The human genome is littered with up to 20,000 pseudogenes, DNA sequences that appear to be truncated or error-riddled copies of other, functional genes—often dismissed as junk DNA. But Shinji Hirotsune of the Saitama Medical School in Japan and his colleagues have found that "real" genes might not be able to function properly without the pseudo ones.
Hirotsune's team made their discovery during an unrelated study in which they inserted a fruit fly gene into embryonic mice. The fruit fly DNA disrupted the mouse pseudogene for makorin1, a gene thought to be associated with bone and kidney development. Most of the mice in this line died within days of birth, exhibiting severe kidney and bone deformities, even though the proper makorin1 gene was unaffected. Putting additional copies of makorin1 or its pseudogene into the mice helped only somewhat. But when Hirotsune reintroduced an intact copy of the original pseudogene into mouse embryos, the animals developed normally.
Jeannie Lee, a geneticist at the Howard Hughes Medical Institute in Boston, suspects the pseudogene may function as a decoy to lure away destructive enzymes or regulatory proteins that would otherwise suppress the activity of the makorin1 gene. However it happens, the interaction between makorin1 and its pseudogene indicates a previously unknown mechanism of genetic regulation at work.
Deformed mice show the vital role of a bit of junk DNA.Photograph courtesy of Shinji Hirotsune.