Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Transposable elements”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

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

At least 379 records · Page 21Linked to original sources
PubMed1989

Structural analysis of Doc transposable elements associated with mutations at the white and suppressor of forked loci of Drosophila melanogaster.

DNA sequences from two spontaneous mutations of Drosophila melanogaster associated with insertion of a Doc transposable element have been cloned. In white-one, the element is inserted in the white locus close to where transcription initiates. In a lethal allele of suppressor of forked, su(f)S2, the element is inserted within the transcription unit in the protein coding region. Four other Doc elements have been cloned from a wild-type strain. Doc is a member of the class of transposable elements known as retroposons, which includes the D. melanogaster F, G, Jockey, and I elements. There is no sequence homology between the ends of the Doc element. The 3' or right end terminates with a polyadenylation signal sequence followed by a stretch of oligo-A. The length of the oligo-A varies between elements, and a duplication of variable size is found as a direct repeat flanking inserted Doc elements. Members of the family are conserved at the 3' end, but may be truncated at the 5' or left end. These structural features suggest a mechanism of transposition via an RNA intermediate.

Alleles↗
PubMed2003

Mu killer causes the heritable inactivation of the Mutator family of transposable elements in Zea mays.

Mutations in a number of genes responsible for the maintenance of transposon silencing have been reported. However, the initiation of epigenetic silencing of transposable elements is poorly characterized. Here, we report the identification of a single dominant locus, Mu killer (Muk), that acts to silence MuDR, the autonomous regulatory transposon of the Mutator family of transposable elements in maize. Muk results in the methylation of MuDR TIRs and is competent to silence one or several active MuDR elements. Silencing by Muk is not dependent on the position of the MuDR element and occurs gradually during plant development. Transcript levels of the MuDR transposase, mudrA, decrease substantially when Muk is present. The other transcript encoded by MuDR, mudrB, also fails to accumulate in the poly(A) RNA fraction when MuDR and Muk are combined. Additionally, plants undergoing MuDR silencing produce small, mudrA-homologous approximately 26-nt RNAs, suggesting a role for RNA-directed DNA methylation in MuDR silencing. MuDR elements silenced by Muk remain silenced even in plants that do not inherit Muk, suggesting that Muk is required for the initiation of MuDR silencing but not for its maintenance.

DNA Methylation↗
PubMed1990

Characterization of the FB-NOF transposable element of Drosophila melanogaster.

FB-NOF is a composite transposable element of Drosophila melanogaster. It is composed of foldback sequences, of variable length, which flank a 4-kb NOF sequence with 308-bp inverted repeat termini. The NOF sequence could potentially code for a 120-kD polypeptide. The FB-NOF element is responsible for unstable mutations of the white gene (wc and wDZL) and is associated with the large TEs of G. Ising. Although most strains of D. melanogaster have 20-30 sites of FB insertion, FB-NOF elements are usually rare, many strains lack this composite element or have only one copy of it. A few strains, including wDZL and Basc have many (8-21) copies of FB-NOF, and these show a tendency to insert at "hot-spots." These strains also have an increased number of FB elements. The DNA sequence of the NOF region associated with TE146(Z) has been determined.

Amino Acid Sequence↗
PubMed1992

Evolutionary dynamics of transposable elements in prokaryotes and eukaryotes.

This paper summarizes some recent theories about the evolution of transposable genetic elements in outbreeding, sexual eukaryotic organisms. The evolutionary possibilities available to self-replicating transposable elements are shown to vary depending on the reproductive biology of the host genome. This effect can be used to explain, in part, the differences in abundance of transposable elements between prokaryotes and eukaryotes. It is argued that the pattern of sexual outbreeding seen in mammals and plants is especially favorable to the spread of transposons. Moreover, because transposon spread is facilitated by zygote formation, the evolutionary origin of sexual conjugation may have been due to selection on transposon-encoded genes. Finally, evidence is also presented that introns could have originated as transposable genetic elements.

Biological Evolution↗
PubMed2003

Identification and characterization of transposable elements of Paracoccus pantotrophus.

