Sci. STKE, 29 February 2000 Differentiation Defining the
Boundary 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