Abstract
DNA transposons are defined as repeated DNA sequences that can move within the host genome through the action of transposases. The transposon superfamily Merlin was originally found mainly in animal genomes. Here, we describe a global distribution of the Merlin in animals, fungi, plants and protists, reporting for the first time their presence in Rhodophyceae, Metamonada, Discoba and Alveolata. We identified a great variety of potentially active Merlin families, some containing highly imperfect terminal inverted repeats and internal tandem repeats. Merlin-related sequences with no evidence of mobilization capacity were also observed and may be products of domestication. The evolutionary trees support that Merlin is likely an ancient superfamily, with early events of diversification and secondary losses, although repeated re-invasions probably occurred in some groups, which would explain its diversity and discontinuous distribution. We cannot rule out the possibility that the Merlin superfamily is the product of multiple horizontal transfers of related prokaryotic insertion sequences. Moreover, this is the first account of a DNA transposon in kinetoplastid flagellates, with conserved Merlin transposase identified in Bodo saltans and Perkinsela sp., whereas it is absent in trypanosomatids. Based on the level of conservation of the transposase and overlaps of putative open reading frames with Merlin, we propose that in protists it may serve as a raw material for gene emergence.
Highlights
Transposable elements (TEs) are defined as repeated DNA sequences that can move within the host genome
As new genomes from a broad range of taxa become available at an ever-increasing pace, it is possible to expand our knowledge about the distribution and evolutionary history of TEs
We first performed a search for Merlin deposited in Repbase and identified 70 sequences, of which 32 displayed the expected DDE_Tnp_IS1595 domain and the DDE motif, an essential part of the catalytic site of transposases [31]
Summary
Transposable elements (TEs) are defined as repeated DNA sequences that can move within the host genome. We found different levels of degeneration, with the transposase pseudogenization occurring in several copies that still contain nearly conserved TIRs and TSDs. From 340 analyzed alveolate genomes, sequences homologous to Merlin were initially found in 7 species by blastp and subsequently in 33 genomes by tblastn.
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