Researchers at the Dana Farber Cancer Institute have discovered a role for pockets of extra-nuclear chromosomes that are often found in cancer cells, according to a study published in Nature last week (January 18). Chromosomes encased by their own membrane in the cytoplasm have a higher rate of breakage and rearrangement during cell division, potentially feeding the cancer conversion.
These so-called micronuclei have been something of a puzzle to researchers, who were unsure if the tiny organelles were a product of the genetically unstable cancer cell, or a factor contributing to cancer formation. So the study’s researchers stained the micronuclei and followed them through the cell-replication cycles. While the nucleic chromosomes replicated normally, micronuclei continued the replication process long after the cell had divided. Because the chromosomes were not replicating in the appropriate environment, they would often break down into smaller pieces within the micronucleus. Rather than being discarded, these fragments would be passed on to daughter cells during the next replication cycle, becoming incorporated into the nuclear chromosomes, contributing potentially cancer-causing errors to the intact genome.
Although erroneous integration of chromosome fragments occurs in “only a few percent of human cancers, our findings suggest that it might be an extreme instance of a kind of chromosome damage that could be much more common," lead author David Pellman said in a press release.