[Evolutional relationship between copia-like transposable genetic elements in Drosophila and retroviruses in vertebrate].
Explore the source record for details and available documents.
Animals↗
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.
Pot2, an inverted repeat transposon from the rice blast fungus Magnaporthe grisea.
We report the cloning and characterisation of Pot2, a putative transposable element from Magnaporthe grisea. The element is 1857 bp in size, has 43-bp perfect terminal inverted repeats (TIRs) and 16-bp direct repeats within the TIRs. A large open reading frame, potentially coding for a transposase-like protein, was identified. This putative protein coding region showed extensive identity to that of Fot1, a transposable element from another phytopathogenic fungus, Fusarium oxysporum. Pot2, like the transposable elements Tc1 and Mariner of Caenorhabditis elegans and Drosophila, respectively, duplicates the dinucleotide TA at the target insertion site. Sequence analysis of DNA flanking 12 Pot2 elements revealed similarity to the consensus insertion sequence of Tc1. Pot2 is present at a copy number of approximately 100 per haploid genome and represents one of the major repetitive DNAs shared by both rice and non-rice pathogens of M. grisea.
Amino Acid Sequence↗
Distribution of unlinked receptor sites for transposed Ac elements from the bz-m2(Ac) allele in maize.
We have shown before that the Ac element from the maize bz-m2(Ac) allele, located in the short arm of chromosome 9 (9S), transposes preferentially to sites that are linked to the bz donor locus. Yet, about half of the Ac transpositions recovered from bz-m2(Ac) are in receptor sites not linked to the donor locus. In this study, we have analyzed the distribution of those unlinked receptor sites. Thirty-seven transposed Ac (trAc) elements that recombined independently of the bz locus were mapped using a set of wx reciprocal translocations. We found that the distribution of unlinked receptor sites for trAs was not random. Ten trAcs mapped to 9L, i.e., Ac had transposed to sites physically, if not genetically, linked to the donor site. Among chromosomes other than 9, the Ac element of bz-m2(Ac) appeared to have transposed preferentially to certain chromosomes, such as 5 and 7, but infrequently to others, such as 1, the longest chromosome in the maize genome. The seven trAc elements in chromosome 5 were mapped relative to markers in 5S and 5L and localized to both arms of 5. We also investigated the transposition of Ac to the homolog of the donor chromosome. We found that Ac rarely transposes from bz-m2(Ac) to the homologous chromosome 9. The clustering of Ac receptor sites around the donor locus has been taken to mean that a physical association between the donor site and nearby receptor sites occurs during transposition. The preferential occurrence of 9L among chromosomes harboring unlinked receptor sites would be expected according to this model, since sites in 9L would tend to be physically closer to 9S than sites in other chromosomes. The nonrandom pattern seen among the remaining chromosomes could reflect an underlying nuclear architecture, i.e., an ordering of the chromosomes in the interphase nucleus, as suggested from previous cytological observations.
Alleles↗
A model for transposon-based eucaryote regulatory evolution.
This paper presents a compact model of the role of transposable elements in eucaryote evolution which, although forward looking, is consistent with both experimental results and theories of gene regulation. The model postulates that a principal factor in the emergence of the eucaryotes was the development of a symbiotic relationship between reverse transcribing transposable elements and RNA based gene regulation, which we will call structural symbiosis. Thus, although transposable elements follow their own evolutionary protocol, structural homologies between "cellular" and "viral" genomes result in selective mutagenesis, a situation where transposon mutations are permitted because they can result in phenotypic mutations of the regulatory process with reduced probability of deleterious mutation of structural genes. The incorporation of this scheme into the life cycle of higher organisms results in two forms of integral evolution. Exogenous, in which differing species in an ecosystem share genetic information through viral transfer, and endogenous in which somatically induced regulatory mutations can be mapped back into the germ line.
Biological Evolution↗
P elements and MITE relatives in the whole genome sequence of Anopheles gambiae.
