Evolution of steroid hormone signaling and size determination in Cnidaria and Xenacoelomorpha

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Steroid hormones control important developmental switches as they induce sexual maturity and mediate termination of the growth phase for many bilaterian species. They set crucial trade-offs for growth, fecundity, developmental time, and resource utilization and are dependent on intrinsic genetic as well as extrinsic environmental signals. Hence, they are key components for developmental plasticity and adaptation. Steroid hormones are recognized by nuclear receptors (NR), a diverse receptor family with various functions in development and physiology. When steroid hormones and the corresponding NRs evolved is insufficiently understood, but information on this topic promises insights in the ancestral function of steroids and their contribution to diverse body plans and life styles. Phylogenetic and biochemical predictions date the evolution of steroid receptors to the cnidarian-bilaterian split, without functional evidences of steroid hormones/ NRs in development in representative species in early emerging Bilateria and Cnidaria.I will study the evolution and function of steroid-binding NRs in the Cnidaria Hydra vulgaris and the Bilateria Hofstenia miamia (Xenacoelomorpha, a sister group to all other Bilateria) to understand their ancestral function in body size regulation under changing environmental conditions. I will use a phylogenetic approach paired with insitu hybridization to identify developmentally and environmentally responsive NRs. Cellular alterations upon changing environments and after mutagenesis of NRs will be observed by cytometry, while steroid hormones will be identified in extracts of the two species by chromatography and mass spectrometry. The project will elucidate the prototypic molecular mechanism and the evolution of environmental dependent developmental decisions (phenotypic plasticity) of all Bilateria.