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Xu XRS, Bulger EA, Gantz VM, Klanseck C, Heimler SR, Auradkar A, Bennett JB, Miller LA, Leahy S, Juste SS, Buchman A, Akbari OS, Marshall JM, Bier E. Active Genetic Neutralizing Elements for Halting or Deleting Gene Drives. Mol Cell 2020; 80:246-262.e4. [PMID: 32949493 PMCID: PMC10962758 DOI: 10.1016/j.molcel.2020.09.003] [Citation(s) in RCA: 41] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2019] [Revised: 05/03/2020] [Accepted: 09/01/2020] [Indexed: 01/02/2023]
Abstract
CRISPR-Cas9-based gene drive systems possess the inherent capacity to spread progressively throughout target populations. Here we describe two self-copying (or active) guide RNA-only genetic elements, called e-CHACRs and ERACRs. These elements use Cas9 produced in trans by a gene drive either to inactivate the cas9 transgene (e-CHACRs) or to delete and replace the gene drive (ERACRs). e-CHACRs can be inserted at various genomic locations and carry two or more gRNAs, the first copying the e-CHACR and the second mutating and inactivating the cas9 transgene. Alternatively, ERACRs are inserted at the same genomic location as a gene drive, carrying two gRNAs that cut on either side of the gene drive to excise it. e-CHACRs efficiently inactivate Cas9 and can drive to completion in cage experiments. Similarly, ERACRs, particularly those carrying a recoded cDNA-restoring endogenous gene activity, can drive reliably to fully replace a gene drive. We compare the strengths of these two systems.
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Affiliation(s)
- Xiang-Ru Shannon Xu
- Section of Cell and Developmental Biology, University of California, San Diego, La Jolla, CA, USA; Tata Institute for Genetics and Society, University of California, San Diego, La Jolla, CA, USA
| | - Emily A Bulger
- Section of Cell and Developmental Biology, University of California, San Diego, La Jolla, CA, USA; Tata Institute for Genetics and Society, University of California, San Diego, La Jolla, CA, USA; Developmental and Stem Cell Biology Graduate Program, University of California, San Francisco, and Gladstone Institutes, San Francisco, CA, USA
| | - Valentino M Gantz
- Section of Cell and Developmental Biology, University of California, San Diego, La Jolla, CA, USA; Tata Institute for Genetics and Society, University of California, San Diego, La Jolla, CA, USA
| | - Carissa Klanseck
- Section of Cell and Developmental Biology, University of California, San Diego, La Jolla, CA, USA; Tata Institute for Genetics and Society, University of California, San Diego, La Jolla, CA, USA
| | - Stephanie R Heimler
- Section of Cell and Developmental Biology, University of California, San Diego, La Jolla, CA, USA; Tata Institute for Genetics and Society, University of California, San Diego, La Jolla, CA, USA
| | - Ankush Auradkar
- Section of Cell and Developmental Biology, University of California, San Diego, La Jolla, CA, USA; Tata Institute for Genetics and Society, University of California, San Diego, La Jolla, CA, USA
| | - Jared B Bennett
- Biophysics Graduate Group, University of California, Berkeley, Berkeley, CA 94720, USA
| | - Lauren Ashley Miller
- Section of Cell and Developmental Biology, University of California, San Diego, La Jolla, CA, USA; Tata Institute for Genetics and Society, University of California, San Diego, La Jolla, CA, USA
| | - Sarah Leahy
- Section of Cell and Developmental Biology, University of California, San Diego, La Jolla, CA, USA
| | - Sara Sanz Juste
- Section of Cell and Developmental Biology, University of California, San Diego, La Jolla, CA, USA; Tata Institute for Genetics and Society, University of California, San Diego, La Jolla, CA, USA
| | - Anna Buchman
- Section of Cell and Developmental Biology, University of California, San Diego, La Jolla, CA, USA; Tata Institute for Genetics and Society, University of California, San Diego, La Jolla, CA, USA
| | - Omar S Akbari
- Section of Cell and Developmental Biology, University of California, San Diego, La Jolla, CA, USA; Tata Institute for Genetics and Society, University of California, San Diego, La Jolla, CA, USA
| | - John M Marshall
- Division of Epidemiology and Biostatistics, School of Public Health, University of California, Berkeley, Berkeley, CA, USA; Innovative Genomics Institute, Berkeley, CA, USA
| | - Ethan Bier
- Section of Cell and Developmental Biology, University of California, San Diego, La Jolla, CA, USA; Tata Institute for Genetics and Society, University of California, San Diego, La Jolla, CA, USA.
