The threefold subdivision of segments and the initiation of legs and wings in insects

Abstract

Segmentation is proposed to result from the serial repetition of three cell states: the well-known compartments (A and P) and a third, as yet hypothetical, region, S. These three regions generate the polar positional information for pattern formation within the segments: a boundary between P and S cells acts as the signal for formation of a segment border, while an A-P border generates a prerequisite for leg and wing formation. This model accounts for many experimental observations.