SEARCH · PubMed Health

Results for “Transposable elements”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 145 records · Page 8Linked to original sources

PubMed1991

Tc4, a Caenorhabditis elegans transposable element with an unusual fold-back structure.

We have identified and characterized a family of transposable elements in the nematode Caenorhabditis elegans. The Tc4 transposable element family is present at about 20 copies per haploid genome in the C. elegans Bristol and Bergerac strains. Although Tc4 transposition events have not been observed in these wild-type strains, we have identified Tc4 transposition events in the mut-2 mutant strain TR679, in which the elements Tc1 and Tc3 also transpose at a higher frequency than in the wild type. We determined the sequence of one Tc4 element. This 1.6-kilobase element contains almost perfect inverted terminal repeats of 774 base pairs (bp) with a 57-bp unique internal sequence. Tc4 is a fold-back element, but its long inverted terminal repeats, unlike those of the fold-back elements of other organisms, do not consist of multiple short repeats. In the two cases studied, Tc4 insertion resulted in duplication of a TNA trinucleotide target site. The family of Tc4 elements differs from other C. elegans transposable element families in structure, degree of structural heterogeneity, and target-site specificity.

Animals↗

PubMed1993

Transposable elements in commercially useful insects: I. Southern hybridization study of silkworms and honeybees using Drosophila probes.

As a first step in surveying transposable elements in silkworms and honeybees, hybridization analyses were carried out using 16 known families of Drosophila transposable elements as probes. jockey and G were the only transposable elements that hybridized with genomic DNA of either honeybees or silkworms under the conditions of this study. jockey hybridized with genomic DNA of both European honeybees (Apis mellifera) and silkworms (Bombyx mori and Antheraea yamamai) and showed significant bands in Southern blots. Banding patterns were highly polymorphic. jockey did not, however, hybridize with any strains of the Asian honeybee (A. cerana). G elements showed a faint signal with the Asian honeybee, but not with any other insects tested. The results suggest that, even though it has some limitations, this approach can be used in practice as a first preliminary step in surveys for the presence of transposable elements in organisms which do not have good genetic information.

Animals↗

PubMed2002

Common physical properties of DNA affecting target site selection of sleeping beauty and other Tc1/mariner transposable elements.

Sleeping Beauty (SB) is the most active Tc1/mariner-type transposable element in vertebrates, and is therefore a valuable vector for transposon mutagenesis in vertebrate models and for human gene therapy. We have analyzed factors affecting target site selection of SB in mammalian cells, by generating transposition events from extrachromosomal plasmids to chromosomes. In contrast to the local hopping observed when transposition is induced from a chromosomal context, mapping of 138 unique SB insertions on human chromosomes showed a fairly random genomic distribution, and a 35% occurrence of transposition into genes. Inspection of the DNA flanking the sites of element integration revealed significant differences from random DNA in both primary sequence and physical properties. The consensus sequence of SB target sites was found to be a palindromic AT-repeat, ATATATAT, in which the central TA is the canonical target site. We found however, that target site selection is determined primarily on the level of DNA structure, and not by specific base-pair interactions. Computational analyses revealed that insertion sites tend to have a bendable structure and a palindromic pattern of potential hydrogen-bonding sites in the major groove of the DNA. These features appear conserved in the Tc1/mariner family of transposons and in other, distantly related elements that share a common catalytic domain of the transposase, and integrate fairly randomly. No similar target site preference was found for non-randomly integrating elements. Our results suggest common factors influencing target site selection of a wide range of transposable elements.

Animals↗

PubMed1999

Homogeneity in the structure of the medaka fish transposable element Tol2.

