Two different cells may each be competent to respond to the same inducing signal, but they may not respond in the same way. The response is dictated by developmental history of the cell. Thus, a certain ligand may be used several different times during development, and it may direct different cell fate changes each time. A cell or tissue may be competent to respond to more than one inducing signal, and different signals may result in different responses. A hormonal signal is one that is transported throughout the animal by a circulatory system.
Paracrine signals are generally soluble molecules.
Juxtacrine signals are often tethered to the cell membrane. The Notch receptor mediates many important juxtacrine signaling events. The Notch gene encodes a large molecule with one membrane spanning domain. The known ligands for Notch include Delta and Serrate, and they are also embedded in the plasma membrane. Upon ligand binding, the Notch receptor is cleaved, and the intracellular domain translocates to the nucleus, where it regulates transcription.