Anterior and posterior compartments in the head of Drosophila

Abstract

A COMPARTMENT¹ is a precisely demarcated region of an adult insect which is made by a group of related cells. This group (a polyclone²) consists of all the descendents of several founder cells which were set aside at an earlier stage. The developmental pathway followed by a growing polyclone depends on the local state of a small number of controlling ‘selector’ genes³. One example is the engrailed gene which is thought to determine the ‘posterior’ rather than the ‘anterior’ pathway of development and is used in several different segments of the developing fly^4–6. The thorax of Drosophila is constructed on these simple principles; each of the three segments consists of two polyclones which generate the anterior and posterior compartments^1,7. The proboscis is similarly subdivided⁸ but the abdominal segments are probably not⁹. The segmental status of the head is controversial^10–12. Here we summarise three lines of evidence which show that the main part of the ‘head’—the cuticular parts formed by the eye-antennal disc¹³—is constructed on the same principles as a thoracic segment.