Biomolecule “Silly Putty”: High-resolution imaging of cell condensates achieved using fluorogen technology

Biomolecular condensates shift the masses of cells that organize cellular material. They are distinct molecular communities made up of DNA, RNA and proteins that “condensate” molecules in critical places, but often go against explanation. Partly because this is so small that it cannot be measured using conventional microscopes.

“These chunks were once said to be “like liquid.” Because some of them were seen kissing, fusion, dripping and flowing like raindrops on the windshield,” said Rohit Papu, a professor of biomedical engineering at McKellibay’s Faculty of Engineering at Washington University in St. Louis.

However, the chunks may look like raindrops, but otherwise calculations are suggested. The molecular tissue within the condensate is similar to the molecular tissue of a network that rearranges on different timescales, giving it a stupid putty-like feature that transforms into a condensate.

Working with the lab of Matthew Lou, an associate professor of electrical and systems engineering at McKelby, Papp and colleagues, all members of Washu’s Biomolecular Condensate Center, tested their computational predictions by peering into the condensate using a new super-resolution microscopy.

A study published in Nature Physics shows Pappu Labs and Lew Labs how scientists can employ environment-sensitive dyes that only shine in certain chemical environments to peer into condensate at high resolutions that they previously could not achieve. With the help of a unique imaging technology developed by Lew Lab, they used these fluorogens one by one to allow them to peer into the condensate at high resolution.

These advances in imaging are central to understanding how condensates function and how they fail in the context of cancer and neurodegenerative diseases associated with functionally abnormal condensates.

Existing techniques rely on averaging the behavior of the entire ensemble of molecules in a condensate. In contrast, this new single fluorescent method allows for single and multidisciplinary resolutions. The Washu team utilizes fluorescent chemical probes that are only lit when encountering the right kind of chemical and viscoelastic environment, and acts as a beacon of the region that appears as hubs within a network of molecules held together by “stickers.”

About these stickers: When you think of condensates as a group of people, stickers are friends who make decisions about where, when to gather, and who to invite, the researchers said.

“Specific individual proteins enabled by the interactions described in protein sequences are hubs of viscoelastic (silly putty) network structures within the condensate,” Lou said. “Our fluorogen sensors don’t brighten until we find these hubs. By tracking the movement of individual fluorogens, we were able to find and track hubs that were formed, moved, and decomposed.”

Pappu described a microscope as similar to sending one ant to map and navigate a dark house. Ants spend more time around sections where sugar is left behind, and the maps they make shine brightest around that sugar.

In practice, a single ants are used to avoid collecting conflicting signals about the topography that occur when researchers see many ants at the same time in existing technology.

With its single powerful signal and super-resolution microscope, scientists can now detect single molecules and track movement at resolutions beyond the diffraction limits.

“Fluorescent materials can swim in the condensate and help map internal tissues for the first time,” Papu said. “This has been made possible by Matt Lew’s innovation and collaboration made possible by our unique center.”