Control of sequential compartment formation in Drosophila.

During development of Drosophila melanogaster, sequential commitment to alternative development programs occurs in neighboring groups of cells. These commitments appear to be reflected by lines of clonal restriction, called compartmental boundaries, which progressively subdivide the early embryo, and later the imaginal discs, which give rise to different adult appendages. We propose that a reaction-diffusion system acts throughout development and generates a sequence of differently shaped chemical patterns. These patterns account for the sequence and geometries of compartmental boundaries, and predict that each terminal compartment is specifiied by a unique combination of binary choices made during its formation. This binary "code" interprets coherently the patterned metaplasia seen in transdetermination and homeotic mutations.