Cells Self-Repair During Division, UCSF Scientists Find

Every second, millions of cells in your body are dividing, and scientists just figured out how they do it without falling apart.

Researchers at UC San Francisco discovered that cells have a built-in repair system that fixes problems as they happen during division. When cells divide, they create a web of protein fibers called a spindle that pulls DNA apart with incredible force, and one small error could lead to cancer or birth defects.

The mystery has always been how these delicate fibers can handle such intense pressure without breaking. Graduate student Caleb Rux found the answer using a tool finer than a human hair to test the spindle's strength.

What he saw changed everything. When Rux pulled on the spindle fibers with his microneedle, they didn't just snap at weak points and fall apart. Instead, the fibers sensed the stress and immediately swapped out weak protein links for stronger ones, reinforcing themselves before breaking.

"We expected the spindle fiber to break at its ends, but instead, it snapped where the needle was pulling," Rux said. The broken end kept its shape perfectly, showing just how strong the repair had made it.

In earlier experiments, zapping fibers with a laser made them disintegrate instantly. But when fibers had time to sense physical stress, they grew stronger by recruiting reinforcement proteins floating nearby.

The Bright Side

This discovery goes far beyond biology textbooks. The spindle stabilizes itself exactly where it faces the most force, creating a self-healing system that works in real time.

Professor Sophie Dumont, who led the research, sees potential applications everywhere. "If you're a structural engineer, you want buildings to survive earthquakes, roads to survive many winters," she said. Engineers could learn from these self-repairing materials to create stronger, more resilient structures.

The research, published in Current Biology in January 2025, helps explain why our bodies are so remarkably reliable at completing trillions of cell divisions throughout our lives. Each successful division depends on this constant self-repair happening at the molecular level.

Understanding how cells protect themselves during division could also help researchers develop better cancer treatments, since cancer often involves errors in this exact process.

Nature has been perfecting self-healing materials for billions of years, and we're just beginning to learn its secrets.