Cell-Cell Junctions and Cadherin Family
164 Questions
0 Views

Choose a study mode

Play Quiz
Study Flashcards
Spaced Repetition
Chat to lesson

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What is the primary function of cadherin-based anchoring junctions?

  • To allow free passage of substances between cells
  • To enable communication between cells
  • To promote cell division
  • To resist external forces that pull cells apart (correct)

    • Which ion is essential for the stability of cadherin-mediated adhesions?

  • Mg2+
  • Ca2+ (correct)
  • K+
  • Na+

    • Which type of junction is described as being dynamic and adaptable during tissue remodeling or repair?

  • Desmosomes
  • Cell–cell anchoring junctions (correct)
  • Tight junctions
  • Gap junctions

    • Which of the following cadherins is primarily found in nerve and muscle cells?

    <p>N-cadherin</p> Signup and view all the answers

    What do nonclassical cadherins have in common?

    <p>They have known adhesive functions</p> Signup and view all the answers

    Which type of cadherin is found primarily in epithelial cells?

    <p>E-cadherin</p> Signup and view all the answers

    How many members are estimated to be in the cadherin superfamily in humans?

    <p>180</p> Signup and view all the answers

    Which of these organisms is known to possess cadherins?

    <p>Choanoflagellates</p> Signup and view all the answers

    What is the primary function of gap junctions in animal tissues?

    <p>To allow ions and small molecules to pass between cells</p> Signup and view all the answers

    What forms a connexon in the plasma membrane?

    <p>A ring of six connexin proteins assembling together</p> Signup and view all the answers

    How do plasmodesmata function in plant cells?

    <p>They create a channel of cytoplasm between cells</p> Signup and view all the answers

    Which statement accurately describes selectins?

    <p>They mediate transient cell-cell adhesion in the bloodstream</p> Signup and view all the answers

    What best describes the Ig superfamily of proteins?

    <p>Proteins involved in cell-cell interactions or antigen recognition</p> Signup and view all the answers

    What is the primary function of gap junctions in electrically excitable tissues?

    <p>To allow rapid spread of action potentials</p> Signup and view all the answers

    What size of molecules can pass through gap junctions?

    <p>Smaller than 1000 daltons</p> Signup and view all the answers

    How many connexin subunits assemble to form a single connexon?

    <p>6</p> Signup and view all the answers

    What type of channel results from the alignment of connexons from two adjacent cells?

    <p>Continuous aqueous channel</p> Signup and view all the answers

    Which of the following is NOT a small molecule that can be shared through gap junctions?

    <p>Proteins</p> Signup and view all the answers

    Which factor does NOT influence the opening and closing of gap junction channels?

    <p>Presence of large macro-molecules</p> Signup and view all the answers

    What is the primary role of Rho in actin filament behavior?

    <p>Promotes formation of actin–myosin stress fibers</p> Signup and view all the answers

    In which type of muscle is the synchronization of contractions mainly facilitated by gap junctions?

    <p>Cardiac muscle</p> Signup and view all the answers

    Which molecules are crucial for linking cadherins to the cytoskeleton?

    <p>Catenins and adaptors</p> Signup and view all the answers

    What is the general structure of a gap-junction channel as revealed by x-ray crystallography?

    <p>A tubular structure</p> Signup and view all the answers

    How does Rac activation influence adherens junctions?

    <p>It encourages the spreading of cell–cell junctions</p> Signup and view all the answers

    Which property of gap junctions can vary based on the combination of connexins present?

    <p>Permeability and regulation</p> Signup and view all the answers

    What is a characteristic of connexin molecules as part of gap junctions?

    <p>They undergo rapid turnover</p> Signup and view all the answers

    What happens to actin–myosin fibers when cadherins first interact at a contact site?

    <p>They experience disassembly</p> Signup and view all the answers

    What type of junctional structure can contain thousands of connexons?

    <p>Gap junctional plaque</p> Signup and view all the answers

    Which proteins are involved in the dynamic linkage to actin filaments at adherens junctions?

    <p>α-catenin, β-catenin, and p120-catenin</p> Signup and view all the answers

    What is the primary function of adherens junctions in response to mechanical stresses?

    <p>Sense and respond to mechanical forces</p> Signup and view all the answers

    Which of the following components is essential in the formation of a gap junction?

    <p>Connexins</p> Signup and view all the answers

    What is the effect of increased contractile activity in one cell on the neighboring cell's adherens junction?