The hAT family is a group of transposable elements of the terminal inverted repeat class, which includes Ac of maize, hobo of Drosophila and Tam3 of Antirrhinum (snapdragon). All the members of this family so far examined are known to comprise complete and defective copies, with a good correspondence to autonomous and non-autonomous elements, respectively. Internal deletion is the most common cause of defective copies. Tol2, a transposable element of the medaka fish Oryzias latipes, is a member of the hAT family. We examined, mainly by the genomic Southern blot analysis, variation in the structure of copies of this element, and revealed that there are few or no internally deleted copies. This situation is unusual in a member of the hAT family. Possible causes of this anomaly are discussed.

Animals↗

PubMed1994

The distribution of transposable elements within and between chromosomes in a population of Drosophila melanogaster. III. Element abundances in heterochromatin.

The total genomic copy numbers of ten families of transposable elements of Drosophila melanogaster in a set of ten isogenic lines derived from a natural population were estimated by slot-blotting. The numbers of euchromatic copies of members of each family were determined for each line by in situ hybridization of element probes to polytene chromosomes. Heterochromatic numbers were estimated by subtraction of the euchromatic counts from the total numbers. There was considerable variation between element families and lines in heterochromatic abundances, and the variance between lines for many elements was much greater for the heterochromatin than for the euchromatin. The data are consistent with the view that much of the beta-heterochromatin consists of sequences derived from transposable elements. They are also consistent with the hypothesis that similar evolutionary forces control element abundances in both the euchromatin and heterochromatin, although amplification of inert sequences derived from transposable elements may be in part responsible for their accumulation in heterochromatin.

Animals↗

PubMed2000

Detection of de novo insertion of the medaka fish transposable element Tol2.

Tol2 is a terminal-inverted-repeat transposable element of the medaka fish Oryzias latipes. It is a member of the hAT (hobo/Activator/Tam3) transposable element family that is distributed in a wide range of organisms. We here document direct evidence for de novo insertion of this element. A Tol2 clone marked with the bacterial tetracycline-resistance gene was microinjected into fertilized eggs together with a target plasmid, and the plasmid was recovered from embryos. The screening of plasmid molecules after transformation into Escherichia coli demonstrated transposition of tet into the plasmid and, by inference, precise insertion of Tol2 in medaka fish cells. De novo excision of Tol2 has previously been demonstrated. The present study provides direct evidence that the Tol2 element has the entire activity necessary for cut-and-paste transposition. Some elements of the mariner/Tc1 family, another widespread group, have already been applied to development of gene tagging systems in vertebrates. The Tol2 element of the hAT family, having different features from mariner/Tc1 family elements, also has potential as an alternative gene tagging tool in vertebrates.

Animals↗

PubMed2004

The tyrosinase gene of the i(b) albino mutant of the medaka fish carries a transposable element insertion in the promoter region.

The i locus of the medaka fish contains the tyrosinase gene whose product is the key enzyme required for melanin biosynthesis. The i(b) allele at this locus, also denoted as i( 5), causes oculocutaneous albinism in homozygous carriers. Its albino phenotype is very weak, characterized mainly by small and varying sized melanophores in juveniles. Cloning and sequencing analyses of the tyrosinase gene for the i (b) allele revealed the presence of a 4.7-kb extra DNA fragment in the 5' untranslated region, this being Tol2, a DNA-based transposable element of the hobo Activator Tam3 (hAT) family which had previously been identified as a cause of another mutant allele i(4). Its insertion point was 85 bp upstream of the main transcription initiation site and 50 bp downstream of the CATGTG motif that has been suggested to be essential for the promoter function of the tyrosinase gene. The transcription level of the tyrosinase gene was decreased in i(b)/i(b) fish, compared with wild-type fish. The insertion is thus a likely cause of the weak albino phenotype. The Tol2 element transposes in a cut-and-paste fashion, and its excision is mostly imprecise, leaving some nucleotides and/or removing excess nucleotides. The i (b) mutant strain can thus be expected to serve as a source from which various other mutations in the promoter region can be derived.

Albinism↗

PubMed1996

Transposable elements behavior following viral genomic stress in Drosophila melanogaster inbred line.

