * To whom correspondence should be addressed. E-mail: (DLS); (LBZ)
| | - Lyle B Zimmerman
- Division of Developmental Biology, National Institute for Medical Research, The Ridgeway, Mill Hill, London, United Kingdom
- * To whom correspondence should be addressed. E-mail: (DLS); (LBZ)
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Abu-Daya A, Steer WM, Trollope AF, Friedeberg CE, Patient RK, Thorne AW, Guille MJ. Zygotic nucleosome assembly protein-like 1 has a specific, non-cell autonomous role in hematopoiesis. Blood 2005; 106:514-20. [PMID: 15811954 DOI: 10.1182/blood-2005-02-0598] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [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] [Indexed: 11/20/2022] Open
Abstract
Nucleosome assembly proteins (NAPs) bind core histones, facilitate chromatin remodeling, and can act as transcriptional coactivators. We previously described the isolation of a Xenopus NAP1-like (xNAP1L) cDNA, which encodes a member of this protein family. Its zygotic expression is restricted to neural cells, the outer cells of the ventral blood island (VBIs), and the ectoderm overlying the blood precursors. Here, we report that depletion of zygotic xNAP1L in embryos produces no obvious morphologic phenotype, but ablates alpha-globin mRNA expression in the VBIs. Transcript levels of the hematopoietic precursor genes SCL and Xaml (Runx-1) are also reduced in the VBIs. SCL expression can be rescued by injection of xNAP1L mRNA into the ectoderm, showing that the effect of xNAP1L can be non-cell autonomous. Fli1 and Hex, genes expressed in hemangioblasts but subsequently endothelial markers, were unaffected, suggesting that xNAP1L is required for the hematopoietic lineage specifically. Our data are consistent with a requirement for xNAP1L upstream of SCL, and injection of SCL mRNA into xNAP1L-depleted embryos rescues alpha-globin expression. Thus, xNAP1L, which belongs to a family of proteins previously believed to have general roles, has a specific function in hematopoiesis.
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Affiliation(s)
- Anita Abu-Daya
- School of Biological Sciences, Institute of Biomedical and Biomolecular Science, University of Portsmouth, Portsmouth PO1 2DT, United Kingdom
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Steer WM, Abu-Daya A, Brickwood SJ, Mumford KL, Jordanaires N, Mitchell J, Robinson C, Thorne AW, Guille MJ. Xenopus nucleosome assembly protein becomes tissue-restricted during development and can alter the expression of specific genes. Mech Dev 2003; 120:1045-57. [PMID: 14550533 DOI: 10.1016/s0925-4773(03)00176-x] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.9] [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: 10/27/2022]
Abstract
Nucleosome assembly proteins have been identified in all eukaryotic species investigated to date and their suggested roles include histone shuttle, histone acceptor during transcriptional chromatin remodelling and cell cycle regulator. To examine the role of these proteins during early development we have isolated the cDNA encoding Xenopus NAP1L, raised an antibody against recombinant xNAP1L and examined the expression pattern of this mRNA and protein. Expression in adults is predominantly in ovaries. This maternal protein remains a major component of xNAP1L within the embryo until swimming tadpole stages. xNAP1L mRNA is initially throughout the embryo but by gastrula stages it is predominantly in the presumptive ectoderm. Later, mRNA is detected in the neural crest, neural tube, eyes, tailbud and ventral blood islands. In order to test whether xNAP1L has a potential role in gene regulation we overexpressed this protein in animal pole explants and tested the effect on expression of a series of potential target genes. The mRNA encoding the transcription factor GATA-2 was markedly up-regulated by this overexpression. These data support a role for xNAP1L in tissue-restricted gene regulation.
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Affiliation(s)
- Wendy M Steer
- Genes and Development, Institute of Biomedical and Biomolecular Sciences, University of Portsmouth, King Henry Building, King Henry 1st Street, Portsmouth PO1 2DY, UK
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Abstract
We have used quantitative DNase I footprinting to examine the ability of distamycin and Hoechst 33258 to discriminate between different arrangements of AT residues, using synthetic DNA fragments containing multiple blocks of (A/T)6or (A/T)10in identical sequence environments. Previous studies have shown that these ligands bind less well to (A/T)4sites containing TpA steps. We find that in (A/T)6tracts distamycin shows little discrimination between the various sites, binding approximately 2-fold stronger to TAATTA than (TA)3, T3A3and GAATTC. In contrast, Hoechst 33258 binds approximately 20-fold more tightly to GAATTC and TAATTA than T3A3and (TA)3. Hydroxyl radical footprinting reveals that both ligands bind in similar locations at the centre of each AT tract. At (A/T)10sites distamycin binds with similar affinity to T5A5, (TA)5and AATT, though bands in the centre of (TA)5are protected at approximately 50-fold lower concentration than those towards the edges. Hoechst 33258 shows a similar pattern of preference, with strong binding to AATT, T5A5and the centre of (TA)5. Hydroxyl radical footprinting reveals that at low concentrations both ligands bind at the centre of (TA)5and A5T5, while at higher concentrations ligand molecules bind to each end of the (A/T)10tracts. At T5A5two ligand molecules bind at either end of the site, even at the lowest ligand concentration, consistent with the suggestion that these compounds avoid the TpA step. Similar DNase I footprinting experiments with a DNA fragment containing T n (n = 3-6) tracts reveals that both ligands bind in the order T3< T4 << T5 = T6.
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Affiliation(s)
- A Abu-Daya
- Division of Biochemistry and Molecular Biology, School of Biological Sciences, University of Southampton, Bassett Crescent East, Southampton SO16 7PX, UK
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14
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Abstract
We have examined the interaction of distamycin, netropsin, Hoechst 33258 and berenil, which are AT-selective minor groove-binding ligands, with synthetic DNA fragments containing different arrangements of AT base pairs by DNase I footprinting. For fragments which contain multiple blocks of (A/T)4 quantitative DNase I footprinting reveals that AATT and AAAA are much better binding sites than TTAA and TATA. Hoechst 33258 shows that greatest discrimination between these sites with a 50-fold difference in affinity between AATT and TATA. Alone amongst these ligands, Hoechst 33258 binds to AATT better than AAAA. These differences in binding to the various AT-tracts are interpreted in terms of variations in DNA minor groove width and suggest that TpA steps within an AT-tract decrease the affinity of these ligands. The behaviour of each site also depends on the flanking sequences; adjacent pyrimidine-purine steps cause a decrease in affinity. The precise ranking order for the various binding sites is not the same for each ligand.
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Affiliation(s)
- A Abu-Daya
- Department of Physiology and Pharmacology, University of Southampton, UK
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