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PubMed1985

Behavior of a Drosophila melanogaster transposable element in Saccharomyces cerevisiae.

The Drosophila melanogaster transposable element 412 is transiently unstable in Saccharomyces cerevisiae when present on a freely replicating plasmid. The 412 element undergoes recombination to form two circular molecules, a 412 deletion plasmid and, presumably, a 412 circle. The 412 deletion plasmid contains a single long terminal repeat which most likely is the result of homologous recombination within the long terminal repeats. This recombination occurs at or shortly after transformation and is independent of both the RAD52 gene product and the Flp gene of 2 micron DNA.

Animals↗

PubMed1991

Molecular analysis of the Ubiquitous (Uq) transposable element system of Zea mays.

The Uq transposable element of maize is the most widely dispersed among different maize populations and genetic testerstrains. Despite intensive genetic characterization, little is known about its molecular structure. In order to obtain information relevant to this topic, we have cloned and sequenced three ruq receptors. Surprisingly, they are all Ds1-like receptor types of the Ac-Ds transposon family. Based on our molecular data, we present a model to explain the functional differences associated with the differential expression of the Uq and Ac transposon systems.

Base Sequence↗

PubMed1991

Evidence for interspecific transfer of the transposable element mariner between Drosophila and Zaprionus.

The transposable element mariner occurs widely in the melanogaster species group of Drosophila. However, in drosophilids outside of the melanogaster species group, sequences showing strong DNA hybridization with mariner are found only in the genus Zaprionus. The mariner sequence obtained from Zaprionus tuberculatus is 97% identical with that from Drosophila mauritiana, a member of the melanogaster species subgroup, whereas a mariner sequence isolated from Drosophila tsacasi is only 92% identical with that from D. mauritiana. Because D. tsacasi is much more closely related to D. mauritiana than is Zaprionus, the presence of mariner in Zaprionus may result from horizontal transfer. In order to confirm lack of a close phylogenetic relationship between the genus Zaprionus and the melanogaster species group, we compared the alcohol dehydrogenase (Adh) sequences among these species. The results show that the coding region of Adh is only 82% identical between Z. tuberculatus and D. mauritiana, as compared with 90% identical between D. tsacasi and D. mauritiana. Furthermore, the mariner gene phylogeny obtained by maximum likelihood and maximum parsimony analyses is discordant with the species phylogeny estimated by using the Adh genes. The only inconsistency in the mariner gene phylogeny is in the placement of the Zaprionus mariner sequence, which clusters with mariner from Drosophila teissieri and Drosophila yakuba in the melanogaster species subgroup. These results strongly suggest horizontal transfer.

Alcohol Dehydrogenase↗

PubMed1992

The distribution of transposable elements within and between chromosomes in a population of Drosophila melanogaster. I. Element frequencies and distribution.

Data were collected on the distribution of nine families of transposable elements among second and third chromosomes isolated from a natural population of Drosophila melanogaster, by means of in situ hybridization of element probes to polytene chromosomes. It was found that the copy numbers per chromosome in the distal sections of the chromosome arms followed a Poisson distribution. Elements appeared to be distributed randomly along the distal sections of the chromosome arms. There was no evidence for linkage disequilibrium in the distal sections of the chromosomes, but some significant disequilibrium was detected in proximal regions. There were many significant correlations between different element families with respect to the identity of the sites that were occupied in the sample. There were also significant correlations between families with respect to sites at which elements achieved relatively high frequencies. Element frequencies per chromosome band were generally low in the distal sections, but were higher proximally. These results are discussed in the light of models of the population dynamics of transposable elements. It is concluded that they provide strong evidence for the operation of a force or forces opposing transpositional increase in copy number. The data suggest that the rate of transposition per element per generation is of the order of 10(-4), for the elements included in this study.

Animals↗

PubMed1988

Organization of the Tgm family of transposable elements in soybean.