BACKGROUND: Miniature Inverted-repeat Terminal Elements (MITEs), which are particular class-II transposable elements (TEs), play an important role in genome evolution, because they have very high copy numbers and display recurrent bursts of transposition. The 5' and 3' subterminal regions of a given MITE family often show a high sequence similarity with the corresponding regions of an autonomous Class-II TE family. However, the sustained presence over a prolonged evolutionary time of MITEs and TE master copies able to promote their mobility has been rarely reported within the same genome, and this raises fascinating evolutionary questions. RESULTS: We report here the presence of P transposable elements with related MITE families in the Anopheles gambiae genome. Using a TE annotation pipeline we have identified and analyzed all the P sequences in the sequenced A. gambiae PEST strain genome. More than 0.49% of the genome consists of P elements and derivates. P elements can be divided into 9 different subfamilies, separated by more than 30% of nucleotide divergence. Seven of them present full length copies. Ten MITE families are associated with 6 out of the 9 Psubfamilies. Comparing their intra-element nucleotide diversities and their structures allows us to propose the putative dynamics of their emergence. In particular, one MITE family which has a hybrid structure, with ends each of which is related to a different P-subfamily, suggests a new mechanism for their emergence and their mobility. CONCLUSION: This work contributes to a greater understanding of the relationship between full-length class-II TEs and MITEs, in this case P elements and their derivatives in the genome of A. gambiae. Moreover, it provides the most comprehensive catalogue to date of P-like transposons in this genome and provides convincing yet indirect evidence that some of the subfamilies have been recently active.
Animals↗
Somatic reversion of some copia-like induced mutations, at the white locus of Drosophila melanogaster, after treatment with alkylating agents.
It has been suggested that transposable elements can be associated with different types of genotoxic effects. For this reason it seems appropriate to outline suitable systems to detect changes in the phenotypic expression of the loci containing transposable elements, as well as those agents that induce such changes. The sex-linked white locus offers a suitable experimental system for studying such events because most of the spontaneous mutations at the white locus are the result of insertions of repeated mobile sequences, and it is easy to follow mutational changes of the locus due to the possibility of detecting even slight changes in eye color. Here we report the results obtained in different strains of Drosophila melanogaster with copia-like induced mutations at the white locus, after treatment with three alkylating agents: ethyl methanesulfonate (EMS), methyl methanesulfonate (MMS), and N-nitroso-N-ethylurea (ENU). The three insertional white mutants used in this work were wa4, wbf, and wsp55, with the wa2 mutation used as control because its mutant phenotype is the result of a point mutation instead of the insertion of a DNA fragment. Our data constitute evidence that EMS, MMS, and ENU induce a clear increase in the frequencies of somatic-revertant sectors in the three strains carrying a white allele with an inserted copia-like element. For the wa2 strain, whose mutant phenotype is the result of a point mutation, only ENU at the highest concentration tested is able to induce a significant increase in the somatic reversion frequency. In addition, our results indicate that the use of D. melanogaster strains with transposable elements in the white locus is suitable for detecting genotoxic damage induced by chemicals.
Alkylating Agents↗
Post-integration behavior of a Mos1 mariner gene vector in Aedes aegypti.
The post-integration behavior of insect gene vectors will determine the types of applications for which they can be used. Transposon mutagenesis, enhancer trapping, and the use of transposable elements as genetic drive systems in insects requires transposable elements with high rates of remobilization in the presence of transposase. We investigated the post-integration behavior of the Mos1 mariner element in transgenic Aedes aegypti by examining both germ-line and somatic transpositions of a non-autonomous element in the presence of Mos1 transposase. Somatic transpositions were occasionally detected while germ-line transposition was only rarely observed. Only a single germ-line transposition event was recovered after screening 14,000 progeny. The observed patterns of transposition suggest that Mos1 movement takes place between the S phase and anaphase. The data reported here indicate that Mos1 will be a useful vector in Ae. aegypti for applications requiring a very high degree of vector stability but will have limited use in the construction of genetic drive, enhancer trap, or transposon tagging systems in this species.
Aedes↗
The unusual telomeres of Drosophila.
The telomeres of most eukaryotes contain short, simple repeats that are highly conserved. Drosophila, on the other hand, does not have such sequences, but carries at the ends of its chromosomes one or more LINE-like retrotransposable elements. Instead of elongation by telomerase, incomplete DNA replication at the termini of Drosophila chromosomes is counterbalanced by transposition of these elements at high frequency specifically to the termini. These transposable elements are not responsible for distinguishing telomeric ends in Drosophila from broken chromosome ends; the structure performing this function is not yet known. Proximal to the terminal array of transposable elements are regions of tandem repeats that are structurally, and probably functionally, analogous to the subterminal regions in other eukaryotes.
Animals↗
The significance of deletions in spontaneous and induced mutations associated with movement of transposable DNA elements: possible implications for evolution and cancer.
Explore the source record for details and available documents.
Animals↗
Structural comparison of the integrative and conjugative elements R391, pMERPH, R997, and SXT.
