Why are cell signaling and differentiation important?

The development and homoeostasis of multicellular organisms relies on a fine-tuned interplay of cell proliferation, cell differentiation and cell death (apoptosis), where signaling between cells and the ability of each cell to specifically respond to different external signals is of fundamental importance. External signals can be quite different in terms of biochemistry and they can come from different sources, e.g. from the extracellular matrix of a tissue or from an infectious agent, triggering the response of the immune system. A well-known and important group of extracellular signals are growth factors which play important roles during development or wound repair but they are also important in human disease, e.g. in different aspects of cancer. Differentiation signals are sensed by specific receptor molecules. Transmembrane receptors communicate ligand binding at the extracellular side of the cell to the cytoplasm. Cytoplasmic receptors sense signals that can pass the cell membrane like steroid hormones do. All these different receptors are connected to intracellular networks of interacting proteins, nucleic acids and small molecules. Those networks integrate and process many different input signals to decide about developmental options and to orchestrate the multiple effects that finally contribute to a complex, biologically meaningful response of the cell. It is of considerable interest to understand how such networks are built and how they work.