Scientists reveal how DNA folds into droplets inside our cells

Your DNA is roughly six feet long. Your cell nucleus is about one-tenth the width of a human hair. Somehow, one fits inside the other—and stays organized enough to actually work.

For decades, scientists knew this packing happened, but not quite how. In 2019, Michael Rosen's team at UT Southwestern discovered something unexpected: DNA-wrapped proteins naturally cluster together into droplets, much like oil beads forming in water. The process is called phase separation, and it seemed to explain how cells compress DNA to fit.

But seeing inside those droplets? That was another problem entirely.

Looking Inside the Droplets

Now, using advanced imaging tools at HHMI's Janelia Research Campus, Rosen's team—working with researchers at UC San Diego, Cambridge, and Janelia itself—has captured the most detailed views yet of what's actually happening inside these droplets. They imaged synthetic droplets under high resolution, then compared them with real chromatin inside actual cells.

What they found matters because it connects two scales of biology that have been hard to link before. Individual molecules have their own properties. Thousands of them together, moving fast and bumping into each other, create something entirely new—emergent properties that don't exist in isolation. Understanding how that transition happens is what Rosen calls "tying the structures of individual molecules to macroscopic properties of their condensates, really for the first time."

One key insight: the length of DNA between nucleosomes (the protein spools that DNA wraps around) shapes how everything arranges inside the droplet. This explains why some chromatin types condense more easily than others, and why different condensates have different physical properties.

Beyond Chromatin

The implications ripple outward. Cells use membrane-less droplets for dozens of essential tasks—controlling which genes turn on or off, responding to stress, managing proteins. When condensation goes wrong, things break. Researchers suspect faulty droplet formation contributes to neurodegenerative diseases, cancer, and other conditions.

"By understanding how abnormal condensation could lead to different diseases," says Huabin Zhou, the study's lead author, "that could help us develop a new generation of therapeutics."

Rosen is careful not to oversell the moment. "I'm certain that we're only at the tip of the iceberg," he says. What comes next is clearer now: better methods for mapping the relationship between molecular structure and cellular behavior, and a framework for studying dozens of other biomolecular condensates that keep cells running.