R391 and SXT are members of a group of eleven chromosome-borne conjugative elements found in the gamma-proteobacteria, whose members carry different antibiotic resistance traits. Recent genomic analysis of R391 and SXT revealed a highly conserved 'backbone' encoding integration/excision, conjugative transfer, and regulation functions, augmented by an array of phenotypic traits and transposable elements. In this study, PCR amplification and sequence analysis were employed to investigate the genomic structure of two further MGE of the R391 family, pMERPH (HgR) and R997 (ApR, SmR, SuR). R997 and pMERPH were found to be structurally related to R391 and SXT and share a number of virtually identical regions with them-including putative integration, conjugative transfer, and regulatory determinants-interrupted by variable DNA segments and transposable elements. The presence of a highly conserved backbone in the four elements strongly suggests their origin in a common ancestral element, which itself was a mosaic of sequences related to phages and plasmids. Subsequent genetic recombination and the acquisition of transposable elements resulted in the possession of variable phenotypic traits among the four MGE, and diversification into two distinct lineages, the first one including R391 and pMERPH, the second one containing SXT and R997.
Conjugation, Genetic↗
Mutation rates in hybrids between sibling species of Drosophila.
It has recently been suggested that sterility or inviability in species hybrids might result from the movement of transposable elements. Because such movement is often detectable by an increased mutation rate, I studied the effect of interspecific hybridization in the Drosophila melanogaster group on the mutation rate of X-linked visibles. This rate did not differ between hybrids and intraspecific controls. This was also true for the germ-line excision rate of a transposable element, although the rate of somatic excision was two to sixfold higher in hybrids than in pure species. Combined with previous work, these results do not support a role for transposable elements in speciation.
Animals↗
The transposition frequency of Tag1 elements is increased in transgenic Arabidopsis lines.
Tag1 was identified as a highly active endogenous transposable element in transgenic Arabidopsis thaliana Landsberg erecta plants carrying the maize transposable element Activator (Ac). Here, we describe experiments designed to determine the basis for the high activity of Tag1. The frequency of transposition of Tag1 elements was compared in lines containing or lacking Ac transposase to assess the effect of Ac transposase on Tag1 activity. Three populations of nontransgenic plants, including nontransformed regenerants, were also analyzed. The high level of activity of Tag1 did not correlate with the presence or absence of Ac transposase but was significantly higher in transgenic lines. This result was maintained through at least six generations after transformation. These data suggest that Tag1 transposition is stimulated by processes that occur during the Agrobacterium transformation and that thereafter remain active. Two Tag1 elements are tightly linked in the Landsberg erecta genome and map to the lower arm of chromosome 1. Tag1 elements were found in only a few A. thaliana ecotypes but were present in four other Arabidopsis species.
Arabidopsis↗
Complex organization and evolution of the tomato pericentromeric region at the FER gene locus.
Tomato (Lycopersicon esculentum) is a model species for molecular biology research and a candidate for large-scale genome sequencing. Pericentromeric heterochromatin constitutes a large portion of the tomato chromosomes. However, the knowledge of the structure, organization, and evolution of such regions remains very limited. Here, we report the analysis of a 198-kb sequence near the FER gene, located in a distal part of pericentromeric heterochromatin on the long arm of tomato chromosome 6. Nine genes, one pseudogene, and 55 transposable elements (TEs) were identified, showing a low gene density (19.8 kb/gene) and a high content of transposable elements (>45% of the sequence). Six genes (56 B23_g3, g5, g7, g8, g9, and g10) have perfect matches (>98% identity) with tomato expressed sequence tags. Two genes (56 B23_g1 and g6), which share <98% sequence identity with expressed sequence tags, were confirmed for transcriptional activity by reverse transcription-PCR. The genes were not uniformly distributed along the sequence and grouped into gene islands separated by stretches of retrotransposons, forming a pattern similar to that found in the gene-rich regions of the large genomes of maize (Zea mays) and Triticeae. Long terminal repeat retrotransposons account for 60% of the TE sequence length. Sixteen of 55 TEs were completely new and remain unclassified. Surprisingly, five of the seven identified DNA transposons were closely associated with coding regions. The action of transposable elements and DNA rearrangements form the molecular basis of the dynamic genome evolution at the FER locus. Multiple rounds of genome duplication in Arabidopsis (Arabidopsis thaliana) and subsequent gene loss have generated a mosaic pattern of conservation between tomato and Arabidopsis orthologous sequences. Our data show that the distal parts of pericentromeric heterochromatin may contain many valuable genes and that these regions form an evolutionary active part of the tomato genome.
Centromere↗
[Transposition as a way of existence: phage Mu].
