BITS of DNA regarded as genetic parasites might play a key role in our development by kickstarting gene expression in embryos.
Much of our genome consists of endless copies of various kinds of 鈥渏umping genes鈥�, or transposons. Often the remnants of ancient viruses, transposons can make copies of their DNA and then paste these randomly into the genome.
The DNA of a complete transposon consists of genes for the enzymes that do the cutting and pasting plus a 鈥渃ontrolling element鈥�, a kind of genetic switch that activates these genes. Often, however, only the DNA of the controlling element is copied.
Advertisement
When Barbara Knowles and her colleagues at the Jackson Laboratory in Bar Harbor, Maine, looked at mouse eggs and embryos, they found that one kind of jumping gene called a retrotransposon was highly active. To their surprise, this activity was also switching on scores of normal mouse genes, because many isolated controlling elements were situated near normal genes.
鈥淭o our knowledge, this is the first report that such elements can initiate synchronous expression of multiple genes,鈥� says Knowles, whose team鈥檚 results appear in Developmental Cell (vol 7, p 597).
The findings suggest that transposons do not just exploit their host genome 鈥� it can also exploit them. Knowles says that because retrotransposons insert into DNA randomly, some may disrupt genes vital for embryonic development 鈥� and so are fatal 鈥� while others drive evolution by accidentally creating new and beneficial gene variants that are preserved. 鈥淲hat we see here are neutral or beneficial insertions that have been retained over evolutionary time.鈥