Juxtacrine

In biology, juxtacrine signalling (or contact-dependent signalling) is a type of cell–cell or cell–extracellular matrix signalling in multicellular organisms that requires close contact. In this type of signalling, a ligand on one surface binds to a receptor on another adjacent surface. Hence, this stands in contrast to releasing a signaling molecule by diffusion into extracellular space, the use of long-range conduits like membrane nanotubes and cytonemes (akin to 'bridges') or the use of extracellular vesicles like exosomes or microvesicles (akin to 'boats'). There are three types of juxtacrine signaling: A membrane-bound ligand (protein, oligosaccharide, lipid) and a membrane protein of two adjacent cells interact. A communicating junction links the intracellular compartments of two adjacent cells, allowing transit of relatively small molecules. An extracellular matrix glycoprotein and a membrane protein interact. Additionally, in unicellular organisms such as bacteria, juxtacrine signaling refers to interactions by membrane contact. Juxtacrine signaling has been observed for some growth factors, cytokine and chemokine cellular signals, playing an important role in the immune response. It has a critical role in development, particularly of cardiac and neural function. Other types of cell signaling include paracrine signalling and autocrine signalling. Paracrine signaling occurs over short distances, while autocrine signaling involves a cell responding to its own paracrine factors. The term "juxtacrine" was originally introduced by Anklesaria et al. (1990) to describe a possible way of signal transduction between TGF alpha and EGFR. In this type of signaling, specific membrane-bound ligands bind to a cell’s membrane. A cell with the appropriate cell surface receptor or cell adhesion molecule can bind to it. An important example is the Notch signaling pathway, notably involved in neural development. In the Notch signaling pathway for vertebrates and Drosophila, the receiving cell is told not to become neural through the binding of Delta and Notch.