The Fight Against Genome Parasites

In the gonads of animals, genome parasites such as transposons pose a serious threat to evolutionary fitness. With their ability to bounce around in the genome, they often cause dangerous mutations.

To protect genomic integrity, animals evolved a sophisticated mechanism -- the so called piRNA pathway -- to silence the deleterious transposons. Not much is known about the molecular processes and the involved factors that constitute the piRNA pathway. Researchers at the Institute of Molecular Biotechnology (IMBA) of the Austrian Academy of Sciences (ÖAW) in Vienna have now identified ~50 genes, that play important roles in the piRNA pathway of the fruitfly Drosophila melanogaster.

With roughly 50%, the human genome is densely populated with genome parasites, and so is the DNA of other animals, plants and fungi. Many of these selfish DNA elements are able to freely move around in the host's genetic material. They are referred to as transposons and their mobility causes DNA breaks and mutations that can lead to severe genome damage. Although they are harmful, most organisms do not specifically eliminate transposons from their DNA. Such a massive intervention might bear too much of a risk for germ cell genomes and hence a species reproductive fitness.

To deal with the potential dangers, plants and animals possess defense systems -- also seen as sort of a 'genome immune system'. In all cases, these are based on small RNA silencing mechanisms and hence date probably back to the early days of eukaryotic evolution. The ancient silencing systems are able to selectively interfere with transposon expression preventing them from causing damage. In animals, the most prominent of these silencing pathways is the so-called piRNA pathway.