The topological role of homeoproteins in the developing central nervous system.

Homeogenes encode homeoprotein transcription factors that have fundamental roles in development. They are key players in genetic networks that lay out the body plan and also determine morphology and physiology at the cellular and multicellular level. However, homeoproteins share activities that extend beyond transcription, including translation regulation and signalling. For example, homeoproteins participate in the definition of territories in the neuroepithelium and also have a function in axonal guidance. Based on these examples, we propose that homeoproteins are not only morphogenetic transcription factors, but also morphogens themselves.