This collaborative HeiKa project between Prof. Stefan Bräse (KIT) und Dr. Annika Guse (COS Heidelberg) aimed to advance our current understanding of the mechanisms underlying intracellular coral-algal-symbiosis. Coral reef ecosystems are of immense ecological and economic importance. However, the molecular principles underlying coral symbiosis are poorly understood, mostly because corals are not suitable as experimental systems. In this project, we followed an interdisciplinary approach by combining organic chemistry, cell and organismal biology to further develop Aiptasia, a marine see anemone as an emerging model system for corals. Together, we screened a chemical compound library to identify biologically relevant effectors and started to synthesize gorgosterol, a peculiar sterol derivative, that is thought to play a key role for coral symbiosis as the basis for functional studies. The initiated experiments are still ongoing and additional ideas have been generated. Accordingly, both PI´s will continue to collaborate and exchange expertise to advance the common goal of uncovering how sterols contribute to establishment and maintenance of coral-algal-symbiosis.