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Abstract
The term ‘horizontal transfer (HT)’ refers to the transfer of genetic material between two reproductively isolated organisms. HT is thought to occur rarely in eukaryotes compared to vertical inheritance, the transmission of DNA from parent to offspring. In a recent study we have provided evidence that a family of DNA transposons, called SPACE INVADERS or SPIN, independently invaded horizontally the genome of seven distantly related tetrapod species and subsequently amplified to high copy number in each of them. This discovery calls for further investigations to better characterize the extent to which genomes have been shaped through HT events. In this addendum, we briefly discuss some general issues regarding the study of HT and further speculate on the sequence of events that could explain the current taxonomic distribution of SPIN. We propose that the presence of SPIN in the opossum (Monodelphis domestica), a taxon endemic to South America, reflects a transoceanic HT event that occurred from Old to New World, between 46 and 15 million years ago.
Acknowledgements
Research in the Feschotte lab is funded by grant R01-GM077582 from the National Institutes of Health.
Figures and Tables
Figure 1 Unrooted phylogeny of the autonomous SPIN DNA transposons.Citation11 This shows that the SPIN of lizard and opossum—two American taxa—are closely related and therefore that they most probably derive from the same American ancestor. Sequences were aligned using BioEdit.Citation26 The alignment was 1,841 bp after removing ambiguous and gapped positions. Phylogenetic analyses were performed using MrBayesCitation27 and PHYML.Citation28 Posterior probability and bootstrap values are indicated at each node. Only one or few full-length SPIN copies were found in opossum, green anole lizard and African clawed frog.Citation11 Thus for these three species the SPIN sequences used for phylogenetic analysis correspond to individual SPIN copies, while the sequences used for bat, bushbaby and tenrec are consensus sequences derived from multiple full-length SPIN copies. This discrepancy explains in part why the branches of the frog, lizard and opossum are much longer than those of the other three species. Note the branch of the opossum SPIN has been reduced by half for the purpose of this illustration.
Addendum to: