The research team discovered that the situation is rescued by small sequences of RNA (called siRNAs) that restore methylation of transposable elements in the embryo. Indeed, they have found siRNA in sperm cells that silence the transposable elements even before fertilisation, in at least some cases. Transposable elements are very common in all known genomes. In the human genome, for example, they make up 45% of the total genome. They are involved in the evolution of genomes, since when integrated back into the genome they can affect the function and organisation of other genes. However, transposable elements are mutagens, and, therefore, their activation needs to be under tight control, as it may be harmful to the cell and the organism. If such harmful mutations occur in sexual cells, they will be transmitted to the progeny and spread in the population.
Says Jrg Becker, 'We have unveiled a mechanism in the sexual cells that can prevent the activation of potentially harmful transposable elements, while at the same time, upon fusion of sperm cell and egg cell, allowing the formation of a cell with full capacity to become any cell type, that will give rise to a new generation. On the other hand, if female siRNAs in the egg cell do not match incoming transposable elements from the male, they might escape silencing in the developing embryo, with potentially harmful implications for the new plant that is generated. Such an uncontrolled activation of transposable elements might at least in part explain existin
|Contact: Ana Mena|
Instituto Gulbenkian de Ciencia