A team of researchers from the Universitat Autònoma de Barcelona (UAB) has discovered that transposons, small DNA sequences that travel through the genomes, can silence the genes adjacent to them by inducing a molecule called antisense RNA. This is a new mechanism for evolution that has been unknown until now.
Transposons are repeated DNA sequences that move through the genomes. For a long time they have been considered as a useless part of genetic material, DNA left overs. However, it is more and more clear that transposons can cause favourable changes for the adaptation and survival of the organism.
In this research project, the UAB scientists have demonstrated that a transposon inserted in the genome of the Drosophila (a model used for a lot of genetic studies) silenced a gene adjacent to it, that is, it reduced its level of expression significantly. The expression of a gene consists in using the DNA as a mould to synthesise a molecule called a messenger RNA, which in its own environment will be used to synthesise a particular protein. According to what the researchers have seen, the transposon stimulates the synthesis of a molecule that is complementary to the normal messenger RNA. This new complementary molecule (that the scientists have called antisense RNA) joins with the normal RNA of the gene obstructing it from synthesising the protein. Even though the research has been carried out on the species Drosophila buzzatii, the researchers state that transposons, that in the human genomes represent 45% of the genetic material, could be provoking the same type of silencing effect in our species.
The work now published is a continuation of previous studies. In 1999, the research team headed by Dr. Alfredo Ruiz, from the Department of Genetics and Microbiology at the UAB, published an article in Science where they demonstrated that a chromosomal inversion in Drosophila buzzatii was generated by the transposon activity. The inversions are formed by turning a chromosome segment upside down so that it is orientated in the opposite direction. In Drosophila it has been demonstrated that the chromosomal inversions often have an adaptive value, that is, that the individuals that have chromosomes with the inversion show some advantages over those that don’t, even though it still unclear what is the mechanism used by the inversions to cause these differences.