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Rahnama M, Novikova O, Starnes JH, Zhang S, Chen L, Farman ML. Transposon-mediated telomere destabilization: a driver of genome evolution in the blast fungus. Nucleic Acids Res 2020; 48:7197-7217. [PMID: 32558886 PMCID: PMC7367193 DOI: 10.1093/nar/gkaa287] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2019] [Revised: 04/03/2020] [Accepted: 04/14/2020] [Indexed: 01/01/2023] Open
Abstract
The fungus Magnaporthe oryzae causes devastating diseases of crops, including rice and wheat, and in various grasses. Strains from ryegrasses have highly unstable chromosome ends that undergo frequent rearrangements, and this has been associated with the presence of retrotransposons (Magnaporthe oryzae Telomeric Retrotransposons-MoTeRs) inserted in the telomeres. The objective of the present study was to determine the mechanisms by which MoTeRs promote telomere instability. Targeted cloning, mapping, and sequencing of parental and novel telomeric restriction fragments (TRFs), along with MinION sequencing of genomic DNA allowed us to document the precise molecular alterations underlying 109 newly-formed TRFs. These included truncations of subterminal rDNA sequences; acquisition of MoTeR insertions by 'plain' telomeres; insertion of the MAGGY retrotransposons into MoTeR arrays; MoTeR-independent expansion and contraction of subtelomeric tandem repeats; and a variety of rearrangements initiated through breaks in interstitial telomere tracts that are generated during MoTeR integration. Overall, we estimate that alterations occurred in approximately sixty percent of chromosomes (one in three telomeres) analyzed. Most importantly, we describe an entirely new mechanism by which transposons can promote genomic alterations at exceptionally high frequencies, and in a manner that can promote genome evolution while minimizing collateral damage to overall chromosome architecture and function.
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Affiliation(s)
- Mostafa Rahnama
- Department of Plant Pathology, University of Kentucky, 1405 Veteran's Dr., Lexington, KY 40546, USA
| | - Olga Novikova
- Department of Plant Pathology, University of Kentucky, 1405 Veteran's Dr., Lexington, KY 40546, USA
| | - John H Starnes
- Department of Plant Pathology, University of Kentucky, 1405 Veteran's Dr., Lexington, KY 40546, USA
| | - Shouan Zhang
- Department of Plant Pathology, University of Kentucky, 1405 Veteran's Dr., Lexington, KY 40546, USA
| | - Li Chen
- Department of Plant Pathology, University of Kentucky, 1405 Veteran's Dr., Lexington, KY 40546, USA
| | - Mark L Farman
- Department of Plant Pathology, University of Kentucky, 1405 Veteran's Dr., Lexington, KY 40546, USA
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Abstract
A recent study by Zhang and colleagues published in the March 15, 2009, issue of Genes & Development (pp. 755-765) demonstrates that maize Ac/Ds transposons mediate translocations and other rearrangements through aberrant execution of the normal transposition process. Ac transposase uses one end from each of two neighboring elements in these events, which may happen more commonly than previously thought. In genomes where there can be many transposon ends scattered across all the chromosomes, such mistakes can have important consequences.
