The study, published in Nature Communications, challenges long-held ideas about how cells organize and deliver proteins to specific locations.

For many years, biology textbooks have described protein movement inside cells as a largely random process called diffusion. In this model, proteins drift until they eventually reach where they are needed. The new research shows that cells do not rely on chance alone. Instead, they generate directed fluid flows that actively push proteins toward the leading edge, where cells extend, move and repair tissue.

From Classroom Observation to Major Discovery

The breakthrough traces back to an unexpected moment during a neurobiology course at the Marine Biological Laboratory in Massachusetts. The study’s co-corresponding authors, Catherine (Cathy) Galbraith, Ph.D., and James (Jim) Galbraith, Ph.D., were running a standard classroom experiment when they noticed something unusual.

“It actually started out as an unexpected finding,” Cathy said. “We were just conducting an experiment with students in class.”

Using a laser, the team temporarily made proteins invisible in a strip at the back of a living cell to track how they moved. This is a common method for studying intracellular transport. During the experiment, they saw an additional dark band appear at the front edge of the cell, the area that extends as the cell moves.

“We kind of did it for fun and then realized this gave us a way of measuring something that wasn’t able to be measured before,” she said.

Further investigation showed that this dark band represented a wave of soluble actin, a key protein involved in cell movement, being rapidly pushed forward. Previously, scientists believed actin mainly reached this region by random diffusion. The new results revealed a different mechanism.

“We realized the cartoon models in textbooks were missing a huge piece,” Jim said. “There had to be some kind of flow in the cell pushing things forward. Cells really do ‘go with the flow.'”

Directed Flows Drive Protein Transport

Cathy and Jim joined OHSU in 2013 after working at the National Institutes of Health, where they collaborated with Nobel Laureate Eric Betzig, Ph.D., at the Howard Hughes Medical Institute’s Janelia Research Campus on advanced imaging techniques.

With specialized imaging tools, the team found that cells actively generate directional fluid flows, which they compare to atmospheric rivers. These flows move actin and other proteins toward the front of the cell much faster than diffusion alone.

“We found that the cell can actually squeeze at the back and target where it sends that material,” Jim said. “If you squeeze half a sponge, the water only goes on that half. That’s basically what the cell is doing.”

These flows are nonspecific, meaning they can carry many types of proteins at once. This creates a highly efficient system that supports cell protrusion, adhesion and rapid shape changes. All of these processes are essential for movement, immune responses and tissue repair.

The researchers also found that these flows occur within a specialized region at the front of the cell. This area is separated from the rest of the cell by an actin-myosin condensate barrier, which acts like a physical boundary and directs proteins to the advancing edge.

Visualizing Cellular Currents With New Imaging

To observe these internal flows, the team developed a modified version of a standard fluorescence method. Instead of removing fluorescence with a laser, they activated fluorescent molecules at a single point and tracked their movement.

They named one of their key experiments FLOP, or Fluorescence Leaving the Original Point.

“It wasn’t a flop at all,” Cathy said. “It was the opposite. It is anything but a flop, because it worked.” The team’s discovery may help explain why certain cancer cells move so aggressively.

Implications for Cancer Cell Migration

The findings could help explain why some cancer cells are highly invasive.

“We know these highly invasive cells have this really cool mechanism to push proteins really fast, really rapidly where they need them at the front of the cell,” Jim said. “All cells have basically the same components inside, much like a Porsche and a Volkswagen have many of the same parts, but when those parts are assembled into the final machine, they behave and function very differently.”

By understanding how cancer cells use this system differently from normal cells, scientists may be able to develop new strategies to slow or stop their spread.

“If you can understand the differences, you can target future therapies based on how cancer cells and normal cells work differently,” he said.

Advanced Imaging and Collaboration

The research brought together experts in engineering, physics, microscopy and cell biology. Key contributions came from collaborators at Janelia Research Campus in Virginia, including specialists in fluorescence correlation spectroscopy and 3D super-resolution imaging.

“The instrumentation we needed doesn’t exist in most places,” Cathy said. “Janelia had a one-of-a-kind setup that let us test and confirm what we were seeing.”

The study relied heavily on advanced imaging tools developed at Janelia, including iPALM, an interferometric technique capable of resolving structures at the nanometer scale.

“iPALM allowed us to physically see the compartments,” Jim said. “There’s no other light-based technique that could do that.”

A Newly Identified “Pseudo-Organelle”

The researchers describe this system as a “pseudo-organelle,” a functional compartment that is not enclosed by a membrane but still plays a major role in organizing cell behavior.

“Just as small shifts in the jet stream can change the weather, small changes in these cellular winds could change how diseases begin or progress,” Cathy said.

The team believes this discovery could influence multiple fields, including cancer research, drug delivery, tissue repair and synthetic biology.

“All you had to do was look,” Cathy said. “The flows were there all along. Now we know how cells use them.”

In addition to the Galbraiths, coauthors on this study are Brian English, Ph.D., of Janelia Research Campus, and Ulrike Boehm, Ph.D., formerly with Janelia and now with Carl Zeiss AG of Germany.

This study was supported by the National Institute of General Medical Sciences, of the National Institutes of Health, under Award number R01GM117188, U.S. National Science Foundation, under Award numbers 2345411 and 171636, the W. M. Keck Foundation, the Howard Hughes Medical Institute Janelia Visiting Scientist Program, and the Howard Hughes Medical Institute. The iPALM work was partly supported by an award from the Advanced Imaging Center at Janelia. The SIM imaging was partly supported by a Core Research Facilities grant from OHSU School of Medicine.