LAUSR

Cells have a challenge in crowded environments. They need to send specific messages to their nearest neighbors but not to cells two or three doorsteps away. This is a common problem in cell-to-cell communication that often arises during processes such as immune recognition and cellular development. To carry on this nearest-neighbor ‘‘conversation,’’ cells resort to a mode of contact-dependent signaling dubbed as juxtacrine, which is in contrast to more conventional forms of cell-tocell communication that involve the release of soluble molecules into the surrounding environment. For example, in paracrine, endocrine, and autocrine signaling, soluble factors are released from the cell and diffuse or are actively transported toward their targets. To ensure high-fidelity, short-range communication between adjacent cells, ligand molecules are expressed on the surface of one cell, and the receptor is expressed on the surface of the proximal target cell. Because juxtacrine signaling requires the formation of a ligand-receptor complex precisely where two cells form an intimate physical touch, signal transmission is heavily influenced by physical processes that transcend conventional