    <p>It leads to increased junction size in the neighbor</p> Signup and view all the answers

    Which molecules are typically NOT exchanged through gap junctions?

    <p>Macromolecules</p> Signup and view all the answers

    Which type of connexon can form in cells expressing different types of connexins?

    <p>Heterotypic connexon</p> Signup and view all the answers

    Which of the following proteins interacts with β-catenin to recruit other proteins for actin linkage?

    <p>α-catenin</p> Signup and view all the answers

    What role does cadherin play in the formation of strong cell adhesions?

    <p>Linkage to the actin cytoskeleton via adaptor proteins</p> Signup and view all the answers

    What type of actin structures does Rho promote during the long-term function of adherens junctions?

    <p>Linear contractile bundles</p> Signup and view all the answers

    What initiates the recruitment of more cadherins at cell junctions?

    <p>Loss of local cortical tension</p> Signup and view all the answers

    What is a key aspect of mechanotransduction at adherens junctions?

    <p>Generating biochemical signals in response to stress</p> Signup and view all the answers

    In the context of adherens junctions, what does p120-catenin specifically do?

    <p>Binds to the cytoplasmic tail of cadherin</p> Signup and view all the answers

    What color represents connexins that are synthesized during the 4- or 8-hour incubation period?

    <p>Red</p> Signup and view all the answers

    What is indicated by the central part of the gap-junction plaque in the fluorescence images?

    <p>Old connexin molecules</p> Signup and view all the answers

    Which structure connects the cytoplasms of adjacent plant cells?

    <p>Plasmodesmata</p> Signup and view all the answers

    What role do connexons in the plasma membrane away from the gap junction typically play?

    <p>Preventing leakage of small molecules</p> Signup and view all the answers

    What is the diameter of the cylindrical channel formed by plasmodesmata?

    <p>20-40 nm</p> Signup and view all the answers

    What is the structure that runs through the center of most plasmodesmata?

    <p>Desmotubule</p> Signup and view all the answers

    What type of adhesion mechanism do selectins mediate?

    <p>Transient cell-cell adhesions</p> Signup and view all the answers

    What is the mass cutoff for molecules that can pass through plasmodesmata?

    <p>800 daltons</p> Signup and view all the answers

    What happens to plasmodesmata as new cell walls are assembled during cell division?

    <p>They are formed</p> Signup and view all the answers

    How are new connexons delivered to the periphery of gap junctions?

    <p>Exocytosis</p> Signup and view all the answers

    What is the primary difference between gap junctions and plasmodesmata?

    <p>Their structural composition</p> Signup and view all the answers

    What is a common fate of plasmodesmata when they are no longer required?

    <p>They are removed</p> Signup and view all the answers

    Which of the following best describes the role of gap junctions in cell signaling?

    <p>They allow direct communication between the cytoplasms of cells</p> Signup and view all the answers

    What is the function of the annulus of cytosol found in plasmodesmata?

    <p>To allow passage of small molecules</p> Signup and view all the answers

    What is the main function of cadherins in cell adhesion?

    <p>To mediate selective cell-cell adhesion</p> Signup and view all the answers

    What is homophilic binding in the context of cadherins?

    <p>Binding between identical or closely related cadherins</p> Signup and view all the answers

    How do cadherin molecules contribute to cell adhesion strength?

    <p>By clustering in parallel to form multiple weak bonds</p> Signup and view all the answers

    Which of the following cadherins do not have a transmembrane domain?

    <p>T-cadherin</p> Signup and view all the answers

    Which ions are crucial for maintaining the structure of cadherin domains?

    <p>Ca2+ ions</p> Signup and view all the answers

    What occurs to cadherin molecules when Ca2+ concentrations are decreased?

    <p>Their flexibility increases, reducing adhesion</p> Signup and view all the answers

    What is a key characteristic of the extracellular portion of cadherins?

    <p>It contains several copies of the extracellular cadherin domain</p> Signup and view all the answers

    What role do the 'knob' and 'pocket' structures play in cadherin interactions?

    <p>They facilitate the binding of cadherins across cell membranes</p> Signup and view all the answers

    How do cadherins differ from receptors for soluble signaling molecules?

    <p>Cadherins typically bind with lower affinity</p> Signup and view all the answers

    What is the significance of cadherin clustering in cell membranes?

    <p>It enhances adhesion strength by increasing the number of interactions</p> Signup and view all the answers

    What was demonstrated about cell selectivity in the 1950s?

