Figure 1.

Hox genes set and maintain body plan and identity during development. Embryogenesis initiates with the developmental cues provided by maternal gene products that set off zygotic transcription in predetermined patterns. Coordinated expression of the Hox genes (depicted as colored patterns defining expression domains) establishes positional and segmental identity and is maintained throughout organogenesis. The domains of Hox expression profiles are tightly regulated by the PcG and trxG complexes and define the developmental plan of the adult (adapted from ref. 130).