To analyze the behavior of endogenous transposable elements under genomic stress, a Drosophila melanogaster inbred line was submitted to three kinds of viral perturbations. First, a retroviral plasmid containing the avian Rous Associated Virus type 2 (RAV-2) previously deleted for the viral envelope coding gene (env) was introduced by P element transformation into the Drosophila genome. An insertion of this avian retroviral sequence was detected by in situ hybridization in site 53C on polytene chromosome arm 2R. Second, Drosophila embryos were injected with RAV-2 particles produced by cell culture after transfection with the retroviral plasmid. Third, the Drosophila melanogaster inbred line was stably infected by the sigma native virus. It appears that neither the offspring of the flies in which the viral DNA was found integrated nor those from the infected sigma flies showed copia or mdg1 element mobilization. Injection of the avian RAV-2 particles led, however, to the observation of somatic transpositions of mdg1 element on the 2L chromosome, the copia element insertion pattern remaining stable. Thus, endogenous transposable elements show more instability in sublines injected with exogenous viral particles than in a transgenic subline containing a foreign viral insert, all transposable elements not being equally sensitive to such genomic stress.

Animals↗

PubMed2000

In vivo transposon mutagenesis of the methanogenic archaeon Methanosarcina acetivorans C2A using a modified version of the insect mariner-family transposable element Himar1.

We present here a method for in vivo transposon mutagenesis of a methanogenic archaeon, Methanosarcina acetivorans C2A, which because of its independence from host-specific factors may have broad application among many microorganisms. Because there are no known Methanosarcina transposons we modified the mariner transposable element Himar1, originally found in the insect Hematobia irritans, to allow its use in this organism. This element was chosen because, like other mariner elements, its transposition is independent of host factors, requiring only its cognate transposase. Modified mini-Himar1 elements were constructed that carry selectable markers that are functional in Methanosarcina species and that express the Himar1 transposase from known Methanosarcina promoters. These mini-mariner elements transpose at high frequency in M. acetivorans to random sites in the genome. The presence of an Escherichia coli selectable marker and plasmid origin of replication within the mini-mariner elements allows facile cloning of these transposon insertions to identify the mutated gene. In preliminary experiments, we have isolated numerous mini-mariner-induced M. acetivorans mutants, including ones with insertions that confer resistance to toxic analogs and in genes that encode proteins involved in heat shock, nitrogen fixation, and cell-wall structures.

Alkanesulfonic Acids↗

PubMed1995

Insertion mutations at the maize Opaque2 locus induced by transposable element families Ac, En/Spm and Bg.

Eight independently isolated unstable alleles of the Opaque2 (O2) locus were analysed genetically and at the DNA level. The whole series of mutations was isolated from a maize strain carrying a wild-type O2 allele and the transposable element Activator (Ac) at the wx-m7 allele. Previous work with another unstable allele of the same series has shown that it was indeed caused by the insertion of an Ac element. Unexpectedly, the remaining eight mutations were not caused by the designated Ac element, but by other insertions that are structurally similar or identical to one of two different autonomous transposable elements. Six mutations were caused by the insertion of a transposable element of the Enhancer/Suppressor-Mutator (En/Spm) family. Two mutations were the result of the insertion of a transposable element of the Bergamo (Bg) family. Genetic tests carried out with plants carrying the unstable mutations demonstrated that all were caused by the insertion of an autonomous transposable element.

Alleles↗

PubMed2003

The medaka fish Tol2 transposable element can undergo excision in human and mouse cells.

Tol2 is an active DNA-based transposable element identified in the medaka fish, Oryzias latipes. Originating from a vertebrate and belonging to the hAT ( hobo/ Activator/ Tam3) transposable element family, featuring a wide distribution among organisms, Tol2 would be expected to be active if introduced into mammals. We, therefore, examined if excision, one part of the transposition reaction, can occur in human and mouse culture cells. A Tol2 clone was introduced into cells and, after incubation, recovered. PCR and sequencing analysis provided evidence for precise and near precise excision in these cells. Tol2 can thus be expected to serve as a material for developing a gene transfer vector and other genetic tools applicable to mammals. It was also suggested that an intact Tol2 element could retain autonomy as a transposable element in mammalian cells.

