During development, uniform populations of cells acquire regional differences to form domains that give rise to distinct organs. Drosophila imaginal discs are good systems in which to study the signalling molecules that control this process. On , Ekas and co-workers reveal that an unsuspected interaction between JAK/STAT and Wingless (Wg) signalling promotes regional specification in the eye imaginal disc. Wg signalling defines which part of this disc forms head tissue, whereas activation of the Drosophila STAT transcription factor Stat92E by the JAK tyrosine kinase Hopscotch is thought to promote disc growth but not patterning. Now, though, the researchers show that tissue lacking stat92E is transformed from retinal tissue into head cuticle (a phenotype also caused by ectopic wg signalling) and that wgexpression is repressed in cells expressing hyperactivated Stat92E. They conclude that repression of wg expression by the JAK/STAT pathway promotes specification in the Drosophila eye imaginal disc and speculate that a similar interaction might control mammalian eye development.