We studied diversity and distribution of transposable elements residing in different strains (DSM 11072, DSM 11073, DSM 65, and LMD 82.5) of a soil bacterium Paracoccus pantotrophus (alpha-Proteobacteria). With application of a shuttle entrapment vector pMEC1, several novel insertion sequences (ISs) and transposons (Tns) have been identified. They were sequenced and subjected to detailed comparative analysis, which allowed their characterization (i.e., identification of transposase genes, terminal inverted repeats, as well as target sequences) and classification into the appropriate IS or Tn families. The frequency of transposition of these elements varied and ranged from 10(-6) to 10(-3) depending on the strain. The copy number, localization (plasmid or chromosome), and distribution of these elements in the Paracoccus species P. pantotrophus, P. denitrificans, P. methylutens, P. solventivorans, and P. versutus were analyzed. This allowed us to distinguish elements that are common in paracocci (ISPpa2, ISPpa3--both of the IS5 family--and ISPpa5 of IS66 family) as well as strain-specific ones (ISPpa1 of the IS256 family, ISPpa4 of the IS5 family, and Tn3434 and Tn5393 of the Tn3 family), acquired by lateral transfer events. These elements will be of a great value in the design of new genetic tools for paracocci, since only one element (IS1248 of P. denitrificans) has been described so far in this genus.

Amino Acid Sequence↗
PubMed1994

The mariner transposable element in the Drosophilidae family.

The distribution of the mariner transposable element among Drosophilidae species was investigated using three different techniques, i.e. squash blots, Southern blots and PCR amplification, using two sets of primers (one corresponding to the Inverted Terminal Repeats and the other to two conserved regions of the putative transposase). Our results and those of others show that the distribution of mariner is not uniform and does not follow the phylogeny of the host species. An analysis of geographical distribution, based on endemic species, shows that mariner is mainly present in Asia and Africa. At least two hypotheses may be proposed to explain the specific and geographical distributions of this element. Firstly, they may be the results of several horizontal transmissions between Drosophila species and/or between Drosophila species and one or several donor species outside the Drosophilidae family. Secondly, these particular distributions may correspond to the evolution of the mariner element from an ancestral copy which was present in the ancestor of the Drosophilidae family.

Animals↗
PubMed2006

Functional dissection of the Tol2 transposable element identified the minimal cis-sequence and a highly repetitive sequence in the subterminal region essential for transposition.

The Tol2 element is a naturally occurring active transposable element found in vertebrate genomes. The Tol2 transposon system has been shown to be active from fish to mammals and considered to be a useful gene transfer vector in vertebrates. However, cis-sequences essential for transposition have not been characterized. Here we report the characterization of the minimal cis-sequence of the Tol2 element. We constructed Tol2 vectors containing various lengths of DNA from both the left (5') and the right (3') ends and tested their transpositional activities both by the transient excision assay using zebrafish embryos and by analyzing chromosomal transposition in the zebrafish germ lineage. We demonstrated that Tol2 vectors with 200 bp from the left end and 150 bp from the right end were capable of transposition without reducing the transpositional efficiency and found that these sequences, including the terminal inverted repeats (TIRs) and the subterminal regions, are sufficient and required for transposition. The left and right ends were not interchangeable. The Tol2 vector carrying an insert of >11 kb could transpose, but a certain length of spacer, <276 but >18 bp, between the left and right ends was necessary for excision. Furthermore, we found that a 5-bp sequence, 5'-(A/G)AGTA-3', is repeated 33 times in the essential subterminal region. Mutations in the repeat sequence at 13 different sites in the subterminal region, as well as mutations in TIRs, severely reduced the excision activity, indicating that they play important roles in transposition. The identification of the minimal cis-sequence of the Tol2 element and the construction of mini-Tol2 vectors will facilitate development of useful transposon tools in vertebrates. Also, our study established a basis for further biochemical and molecular biological studies for understanding roles of the repetitive sequence in the subterminal region in transposition.

Animals↗
PubMed1998

Molecular evolution of P transposable elements in the genus Drosophila. III. The melanogaster species group.

