Transposable Element - Evolution

Evolution

The evolution of TEs and their effect on genome evolution is currently a dynamic field of study.

TEs are found in many major branches of life. They may have originated in the last universal common ancestor, or arisen independently multiple times, or perhaps arisen once and then spread to other kingdoms by horizontal gene transfer. While some TEs may confer benefits on their hosts, most are regarded as selfish DNA parasites. In this way, they are similar to viruses. Various viruses and TEs also share features in their genome structures and biochemical abilities, leading to speculation that they share a common ancestor.

Since excessive TE activity can destroy a genome, many organisms have developed mechanisms to inhibit this activity. Bacteria may undergo high rates of gene deletion as part of a mechanism to remove TEs and viruses from their genomes while eukaryotic organisms use RNA interference (RNAi) to inhibit TE activity. Nevertheless, some TEs generated large families often associated with speciation events.

Evolution has been particularly harsh on DNA transposons. In vertebrate animal cells nearly all >100,000 DNA transposons per genome have genes that encode inactive transposase polypeptides. In humans, all of the Tc1-like transposons are inactive. As a result the first DNA transposon used as a tool for genetic purposes, the Sleeping Beauty transposon system, was a Tc1/mariner-like transposon that was resurrected from a long evolutionary sleep.

Interspersed Repeats within genomes are created by transposition events accumulating over evolutionary time. Because interspersed repeats block gene conversion, they protect novel gene sequences from being overwritten by similar gene sequences and thereby facilitate the development of new genes.

TEs may have been co-opted by the vertebrate immune system as a means of producing antibody diversity: The V(D)J recombination system operates by a mechanism similar to that of some TEs.

TEs contain many type of genes- including those conferring antibiotic resistance and ability to transpose to conjugative plasmid. Some TEs also contain integrons(genetic elements that can capture and express genes from other sources) that contain integrase enzyme which can integrate gene cassettes. There are over 40 antibiotic resistance genes identified on cassettes, also virulence genes.