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Interactions of Transposons with the Cellular DNA Repair Machinery. TRANSPOSONS AND THE DYNAMIC GENOME 2009. [DOI: 10.1007/7050_2008_043] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/03/2022]
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Ghosh-Roy A, Kulkarni M, Kumar V, Shirolikar S, Ray K. Cytoplasmic dynein-dynactin complex is required for spermatid growth but not axoneme assembly in Drosophila. Mol Biol Cell 2004; 15:2470-83. [PMID: 15020714 PMCID: PMC404038 DOI: 10.1091/mbc.e03-11-0848] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Spermatids derived from a single gonial cell remain interconnected within a cyst and elongate by synchronized growth inside the testis in Drosophila. Cylindrical spectrin-rich elongation cones form at their distal ends during the growth. The mechanism underlying this process is poorly understood. We found that developing sperm tails were abnormally coiled at the growing ends inside the cysts in the Drosophila Dynein light chain 1 (ddlc1) hemizygous mutant testis. A quantitative assay showed that average number of elongation cones was reduced, they were increasingly deformed, and average cyst lengths were shortened in ddlc1 hemizygous testes. These phenotypes were further enhanced by additional partial reduction of Dhc64C and Glued and rescued by Myc-PIN/LC8 expression in the gonial cells in ddlc1 backgrounds. Furthermore, DDLC1, DHC, and GLUED were enriched at the distal ends of growing spermatids. Finally, ultrastructure analysis of ddlc1 testes revealed abnormally formed interspermatid membrane, but the 9 + 2 microtubule organization, the radial spoke structures, and the Dynein arms of the axoneme were normal. Together, these findings suggest that axoneme assembly and spermatid growth involve independent mechanisms in Drosophila and DDLC1 interacts with the Dynein-Dynactin complex at the distal ends of spermatids to maintain the spectrin cytoskeleton assembly and cell growth.
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Preston CR, Engels W, Flores C. Efficient repair of DNA breaks in Drosophila: evidence for single-strand annealing and competition with other repair pathways. Genetics 2002; 161:711-20. [PMID: 12072467 PMCID: PMC1462149 DOI: 10.1093/genetics/161.2.711] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
Abstract
We show evidence that DNA double-strand breaks induced in the Drosophila germ line can be repaired very efficiently by the single-strand annealing (SSA) mechanism. A double-strand break was made between two copies of a 1290-bp direct repeat by mobilizing a P transposon. In >80% of the progeny that acquired this chromosome, repair resulted in loss of the P element and loss of one copy of the repeat, as observed in SSA. The frequency of this repair was much greater than seen for gene conversion using an allelic template, which is only approximately 7%. A similar structure, but with a smaller duplication of only 158 bp, also yielded SSA-like repair events, but at a reduced frequency, and gave rise to some products by repair pathways other than SSA. The 1290-bp repeats carried two sequence polymorphisms that were examined in the products. The allele nearest to a nick in the putative heteroduplex intermediate was lost most often. This bias is predicted by the SSA model, although other models could account for it. We conclude that SSA is the preferred repair pathway in Drosophila for DNA breaks between sequence repeats, and it competes with gene conversion by the synthesis-dependent strand annealing (SDSA) pathway.
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Affiliation(s)
- Christine R Preston
- Laboratory of Genetics, University of Wisconsin, Madison, Wisconsin 53706, USA
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Guichard A, Srinivasan S, Zimm G, Bier E. A screen for dominant mutations applied to components in the Drosophila EGF-R pathway. Proc Natl Acad Sci U S A 2002; 99:3752-7. [PMID: 11904431 PMCID: PMC122596 DOI: 10.1073/pnas.052028699] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The Drosophila epidermal growth factor receptor (EGF-R) controls many critical cell fate choices throughout development. Several proteins collaborate to promote localized EGF-R activation, such as Star and Rhomboid (Rho), which act sequentially to ensure the maturation and processing of inactive membrane-bound EGF ligands. To gain insights into the mechanisms underlying Rho and Star function, we developed a mutagenesis scheme to isolate novel overexpression activity (NOVA) alleles. In the case of rho, we isolated a dominant neomorphic allele, which interferes with Notch signaling, as well as a dominant-negative allele, which produces RNA interference-like flip-back transcripts that reduce endogenous rho expression. We also obtained dominant-negative and neomorphic Star mutations, which have phenotypes similar to those of rho NOVA alleles, as well as dominant-negative Egf-r alleles. The isolation of dominant alleles in several different genes suggests that NOVA mutagenesis should be widely applicable and emerge as an effective tool for generating dominant mutations in genes of unknown function.
