simplified and unified view of the multi-level cross-talk. TGF-β/BMP communicates with other signals at several levels. Physical interactions between pathway components, both in the cytoplasm and in the nucleus, can lead to protein redistribution and/or post-translational modifications, and eventually changes in target gene expression. Often the ligands themselves, as well as certain extracellular regulators of the ligands, are transcriptional targets of other pathways. All these events are context-dependent.