The <i>Hydra</i> FGF family – dispersed across the genome and expressed locally

Although the nonbilaterian <i>Hydra</i> has a simple body architecture, its signaling systems are as complex as those of Bilateria. We here add data to the fibroblast growth factor signaling system which has previously been identified in <i>Hydra</i> as essential for bud detachment. The localized expression patterns of its, now fifteen, FGFs indicate additional, yet unidentified, functions in sometimes very small subsets of cells at the body termini and/or during budding or in testes. Presence of a typical signal sequence (prediction >93%) in only 30% of the <i>Hydra</i> FGFs suggests mechanisms of action (and/or secretion) other than the canonical ones. A knockdown approach using siRNA revealed a potential role for Hv-FGF-c in tentacle morphogenesis. Our results document a high complexity of FGF signaling sites in <i>Hydra</i> and open the field for a detailed analysis of their functions.