US researchers have discovered a family of DNA transposons they have dubbed Space Invaders in the genomes of several mammals and tetrapods.

Horizontal transfer by phages, plasmids and transposons is common in prokaryotes and is considered to be central to unicellular organism evolution. It involves non-native genetic elements incorporating themselves into a host genome.

Now, researchers from the University of Texas have discovered elements of the hAT (hobo/Activator/Tam3) transposon family in the genomes of rodents, the bushbaby, the little brown bat, the small Madagascan mammals called tenrecs, the opossum and even a frog and a lizard.

The Space Invaders (or SPIN for short) were undetectable in the 19 other mammals with whole-genome assemblies.

The researchers, led by Cedric Feschotte, show the infiltrations occurred around the same evolutionary time – 15 to 46 million years ago – “and spawned some of the largest bursts of DNA transposon activity every recorded in any species lineage”.

For example, in the tenrec they found nearly 100,000 SPIN copies per haploid genome and that the process led to the emergence of a new gene in mice. They believe horizontal transfer contributed significantly to the diversification of genomes in many mammalian species.

“Repeated horizontal transfer of a DNA transposon in mammals and other tetrapods” by John K. Pace et al is published in the Proceedings of the National Academy of Sciences [doi: 10.1073/pnas.o806548105]