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Affiliation(s)
- Annabel Guichard
- Section of Cell and Developmental Biology, University of California at San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0349, USA
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8
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Timakov B, Liu X, Turgut I, Zhang P. Timing and targeting of P-element local transposition in the male germline cells of Drosophila melanogaster. Genetics 2002; 160:1011-22. [PMID: 11901118 PMCID: PMC1462012 DOI: 10.1093/genetics/160.3.1011] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
The P element in Drosophila melanogaster preferentially transposes into nearby sites. The local insertions display a preferential orientation toward the starting element. We investigated the mechanism of the P-element local transposition by isolating and characterizing local insertions in the male germline. We designed a genetic screen employing a marker gene that is carried in the P element and is dose sensitive. This dose effect allows isolation of flies containing newly transposed P elements in the presence of the starting element. A rapid molecular screen with PCR was used to identify 45 local insertions located within an approximately 40-kb genomic region on both sides of the starting element. Our system permits the isolation of the cluster progeny derived from a single insertion event, but none was isolated. The data suggest that local transposition occurs in the meiotic cell cycle. Nearly all of the local insertions were located within the promoter regions of the genes that were active in the male germline cells, suggesting that local insertions target predominantly active promoters. Our analysis shows that local transposition of the P element is highly regulated, displaying a cell-type specificity and a target specificity.
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Affiliation(s)
- Benjamin Timakov
- Department of Molecular and Cell Biology, University of Connecticut, Storrs, Connecticut 06269-2131, USA
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Abstract
Transposable elements (TEs) promote various chromosomal rearrangements more efficiently, and often more specifically, than other cellular processes(1-3). One explanation of such events is homologous recombination between multiple copies of a TE present in a genome. Although this does occur, strong evidence from a number of TE systems in bacteria, plants and animals suggests that another mechanism - alternative transposition - induces a large proportion of TE-associated chromosomal rearrangements. This paper reviews evidence for alternative transposition from a number of unrelated but structurally similar TEs. The similarities between alternative transposition and V(D)J recombination are also discussed, as is the use of alternative transposition as a genetic tool.
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Affiliation(s)
- Y H Gray
- Molecular Genetics and Evolution Group, Research School of Biological Sciences, Australian National University, ACT 2601, Canberra, Australia.
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Ring BC, Bass HW, Garza D. Construction and transposition of a 100-kilobase extended P element in Drosophila. Genome Res 2000; 10:1605-16. [PMID: 11042158 PMCID: PMC310958 DOI: 10.1101/gr.151700] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
We have used P element deletion derivatives at defined locations in the Drosophila genome to construct a 100-kb extended P element more than twice the size of any previously available. We demonstrate that this prototypical extended P element is capable of transposition to new sites in the genome. The structural and functional integrity of a transposed extended P element was confirmed using molecular, genetic, and cytogenetic criteria. This is the first method shown to be capable of producing large, unlinked transpositional duplications in Drosophila. The ability to produce functional transposable elements from half-elements is novel and has many potential applications for the functional analysis of complex genomes.
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Affiliation(s)
- B C Ring
- Department of Biological Science, Florida State University, Tallahassee, Florida 32306-4370, USA
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11
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Richard GF, Pâques F. Mini- and microsatellite expansions: the recombination connection. EMBO Rep 2000; 1:122-6. [PMID: 11265750 PMCID: PMC1084263 DOI: 10.1093/embo-reports/kvd031] [Citation(s) in RCA: 138] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2000] [Revised: 06/21/2000] [Accepted: 06/28/2000] [Indexed: 11/14/2022] Open
Abstract
It is widely accepted that the large trinucleotide repeat expansions observed in many neurological diseases occur during replication. However, genetic recombination has emerged as a major source of instability for tandem repeats, including minisatellites, and recent studies raise the possibility that it may also be responsible for trinucleotide repeat expansions. We will review data connecting tandem repeat rearrangements and recombination in humans and in eukaryotic model organisms, and discuss the possible role of recombination in trinucleotide repeat expansions in human neurological disorders.
