BUDHEAD, A FORK HEAD HNF-3 HOMOLOG, IS EXPRESSED DURING AXIS FORMATION AND HEAD SPECIFICATION IN HYDRA

Accumulating evidence indicates that a common set of genes and mechani sms regulates the developmental processes of a variety of triploblasti c organisms despite large variation in their body plans. To what exten t these same genes and mechanisms are also conserved among diploblasts , which arose earlier in metazoan evolution, is unclear. We have chara cterized a hydra homologue of the fork head/HNF-3 class of winged-heli x proteins, termed budhead, whose expression patterns suggest a role(s ) similar to that found in vertebrates. The vertebrate HNF-3 beta homo logues are expressed early in embryogenesis in regions that have organ izer properties, and later they have several roles, among them an impo rtant role in rostral head formation. In the adult hydra, where axial patterning processes are continuously active, budhead is expressed in the upper part of the head, which has organizer properties. It is also expressed during the formation of a new axis as part of the developme nt of a bud, hydra's asexual form of reproduction. Expression during l ater stages of budding, during head regeneration and the formation of ectopic heads, indicates a role in head formation. It is likely that b udhead plays a critical role in head as well as axis formation in hydr a. (C) 1997 Academic Press.