N. V. Lyubomirskaya

The introduction of a transpositionally active copy of retrotransposon GYPSY into the Stable Strain of Drosophila melanogaster causes genetic instability

A previously described genetic system comprising a Mutator Strain (MS) and the Stable Strain (SS) from which it originated is characterized by genetic instability caused by transpositions of the retrotransposon gypsy. A series of genetic crosses was used to obtain three MS derivatives, each containing one MS chromosome (X, 2 or 3) in the environment of SS chromosomes. All derivatives are characterized by elevated frequencies of spontaneous mutations in both sexes. Mutations appear at the premeiotic stage and are unstable. Transformed derivatives of SS and another stable strain 208 were obtained by microinjection of plasmid DNA containing transpositionally active gypsy inserted into the Casper vector. In situ hybridization experiments revealed amplification and active transposition of gypsy in SS derivatives, while the integration of a single copy of gypsy into the genome of 208 does not change the genetic properties of this strain. We propose that genetic instability in the MS system is caused by the combination of two factors: mutation(s) in gene(s) regulating gypsy transposition in SS and its MS derivatives, and the presence of transpositionally active gypsy copies in MS but not SS.

Retrotransposon gtwin: Structural Analysis and Distribution in Drosophila Strains

A search for noncanonical variants of the gypsy retrotransposon (MDG4) in the genome of the Drosophila melanogaster strain G32 led to the cloning of four copies of the poorly studied 7411-bp gtwin element. Sequence analysis showed that gtwin belongs to a family of endogeneous retroviruses, which are widespread in the Drosophila genome and have recently been termed insect erantiviruses. The gtwin retrotransposon is evolutionarily closest to MDG4, as evident from a good alignment of their nucleotide sequences including ORF2 (the pol gene) and ORF3 (the env gene), as well as the amino acid sequences of their protein products. These regions showed more than 75% homology. The distribution of gtwin was studied in several strains of the genus Drosophila. While strain G32 contained more than 20 copies of the element, ten other D. melanogaster strains carried gtwin in two to six copies per genome. The gtwin element was not detected in D. Hydei or D. Virilis. Comparison of the cloned gtwin sequences with the gtwin sequence available from the D. melanogaster genome database showed that the two variants of the mobile element differ by the presence or absence of a stop codon in the central region of ORF3. Its absence from the gtwin copies cloned from the strain G32 may indicate an association between the functional state of ORF3 and amplification of the element.

Retrotransposon gypsy and Its Role in Genetic Instability of a Mutator Strain of Drosophila melanogaster

This article summarizes the results of a ten-year study of genetic instability of a mutator strain of Drosophila melanogaster caused by transposition of the gypsy retrotransposon. The results of other authors working with an analogous system are analyzed. Possible mechanisms are suggested for the interaction of gypsy with the cell gene flamenco that participates in transposition control of this mobile element.

Retrotransposon Gtwin Specific for the Drosophila melanogaster Subgroup

Eukaryotic genome contains a vast variety of transposable elements. They have a great effect of the vital functional of the cell and adaptability of the organism to environmental conditions. Transposable elements, in turn, are subject to control by the cell. The evolutionary development of transposable elements and its dependence on the cell genome are of particular interest. The long terminal repeat (LTR) retrotransposon gtwin , which is classified into the group Gypsy , was discovered in the Drosophila melanogaster genome by the methods of computer analysis [1, 2]. This retrotransposon was first clones in our laboratory in search for the retroelements that share significant homology with the endogenous retrovirus MDG4 ( gypsy ) [3]. MDG4 is the best studied transposable element of Drosophila ; it contains three open reading frames (ORFs), which makes it similar to vertebrate retroviruses. Studying the infective properties of retrotransposons, such as MDG4 and gtwin , is of great interest. When the distribution of gtwin in different strains of the genus Drosophila was studied, this retrotransposon was not detected in the species evolutionarily remote from D. melanogaster , namely, in D. funebris, D. hydei , and D. virilis , although it is known that their genomes contain MDG4 copies. However, gtwin copies were found in all D. melanogaster strains studied by us [3]. These data apparently indicate that retrotransposon gtwin is sufficiently evolutionarily young. This study is devoted to the search for the transposable element gtwin in the genomes of evolutionarily close species composing the melanogaster subgroup. This subgroup, besides D. melanogaster per se, is represented by eight species: D. simulans, D. erecta, D. mauritiana, D. yakuba, D. santomea, D. orena, D. teissieru , and D. sechellia. Analysis of our data showed that the genomes of all of them contain retrotransposon gtwin. At the first stage of this study, we performed the search for the transposable element gtwin by Southern hybridization. Genomic DNA isolated from flies as described by Maniatis et al. [4] was treated with the restriction endonuclease Hind III. The restriction fragments were separated by electrophoresis in agarose gel, transferred onto a Nylon membrane, and hybridized with 32 P-labeled DNA fragment from the leader region

Mobile Genetic Element gypsy(MDG4) in Drosophila melanogasterStrains: Structural Characteristics and Regulation of Transposition

Distribution of two structural functional variants of the gypsy(MDG4) mobile genetic element was examined in 44 strains of Drosophila melenogaster. The results obtained suggest that less transpositionally active gypsyvariant is more ancient component of the Drosophilagenome. Using Southern blotting, five strains characterized by increased copy number of gypsywith significant prevalence of the active variant over the less active one were selected for further analysis. Genetic analysis of these strains led to the suggestion that some of them carry factors that mobilize gypsyindependently from the cellular flamencogene known to be responsible for transposition of this element. Other strains probably contained a suppressor of the flam–mutant allele causing active transpositions of the gypsy. Thus, the material for studying poorly examined relationships between the retrovirus and the host cell genome was obtained.

Amplification of “defective” retrotransposon gtwin in D. melanogaster strain carrying large complex chromosomal aberration

Transposable elements (TE) are found in all eukaryotic genomes and play a significant role in their structure and functioning. The majority of mobile elements are silent in the genomes indicating the existence of cell control mechanisms of their activity. Establishment of immunity to TE is of great interest, but it cannot be studied directly and there are only few examples of present or recent active transpositions of mobile elements. G32, a Drosophila melanogaster strain, is characterized by the presence of large complex chromosomal aberration in the 3rd chromosome, active transpositions of gtwin in the past, and its stability at present. To address the question as to what had happened to the element while the cell took it under the control, we performed the detailed cytological and molecular analyses of gtwin’s structure and its distribution in G32. Two variants of gtwin were found, one of which is amplified in G32 despite the alteration of tRNA-primer binding site. This element is accumulated in the aberrant chromosome and associated with the inversions breakpoints. Gtwin copies are predominantly localized in euchromatic regions and at least three of them are situated in heterochromatin. One copy was found in the piRNA cluster that might have caused silencing of the element.

Structural Polymorphism of the Transposable Element MDG4 (gypsy) in Drosophila melanogasterStrains

We studied the frequencies of these variants of the retrovirus-like transposable element MDG4 ( gypsy ) in D. melanogaster strains obtained from wild populations. We examined 44 strains for the presence of subfamilies homologous with respect to the Hind III site and determined the number of copies in them. The Hind III site is a marker that permits distinguishing the two MDG4 variants with different retrotransposition activities. The data obtained allow us to suggest that the inactive transposable element has emerged in the D. melanogaster genome considerably earlier than the active one. In five strains, MDG4 was amplified, which might be related to genetic instability caused by its transpositions. These strains may serve as a model for further studying the genetic control of retrotransposition. Southern blotting was used for screening of the