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Affiliation(s)
- G F Richard
- Unité de Génétique Moléculaire des Levures, URA 2171 CNRS, Paris, France.
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12
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Albornoz J, Domínguez A. Spontaneous changes in Drosophila melanogaster transposable elements and their effects on fitness. Heredity (Edinb) 1999; 83 ( Pt 6):663-70. [PMID: 10651910 DOI: 10.1046/j.1365-2540.1999.00590.x] [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: 11/20/2022] Open
Abstract
Twenty-eight spontaneous alterations modifying the hybridization banding pattern of six families of transposable elements (297, Foldback, copia, jockey, P and hobo) have been fixed in a set of mutation-accumulation lines of Drosophila melanogaster. Their effect on fitness has been studied by competition with the original pattern. Most alterations affecting transposable elements were shown to be rearrangements with no detectable effect on fitness, showing that spontaneous transposable element mutations mainly generate minor fitness mutations.
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Affiliation(s)
- J Albornoz
- Area de Genética, Departamento de Biología Funcional, Universidad de Oviedo, 33071 Oviedo, Spain.
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13
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Pâques F, Haber JE. Multiple pathways of recombination induced by double-strand breaks in Saccharomyces cerevisiae. Microbiol Mol Biol Rev 1999. [PMID: 10357855 DOI: 10.0000/pmid10357855] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/07/2023] Open
Abstract
The budding yeast Saccharomyces cerevisiae has been the principal organism used in experiments to examine genetic recombination in eukaryotes. Studies over the past decade have shown that meiotic recombination and probably most mitotic recombination arise from the repair of double-strand breaks (DSBs). There are multiple pathways by which such DSBs can be repaired, including several homologous recombination pathways and still other nonhomologous mechanisms. Our understanding has also been greatly enriched by the characterization of many proteins involved in recombination and by insights that link aspects of DNA repair to chromosome replication. New molecular models of DSB-induced gene conversion are presented. This review encompasses these different aspects of DSB-induced recombination in Saccharomyces and attempts to relate genetic, molecular biological, and biochemical studies of the processes of DNA repair and recombination.
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Affiliation(s)
- F Pâques
- Rosenstiel Center and Department of Biology, Brandeis University, Waltham, Massachusetts 02454-9110, USA
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14
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Pâques F, Haber JE. Multiple pathways of recombination induced by double-strand breaks in Saccharomyces cerevisiae. Microbiol Mol Biol Rev 1999; 63:349-404. [PMID: 10357855 PMCID: PMC98970 DOI: 10.1128/mmbr.63.2.349-404.1999] [Citation(s) in RCA: 1649] [Impact Index Per Article: 66.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The budding yeast Saccharomyces cerevisiae has been the principal organism used in experiments to examine genetic recombination in eukaryotes. Studies over the past decade have shown that meiotic recombination and probably most mitotic recombination arise from the repair of double-strand breaks (DSBs). There are multiple pathways by which such DSBs can be repaired, including several homologous recombination pathways and still other nonhomologous mechanisms. Our understanding has also been greatly enriched by the characterization of many proteins involved in recombination and by insights that link aspects of DNA repair to chromosome replication. New molecular models of DSB-induced gene conversion are presented. This review encompasses these different aspects of DSB-induced recombination in Saccharomyces and attempts to relate genetic, molecular biological, and biochemical studies of the processes of DNA repair and recombination.
