Control of compartmental affinity boundaries by Hedgehog

Analysis of cell affinities in the developing wing of Drosophila shows a division into the anterior (A) and posterior compartments (P), mediated by the transcription factor Engrailed (En) in P cells. Under control of En, P cells secrete the signalling protein Hedgehog (Hh), to which they cannot respond. It is hypothesized that the failure of A and P cells to intermix is caused by the Hh secreted by the P cells. A mutation of the gene smoothened is used to show that the affinity boundary that segregates the A and P cells is mainly a consequence of local Hh signalling.