Peptides serve as important signalling molecules in development and differentiation in the simple metazoan Hydra. A systematic approach (The Hydra Peptide Project) has revealed that Hydra contains several hundreds of peptide signalling molecules, some of which are neuropeptides and others emanate from epithelial cells. These peptides control biological processes as diverse as muscle contraction, neuron differentiation, and the positional value gradient. Signal peptides cause changes in cell behaviour by controlling target genes such as matrix metalloproteases. The abundance of peptides in (...) Hydra raises the question of whether, in early metazoan evolution, cell–cell communication was based mainly on these small molecules rather than on the growth‐factor‐like cytokines that control differentiation and development in higher animals. BioEssays 23:420–427, 2001. © 2001 John Wiley & Sons, Inc. (shrink)

It has been convincingly shown that peptides play important roles in the regulation and maintenance of a variety of tissues and organs in living animals. However, little is known concerning the potential role of peptides as signaling molecules in developmental processes. In Hydra, there is circumstantial evidence that small diffusible molecules act as morphogens in the regulation of patterning processes. In order to view the entire spectrum of peptide signaling molecules, we initiated a project aiming at the systematic identification of (...) peptide signaling molecules in Hydra. In this review, we describe three peptide signaling molecules and one family of peptides that function as signaling molecules in the processes of axial pattern formation and neuron differentiation in Hydra. These peptides are produced by epithelial cells and are therefore termed “epitheliopeptides”. We discuss the importance of epitheliopeptides in developmental processes within a subset of hydrozoans. (shrink)