Phylogenetic relationships were determined for 76 partial P-element sequences from 14 species of the melanogaster species group within the Drosophila subgenus Sophophora. These results are examined in the context of the phylogeny of the species from which the sequences were isolated. Sequences from the P-element family fall into distinct subfamilies, or clades, which are often characteristic for particular species subgroups. When examined locally among closely related species, the evolution of P elements is characterized by vertical transmission, whereby the P-element phylogeny traces the species phylogeny. On a broader scale, however, the P-element phylogeny is not congruent with the species phylogeny. One feature of P-element evolution in the melanogaster group is the presence of more than one P-element subfamily, differing by as much as 36%, in the genomes of some species. Thus, P elements from several individual species are not monophyletic, and a likely explanation for the incongruence between P-element and species phylogenies is provided by the comparison of paralogous sequences. In certain instances, horizontal transfer seems to be a valid alternative explanation for lack of congruence between species and P-element phylogenies. The canonical P-element subfamily, which represents the active, autonomous transposable element, is restricted to D. melanogaster. Thus, its origin clearly lies outside of the melanogaster species group, consistent with the earlier conclusion of recent horizontal transfer.

Animals↗
PubMed1983

Structure of the archaebacterial transposable element ISH50.

We have sequenced in its entirety a new transposable element from the archaebacterium Halobacterium halobium. This 996 bp element shows some features not unlike those of insertion sequences from eubacteria, although it clearly differs from them in sequences which may be involved in transcription and or translation initiation.

Base Sequence↗
PubMed1992

Evolution of the transposable element Uhu in five species of Hawaiian Drosophila.

The complete DNA sequence of three independent isolates of Uhu, a member of the Tc1-like class of transposable elements from D. heteroneura (Uhu-1, Uhu-3, and Uhu-4), has been determined. These isolates have between 95 and 96.4% nucleotide sequence identity indicating that Uhu is well conserved within this species. A comparison of the DNA sequences of Uhu and the D. melanogaster Hb1 transposable element shows that the nucleotide substitution rate for Uhu is comparable to the synonymous rate for the Adh gene in these species. Uhu has been identified in four other species of endemic Hawaiian Drosophila, D. silvestris, D. differens, D. planitibia and D. picticornis, and nine Uhu elements were isolated from genomic libraries of these four species. A 444 base pair region from within the coding region of the Uhu element, with well conserved ends, was amplified by the polymerase chain reaction and used for sequence comparison of elements from different species. The analysis of the sequence similarities between the elements within and between the species shows a grouping of the two pairs of most closely related species (D. heteroneura and D. silvestris, and D. differens and D. planitibia), but shows a much larger variation within the most recently diverged species (D. heteroneura and D. silvestris) than expected. There are extensive nucleotide substitutions and deletions in the Uhu elements from D. picticornis showing that they are degenerating and being lost in this species. These observations indicate that the Uhu element has been transmitted vertically and that transposition may have been activated at the time of formation of each species as it colonized the newly formed islands of the Hawaiian archipelago.

Amino Acid Sequence↗
PubMed1992

HeT-A, a transposable element specifically involved in "healing" broken chromosome ends in Drosophila melanogaster.

Eight terminally deleted Drosophila melanogaster chromosomes have now been found to be "healed." In each case, the healed chromosome end had acquired sequence from the HeT DNA family, a complex family of repeated sequences found only in telomeric and pericentric heterochromatin. The sequences were apparently added by transposition events involving no sequence homology. We now report that the sequences transposed in healing these chromosomes identify a novel transposable element, HeT-A, which makes up a subset of the HeT DNA family. Addition of HeT-A elements to broken chromosome ends appears to be polar. The proximal junction between each element and the broken chromosome end is an oligo(A) tract beginning 54 nucleotides downstream from a conserved AATAAA sequence on the strand running 5' to 3' from the chromosome end. The distal (telomeric) ends of HeT-A elements are variably truncated; however, we have not yet been able to determine the extreme distal sequence of a complete element. Our analysis covers approximately 2,600 nucleotides of the HeT-A element, beginning with the oligo(A) tract at one end. Sequence homology is strong (greater than 75% between all elements studied). Sequence may be conserved for DNA structure rather than for protein coding; even the most recently transposed HeT-A elements lack significant open reading frames in the region studied. Instead, the elements exhibit conserved short-range sequence repeats and periodic long-range variation in base composition. These conserved features suggest that HeT-A elements, although transposable elements, may have a structural role in telomere organization or maintenance.