We have compared the organization of six Tgm elements that were selected from a genomic library of soybean DNA on the basis of hybridization with subcloned regions of Tgm 1 (transposon, Glycine max) from the seed lectin gene. These elements ranged in size from 1.6 kbp to greater than 12 kbp. Tgm2, Tgm3, Tgm4 and Tgm5 represent partial isolates in which the genomic clone contained a 3' but not a 5' terminus of the element; while Tgm6 and Tgm7, like Tgm1, were small isolates flanked by both 5' and 3' nonelement sequences. Cross-hybridization studies between subcloned portions of these seven elements identified regions of homology which suggest that the Tgm transposable elements of soybean form a family of deletion derivatives. In addition to internal deletion events, numerous deletions and base substitutions are also present within the borders of these elements which are comprised of the same tandemly repeated sequence. The 39% amino acid homology between a 1 kb portion of an open reading frame in Tgm4 and Tgm5 and ORF1, an open frame from the first intron of the maize Enhancer (Suppressor-mutator) transposable element, suggests that both elements encode a common function that requires a high degree of protein conservation.

Base Sequence↗

PubMed1990

Characterization and purification of DNA-RNA complexes related with 1731 and copia-like transposable elements in a Drosophila cell line.

DNA-RNA complexes were characterized and purified in a Drosophila melanogaster cell line. Such duplexes were shown to be specific of 1731 and other "copia-like" transposable elements. DNA-RNA complexes were purified through a Sephadex G-75 column from a global nucleic acid preparation or from a total RNA fraction prior to DNA-A and RNA-A treatment. They incorporated both labelled thymidine and uridine and their resistance or sensibility to enzymes or chemicals was consistent with that being expected with such hybrid molecules. From that intermediate form of reverse transcription, the resulting labelled cDNAs were obtained and were shown to be homologous to different drosophila "copia-like" transposable elements. These results suggest that most of the "copia-like" transposable elements were amplified through a reverse transcription pathway in Drosophila melanogaster.

Animals↗

PubMed1987

Developmental expression of Drosophila melanogaster retrovirus-like transposable elements.

We have determined the pattern of temporal expression of several Drosophila retrovirus-like transposable elements. Some of these elements can be grouped into classes whose members show a similar profile of developmental transcription. The members of the 412 class, which includes 412, mdg1, 17.6 and 3S18, are transcribed mainly in the early larval and pupal stages of development, with small differences among the various members. HMS Beagle and Springer constitute another class where RNA accumulation in the larval stages is higher than in pupae and the adult flies accumulate more RNA than any other stage of development. Finally, the transcription of other elements such as copia, 297 and B104 follows a specific and individual pattern distinct from those described above. These results suggest the existence of evolutionary relationships among different transposable elements in Drosophila and the involvement of different cellular genes in the control of their expression.

Animals↗

PubMedDate not supplied

Mys, a family of mammalian transposable elements isolated by phylogenetic screening.

It has recently been demonstrated both emperically and mathematically that transposable elements may spread rapidly throughout a population once introduced even when they dramatically reduce the fitness of individuals that carry them. Such events result in pronounced differences in the phylogenetic distribution of genetic elements capable of rapid genome invasion. Using a simple and general procedure to screen the genome of the white-footed mouse Peromyscus leucopus, we have isolated a family of retrovirus-like elements which is apparently absent from the genome of the house mouse Mus domesticus. Here, we report this procedure and an analysis of the organization, phylogenetic distribution and sequence of this family of transposable elements.

Animals↗

PubMedDate not supplied

Activation of a transposable element in the germ line but not the soma of Caenorhabditis elegans.

The genetic activity of transposable elements is tightly controlled in many species. Transposons that are relatively quiescent under certain circumstances can excise or transpose at greatly increased rates under other circumstances. For example, 'genomic shock' can activate quiescent maize transposons, 'cytotype' and tissue-specific splicing regulate Drosophila P factors, copy number controls Tn5 transposition in bacteria, and developmental timing affects the production of transposon-like intracisternal A-particles in mouse embryos. The Caenorhabditis elegans transposable element Tc1 is subject to both strain-specific and tissue-specific control. Multiple copies of Tc1 are present in the genome of all C. elegans strains collected from nature. However, these elements are genetically active in only certain isolates. For example, in C. elegans variety Bristol transposition and excision of Tc1 are undetectable, but in variety Bergerac transposition and excision are frequent. Moreover, in variety Bergerac, Tc1 is about 1,000-fold more active in somatic cells than in germ cells. We have investigated the genetic basis for the germ/soma regulation of Tc1 activity. We have isolated mutants that exhibit increased frequencies of Tc1 excision in the germ line. The frequencies of Tc1 excision in the soma are unaltered in these mutants. These mutants also exhibit high frequencies of Tc1 germ-line transposition, and this results in a mutator phenotype. Nearly all mutator-induced mutations are caused by insertion of Tc1.

