Control of Body Segment Differentiation in Drosophila by the Bithorax Gene Complex

The bithorax complex (BX-C) in Drosophila is a giant cluster of closely linked genes that plays a major role in determining the segmentation pattern of the organism. From developmental and cytogenetic studies of this complex it now appears that orderly derepression of BX-C genes controls the orderly differentiation of body segments commencing with the thorax and proceeding posteriorly. The available evidence also suggests that the level of development which a given one of these segments achieves is a function of the particular subset of BX-C genes that is active in that segment. This paper summarizes the current status of our knowledge of what the BX-C genes do during development and how they are regulated.