A long interspersed repetitive element--the I factor of Drosophila teissieri--is able to transpose in different Drosophila species.

Abstract

Long interspersed repetitive elements (LINEs) are transposable elements present in many species. In mammals they are difficult to study because most of them are defective and their transposition frequency is low. The I factor of Drosophila melanogaster is a LINE element that is particularly interesting because its transposition occurs at high frequency during I-R hybrid dysgenesis. This phenomenon occurs when males from the class of inducer strains are crossed with females from the class of reactive strains. Inducer strains contain several complete 5.4-kilobase I factors at various sites on the chromosomal arms. Reactive strains are devoid of complete I factors. Many results indicate that active I factors have invaded the D. melanogaster genome recently. To study the evolutionary history of I elements, we have cloned and sequenced a potentially active I factor from Drosophila teissieri. It is flanked by a target-site duplication and terminates at the 3' end by tandem repeats of the sequence TAA. When introduced into the germ line of a reactive strain of D. melanogaster by P element-mediated transformation, it is able to transpose and induces hybrid dysgenesis. This strengthens the hypothesis of a recent reinvasion of the D. melanogaster genome by active I factors giving rise to the inducer strains. They could have originated by horizontal transfer from another species. Such events also could occur for other LINE elements and might explain the spread of new variants in mammalian genomes. Moreover, the results give a further insight into I factor functional organization.

Abundance, distribution and dynamics of retrotransposable elements and transposons: similarities and differences

“…This phenomenon occurs more frequently in TEs than in regular genes. In Drosophila, at least four different events have been suggested; two for the retroelements I (Abad et al, 1989) and Copia (Jordan et al, 1999) and, two for the DNA elements P (Daniels et al, 1990b) and hobo (Daniels et al, 1990a). Since the first description of the transfer of the P element, probably from D. willistoni to D. melanogaster, many more suspected HTs have been suggested (Clark et al, 1995(Clark et al, , 1998Clark and Kidwell, 1997).…”

Distinct families of site-specific retrotransposons occupy identical positions in the rRNA genes of Anopheles gambiae.

“…Support for this assertion comes from a sequence comparison between functional I factors from D. melanogaster and D. teissieri (1). Sequences that hybridize to I-factor probes have been detected in all but 1 of the 21 members of the D. melanogaster group and four species outside it, leading to the suggestion that I elements are evolutionarily old components of the genomes of these species (28).…”

I elements in <i>Drosophila:</i> in vivo retrotransposition and regulation

“…D. teissieri also contains both types of elements (Simonelig et al, 1988). The putatively active ele-ments of this species are able to transpose at high frequency when introduced by transgenesis in an R strain of D. melanogaster and to convert this stock into an inducer strain (Abad et al, 1989;Vaury et al, 1993).…”

“…After several generations, the transgenic stocks contained multiple transposed copies, indicating that the mutated elements retained the ability to retrotranspose and therefore that the TAA repeats are not absolutely required for retrotransposition. Any sequence or structure that is recognised by the reverse transcriptase may lie in the 3) UTR since I factors from D. melanogaster and D. teissieri show strong similarities in this region (Abad et al, 1989). Transposed copies of these mutated elements isolated in the transgenic stocks terminate at the 3) end by tandem repeats, either long stretches of A or more complex tandem duplications of sequences that were adjacent to the progenitor element (Chaboissier et al, 2000).…”

“…ORF2 encodes a putative product showing similarities to apurinic-apyrimidic endonucleases, reverse transcriptases and RNAses H, and containing also a cysteine-rich domain. I factors are flanked by target site duplications created upon insertion that vary in sequence and length (Fawcett et al, 1986;Abad et al, 1989). Therefore the I factor is a non-site-specific retrotransposon.…”