Animals↗
PubMed1992

The pogo transposable element family of Drosophila melanogaster.

A 190 bp insertion is associated with the white-eosin mutation in Drosophila melanogaster. This insertion is a member of a family of transposable elements, pogo elements, which is of the same class as the P and hobo elements of D. melanogaster. Strains typically have many copies of a 190 bp element, 10-15 elements 1.1-1.5 kb in size and several copies of a 2.1 kb element. The smaller elements all appear to be derived from the largest by single internal deletions so that all elements share terminal sequences. They either always insert at the dinucleotide TA and have perfect 21 bp terminal inverse repeats, or have 22 bp inverse repeats and produce no duplication upon insertion. Analysis by DNA blotting of their distribution and occupancy of insertion sites in different strains suggests that they may be less mobile than P or hobo. The DNA sequence of the largest element has two long open reading frames on one strand which are joined by splicing as indicated by cDNA analysis. RNAs of this strand are made, whose sizes are similar to the major size classes of elements. A protein predicted by the DNA sequence has significant homology with a human centrosomal-associated protein, CENP-B. Homologous sequences were not detected in other Drosophila species, suggesting that this transposable element family may be restricted to D. melanogaster.

Amino Acid Sequence↗
PubMed1983

The effect of homozygosity of selective differences between sites of transposable elements.

The behavior of the frequency spectrum of sites of transposable elements for the model proposed by Langley, Brookfield, and Kaplan ((1983) Genetics 104) is studied when some of the sites have weak additive selection against the host. In particular, it is shown that under certain conditions, the expected homozygosity at equilibrium will always be larger when there is variation in selection between sites than when such variation is absent.

Animals↗
PubMed1986

Somatic excision of transposable element Tc1 from the Bristol genome of Caenorhabditis elegans.

We investigated the ability of the transposable element Tc1 to excise from the genome of the nematode Caenorhabditis elegans var. Bristol N2. Our results show that in the standard lab strain (Bristol), Tc1 excision occurred at a high frequency, comparable to that seen in the closely related Bergerac strain BO. We examined excision in the following way. We used a unique sequence flanking probe (pCeh29) to investigate the excision of Tc1s situated in the same location in both strains. Evidence of high-frequency excision from the genomes of both strains was observed. The Tc1s used in the first approach, although present in the same location in both genomes, were not known to be identical. Thus, a second approach was taken, which involved the genetic manipulation of a BO variant, Tc1(Hin). The ability of this BO Tc1(Hin) to excise was retained after its introduction into the N2 genome. Thus, we conclude that excision of Tc1 from the Bristol genome occurs at a high frequency and is comparable to that of Tc1 excision from the Bergerac genome. We showed that many Tc1 elements in N2 were apparently functionally intact and were capable of somatic excision. Even so, N2 Tc1s were prevented from exhibiting the high level of heritable transposition displayed by BO elements. We suggest that Bristol Tc1 elements have the ability to transpose but that transposition is heavily repressed in the gonadal tissue.

Animals↗
PubMed1993

Mobility of the maize transposable element En/Spm in Arabidopsis thaliana.

The autonomous element En-1 of the maize En/Spm transposable element system is capable of frequent somatic and germinal excision in the heterologous host Arabidopsis thaliana. The pattern of En-homologous transcripts generated in transgenic Arabidopsis resembles En transcription in maize. An excision reporter construct based on NPT-II gene (pKEn2) can be used reliably for the isolation of En-1 germinal revertants by seed germination on kanamycin-containing medium. Re-insertion after germinal excision is apparently frequent. A dSpm receptor element can be efficiently trans-activated in Arabidopsis either by En-1 or by expressing cDNAs of tnpA and tnpD. Excision and re-insertion of En/Spm take place with similar characteristics as in maize. This is the first description of En/Spm transposition in Arabidopsis and the parameters analysed here suggest that transposon tagging with En should be feasible in this species.