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Affiliation(s)
- F Pâques
- Rosenstiel Center and Department of Biology, Brandeis University, Waltham, Massachusetts 02454-9110, USA
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15
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Rong YS, Golic KG. Dominant defects in Drosophila eye pigmentation resulting from a euchromatin-heterochromatin fusion gene. Genetics 1998; 150:1551-66. [PMID: 9832531 PMCID: PMC1460429 DOI: 10.1093/genetics/150.4.1551] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
We have isolated a dominant mutation, pugilistDominant (pugD), that causes variegated reductions in pteridine and ommochrome pigmentation of the Drosophila eye. The effect of pugD on pteridine pigmentation is most dramatic: the only remaining pigment consists of a thin ring of pigment around the periphery of the eye with a few scattered spots in the center. The pugD mutation disrupts a gene that encodes a Drosophila homolog of the trifunctional enzyme methylenetetrahydrofolate dehydrogenase (MTHFD; E.C.1.5.1.5, E.C.3.5. 4.9, E.C.6.3.4.3). This enzyme produces a cofactor that is utilized in purine biosynthesis. Because pteridines are derived from GTP, the pigment defect may result from an impairment in the production of purines. The mutant allele consists of a portion of the MTHFD coding region fused to approximately 1 kb of highly repetitive DNA. Transcription and translation of both parts are required for the phenotype. The repetitive DNA consists of approximately 140 nearly perfect repeats of the sequence AGAGAGA, a significant component of centric heterochromatin. The unusual nature of the protein produced by this gene may be responsible for its dominance. The repetitive DNA may also account for the variegated aspect of the phenotype. It may promote occasional association of the pugD locus with centric heterochromatin, accompanied by inactivation of pugD, in a manner similar to the proposed mode of action for brownDominant.
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Affiliation(s)
- Y S Rong
- Department of Biology, University of Utah, Salt Lake City, Utah 84112, USA
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16
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Eggert H, Bergemann K, Saumweber H. Molecular screening for P-element insertions in a large genomic region of Drosophila melanogaster using polymerase chain reaction mediated by the vectorette. Genetics 1998; 149:1427-34. [PMID: 9649531 PMCID: PMC1460217 DOI: 10.1093/genetics/149.3.1427] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
As an alternative to existing methods for the detection of new insertions during a transposon mutagenesis, we adapted the method of vectorette ligation to genomic restriction fragments followed by PCR to obtain genomic sequences flanking the transposon. By combining flies containing a defined genomic transposon with an excess of flies containing unrelated insertion sites, we demonstrate the specificity and sensitivity of the procedure in the detection of integration events. This method was applied in a transposon-tagging screen for BJ1, the Drosophila homolog of the vertebrate gene Regulator of Chromosome Condensation (RCCI). Genetic mobilization of a single genomic P element was used to generate preferentially new local insertions from which integrations into a genomic region surrounding the BJ1 gene were screened. Flies harboring new insertions were phenotypically selected on the basis of the zeste1-dependent transvection of white. We detected a single transposition to a 13-kb region close to the BJ1 gene among 6650 progeny that were analyzed. Southern analysis of the homozygous line confirmed the integration 3 kb downstream of BJ1.
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Affiliation(s)
- H Eggert
- Biologie, Abteilung Cytogenetik, Humboldt Universität, 10115 Berlin, Germany. harald=
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17
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Netter S, Fauvarque MO, Diez del Corral R, Dura JM, Coen D. white+ transgene insertions presenting a dorsal/ventral pattern define a single cluster of homeobox genes that is silenced by the polycomb-group proteins in Drosophila melanogaster. Genetics 1998; 149:257-75. [PMID: 9584101 PMCID: PMC1460120 DOI: 10.1093/genetics/149.1.257] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
We used the white gene as an enhancer trap and reporter of chromatin structure. We collected white+ transgene insertions presenting a peculiar pigmentation pattern in the eye: white expression is restricted to the dorsal half of the eye, with a clear-cut dorsal/ventral (D/V) border. This D/V pattern is stable and heritable, indicating that phenotypic expression of the white reporter reflects positional information in the developing eye. Localization of these transgenes led us to identify a unique genomic region encompassing 140 kb in 69D1-3 subject to this D/V effect. This region contains at least three closely related homeobox-containing genes that are constituents of the iroquois complex (IRO-C). IRO-C genes are coordinately regulated and implicated in similar developmental processes. Expression of these genes in the eye is regulated by the products of the Polycomb-group (Pc-G) and trithorax-group (trx-G) genes but is not modified by classical modifiers of position-effect variegation. Our results, together with the report of a Pc-G binding site in 69D, suggest that we have identified a novel cluster of target genes for the Pc-G and trx-G products. We thus propose that ventral silencing of the whole IRO-C in the eye occurs at the level of chromatin structure in a manner similar to that of the homeotic gene complexes, perhaps by local compaction of the region into a heterochromatin-like structure involving the Pc-G products.
