Abstract
Transposable elements are widely distributed within genomes where they may significantly impact their evolution and cell functions. Short interspersed elements (SINEs) are non-autonomous, fast-evolving elements, but some of them carry a highly conserved domain (HCD), whose sequence remained substantially unchanged throughout the metazoan evolution. SINEs carrying the HCD called V are absent in amniote genomes, but V-like sequences were found within the miniature inverted-repeat transposable element (MITE) MER6 in Homo sapiens. In the present work, the genomic distribution and evolution of MER6 are investigated, in order to reconstruct the origin of human V domain and to envisage its possible functional role. The analysis of 85 tetrapod genomes revealed that MER6 and its variant MER6A are found in primates, while only the MER6A variant was found in bats and eulipotyphlans. These MITEs appeared no longer active, in line with literature data on mammalian DNA transposons. Moreover, they appeared to have originated from a Mariner element found in turtles and from a V-SINE from bony fishes. MER6 insertions were found within genes and conserved in mRNAs: in line with previous hypothesis on functional role of HCDs, the MER6 V domain may be important for cell function also in mammals.
Highlights
Transposable elements (TEs) are DNA sequences able to replicate and insert within genomes [1,2]
MER6 and MER6A have been isolated for the first time in H. sapiens and later labelled as primate-specific elements [26,28]
Looking at mammalian phylogeny (Figure 5), MER6A was present in two different lineages: the Euarchontoglires, to which primates belong, and the Laurasiatheria, which includes bats and eulipotyphlans
Summary
Transposable elements (TEs) are DNA sequences able to replicate and insert within genomes [1,2] Since their first discovery [3], TEs are known to impact host genome evolution and cell functions in several ways; for example, they can modify gene regulatory networks, mediate genomic rearrangement or even be exapted as new genes or gene components [2]. SINEs are widespread among vertebrates and they were found well-represented in cartilaginous fishes, the coelacanth and mammals [6] They are very short sequences (200–600 bp) composed by three “modules”: an RNA-related head, which may originate from tRNA, 7SL, or 5S rDNA genes, a tail homologous to that of long interspersed repeats (LINEs), which allows to exploit the LINE reverse transcriptase, and a body linking the head and the tail [4]. An implication for some HCDs, such as CORE, Deu and V domains, as regulatory elements has been suggested based on mRNAs and miRNA genes analyses in fishes [23,24]
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