• Multicellular organisms consist of cells and extracellular matrix (secretory substances).
  • Extracellular matrix consists of many types of components and acts as a support for the body structure, a signaling molecule and an adhesive molecule for cells.
  • Cells adhere to other cells as well as to extracellular matrix around them.
  • Cell adhesion plays an important role in forming tissues and organs as well as in intercellular communication and obtaining extracellular information.
  • The main molecules involved in cell adhesion are transmembrane proteins located on the plasma membrane, and are classified into several groups.
  • Cell adhesion molecules convey extracellular signals, obtained through cell-cell adhesion and cell-extracellular matrix adhesion, into the cell.
  • The signals conveyed into the cell via cell adhesion molecules influence various cellular functions (e.g., cell migration, growth and differentiation, and intracellular material transport) through the intracellular signal transduction system.
  • Epithelial tissues are the main tissues formed by cell adhesion, and many parts of animal bodies consist of these tissues.
  • The epithelial cells that make up epithelial tissues have directionality (cell polarity), and the apical and basal sides face the outside and inside of the body, respectively.
  • Epithelial tissues serve as a wall separating two environments as well as a medium of transport between the environments.
  • Plant cells have extracellular matrix consisting of cellulose and other substances, and intercellular communication is made through plasmodesmata.

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