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Affiliation(s)
- S Netter
- Embryologie Moléculaire et Expérimentale-Centre National de la Recherche Scientifique/Unité de Recherche Associée 2227, Université Paris Sud, 91405 Orsay Cedex, France
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18
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Pâques F, Leung WY, Haber JE. Expansions and contractions in a tandem repeat induced by double-strand break repair. Mol Cell Biol 1998; 18:2045-54. [PMID: 9528777 PMCID: PMC121435 DOI: 10.1128/mcb.18.4.2045] [Citation(s) in RCA: 177] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/1997] [Accepted: 01/16/1998] [Indexed: 02/07/2023] Open
Abstract
Repair of a double-strand break (DSB) in yeast can induce very frequent expansions and contractions in a tandem array of 375-bp repeats. These results strongly suggest that DSB repair can be a major source of amplification of tandemly repeated sequences. Most of the DSB repair events are not associated with crossover. Rearrangements appear in 50% of these repaired recipient molecules. In contrast, the donor template nearly always remains unchanged. Among the rare crossover events, similar rearrangements are found. These results cannot readily be explained by the gap repair model of Szostak et al. (J. W. Szostak, T. L. Orr-Weaver, R. J. Rothstein, and F. W. Stahl, Cell 33:25-35, 1983) but can be explained by synthesis-dependent strand annealing (SDSA) models that allow for crossover. Support for SDSA models is provided by a demonstration that a single DSB repair event can use two donor templates located on two different chromosomes.
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Affiliation(s)
- F Pâques
- Rosenstiel Center and Department of Biology, Brandeis University, Waltham, Massachusetts 02254-9110, USA
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19
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Keeler KJ, Gloor GB. Efficient gap repair in Drosophila melanogaster requires a maximum of 31 nucleotides of homologous sequence at the searching ends. Mol Cell Biol 1997; 17:627-34. [PMID: 9001216 PMCID: PMC231788 DOI: 10.1128/mcb.17.2.627] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
Double-strand breaks (DSB) were generated in the Drosophila melanogaster white gene by excision of the P-w(hd) element. An ectopic P-element vector carrying a modified white gene was used as a template for DSB repair. All template-dependent repair events were examined, and four different classes of events were recovered. The two most common products observed were gene conversions external to the P-w(hd) element and gene conversions (targeted transpositions) internal to the P-w(hd) element. These two events were equally frequent. Similar numbers for both orientations of internal conversion events were recovered. The results suggest that P-element excision occurs by a staggered cut that leaves behind at least 33 nucleotides of single-stranded sequence. Our results further demonstrate that an efficient homology search is conducted by the broken end with less than 31 nucleotides.
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Affiliation(s)
- K J Keeler
- Department of Biochemistry, University of Western Ontario, London, Canada
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Abstract
Transposable elements are discrete mobile DNA segments that can insert into non-homologous target sites. Diverse patterns of target site selectivity are observed: Some elements display considerable target site selectivity and others display little obvious selectivity, although none appears to be truly "random." A variety of mechanisms for target site selection are used: Some elements use direct interactions between the recombinase and target DNA whereas other elements depend upon interactions with accessory proteins that communicate both with the target DNA and the recombinase. The study of target site selectivity is useful in probing recombination mechanisms, in studying genome structure and function, and also in providing tools for genome manipulation.
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Affiliation(s)
- N L Craig
- Howard Hughes Medical Institute, Department of Molecular Biology and Genetics, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA
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