You might find it slightly unnerving that your cells sometimes compete fiercely with one another, but the process has been proposed to be a way in which organs control their size. Two groups have now taken a closer look at cell competition. Both describe what happens when levels of the growth-regulatory protein dMyc — the human counterpart of which is often hyperactive in cancer — are varied in developing fruitfly wings.

Laura A. Johnston and colleagues (Cell 117, 107–116; 2004) generated patches of cells that express high levels of dMyc, and found that these patches were much larger than controls, with bigger cells. Adjacent patches were smaller than usual, hinting that these cells were hampered by their faster-growing neighbours; in fact, the disadvantaged cells were killing themselves. This competition ensures that the excessive growth of cells with too much dMyc does not produce a bigger wing, as shown here — a control wing (blue outline) is overlaid with one containing dMyc-overexpressing cells (orange).

Eduardo Moreno and Konrad Basler (Cell 117, 117–129; 2004) came up with similar results. They suggest that excess dMyc prompts more protein synthesis and thus growth and proliferation, and that nearby cells — being smaller and less prolific — might be dying because they lose out in the competition for external factors.

Whether cell competition controls organ size under normal circumstances remains to be seen. A further possibility — which prompted Moreno and Basler's study — is that a slight excess of growth regulator could result in adult cells ousting their normal neighbours and becoming cancerous.