A new study sheds light on events orchestrating the changes when mammalian eggs are fertilized and become embryos. Researchers have discovered that expression of genes in mouse eggs and very early embryos is activated in part by regions of DNA called retrotransposons, which may have originated from retroviruses. These regions, found in DNA of human, mouse, and other mammals in hundreds of thousands of copies, are called retrotransposons because they have the ability to propagate and insert themselves into different positions within the genome. The research, published in the October issue of Developmental Cell, suggests that retrotransposons may not be just the “junk DNA” once thought, but rather appear to be a large repository of start sites for initiating gene expression. Therefore, more than one third of the mouse and human genomes, previously thought to be non-functional, may play some role in the regulation of gene expression and promotion of genetic diversity.
