Stress stunts organ growth

Organ size is controlled by a combination of morphogens and mechanical stress, propose Lars Hufnagel, Boris Shraiman (University of California, Santa Barbara, CA), and colleagues. Morphogen gradients, they show, are not sufficient to prevent overgrowth.

The popular gradient model proposes that differences in morphogen concentration across an organ are sensed by individual cells, which respond by proliferating. As a tissue grows, this gradient flattens until it no longer prods division. But Shraiman and colleagues now show that a morphogen's gradient does not change with organ size.

In the developing fly wing, the Dpp morphogen is made in a central stripe, and its concentration decays outward in both directions. By comparing fly larvae at various developmental stages, the group shows that this concentration pattern depends mainly on its diffusion and...