Difference drives division

Morphogens that spread from a point or line source are useful for patterning and for defining the outer bounds of a tissue. How to convert such a gradient into uniform cellular growth is, however, far from obvious. Can a pro-growth morphogen avoid encouraging excessive growth near its source and inadequate growth further away?Dragana Rogulja and Kenneth Irvine (Rutgers, Piscataway, NJ) now provide one possible solution for cells that will become fly wings. The cells, they find, make their division decision in response to a gradient rather than absolute concentrations of the Decapentaplegic (DPP) morphogen.

The Rutgers group expressed or repressed the DPP pathway in small clones. In both cases they saw new cell division both within the clone and in neighboring areas. This nonautonomous growth had not been evident in previous...