Transposition is a special mode of DNA recombination that produces a transfer of a DNA segment (transposable element, TE) from one chromosome region to a nonhomologous genomic loci. Bacterial TEs have chosen two principal strategies of their movement within and among genomes: conservative transposition (resulting in a simple insertion) and/or replicative transposition (accompanied by complete DNA replication and producing a cointegrate). Variations of transposition strategies concern the number and nature of cuts that sever the transposon from the flanking donor DNA: one-strand break (phage Mu) or double-strand breaks (Tn7, IS10 and members of IS3 family) and the possibility of accompanying TE replication, which leads to different end-products of transposition. Phage Mu combines properties of a temperate phage and a transposable element. Among transposons, it is studied in most detail. As a transposable element phage Mu is remarkable because its life-cycle involves two transposition modes: non-replicative resulting in lysogeny and replicative leading to multiple copying of phage DNA during the lytic growth. There are several levels of transcription regulation (or choice of developmental pathway). The genetic transposition reaction mediated by phage Mu A transposase A in the transpososome complex involves elaborate protein-nucleic acid and protein-protein interactions.
Animals↗
Regulation of activator/dissociation transposition by replication and DNA methylation.
In maize the transposable elements Activator/Dissociation (Ac/Ds) transpose shortly after replication from one of the two resulting chromatids ("chromatid selectivity"). A model has been suggested that explains this phenomenon as a consequence of different affinity for Ac transposase binding to holo-, hemi-, and unmethylated transposon ends. Here we demonstrate that in petunia cells a holomethylated Ds is unable to excise from a nonreplicating vector and that replication restores excision. A Ds element hemi-methylated on one DNA strand transposes in the absence of replication, whereas hemi-methylation of the complementary strand causes a >6.3-fold inhibition of Ds excision. Consistently in the active hemi-methylated state, the Ds ends have a high binding affinity for the transposase, whereas binding to inactive ends is strongly reduced. These results provide strong evidence for the above-mentioned model. Moreover, in the absence of DNA methylation, replication enhances Ds transposition in petunia protoplasts >8-fold and promotes formation of a predominant excision footprint. Accordingly, replication also has a methylation-independent regulatory effect on transposition.
DNA Damage↗
Cell-autonomous behavior of the rolC gene of Agrobacterium rhizogenes during leaf development: a visual assay for transposon excision in transgenic plants.
We describe a genetic switch based on the Ac transposable element of maize and the rolC gene of Agrobacterium rhizogenes, a dominant gene, which has pleiotropic effects on plant growth and morphology. Moreover, rolC gene expression under the control of the 35S cauliflower mosaic virus promoter decreases chlorophyll content in transgenic tobacco plants. Chlorophyll is a visible cell-autonomous marker, and it is shown here that the reduction in chlorophyll content caused by the rolC gene product allows us to monitor, in palisade or spongy mesophyll cells, Ac excision events resulting in rolC gene expression as pale-green sectors and spots. Our results indicate that the rolC gene product behaves in a cell-autonomous manner during leaf development, at least as far as chlorophyll accumulation is concerned. In addition, the rolC gene can be useful to evaluate visually if and when a transposable element is active. Most important, we propose the use of a transposable element as a tool to activate expression of morphogenetic genes in a clonal population of cells. This could be particularly useful when studying genes affecting growth and development whose constitutive expression can severely impair regeneration of transgenic plants.
Brassica↗
Hobo transposons causing chromosomal breakpoints.
Several laboratory surveys have shown that transposable elements (TEs) can cause chromosomal breaks and lead to inversions, as in dysgenic crosses involving P-elements. However, it is not presently clear what causes inversions in natural populations of Drosophila. The only direct molecular studies must be taken as evidence against the involvement of mobile elements. Here, in Drosophila lines transformed with the hobo transposable element, and followed for 100 generations, we show the appearance of five different inversions with hobo inserts at breakpoints. Almost all breakpoints occurred in hobo insertion sites detected in previous generations. Therefore, it can be assumed that such elements are responsible for restructuring genomes in natural populations.
Animals↗
Pleiotropic fitness effects of the Tre1-Gr5a region in Drosophila melanogaster.
The abundance of transposable elements and DNA repeat sequences in mammalian genomes raises the question of whether such insertions represent passive evolutionary baggage or may influence the expression of complex traits. We addressed this question in Drosophila melanogaster, in which the effects of single transposable elements on complex traits can be assessed in genetically identical individuals reared in controlled environments. Here we demonstrate that single P-element insertions in the intergenic region between the gustatory receptor 5a (Gr5a, also known as Tre) and trapped in endoderm 1 (Tre1), which encodes an orphan receptor, exert complex pleiotropic effects on fitness traits, including selective nutrient intake, life span, and resistance to starvation and heat stress. Mutations in this region interact epistatically with downstream components of the insulin signaling pathway. Transposon-induced sex-specific and sex-antagonistic effects further accentuate the complex influences that intergenic transposable elements can contribute to quantitative trait phenotypes.
Animals↗