Xena, a Full-Length Basal Retroelement from Tetraodontid Fish

Abstract

Mobile genetic elements are ubiquitous throughout the eukaryote superkingdom. We have sequenced a highly unusual full-length retroelement from the Fugu fish, Takifugu rubripes. This element, which we have named Xena, is similar in structure and sequence to the Penelope retroelement from Drosophila virilis and consists of a single long open reading frame containing a reverse transcriptase domain flanked by identical direct long terminal repeat (LTR) sequences. These LTRs show an organization similar to the terminal repeats already described in the Penelope retrotransposon of Drosophila but are structurally and functionally distinct from the LTRs carried by LTR-retrotransposons. In view of their distinctness, we refer to these repeats as PLTRs (Penelope-LTRs). Whereas the element contains a reverse transcriptase, no other domains or motifs commonly associated with retroelements are present. In the full-length Fugu element, the 5' direct PLTR is preceded by an inverted PLTR fragment. Additional elements, many showing various degrees of deletion, are described from the Fugu genome and from that of the freshwater pufferfish Tetraodon nigroviridis. Many of these additional elements are also preceded by inverted PLTR sequences. Xena-like elements are also described from the genomes of several other organisms. The Penelope-Xena lineage is apparently a basal group within the retrotransposons and therefore represents an evolutionarily important class of retroelement.

Small RNA-based silencing strategies for transposons in the process of invading Drosophila species

“…PLEs are present in many animal genomes, and their reverse transcriptase moiety can be also found in several protists, fungi, and plants, indicating an ancient origin (Evgen'ev and Arkhipova 2005). These unusual elements are probably active only within the virilis group of Drosophila and perhaps also within a few fish species (Dalle Nogare et al 2002).…”

Clustering of C‐Type Lectin Natural Killer Receptor‐Like Loci in the Bony Fish Oreochromis niloticus

“…The Xena element is a retrotransposon which spreads via an RNA intermediate. It was originally identified in the puffer fish, Takifugu rubripes [26], by its resemblance to the Penelope retroelement of Drosophila virilis [27]. CR1 elements are retrotransposons of the non-LTR type found in birds [28], turtles [29] and the puffer fish [30].…”

Divergent long-terminal-repeat retrotransposon families in the genome of Paragonimus westermani

“…Otherwise, the sequences were directly translated from each single clone after correcting the sequences to increase homology values with the RTs of other retrotransposons. The evolutionary positions of the trematode retrotransposons were estimated by a phylogenetic analysis of 47 retrotransposons, including all the sequences from this study and a number of other representatives of LTR-containing genetic elements (Malik and Eickbush, 2001;Dalle Nogare et al, 2002).…”

“…The Metaviridae are further split according to the presence of the env gene (genus Errantivirus) or its absence (genus Metavirus) (Pringle, 1999). However, the taxonomical classification of LTR retrotransposons are likely to be more complex due to the recent identifications of new subgroups such as Bel, Xena, and DIRS, which show different structural or sequential features from the existing elements (Malik and Eickbush 2001;Dalle Nogare et al, 2002).…”