Microscope invented at marine biological laboratory illuminates chromosomal 'dark matter'

Using a microscope invented at the Marine Biological Laboratory (MBL), a collaborative team of biologists, instrument developers, and computational scientists has for the first time measured the density of a relatively inscrutable, highly condensed form of chromosomal material that appears in the cells of human beings and other eukaryotes. MBL scientists Michael Shribak (the microscope's inventor) and Tomomi Tani, together with Kazuhiro Maeshima of the National Institute of Genetics, Japan, recently reported their findings in Molecular Biology of the Cell.

The scientists measured the density of heterochromatin, a tightly packed form of chromatin that appears as dark, scattered regions in the cell nucleus. Until recently, this chromosomal "dark matter" was thought to contain either noncoding DNA or silenced genes; however, new research suggests that heterochromatin DNA is not, in fact, fully inactive. To investigate this possibility, the physical properties of heterochromatin need to be described in live cells, which has been a significant challenge using traditional microscopy. The team was able to measure the density of heterochromatin in its natural state using a novel type of microscopy, orientation-independent differential interference contrast (OI-DIC), which Shribak first developed in collaboration with MBL Distinguished Scientist Shinya Inoué in the mid-2000s and has continued to improve.

This study, Shribak said, is "the first important application of OI-DIC," a technology that "is ideal for studying structure and motion in unstained, living cells and isolated organelles, because they can be followed for long periods of time non-invasively."

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