Cell nuclei physically block or allow tissue flow, controlling when jammed cells suddenly move.

In dense living tissues, cells can get stuck in place like cars in a traffic jam. Sometimes they unjam and start moving together, which matters during embryo development and cancer spread. Scientists did not fully understand what causes this transition. Existing computer models either ignored cell centers, called nuclei, or treated them as stiff balls that cannot change shape. To solve this, researchers built a new computer simulation of tightly packed cells with bendable, squishy nuclei. They discovered that nuclear size and shape directly control whether cells can unjam. Elongated nuclei help cells move. The researchers confirmed these rules by testing living breast cell layers in the lab, showing that nuclear mechanics control collective movement across entire tissues.

Why it matters

Tissues jam into place during development and in tumors. This work shows that the nucleus — the cell's stiffest, largest organelle — sets the timing of when whole groups of cells can start moving. That could matter for healing, embryo formation, and predicting whether cancer cells can escape a tumor.

Questions answered