Animals↗

PubMed1990

A new transposable element in Chironomus thummi.

A 1.7 kb long transposable element called TECth1 was found in the 3' flanking region of a Chironomus thummi Balbiani ring gene. As shown by sequence comparison with a second copy, TECth1 is characterized by a perfect terminal inverted repeat of 17 bp flanked by a duplicated target site of 8 bp, four internal imperfect inverted repeats of 17 to 26 bp and terminal regions of about 0.25 kb with a high number of short direct repeats of the consensus sequence ACTTT or permutated and mutated forms such as TTTAC or ACTAT. The terminal inverted repeats and the 8 bp target site duplication are reminiscent of Drosophila P and hobo elements but no long open reading frame starting with ATG is present, suggesting that the two TECth1 copies studied represent deletion derivatives of a longer element coding for its own transposase. In situ hybridization revealed about 75 labelled sites distributed over all chromosomes with the Balbiani ring locus most strongly labelled. Fifty percent of the sites are specific for a given individual, and these variable sites are often heterozygous for the element.

Animals↗

PubMed1991

Transposable elements in natural populations with a mixture of selected and neutral insertion sites.

This paper examines models of the population dynamics of transposable elements when chromosomal sites vary with respect to the effect on fitness of mutations caused by element insertions. Element abundance is assumed to be stabilised solely by the joint results of transposition, excision, and selection against insertional mutations. When there are only two classes of site, selected and neutral, it is hard to find parameter values for which numbers of elements are maintained that match the findings from surveys of Drosophila populations, as elements tend to accumulate at high frequencies at the neutral sites. It is similarly hard to produce realistic equilibria with three classes of site (strongly selected, weakly selected, and neutral), when elements can transpose out of the neutral sites. If transposition from neutral sites is impossible, as might be the case for elements inserted into centric heterochromatin, then realistic equilibria can be generated if there is very weak selection against elements inserted into the majority of non-neutral sites. This model predicts a modest over-representation of elements at the neutral sites. It also predicts that elements should be under-represented on the X chromosome compared with the autosomes, but this is not generally found to be the case. It is concluded that selection against insertional mutations is unlikely to be the major factor involved in the containment of element abundance.

Animals↗

PubMed1989

The bz-rcy allele of the Cy transposable element system of Zea mays contains a Mu-like element insertion.

The receptive component of the Cy transposable element system (rcy:Mu7) at the Bz locus of Zea mays L. is 2.2 kb and has long terminal inverted repeats. The insertion is flanked by a 9 bp duplication. In the presence of an autonomous Cy element in the genome, rcy:Mu7 is excised from bz-rcy in a manner consistent with a model suggested previously. The termini of rcy:Mu7 have 85% sequence similarity with the Mu1 element of Z. mays. This is consistent with the observation that Mu1 can behave genetically like a receptive component of the Cy system.

Alleles↗

PubMed1987

Isolation and characterization of a nematode transposable element from Panagrellus redivivus.

We have isolated a transposable element, designated PAT-1, from the free-living nematode Panagrellus redivivus. P. redivivus strain C15 was found to have a high spontaneous mutation frequency compared to the standard Caenorhabditis elegans laboratory strain N2. To characterize the genetic lesions occurring in spontaneous C15 mutants, we molecularly cloned the homolog of the C. elegans unc-22 gene from wild-type P. redivivus and two strains carrying spontaneous mutations in this gene. One of these mutations resulted from the insertion of a 4.8-kilobase segment of repetitive DNA. This repetitive element (PAT-1) varies in copy number (10-50 copies) and location in different P. redivivus strains and is absent from C. elegans. The element could be useful as a transformation vector for C. elegans. Our approach is a general one that could be used to isolate additional nematode transposons from other species.

