To complement the LINCS efforts of profiling human cells response to small molecule and gene knockdown perturbations, it would be useful to have a collection of gene expression signatures collected from before and after treatment of human or mouse cells with endogenous ligands. Endogenous ligands are extracellular molecules that can be found in the body naturally. These ligands bind to receptors at the cell surface or can travel into the cell and bind to transcription factors. These small molecules signal to the cell about the status of the extracellular environment and whether the cell should take action and change its phenotypic behavior. Endogenous ligands include hormones such as growth factors, cytokines or chemokines. A complete list of such molecules can be found here. Using GEO2Enrichr and the crowdsourcing portal you can contribute signatures to this collection. The hashtag for this project is #LIGANDS_BD2K_LINCS_DCIC_COURSERA.