3T3 Cells↗

PubMed1990

Properties of the maize transposable element Activator in transgenic tobacco plants: a versatile inter-species genetic tool.

The maize controlling element Activator (Ac) transposes autonomously from an integrated T-DNA vector to new sites in the genomes of tobacco and other heterologous plant species. Here we demonstrate that critical functions required for transposition of Ac in maize are conserved in tobacco and that Ac transposes at high frequency for at least five generations. Ac structure and terminal sequences are conserved upon transposition and a characteristic 8-bp duplication of target sequences is generated upon integration. Ac remains unmethylated, transcriptionally active, and capable to trans-activate transposition of the nonautonomous Dissociation (Ds) element throughout several generations. In tobacco, as in maize, Ac transposes adjacent to low copy or unique DNA, and transcriptional analysis of unique target DNA provides evidence that an Ac element transposed into a gene. In maize, increasing copies of Ac delay the timing and reduce the frequency of early transposition of Ac and Ds. In tobacco, increasing copies of Ac correlate with an increased frequency of Ds trans-activation. These data firmly establish that the Ac and Ds transposable elements are versatile genetic tools well suited for use as insertional mutagens and demonstrate that thorough investigation of mechanism and regulation of transposition is facilitated in heterologous settings.

Base Sequence↗

PubMed1985

Genetic differentiation of transposable elements under mutation and unbiased gene conversion.

A model is developed to predict the extent of genetic differentiation in a family of transposable elements under the combined effects of genetic drift, transposition, mutation and unbiased gene conversion. The model is based on simplifying assumptions that are valid when transposition is always to new sites and copy number per site is low. In the absence of gene conversion, the degree of differentiation as measured by the probability of identity of different elements is the same as at a single locus with the same mutation rate but in a population of effective size Nc/2, where N is the population size and c is the number of copies per individual. The inclusion of unbiased gene conversion does not significantly change this result. If, as seems to be the case, families of transposable elements are relatively homogeneous, then the model implies either that mutation rates for transposable elements are much lower than at comparable single-copy loci or that some other force, such as natural selection or biased gene conversion, is at work. Transposition is a very ineffective force for homogenizing a family of transposable elements.

DNA Transposable Elements↗

PubMed1991

Eukaryotic transposable elements with short terminal inverted repeats.

Transposable elements with short terminal inverted repeats are believed to transpose directly from DNA to DNA via excision and integration. The cis/trans requirements for transposition have recently been characterized for some of these elements. Common features seem to emerge for the mechanisms of excision of these elements, with the mechanisms apparently similar for the different elements.

Animals↗

PubMed1997

Regulation of the transposable element mariner.

The mariner/Tcl superfamily of transposable elements is widely distributed in animal genomes and is especially prevalent in insects. Their wide distribution results from their ability to be disseminated among hosts by horizontal transmission and also by their ability to persist in genomes through multiple speciation events. Although a great deal is known about the molecular mechanisms of transposition and excision, very little is known about the mechanisms by which transposition is controlled within genomes. The issue of mariner/Tcl regulation is critical in view of the great interest in these elements as vectors for germline transformation of insect pests and vectors of human disease. Several potentially important regulatory mechanisms have been identified in studies of genetically engineered mariner elements. One mechanism is overproduction inhibition, in which excessive wild-type transposase reduces the rate of excision of a target element. A second mechanism is mediated by certain mutant transposase proteins, which antagonize the activity of the wild-type transposase. The latter process may help explain why the vast majority of MLEs in nature undergo 'vertical inactivation' by multiple mutations and, eventually, stochastic loss. Another potential mechanism of regulation may result from transposase titration by defective elements that retain their DNA binding sites and ability to transpose. There is also evidence that some mariner/Tcl elements can be mobilized in a type of hybrid dysgenesis.