Animals↗

PubMed1988

Mutational analysis of the open reading frames in the transposable element IS1.

IS1 is one of the smallest transposable elements found in bacteria (768 bp). It contains eight overlapping open-reading-frames (ORFs) greater than 50 codons, designated insA to insG and insB'. To determine which of the ORFs actually code for proteins involved in transposition, we have introduced amber codons into each ORF by site-directed mutagenesis which make neutral changes in the overlapping ORFs. Each mutant IS1 was then tested for its ability to mediate cointegrate formation in Su+ and Su- backgrounds. The mutant elements were also tested for trans-complementation in an IS1-free Salmonella background. Our results show that the products of the insA and insB genes are the only ones essential for cointegrate formation. We suggest that other ORFs may, however, encode accessory proteins.

Amino Acid Sequence↗

PubMed2025

Transposable elements are dysregulated in brains of individuals with major depressive disorder.

Transposable elements (TEs) are repetitive DNA sequences capable of being transcribed and re-integrated, or transposed, into distinct loci throughout the genome. While thought to be largely transcriptionally silenced in brain, TE transcription is increasingly recognized as dynamic and involved in human health and disease states, including in disorders of the brain. In this study, we annotated TE transcripts in publicly available RNA sequencing (RNAseq) of postmortem human brain tissue to investigate the expression profile of TE transcripts in individuals with major depressive disorder (MDD) compared to healthy controls. Our findings reveal a robust impact to TE transcript expression in the brains of subjects with MDD relative to controls. This work points to the aberrant transcription of cortical TEs as a potentially overlooked molecular signature of MDD.

Humans↗

PubMed1991

Capture of flanking DNA by a P element in Drosophila melanogaster: creation of a transposable element.

A 6.1-kilobase insertion into the rudimentary (r) gene was cloned and partially sequenced. The insertion consists of a 703-base-pair (bp) P element next to a 5.4-kilobase single-copy sequence. The normal position of the single-copy sequence is near the tip of the X chromosome. Upon insertion into the r gene, this chimeric element generated an 8-bp target-site duplication, characteristic of P elements. At the non-P-element end of the insertion, the first 8 bp are identical to the first 8 bp of the inverted terminal repeats of the P element. Thus, this element has inverted terminal repeats of 8 bp. This large element can excise from the r gene under conditions of hybrid dysgenesis, which indicates that it behaves like a normal P element. These data support the conclusion that a normally stable single-copy sequence has now become unstable and duplicated within the genome.

Animals↗

PubMed1988

Phenotypic diversity mediated by the maize transposable elements Ac and Spm.

Mutations caused by the insertion of members of the Ac or Spm family of transposable elements result in a great diversity of phenotypes. With the cloning of the mutant genes and the characterization of their products, the mechanisms underlying phenotypic diversity are being deciphered. These mechanisms include (i) imprecise excision of transposable elements, which can result in the addition of amino acids to proteins; (ii) DNA methylation, which has been correlated with the activity of the element; (iii) transposase-mediated deletions within elements, which can inactivate an element or lead to a new unstable phenotype; and (iv) removal of transcribed elements from RNA, which can facilitate gene expression despite the insertion of elements into exons. An understanding of the behavior of the maize elements has provided clues to the function of cryptic elements in all maize genomes.

Alleles↗

PubMed1990

Rapid proliferation of the maize transposable element Activator in transgenic tomato.

We have found that the maize transposable element Activator (Ac) can rapidly proliferate when transformed into tomato plants. The fate of transposed Ac elements in self-pollinated progeny of independent transgenic tomato plants was examined by DNA gel blot hybridizations. When a single copy of Ac was introduced into a transformant, the number of copies usually remained low in subsequent generations. In one lineage, however, the number of Ac elements increased from one to more than 15 copies in only two generations. DNA gel blot analyses indicated that the amplified elements were not grossly rearranged. Amplified copies of Ac resided at unique sites in the genome, and segregation analysis indicated that these sites were not tightly linked at one genetic locus. Taken together, these observations indicate that the mechanism of Ac amplification is associated with transposition.

DNA Transposable Elements↗