The Drosophila wing precursor is divided into two non-intermingling groups of cells, the Anterior (A) compartment and the Posterior (P) compartment. Dahmann and Basler addressed the issue of how the boundary between the A and P compartment is established. The P cells express Hedgehog (Hh) and Engrailed (En); the A cells express the Hh receptor, Smo, which, upon Hh stimulation, converts the transcription factor Cubitus interruptus (Ci) from the repressor to the activator form. Transgenic cells, in which the Hh signaling pathway or the En pathway was altered, were introduced into fly larvae, and the wing precursors from such flies were analyzed to identify the positions (A or P) of the mutant cells and the amount of intermingling with the neighboring cells. Segregation into the A or P compartments was dependent on the balance between the activator form of Ci and the repressor form. Without Ci, the cells segregated away from both the A and P cells and assumed a position that straddled the A/P boundary. The authors also propose that the boundary may be defined by the abundance of the adhesion molecule DE-cadherin because cells engineered to overexpress DE-cadherin segregated away from neighboring cells in both the A and P compartments.
Dahmann, C. and Basler, K. (2000) Opposing transcriptional outputs of Hedghog signaling and Engrailed control compartmental cell sorting at the Drosophila A/P boundary. Cell 100: 411-422. [Online Journal]