News from CRG
Due to the lack of suitable techniques and instruments, the chromatin organisation inside a cell nucleus could not be observed in a non-invasive way with the sufficient resolution. Now, for the first time, a group of scientists at the CRG and ICFO in Barcelona, have been able to visualise and even count the smallest units which, packaged together, form our genome. This study was possible thanks to the use of super-resolution microscopy, a new cutting-edge optical technique that received the Nobel Prize in Chemistry in 2014. In combination with innovative quantitative approaches and numerical simulations, they were also able to define the genome architecture at the nano-scale. Most importantly, they found that the nucleosomes are assembled in irregular groups across the chromatin and nucleosome-free-DNA regions separate these groups.Biologists and physicists have been working together to take a step forward in chromatin fibre observations and studies. “By using the STORM technique, a new super-resolution microscopy method, we have been able to view and even count nucleosomes across the chromatin fibers and determine their organisation. STORM overcomes the diffraction limit that normally restricts the spatial resolution of conventional microscopes and enables us to precisely define the chromatin fibre structure”, states Prof. Melike Lakadamyali, group leader at ICFO.
This enabling technique allowed the researchers to go deeper and, by comparing stem cells to differentiated cells (specialised cells that have already acquired their role), they observed key differences in the chromatin fibre architectures of both cells. Pia Cosma, group leader and ICREA research professor at the CRG explains, “We found that stem cells have a different chromatin structure than somatic (specialised) cells. At the same time, this difference correlates with the level of pluripotency. The more pluripotent a cell is, the less dense is its packaging. It gives us new clues to understand the stem cells functioning and their genomic structure, which will be helpful for example, in studying cell reprogramming”.
Ricci et al.: "Chromatin fibers are formed by heterogeneous groups of nucleosomes in vivo" Published in Cell on March 12 2015. Doi: http://dx.doi.org/10.1016/j.cell.2015.01.054