Researchers from the University of
Cambridge and the MRC Laboratory of Molecular Biology used a combination of
imaging and up to 100,000 measurements of where different parts of the DNA are
close to each other to examine the genome in a mouse embryonic stem cell. Stem
cells are 'master cells', which can develop -- or 'differentiate' -- into
almost any type of cell within the body.
Most people are familiar with the
well-known 'X' shape of chromosomes, but in fact chromosomes only take on this
shape when the cell divides. Using their new approach, the researchers have now
been able to determine the structures of active chromosomes inside the cell,
and how they interact with each other to form an intact genome. This is
important because knowledge of the way DNA folds inside the cell allows
scientists to study how specific genes, and the DNA regions that control them,
interact with each other. The genome's structure controls when and how strongly
genes -- particular regions of the DNA -- are switched 'on' or 'off'. This
plays a critical role in the development of organisms and also, when it goes
awry, in disease.
The researchers have illustrated the
structure in accompanying videos, which show the intact genome from one particular mouse
embryonic stem cell. In the film, above, each of the cell's 20 chromosomes is
coloured differently.
In a second video regions of the chromosomes where genes are active are coloured blue,
and the regions that interact with the nuclear lamina (a dense fibrillar
network inside the nucleus) are coloured yellow. The structure shows that the
genome is arranged such that the most active genetic regions are on the interior
and separated in space from the less active regions that associate with the
nuclear lamina. The consistent segregation of these regions, in the same way in
every cell, suggests that these processes could drive chromosome and genome
folding and thus regulate important cellular events such as DNA replication and
cell division.
For further details see:
Posted by Dr. Tim Sandle
