Retroviruses in invertebrates: the gypsyretrotransposon is apparently an infectious retrovirus of Drosophilamelanogaster.

Abstract

Retroviruses are commonly considered to be restricted to vertebrates. However, the genome of many eukaryotes contains mobile sequences known as retrotransposons with long terminal repeats (LTR retrotransposons) or viral retrotransposons, showing similarities with integrated proviruses of retroviruses, such as Ty elements in Saccharomyces cerevisiae, copia-like elements in Drosophila, and endogenous proviruses in vertebrates. The gypsy element of Drosophila melanogaster has LTRs and contains three open reading frames, one of which encodes potential products similar to gag-specific protease, reverse transcriptase, and endonuclease. It is more similar to typical retroviruses than to LTR retrotransposons. We report here experiments showing that gypsy can be transmitted by microinjecting egg plasma from embryos of a strain containing actively transposing gypsy elements into embryos of a strain originally devoid of transposing elements. Horizontal transfer is also observed when individuals of the "empty" stock are raised on medium containing ground pupae of the stock possessing transposing elements. These results suggest that gypsy is an infectious retrovirus and provide evidence that retroviruses also occur in invertebrates.

Activation of transcription and retrotransposition of a novel retroelement, Steamer , in neoplastic hemocytes of the mollusk Mya arenaria

“…Those elements that do encode envelope proteins [such as ZAM (37) and gypsy itself (38)] can act as infectious retroviruses and can transmit from cell to cell and from one animal to another, perhaps with the help of cellular vesicle trafficking machinery (37)(38)(39). However, such infection events may take place even without the use of the envelope protein encoded by the element (40), and in these cases an envelope-like protein from the cell, or from a complementing retroelement, may provide the functionality in trans.…”

Vertically transmitted viral endosymbionts of insects: do sigma viruses walk alone?

“…The only virus we are currently aware of that has evolved this strategy is the gypsy element in Drosophila melanogaster [15], which can produce infectious virions that are transmitted to the next generation in eggs, enabling the virus to spread through populations as a selfish genetic element [16]. Gypsy elements are widely distributed in other species of Drosophilidae and show evidence of switching between host species, suggesting that they may also produce infectious particles [17].…”

Revisiting horizontal transfer of transposable elements in Drosophila

“…In D. melanogaster, the gypsy virus-like particles are capable of efficiently infecting the germ line of strains devoid of active gypsy, and a high level of insertion activity is observed in their progeny (Song et al, 1994). Its infectious properties result from the expression of the env gene, encoding a protein responsible for its infectivity (Kim et al, 1994;Song et al, 1994;Teysset et al, 1998;Chalvet et al, 1999). Therefore, gypsy can potentially be transmitted as intracellular virus-like particles without the need of any vector.…”