Taming the genome's "jumping" sequences
EPFL scientists have discovered how a family of proteins that regulates the activity of transposable elements in the genome allows them to make inheritable changes to the growing fetus. The human genome is fascinating. Once predicted to contain about a hundred thousand protein-coding genes, it now seems that the number is closer to twenty thousand, and maybe less. And although our genome is made up of about three billion units - "base pairs" - many of them don't seem to belong to specific genes, and for that reason they were delegated to the dustbin of genetics: they were literally called "junk DNA". But as it turned out, junk DNA is actually critical in coordinating and regulating the work of actual genes. For example, there are sequences of DNA that "jump" around the genome and influence gene expression. These jumping units are called "transposable elements" and their number is estimated at over 4.5 million in a single genome. Transposable elements frequently contain sequences that are binding sites for transcription factors - proteins that regulate the rate of transcription of DNA to RNA, marking the first step of gene expression. By moving around the entire genome, transposable elements renew the pool of binding sites for transcription factors, becoming a "motor" of genome evolution. But at the same time, transposable elements can also be very dangerous to the host; they are genotoxic, meaning that they can cause mutations that can incapacitate genes, leading to severe diseases and even death. The question is, how is the genotoxic potential of transposable elements kept in check without compromising their ability to regulate the genome?
