Scientists have found a new function of the nuclear membrane, the envelope that encases and protects DNA in the nucleus of a cell - it fixes potentially fatal breaks in DNA strands.

Previously, the nuclear membrane was thought to be mostly just a protective bubble around the nuclear material, with pores acting as channels to transport molecules in and out. But in a study published in Nature Cell Biology, a research team documents how broken strands of a portion of DNA known as heterochromatin are dragged to the nuclear membrane for repair.

DNA exists inside of a cell's nucleus in two forms: euchromatin and heterochromatin. Euchromatin gets all of the attention because it encodes most of the genome, while heterochromatin, which is mostly composed of repeated DNA sequences, has long been ignored as "junk DNA."

"Heterochromatin is not only essential for chromosome maintenance during cell division; it also poses specific threats to genome stability. Heterochromatin is potentially one of the most powerful driving forces for cancer formation, but it is the 'dark matter' of the genome. We are just beginning to unravel how repair works here," said the author.

Working with the fruit fly Drosophila melanogaster, the team observed that breaks in heterochromatin are repaired after damaged sequences move away from the rest of the chromosome to the inner wall of the nuclear membrane. There, a trio of proteins mends the break in a safe environment, where it cannot accidentally get tangled up with incorrect chromosomes.

This study may help reveal how and why organisms become more predisposed to cancer as they age - the nuclear membrane progressively deteriorates as an organism ages, removing this bulwark against genome instability.

http://news.usc.edu/88127/nuclear-membrane-repairs-the-dark-matter-of-dna/