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Unformatted text preview: Chapter 6 Integrating Cells into Tissues • The coordinated functioning of many types of cells within tissues and of multiple specialized tissues permits the organism as a whole to move, metabolize, reproduce, and carry out other essential activities. A key step in the evolution of mutlicellular organisms must have been the ability to contact tightly and interact specifically with other cells. • Cell-adhesion molecules (CAMs) is a collective term for various integral membrane proteins enable many animal cells to adhere tightly and specifically with cell of the same or similar type. These interactions allow population of cells to segregate into distinct tissues ( Fig 6-1 ). • Cell junctions stabilize these interactions and promote local communication between adjacent cells. • The extracellular matrix (ECM) is secreted by animal cells. It is basically a complex network of proteins and carbohydrates that creates a special environment in the spaces between cells. The matrix helps to bind cells together and is a reservoir for many hormones controlling growth and differentiation. The matrix also provides a structural lattice through which cells can move particularly during the early stages of differentiation. • The ECM has three major components; proteoglycans, collagen fibers, and multiadhesive matrix proteins. • Specific tissues have different combinations of these components that tailor the strength of the ECM for a structural purpose. For example tendons contain a high fraction of collagen fibers, whereas smooth muscle which surround arteries must be strong but flexible and contain lots of laminin . The ECM is not inert framework , but also can serve to feed back signals to adherent cells such as hepatocytes-the principle cells in liver-to express liver specific proteins. • ECM components can directly activate cytosolic signal transduction pathways by binding to adhesion protein receptors in the plasma membrane (PM). By binding with high affinity to certain growth factors and other hormones the matrix can sequester or present these molecules to cells. Examples are found in morphogenesis-the later stage of embryonic development. Wound healing- degradation and synthesis of ECM supporting tissue and blood vessels. 6.1 Cell-Cell and Cell-Matrix Adhesion: An Overview. • A number of cell surface proteins (CAMs) mediate homophilic (like molecules binding like) and heterophilic (two different receptor-ligand interactions). Most CAMs are distributed along the regions of PM that contact other cells, and the cytosolic facing domains of these proteins are usually connected to elements of the cytoskeleton. • There are four major families of CAMs ( Fig 6-2 ): Cadherins, Immunoglubuilin (Ig) superfamily, Integrins, & Selectins • Many cell-cell adhesions involving such as binding of cadherins and selectins require Ca ions . In order for cells in tissues to function in an integrated manner specialized junctions consisting of clustered cell adhesion molecules are essential....
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- Spring '06
- cells, Collagen, ECM