Conserved Hox transcription factors direct the formation of distinct structures along the anteroposterior axis of bilaterian animals. Given that Hox genes probably all derive from a single unique gene by duplication, might they also share a common function? On , Coiffier and co-workers propose that this is the case by showing that all Drosophila central and posterior (CP) Hox genes repress head formation in the fly's trunk, in addition to their well-known roles in segment identity. Hox genes of many species fall into CP and anterior classes based on their expression pattern and sequence similarities. The researchers report that, in Drosophila, the central Hox proteins (including Antennapedia and Ultrabithorax) and the posterior Hox protein Abdominal B prevent the expression of the head-specific gene optix in the trunk. Furthermore,several non-Hox genes, including Teashirt and Wingless/Wnt,contribute to this repression. The researchers propose, therefore, that an early function of Hox genes was to repress the head and that novel Hox functions that specialise the trunk appeared later.
