Cell Adhesion and Signalling Quiz

Cell Adhesion and Cell Signalling

• Multicellular organisms rely on cell adhesion to each other and the extracellular matrix (ECM) for tissue formation.
• Some adhesive interactions are stable, like the firm adhesion of muscle cells to each other and connective tissue in tendons to transmit force to the skeleton. Other adhesive interactions are more transient, such as leukocytes binding to endothelial cells before extravasation into tissues or cell attachment to the ECM during migration. This includes strong adhesion and less permanent adhesion.

Cellular Adhesion

• Multicellular organisms depend on cell adhesion to form tissues.
• Stable adhesive interactions transmit force (e.g., muscle cells to tendons), resist abrasion (e.g., skin epithelial cells to each other), and hold tissues together.
• Transient adhesive interactions facilitate processes such as leukocyte binding to blood vessel linings for extravasation into tissues.

Cell Junctions

• Cell-cell junctions (adherens junctions, desmosomes) and cell-matrix adhesions (actin-linked, hemidesmosomes) connect cells to each other and the ECM. They are linked to the cytoskeleton to transmit forces.
• Tight junctions (septate junctions) seal gaps between cells.
• Gap junctions allow passage of small molecules and ions between cells, facilitating signalling.

Different Types of Cadherins

• Cadherins are a family of adhesion proteins mediating calcium-dependent homophilic adhesion.
• Different types include classical cadherins (E-cadherin), fat-like cadherins, seven-pass transmembrane cadherins, protein kinase cadherins, desmosomal cadherins, cadherin 23, and protocadherins.

Cell Segregation During Embryonic Development

• Cells expressing different cadherins segregate during embryonic development, forming tissues with specific cell types.

Catenins

• Catenins link classical cadherins to the actin cytoskeleton.
• Extracellular cadherin domains bind together to mediate adhesion.
• Cytoplasmic cadherin domains, via anchor proteins (catenins), link to the actin cytoskeleton. The β-catenin also functions in signal transduction pathways such as the Wnt pathway.

Gap Junctions

• Gap junctions connect cells through channels allowing small molecules (ions and small molecules) passing between cells, enabling communication and signal transduction.

Small Molecule Transfer

• Gap junctions allow the passage of inorganic ions, sugars, amino acids, nucleotides, vitamins, and intracellular signalling molecules (like cyclic AMP and inositol trisphosphate) to communicate. Size is a crucial determinant in the passage of these small molecules through these channels.

Tight Junctions

• Tight junctions form a permeability barrier between cells.
• Tight junctions seal adjacent cells together via transmembrane proteins.

Selectins

• Selectins are cell surface carbohydrate binding proteins, binding to cell surface glycoproteins, such as mucins.
• Selectins are Ca2+ dependent and are expressed on white blood cells, platelets, and endothelial cells.
• Selectins and their interactions are involved in cell-cell adhesion, especially in inflammatory responses.

Cell Adhesion Molecules and T cells

• Lymphocytes bind to vascular endothelium in lymph nodes through interactions between L-selectin and vascular addressins
• T cells and T cell receptors (TCR) utilize cell adhesion molecules via integrins like LFA-1 for antigen recognition, signalling and binding with other cells.

Cell Adhesion Molecules and Neutrophils

• Selectin-mediated interactions between selectins on endothelial cells and carbohydrate ligands on neutrophils are transient, weak interactions that allow the cells to attach and roll along blood vessels, slow down cellular processes and are crucial to chemotaxis.

Integrins

• Integrins are transmembrane heterodimers involved in cell adhesion to the ECM.
• Integrins have extracellular domains interacting with ligands (ECM proteins) and cytoplasmic domains binding to intracellular proteins.
• Integrin activation involves changes in conformation for both outside-in (ligand activation, conformational change in extracellular portion) and inside-out (cytoplasmic signalling and conformational changes in cytoplasmic tails) signaling pathways.
• Integrins are implicated in focal adhesions and podosomes, critical for cell motility in various cell types such as those involved in inflammatory processes or in developmental processes.

Integrin based cell–matrix adhesion

• Integrin based cell-matrix adhesion utilizes specialized structures like focal adhesions, vital for cell motility, and podosomes, specifically important in some types of immune cells. Both focal adhesions and podosomes strongly link the actin cytoskeleton to the extracellular matrix.

Integrins in cell-cell adhesion

• Integrins can bind to other cellular adhesion molecules, such as those from the Ig family.
• These interactions are important for processes like antigen recognition by T cells.

Syndecans

• Syndecans are cell surface proteoglycans mediating cell adhesion to the ECM and binding to growth factors and cytokines.
• Many cell types express syndecans.

Desmosomes

• Desmosomes link cells together via intermediate filaments and non-classical cadherins such as desmoglein and desmocollin.
• Desmosomes are important cellular junctions holding skin tissues together resisting mechanical stress.

Hemidesmosomes

• Hemidesmosomes link cells to the basement membrane with help of integrins proteins, and via linker proteins like plectin and dystonin, linking to keratin filament systems within epidermal cells.
• Hemidesmosomes are key to attaching cells to the basement membrane, and provide structural support to tissues.

Explore the critical roles of cell adhesion and signaling in multicellular organisms. This quiz covers stable and transient adhesive interactions, as well as cell junctions and their importance in tissue formation and function. Test your understanding of how these processes affect cellular behavior and migration.