Question

. In general, what are cell-to-cell adhesion molecules (CAMs) and how do they play a role in development? Briefly, explain how a particular stage of development could be disrupted if you were to block the production of these molecules

Answer 1

Cell adhesion molecules (CAMs) are proteins located on the cell surface involved in binding with other cells or with the extracellular matrix in the process called cell adhesion. CAMs help cells stick to each other and to their surroundings. CAMs are involved in the developmental processes of fertilization, embryogenesis, implantation, placentation, and embryonic development.

There are five principal classes of CAMs : cadherins, the immunoglobulin (Ig) superfamily, selectins, mucins, and integrins. Cell-cell adhesion involving cadherins and selectins depends on Ca2+ ions, whereas interactions involving integrin and Ig-superfamily CAMs do not.

In order for cells in tissues to function in an integrated manner, specialized junctions consisting of clustered cell-adhesion molecules are essential. There are four major classes of junctions: the tight junction, gap junction, cell-cell, and cell-matrix junctions

Cell-cell and cell-matrix junctions perform a simple structural role, to hold cells into a tissue. They carry out this role by connecting the internal cytoskeleton directly to the cell exterior, either another cell or the extracellular matrix, via two cell-adhesion molecules?—?cadherins and integrins.

All cytoskeleton-associated junctions are organized into three parts: cell-adhesion molecules, which connect the cell to another cell or to the extracellular matrix; adapter proteins, which connect the CAMs to actin or keratin filaments; and lastly the bundle of cytoskeletal filaments.

Cadherins are calcium dependent. They form adherens junctions to bind cells within tissues together. They are responsible for the different tissue layers and cellular migration.

Integrins are transmembrane receptors that are the bridges for cell-cell and cell-extracellular interactions. They are calcium dependent. An example of an integrin in action would be when a white blood cell is dragged through the capillary wall to go to a wound.

The immunoglobulin superfamily is a large group of cell surface and soluble proteins. Molecules are placed in this protein family based on similar structural features of immunoglobulins, or antibodies.A function of this group is support in establishing neural connections.?Ca2+-independent homophilic interactions between cells are mediated by N-CAMs, which belong to the Ig superfamily

Selectins are also calcium dependent and they are single-chain transmembrane glycoproteins. An example of a selectin carrying out one of its processes would be when a white blood cell is slowed down when it goes to a wound. A selectin coats the white blood cell and causes traction. Selectins, which bind to carbohydrate groups on mucin-like CAMs via their distal lectin domain, mediate Ca2+-dependent heterophilic cell-cell interactions. P-selectin on the surface of activated vascular endothelial cells plays an important role in the extravasation of leukocytes into tissues.

?In all cell-adhesion junctions, clusters of transmembrane cell-adhesion molecules are linked via various adapter proteins in cytoplasmic plaques to the cytoskeleton.

?Adherens junctions and desmosomes are cadherin-containing junctions that bind the membranes of adjacent cells in a way that gives strength and rigidity to the entire tissue

Cells in tissues are in direct communication through gap junctions. Gap junctions are distributed along the lateral surfaces of adjacent cells and allow them to exchange small molecules. Gap junctions at electric synapses allow ions to pass from one nerve cell to the next, thereby allowing a presynaptic cell to induce an action potential in the postsynaptic cell without a lag period. But gap junctions also are present in many non-neuronal tissues, where they help to integrate the metabolic activities of all the cells in a tissue by permitting exchange of ions and small molecules like cyclic AMP and precursors of DNA and RNA.

CAMs guide cells around an embryo to grow and form the placenta, the organ linking a woman to the fetus.