How Cells Find North: Movement Draws the Map

Run a hand along your arm and every hair leans the same way. Inside your ear, microscopic sensory structures are aligned with similar precision. That coordination is not decoration: tissues are built with a sense of direction, and when the direction is wrong, structures form improperly or fail to work at all.

Biologists call this property planar cell polarity — the coordinated orientation of cells within a sheet, or epithelium, of the kind that covers your body's surfaces and lines its organs. The puzzle is how the coordination begins. A developing tissue starts as a crowd of cells with no shared compass. Somehow, front and back get agreed upon, cell by cell, across the whole sheet.

Researchers in the lab of Whitehead Institute member Pulin Li have now recreated that beginning in engineered epithelial cells and watched polarity emerge in real time. Their findings, led by graduate student Leah Wallach with Connor Thomas and published in the Proceedings of the National Academy of Sciences on October 15, 2026, point to a surprisingly simple cue: movement itself.

As the engineered cells migrate collectively, they generate the signal that organises them. The study identifies CELSR, a protein found at the junctions between cells, as a key driver of polarity initiation: it responds to the cells' movement by helping form new front-back patterns. In other words, the cells do not first receive a map and then walk it. They walk, and the walking draws the map.

That ordering matters for how we think about development. If polarity were handed down only by fixed external gradients, a tissue would be a passive reader of instructions. A movement-based mechanism is more robust and more local: each neighbourhood of cells can establish direction from its own collective behaviour, then align that direction with the neighbourhoods around it. It also suggests new ways things can go wrong — and, eventually, new questions about how migrating cell groups in other contexts, from wound healing to disease, establish or lose their orientation.

There is a pleasing parallel with the snail shells and handed molecules that show up elsewhere in biology: living systems are full of left-right and front-back decisions that look simple from the outside and turn out to be careful molecular negotiations underneath. A sheet of cells agreeing on north is one of those negotiations, caught here on camera for the first time at the moment the agreement starts.

The work is early and in engineered cells, not a complete account of how every tissue polarises. But it converts a long-standing question — where does the first sense of direction come from? — into a mechanism that can be tested, perturbed and watched. Cells, it turns out, find north together.

Source: Whitehead Institute / Phys.org report of the PNAS study, October 15, 2026. Curious about the code underneath all this? See our Genetically Curious T-Shirt.