Animals↗

PubMed1993

The mariner transposable element is widespread in insects.

The mariner transposable element is a small member of the short inverted terminal repeat class thought to transpose through a DNA intermediate. Originally described in Drosophila mauritiana, it is now known in several species of the family Drosophilidae, and in a moth Hyalophora cecropia. Here I use primers designed to represent regions of amino-acid conservation between the putative transposase genes of the D. mauritiana and H. cecropia elements to amplify equivalent regions of presumed mariner elements from ten other insects representing six additional orders, including the malaria-vector mosquito, Anopheles gambiae. Sequences of multiple clones from each species reveal a diverse array of mariner elements, with multiple subfamilies in the genomes of some insects, indicating both vertical inheritance and horizontal transfers. An intact open reading frame in at least one clone from each species suggests each may carry functional transposable elements. Therefore the mariner element is an excellent candidate for development of genetic transformation systems for non-drosophilid insects, and possibly other arthropods.

Amino Acid Sequence↗

PubMedDate not supplied

Bmmar1: a basal lineage of the mariner family of transposable elements in the silkworm moth, Bombyx mori.

We describe a transposable element, called Bmmar1, from the genome of the silkworm moth, Bombyx mori. This element has features of the Tc1-mariner superfamily of transposable elements. Bmmar1 was first detected as a fragment in the 5' region of the larval serum protein (BmLSP) gene. Six genomic clones characterized each differed from a consensus sequence by 3-5 insertions and deletions, as well as an average of 2.3% in nucleotide sequence. The genome contains approximately 2400 copies of Bmmar1. Maximum parsimony phylogenetic analysis of the relationship of Bmmar1 and other members of the Tc1-mariner superfamily, based on their encoded transposase amino acid sequences, indicates that it represents a basal lineage of the mariner family. In particular Bmmar1 encodes a D,D37D motif thought to be the catalytic domain of mariner transposases. Bmmar1 considerably increases the known diversity of this widespread family of transposons. A new naming system is proposed for members of the family.

Amino Acid Sequence↗

PubMed1993

Somatic variegation and germinal mutability reflect the position of transposable element Dissociation within the maize R gene.

The R gene regulates the timing and tissue-specificity of anthocyanin deposition during maize development. The Ac/Ds system of transposable elements was used to induce insertional mutants of the R-sc:124 allele during two cycles of mutagenesis. Of 43 unstable, spotted-aleurone mutants generated, 42 contain inserts of the Ds6 transposable element differing only in the position and orientation of the element. The remaining mutant, r-sc:m1, contained an insert of a Ds element of the approximate size of the Ds1 transposable element. The patterns of somatic variegation of these mutants, resulting from excision of Ds, define a spectrum of phenotypes ranging from sparse to dense variegation. The sparsely variegated mutants produce few germinal revertants but relatively many stable null derivative alleles; densely variegated mutants produce many germinal revertants and few stable null derivatives. Molecular analysis shows that the sparsely variegated alleles are caused by Ds6 insertions in protein coding regions of R-sc:124 whereas the densely variegated mutants result from insertions in introns or in flanking regions of the gene. The excision rate of Ds6 from R, estimated as the proportion of R genomic DNA restriction fragments lacking the element, was uniform regardless of position, orientation or whether the element was inserted in R-sc:124 or another R allele. The excision rate was greater, however, for the mutable alleles involving the Ds element from r-sc:m1. These data indicate that, although the excision rates are uniform for a given Ds element, the somatic and germinal mutability patterns of alleles associated with that element vary widely and depend primarily on the position of the transposable element within coding or noncoding regions of the gene.

Alleles↗