A lipid switch at organelle contact sites. Many lipids are powerful signalling molecules involved in many central processes, with at times specific functions in different organelles. Control over subcellular levels of signalling lipids is achieved by tightly regulating biosynthesis, catabolism and transport. In this project, we are interested in the endo-/lysosomal system as one such control checkpoint. Using caged, photoactivatable and clickable lipid probes, we aim to acutely manipulate lipid levels, identify the protein machinery triggered by such elevation and investigate how the lipid content of endosomes and lysosomes governs inter-organellar communication and lipid transport.