Splits in fruitfly Hox gene complexes

Abstract

The homeotic genes are strikingly conserved between invertebrates and vertebrates. There is conservation, not only of the homeobox sequences, but also of their collinear order on the chromosome. The genes are found in clusters or 'complexes', and are arranged on the chromosome in the order of their function along the anteroposterior body axis (for review, see ref. 1). In the fruitfly Drosophila melanogaster, the homeotic genes are split into two separate clusters, the Antennapedia complex (ANTP-C) and the Bithorax complex (BX-C), which direct development of the anterior and posterior segments, respectively. We show that in Drosophila virilis, a closely related species, the homeotic genes are also in two clusters, but the split occurs within the BX-C. The existence of two independent splits in the Drosophila lineage suggests that these flies lack the molecular constraint responsible for the ordered clusters in other animals.