Arabidopsis↗
PubMed2000

Sex chromosomal transposable element accumulation and male-driven substitutional evolution in humans.

We sequenced the genomic region containing the human Y-linked zinc finger gene (ZFY). Comparison of ZFY to the related region on the X chromosome (ZFX) and to autosomal sequences reveals a significant accumulation of transposable elements on the sex chromosomes. In addition, five times as many retroviruslike elements (RLEs) are present in the ZFY region as in the ZFX region. Thus, transposable elements accumulate more rapidly on the sex chromosomes, and the insertion of RLEs may occur more frequently in the male than in the female germ line. When the accumulation of substitutions in Alu elements was analyzed, it was found that the Alu elements at the Y-chromosomal locus diverged significantly faster than those at the X-chromosomal locus, whereas the divergence of autosomal Alu elements was intermediate. The male-to-female mutation rate ratio was estimated to be 2.5.

Alu Elements↗
PubMed2025

Transposable elements drive evolution and perturb gene expression in Brassica rapa and B. oleracea.

Transposable elements (TEs) significantly influence genomic diversity and gene regulation in plants. Brassica rapa and B. oleracea, with their distinct domestication histories, offer excellent models to explore TE dynamics. Here, we developed a refined TE classification method and systematically analyzed TEs across 12 B. rapa and B. oleracea genomes, identifying 1878 TE families. Approximately half (49.5%) of these TE families were shared between the two species, reflecting a common evolutionary origin, whereas species-specific expansions, particularly among long-terminal repeat (LTR) retrotransposons, underscore their roles in genomic differentiation. We notably characterized a heat-responsive Ty1-copia family (Copia0035) in B. oleracea roots, distinguished by low GC content and the absence of CG and CHG methylation motifs, sharing regulatory similarities with the Arabidopsis heat-induced ONSEN element. Syntenic analyses of gene-TE associations highlighted significant intraspecies TE insertion variability, with more accession-specific insertions in B. rapa and more conserved insertions, often associated with distinct morphotypes in B. oleracea. Gene ontology enrichment indicated TE involvement in developmental, reproductive, and stress response pathways. Transcriptome analysis across diverse accessions revealed that genes proximal to TEs, particularly those regulating floral development and flowering time, exhibit increased expression variability. These findings advance our understanding of TE-mediated genome evolution in Brassica species and underscore their potential utility in breeding and genome engineering strategies for crop improvement.

DNA Transposable Elements↗
PubMed2004

Genome-wide comparative analysis of the transposable elements in the related species Arabidopsis thaliana and Brassica oleracea.

Transposable elements (TEs) are the major component of plant genomes where they contribute significantly to the >1,000-fold genome size variation. To understand the dynamics of TE-mediated genome expansion, we have undertaken a comparative analysis of the TEs in two related organisms: the weed Arabidopsis thaliana (125 megabases) and Brassica oleracea ( approximately 600 megabases), a species with many crop plants. Comparison of the whole genome sequence of A. thaliana with a partial draft of B. oleracea has permitted an estimation of the patterns of TE amplification, diversification, and loss that has occurred in related species since their divergence from a common ancestor. Although we find that nearly all TE lineages are shared, the number of elements in each lineage is almost always greater in B. oleracea. Class 1 (retro) elements are the most abundant TE class in both species with LTR and non-LTR elements comprising the largest fraction of each genome. However, several families of class 2 (DNA) elements have amplified to very high copy number in B. oleracea where they have contributed significantly to genome expansion. Taken together, the results of this analysis indicate that amplification of both class 1 and class 2 TEs is responsible, in part, for B. oleracea genome expansion since divergence from a common ancestor with A. thaliana. In addition, the observation that B. oleracea and A. thaliana share virtually all TE lineages makes it unlikely that wholesale removal of TEs is responsible for the compact genome of A. thaliana.

Arabidopsis↗