Juxtacrine signalling

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. Some of the cell signaling pathways that are involved in cell-to-cell communication include: Notch-Delta, FGF, Wnt, EGF, TGF-beta, Hedgehog, Hippo, Jun kinase, Nf-kB, and retinoic acid receptor. Of all these pathways, juxtracrine signaling utilizes Notch and Hippo the most as they involve a more direct cell-to-cell contact signaling. 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. Within the eye of vertebrates, which cells become optic neurons and which become glial cells is regulated by Notch and its ligands. Some cells, like ephrin-Eph, are only able to communicate through juxtacrine signaling. Eph ligands can only activate receptors when bound to a membrane. This is because a high density of the Eph ligand is necessary for the receptor to bind to it. Ephrin-Eph is used for axon guidance, angiogenesis, and epithelial and neuronal cell migration. ==Communicating junctions==

Two adjacent cells can construct communicating conduits between their intracellular compartments: gap junctions in animals and plasmodesmata in plants. Gap junctions act as communication channels between adjacent cells. They are made of connexins in vertebrates and innexins in invertebrates. They connect the cytoplasm of cells and exchange ions and messenger signals. Electrical synapses are electrically conductive gap junctions between neurons. Gap junctions are critical for cardiac myocytes; mice and humans deficient in a particular gap junction protein have severe heart development defects. Plasmodesmata in plants are cytoplasmic strands that pass through cell walls and facilitate connections with adjacent cells. Plasmodesmata are highly dynamic in both strucutural modifications and biogenesis. They are able to organize cells in domains, serving as basic developmental units for plants, as well as mediate the intracellular movement of a variety of proteins and nucleic acids. == Cell–extracellular matrix signaling ==

The extracellular matrix is composed of glycoproteins (proteins and mucopolysaccharides (glycosaminoglycan)) produced by the organism's cells. They are secreted not only to build a supportive structure but also to provide critical information on the immediate environment to nearby cells. One of the main general adhesive molecules in the ECM is fibronectin; this glycoprotein dimer links cells to each other and other noncellular materials. It also plays an important role in cell migration as it provides a surface for migrating cells. Other examples of molecules include collagens and vitronectin. Also, the cells can themselves interact by contact with extracellular matrix molecules and as such, this can be considered an indirect cell / cell communication. This signaling can influence the cell cycle and cellular differentiation by directing which cells live or die, which cells proliferate, or which cells are able to exit the cell cycle and differentiate. Cellular differentiation involves a cell changing its phenotypical or functional type. Integrins are one of the major regulators of the cell's function. ==See also==