Function of FGFR signaling in positioning and detachment of buds (autotomy) in Hydra

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We showed previously that in Hydra a single fibroblast growth factor receptor (FGFR), Kringelchen, controls detachment of asexually growing buds. Why Kringelchen mRNA is dynamically expressed also in early phases of budding remained open. Recently established, stably transgenic lines developed strong phenotypes: constitutive Kringelchen overexpression induces autotomy of the body column. Buds carrying a putatively dominant-negative variant fail to detach despite having formed an apparently normal foot. In both, synchronous budding occurs, indicating a role of the extracellular domain of FGFR in bud positioning. Our aim is to identify the molecular players and pathways targeted by Kringelchen, which control synchronous budding, detachment and autotomy. (i) The properties of the transgenic tissue will be investigated e.g. by transplantations and marker gene analysis. (ii) A potential FGF ligand will be characterized by binding- and bioassays. (iii) We will isolate downstream coupling proteins (FRS2, Dof) and elucidate by pharmacological inhibition and expression analysis which signaling elements are used to establish positive or negative feedback loops (PI-PKC, PI3-kinase, Ras/MAPK; Sprouty, Sef). Our study will help to understand the role of FGFR in bud positioning and instruction of tissue at the bud base.