A PLANARIAN ORTHOPEDIA HOMOLOG IS SPECIFICALLY EXPRESSED IN THE BRANCH REGION OF BOTH THE MATURE AND REGENERATING BRAIN

To analyze the organization of planarian brain, a homolog of the homeo box-containing gene Orthopedia (Otp) from planarian, Djotp, was isolat ed. The homeodomain of Djotp differs from mouse Otp by only two amino acids. This conservation extends to include a 12 amino acid motif down stream of the homeodomain. Whole mount in situ hybridization studies i ndicated that Djotp is specifically expressed in the branch structures of the normal planarian adult brain. During regeneration, Djotp is ex pressed in the presumptive branch region prior to branch formation. Th ese observations implicate a role for Djotp in establishing and mainta ining the identity of the planarian brain branch region. The results s uggest that recruitment of OtP for its role in brain pattern formation occurred very early in evolution.