Compartments in the abdomen of Drosophila and the role of the engrailed locus.

A clonal analysis has shown that the dorsal surface of the first abdominal segment of Drosophila melanogaster is subdivided into anterior and posterior compartments. Cells of the posterior compartment grow up to but not beyond the anterior-posterior compartment border within the first abdominal segment and the intersegmental border that defines the boundary between the first and second abdominal segments. Growing within these boundaries, a narrow band of tissue clonally isolated from the adjoining tissue is formed. When these posterior cells are deficient for the engruiled locus, however, neither the compartment nor the segment border is maintained. The implications, that compartmentalization is essential for segmentation, and that all insect segments are subdivided by anterior and posterior compartments, are discussed.