A companion study showed that centromeres, small structures on chromosomes once believed to work on their own, play a guiding role in directing CENP-E so it can help the division process unfold correctly. Together, these results overturn two decades of accepted teaching and carry major implications, since mistakes in chromosome attachment are linked to many cancers and genetic disorders.

Why Early Chromosome Positioning Matters

Every moment, in countless cells across the body, division takes place with extraordinary precision. A single cell duplicates three billion DNA letters and manages to distribute perfect copies to both daughter cells.

When that delicate process fails, the consequences can be serious. Even one chromosome in the wrong place can disrupt development, contribute to infertility, or trigger cancer. Cell division offers little room for error.

For many years, researchers believed they understood one of the central players: CENP-E, often described as a motor protein that hauled stray chromosomes toward the middle of the dividing cell. The idea was simple, widely taught, and ultimately incorrect.

Researchers Uncover a Different Role for CENP-E

Two studies from RBI, published in Nature Communications and led by Dr. Kruno Vukušić and Professor Iva Tolić, break down the earlier model and present a new explanation. Dr. Vukušić trained as a postdoctoral researcher within a highly selective ERC Synergy team and is now preparing to lead his own group at RBI. Prof. Tolić, a recognized global expert in cell biophysics and head of the Laboratory for Cell Biophysics at RBI, holds two ERC grants and is a member of EMBO and Academia Europaea. Their work shows that CENP-E is not the "muscle" dragging chromosomes into place but a key regulator that activates at the right moment to allow everything else to fall into line.

"CENP-E is not the engine pulling chromosomes to the center," Vukušić says. "It is the factor that ensures they can attach properly in the first place. Without that initial stabilization, the system stalls."

Chromosome Movement as a City of Traffic

Picture a huge city at peak traffic. Millions of vehicles fill countless intersections, and a single mistake can stop the entire flow.

Now imagine this scene scaled down to the inside of a cell. Chromosomes act like trains carrying DNA cargo, and microtubules form the rails guiding them. For division to succeed, each chromosome must connect to the correct set of tracks and move into position at the center.

The long-standing model cast CENP-E as the locomotive pulling lagging chromosomes into place. The Zagreb team found a more precise function. Instead of the engine, CENP-E behaves like a coupling that secures the link between a chromosome and the microtubule. When that coupling is weak or missing, the trains stall at the station's outskirts and cannot advance.

What Controls When Chromosomes Move

Why do some chromosomes pause at the edges of the cell? The answer involves Aurora kinases, a group of proteins that operate like strict traffic lights. They generate strong "red" signals that prevent chromosomes from making incorrect early attachments.

This system protects against mistakes near the poles of the cell, but it can also hold chromosomes back too aggressively. CENP-E helps restore balance by adjusting those signals so that the first proper connections can form. Once that initial stable attachment appears, alignment follows naturally through the geometry of the spindle and the behavior of microtubules.

"It's not about brute force," Tolić explains. "It's about creating the conditions for the system to run smoothly. CENP-E's key role is to stabilize the start, and once that happens, the rest of mitosis unfolds correctly."

Rethinking a Long-Standing Textbook Model

For almost twenty years, textbooks described CENP-E as a motor that pulled chromosomes to the metaphase plate. The new research contradicts that view.

"Congression, the alignment of chromosomes, is intrinsically linked to biorientation," says Tolić. "What we show is that CENP-E doesn't contribute significantly to the movement itself. Its crucial role is stabilizing end-on attachments at the start. That is what allows the system to proceed correctly."

This shift replaces a force-based explanation with one focused on regulation and timing. The implications stretch far beyond classroom learning.

Why This Discovery Matters for Human Health

To someone outside the field, the distinction may appear small. In cell biology, small shifts often reveal major truths. Errors in chromosome segregation are a hallmark of cancer. Tumor cells commonly show duplicated or missing chromosome segments, and these abnormalities often trace back to mistakes in the attachment process.

By demonstrating that CENP-E regulates the earliest attachments and by connecting this regulation to Aurora kinase activity, the Zagreb team linked two processes previously thought to act separately. This connection exposes a potential weak point in dividing cells and may point the way toward therapies that correct or slow dangerous divisions.

"This isn't just about rewriting a model," Vukušić says. "It's about identifying a mechanism that directly links to disease. That opens doors for diagnostics and for thinking about new therapies."

Support From Europe and Croatia

The research was made possible through significant competitive funding, including the European Research Council's Synergy Grant, the Croatian Science Foundation, Swiss Croatian bilateral projects, and EU development programs.

The work also depended on advanced computing resources at the University of Zagreb's SRCE center. "Modern biology isn't just microscopes and test tubes," Tolić says. "It's also computation and collaboration across disciplines and borders."

Finding Structure in Cellular Complexity

At its core, the discovery sheds light on how cells maintain order amid constant motion. Trillions of cell divisions occur daily in the human body, and each event must fight against the natural pull of disorder. The new understanding from Zagreb helps reveal one of the hidden strategies behind that consistency. By reinterpreting the role of CENP-E and connecting it to other cellular regulators, the team has added clarity to a process that operates under immense pressure.

"By uncovering how these microscopic regulators cooperate," Tolić says, "we are not only deepening our understanding of biology but also moving closer to correcting the failures that underlie disease."