<P> Desmosomes are structurally similar to adherens junctions but composed of different components . Instead of classical cadherins, non-classical cadherins such as desmogleins and desmocollins act as adhesion molecules and they are linked to intermediate filaments instead of actin filaments . No catenin is present in desmosomes as intracellular domains of desmosomal cadherins interact with desmosomal plaque proteins, which form the thick cytoplasmic plaques in desmosomes and link cadherins to intermediate filaments . Desmosomes provides strength and resistance to mechanical stress by unloading forces onto the flexible but resilient intermediate filaments, something that cannot occur with the rigid actin filaments . This makes desmosomes important in tissues that encounter high levels of mechanical stress, such as heart muscle and epithelia, and explains why it appears frequently in these types of tissues . </P> <P> Tight junctions are normally present in epithelial and endothelial tissues, where they seal gaps and regulate paracellular transport of solutes and extracellular fluids in these tissues that function as barriers . Tight junction is formed by transmembrane proteins, including claudins, occludins and tricellulins, that bind closely to each other on adjacent membranes in a homophilic manner . Similar to anchoring junctions, intracellular domains of these tight junction proteins are bound with scaffold proteins that keep these proteins in clusters and link them to actin filaments in order to maintain structure of the tight junction . Claudins, essential for formation of tight junctions, form paracellular pores which allow selective passage of specific ions across tight junctions making the barrier selectively permeable . </P> <P> Gap junctions are composed of channels called connexons, which consist of transmembrane proteins called connexins clustered in groups of six . Connexons from adjacent cells form continuous channels when they come into contact and align with each other . These channels allow transport of ions and small molecules between cytoplasm of two adjacent cells, apart from holding cells together and provide structural stability like anchoring junctions or tight junctions . Gap junction channels are selectively permeable to specific ions depending on which connexins form the connexons, which allows gap junctions to be involved in cell signalling by regulating the transfer of molecules involved in signalling cascades . Channels can respond to many different stimuli and are regulated dynamically either by rapid mechanisms, such as voltage gating, or by slow mechanism, such as altering numbers of channels present in gap junctions . </P> <P> Selectins are a family of specialised CAMs involved in transient cell--cell adhesion occurring in the circulatory system . They mainly mediate the movement of white blood cells (leukocytes) in the bloodstream by allowing the white blood cells to "roll" on endothelial cells through reversible bindings of selections . Selectins undergo heterophilic bindings, as its extracellular domain binds to carbohydrates on adjacent cells instead of other selectins, while it also require Ca ions to function, same as cadherins . cell--cell adhesion of leukocytes to endothelial cells is important for immune responses as leukocytes can travel to sites of infection or injury through this mechanism . At these sites, integrins on the rolling white blood cells are activated and bind firmly to the local endothelial cells, allowing the leukocytes to stop migrating and move across the endothelial barrier . </P>

Fibronectins and laminins attache cells to the extracellular matrix by binding to