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Chromatin is highly folded and locally compacted to a variable degree, to regulate gene expression. 

91�������לChromatin regions are more compact or less compact, based on usage,91�������ם said of University of Massachusetts Chan Medical School, the group91�������יs fourth PI. 91�������לFor example, you don91�������יt need fingernails in your liver, right?91�������ם Right, so in liver cells, the fingernail-making stretch of the genome remains inactive.

The big question then, is, what 91�������לopens up91�������ם a stretch of chromatin, makes it accessible to the cell for gene activation? Many labs and biotech companies are asking this very thing.

 91�������לIf we can understand how chromatin organization controls gene activation -- which is necessary for all of biology -- we can understand what happens when it goes awry, causing changes in the genome and therefore disease,91�������ם Rosen said.

Phase separation and chromatin

The group is betting that chromatin compaction is governed by liquid-liquid phase separation (LLPS), a biophysical process akin to oil separating from water. (See, which Collepardo-Guevara called 91�������לtransformative in the field of chromatin research.91�������ם)

 91�������לIf chromatin were to compact into a solid, it couldn91�������יt function in the cell,91�������ם said Rosen. 91�������לIts molecules need to be able to move.91�������ם That dynamism is offered by LLPS, where molecules condense into membrane-free liquid droplets, as needed by the cell.

91�������לBiology uses LLPS to concentrate molecules in general, but in this case, we think, to compact chromatin while allowing it to still maintain function,91�������ם Rosen said. The group is bearing down on two big questions:  How does LLPS dynamically 91�������לcompartmentalize91�������ם chromatin, and what are the functions of this compartmentalization?

91�������לWe91�������יre coming at this from very different starting points,91�������ם cell biologist Gerlich said. 91�������לIn my lab, we look in cells, where things are complex and hard to understand. Mike Rosen and Sy Redding are biochemists 91�������ד they take the cellular components, purify them, study them in vitro, and characterize them with sophisticated techniques under very defined conditions.91�������ם Collepardo-Guevara, a computational biophysicist, develops theoretical models at many scales, ranging from single atoms up to collections of molecules condensing, to try and recapitulate the mechanistic forces taking place. 91�������לBecause we have different areas of expertise, we can cover all these scales,91�������ם Rosen said.

91�������לAt large scale, the chromatin inside a nucleus is not a liquid,91�������ם Gerlich said. 91�������לChromatin fibers themselves have very constrained mobility because the material, like the long stretches of DNA, is very viscous. One of our goals is to understand how, at a local scale, you have mobility in a liquid-like state and how that translates to long-range structural organization.91�������ם

What91�������יs the recipe for early discovery?

The MBL has been home turf for scientists studying LLPS since the phenomenon was first course. Immediately recognized as a new way for cells to organize internally, the study of LLPS (a process that can generate certain biomolecular condensates, or cellular compartments that form without a surrounding membrane) opened a floodgate of discovery. Evidence has mounted that condensates regulate critical cellular processes, from cell division to gene expression, and are involved in the development of cancer, neurodegenerative disease, and many other disorders. ( of pioneering research on LLPS at the MBL.)

In 2013, with support from the Howard Hughes Medical Institute, Rosen, Ron Vale, and Jim Wilhelm founded the which convened more than 70 scientists from around the world at MBL over five consecutive summers. Their goal was generating knowledge in the just-emerging field of biomolecular condensates. The Summer Institute was fantastically productive, resulting in at least 25 published papers and quantum leaps in understanding how condensates form and behave in the cell.

The success of the Summer Institute was on Rosen91�������יs mind as last summer91�������יs collaboration, which they call 91�������לThe Chromatin Consortium,91�������ם took shape.

91�������לThese programs focus on the initial discovery part of science, the spark of creativity that will eventually lead to a project that a granting agency will fund,91�������ם Rosen said. 91�������לIt91�������יs very hard to find funding to gather people to allow that initial spark to happen. But being back at MBL again, feeling the excitement and seeing the pace of discovery, makes me think we, as a scientific community, need to find ways of enabling this. It takes the science up another click and allows the next set of questions to be addressed.91�������ם