The structure of heterochromatin has reportedly been visualized for the first time by a team of scientists from Waseda University, Okinawa Institute of Science and Technology, and the National Institute for Basic Biology. Their methodology was published recently in Molecular Cell.
"We discovered that heterochromatin looks something like a wireless headphone," says Hitoshi Kurumizaka, professor of structural biology at Waseda University. "Imaging heterochromatin became possible because of cryo-electron microscopy."
The research group first reconstituted heterochromatin samples in vitro using heterochromatin protein 1 (HP1) and two nucleosomes linked together, which include histones mimicking a particular chemical modification (H3 lysine 9 tri-methylation). The samples were then purified for high-contrast imaging in cryo-electron microscopy, and from this image, the scientists found that heterochromatin is formed by HP1 binding with chromatin while bridging the nucleosomes positioned side by side.
Professor Kurumizaka points out that defining the heterochromatin structure could help better understand the mechanism of gene regulation and how certain kinds of diseases occur. "Damage to the heterochromatin structure is reported to increase chromatin abnormalities and cancer risks, and heterochromatin is closely associated with virus infections such as HIV. The results of this study could become valuable in developing treatment for such serious diseases."
In the future, the team hopes to study even more complex, higher order structures, such as an entire string of nucleosomes, using the method established in this study.
Image: Heterochromatin structure. Image courtesy of Waseda University.