Y. V. Ilyin

The endogenous Drosophila melanogaster retrovirus gypsy can propagate in Drosophila hydei cells.

Abstract. The endogenous Drosophila melanogaster retrovirus gypsy (mdg4) forms virus-like particles (VLPs) which are found as extracellular particles in the medium used to culture D. melanogaster cells. The D. hydei somatic cell line DH14, which does not harbour gypsy sequences, was exposed to D. melanogaster VLPs. Subsequent PCR and Southern analysis revealed that gypsy elements had penetrated into the D. hydei cells, suggesting interspecific transmission of the retrovirus. A D. hydei cell line containing gypsy sequences was established and grown in a mixed culture together with the G418-resistant D. hydei cell line DH33, and gypsy was shown to be transmitted from cell to cell. The proportion of cells carrying gypsy increased with time. The rate of gypsy invasion of the lines DH14 and DH33 was 10–3 and 10–2 per cell per generation, respectively. The results demonstrate the possibility of interspecific horizontal transfer of gypsy in the form of its VLPs.

Evidence for horizontal transfer of the LTR retrotransposon mdg3, which lacks an env gene

Abstract. Horizontal (interspecific) transfer is regarded as a possible strategy for the propagation of transposable elements through evolutionary time. To date, however, conclusive evidence that transposable elements are capable of horizontal transfer from one species to another has been limited to class II or DNA-type elements. We tested the possibility of such transfer for several Drosophila melanogaster LTR retrotransposons of the gypsy group in an experiment in which D. melanogaster and D. virilis somatic cell lines were used as donor and recipient cells, respectively. This approach was chosen in light of the high levels of LTR retrotransposon amplification and expression observed in cultured D. melanogaster cells. In the course of the experiment, parallel analysis for mdg1, mdg3, 17.6, 297, 412 and B104/roo retrotransposons was performed to detect their presence in the genome of recipient cells. Only the mdg3 retrotransposon, which lacks an env gene, was found to be transmitted into recipient cells. This model, based on the use of cultured cells, is a promising system for further investigating the mechanisms of LTR retrotransposon transfer.

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.

The functional motifs that are revealed in the gypsy Gag amino acid sequence.

Erantiviruses (IERV) of Drosophila are a convenient model for studying the biology of endogenous retroviruses—a class of retroelements that occur in the genome of different organisms, from insects to the human [1]. The data on IERV biology are largely based on the analysis of the element gypsy , which is the main model for describing the retroviruses of invertebrates. The structural protein Gag, encoded by this retrovirus, forms retroelement particles capable of intercellular transpositions [2, 3]. An interesting feature of gypsy Gag is the fact that it does not contain known canonical motifs characteristic of the majority of retroviral Gag [1]. Nevertheless, this protein and particles formed by it exhibit almost all properties and functions characteristic of retroviruses. In the past years, the question on the role of cell factors involved in the process of retrovirus formation is one of the main questions to be answered. The interest to it is caused by the observations showing that retroviral particles contain a number of proteins encoded by the host cell [4]. Although the role the cell proteins required for vital activity of retroviruses is not understood completely, it was found that the amino acid sequences of structural retroviral proteins of vertebrates contain short conservative motifs that bind to several proteins encoded by the host cell [4, 5]. These motifs are absent in the gypsy Gag sequence.