LTR-Retrotransposons from Bdelloid Rotifers Capture Additional ORFs Shared between Highly Diverse Retroelement Types

Viruses. 2017 Apr 11;9(4):78. doi: 10.3390/v9040078.


Rotifers of the class Bdelloidea, microscopic freshwater invertebrates, possess a highlydiversified repertoire of transposon families, which, however, occupy less than 4% of genomic DNA in the sequenced representative Adineta vaga. We performed a comprehensive analysis of A. vaga retroelements, and found that bdelloid long terminal repeat (LTR)retrotransposons, in addition to conserved open reading frame (ORF) 1 and ORF2 corresponding to gag and pol genes, code for an unusually high variety of ORF3 sequences. Retrovirus-like LTR families in A. vaga belong to four major lineages, three of which are rotiferspecific and encode a dUTPase domain. However only one lineage contains a canonical envlike fusion glycoprotein acquired from paramyxoviruses (non-segmented negative-strand RNA viruses), although smaller ORFs with transmembrane domains may perform similar roles. A different ORF3 type encodes a GDSL esterase/lipase, which was previously identified as ORF1 in several clades of non-LTR retrotransposons, and implicated in membrane targeting. Yet another ORF3 type appears in unrelated LTR-retrotransposon lineages, and displays strong homology to DEDDy-type exonucleases involved in 3'-end processing of RNA and single-stranded DNA. Unexpectedly, each of the enzymatic ORF3s is also associated with different subsets of Penelope-like Athena retroelement families. The unusual association of the same ORF types with retroelements from different classes reflects their modular structure with a high degree of flexibility, and points to gene sharing between different groups of retroelements.

Keywords: DEDDy exonuclease; GDSL esterase; dUTPase; envelope gene (ENV); retrovirus-like transposable elements.

Publication types

  • Research Support, U.S. Gov't, Non-P.H.S.
  • Research Support, N.I.H., Extramural

MeSH terms

  • Animals
  • Genetic Variation*
  • Open Reading Frames*
  • Retroelements*
  • Rotifera / genetics*
  • Sequence Homology*


  • Retroelements