Princeton researchers created new tools to study the separation of liquids inside of cells into compartments, so-called membraneless organelles. The significance of this intracellular liquid phase separation has only recently been recognized. Dysfunction in membrane less organelle has been linked to various diseases including cancer and ALS. Two papers reported in Cell describe new technologies called Corelets and CasDrop and the new findings, including how membraneless organelles influence gene expression. Below, check out the video abstract for the reports.
"These technology systems we've recently developed to control intracellular phase transitions should prove to be powerful tools for basic research and have many applications, particularly with regard to human health," said Clifford Brangwynne. He is an associate professor of chemical and biological engineering, leader of the research teams, and a Howard Hughes Medical Institute Investigator.
The researchers developed a system called Corelets, which uses proteins that are engineered to change their shape and behavior when they’re exposed to light. For this work, the tool was used to measure the levels of proteins that were promoting phase separation. The protein levels influence how membrane less organelle assemble. The researchers can thus generate a phase diagram, which describes protein concentrations.
In this study, ferritin, a protein in human blood, concentrate into a sphere and when exposed to blue light, other proteins adhere to that sphere. The researchers can trigger phase separation in different parts of the cell with different parameter changes.
"With these light-activated tools, we have gained unprecedented insight into controlling the phase transitions inside cells," explained the lead author of this study, Dan Bracha, a postdoctoral researcher.
The other study describes how membraneless organelle formation affects the cell. Another tool called CasDrop enabled the scientists to analyze the combination of DNA and proteins, called chromatin, in the cell’s nucleus. When the membraneless organelles form, the chromatin gets deformed, which can push out unnecessary genes while pulling targeted genes together. That suggests the membraneless organelles act to restructure the genome.
CasDrop was described by the researchers as “a novel CRISPR-Cas9-based optogenetic technology.” When light is applied, proteins bind to a gene and cause a local phase separation occurs. Droplets then form on the chromatin. Check out the video below for a description of CRISPR-Cas9 technology.
"Brangwynne and colleagues have invented a novel method to investigate how interactions between proteins dynamically form condensates with phase transition properties in living cells," said Phillip Sharp, a Nobel laureate and professor at the Koch Institute for Integrative Cancer Research at the Massachusetts Institute of Technology who was not involved in the studies. "The two papers highlight exciting discoveries at the interface of physics and cell biology that will lead to new treatments for diseases ranging from cancer to Alzheimer's."
Check out the video above to hear more from Brangwyne about liquid phase separation in cells.