    <p>Certain cell types prefer to associate with similar types</p> Signup and view all the answers

    Which of the following is true regarding the intracellular portion of cadherins?

    <p>It varies and interacts with different intracellular ligands</p> Signup and view all the answers

    What analogy is used to describe the strength and flexibility of cadherin-mediated junctions?

    <p>Like Velcro fabric</p> Signup and view all the answers

    Which of the following best describes the binding mechanics of cadherin domains?

    <p>They form interactions via flexible hinge regions</p> Signup and view all the answers

    What role do cadherins play in tissue organization during embryonic development?

    <p>They facilitate selective cell–cell recognition which leads to tissue segregation.</p> Signup and view all the answers

    During the formation of the neural tube in vertebrates, E-cadherin is lost and replaced by which cadherin?

    <p>N-cadherin</p> Signup and view all the answers

    What happens when N-cadherin is artificially overexpressed in neural crest cells?

    <p>The cells remain in the neural tube and do not escape.</p> Signup and view all the answers

    What is required for the assembly of strong adherens junctions in cells?

    <p>Alterations in the actin cytoskeleton and decreased cortical tension.</p> Signup and view all the answers

    What occurs during the reaggregation of dissociated cells from an embryo?

    <p>The cells form structures based on their differentiated tissue type.</p> Signup and view all the answers

    In cultured L cells that do not express cadherins, what happens when they are transfected with E-cadherin?

    <p>Cell–cell adhesion occurs through E-cadherin binding.</p> Signup and view all the answers

    Which factor contributes to the reduction of cortical tension required for cell adhesion?

    <p>Inhibition of actin–myosin fiber formation.</p> Signup and view all the answers

    What phenomenon is observed when L cells expressing different cadherins are mixed together?

    <p>They segregate and aggregate separately based on cadherin type.</p> Signup and view all the answers

    What is the relationship between cadherin expression and tissue segregation?

    <p>Different cadherins promote cell segregation and adhesion based on type.</p> Signup and view all the answers

    Which of the following is NOT a change observed in cadherin expression during embryonic development?

    <p>E-cadherin levels decrease in all cell types.</p> Signup and view all the answers

    How does cortical tension affect cell adhesion initially?

    <p>It prevents the spreading of the adhesion surface and restricts interaction.</p> Signup and view all the answers

    Which GTPases are involved in the changes that support strong cell–cell adhesion?

    <p>Rac and Rho</p> Signup and view all the answers

    What important role do changes in cadherin expression play during the development of a vertebrate nervous system?

    <p>They dictate the migration patterns of neural crest cells.</p> Signup and view all the answers

    How do cells in an early amphibian embryo sort themselves when dissociated and mixed?

    <p>They rearrange according to their origin from differentiated tissues.</p> Signup and view all the answers

    What is the primary function of integrins?

    <p>Cell–matrix adhesion</p> Signup and view all the answers

    What is a characteristic of selectins in the context of cell adhesion?

    <p>Bind specifically to oligosaccharides</p> Signup and view all the answers

    Which type of selectin is located on white blood cells?

    <p>L-selectin</p> Signup and view all the answers

    How do selectins and integrins collaborate during white blood cell migration?

    <p>Selectins mediate weak adhesion followed by integrin activation</p> Signup and view all the answers

    What role do ICAMs (intercellular cell adhesion molecules) play in adhesion?

    <p>They mediate heterophilic binding to integrins</p> Signup and view all the answers

    Which protein family is primarily responsible for strong cell–cell adhesion in epithelial tissues?

    <p>Cadherins</p> Signup and view all the answers

    What is the effect of the long polysialic acid chains on NCAM?

    <p>They inhibit cell adhesion</p> Signup and view all the answers

    Which component is responsible for the weak adhesion in the initial stage of white blood cell migration?

    <p>Selectins</p> Signup and view all the answers

    How do nectins contribute to cell arrangement in the auditory and olfactory epithelia?

    <p>By promoting heterophilic interactions between different cell types</p> Signup and view all the answers

    What is the role of cadherins at adherens junctions?

    <p>To detect tension and respond to regulatory signals</p> Signup and view all the answers

    Which of the following is NOT a type of selectin?

    <p>T-selectin</p> Signup and view all the answers

    Which statement is true regarding the role of endothelial cells in inflammation?

    <p>They upregulate selectin expression to flag white blood cells</p> Signup and view all the answers

    Which structure is primarily formed by claudins?

    <p>Tight junctions</p> Signup and view all the answers

    What distinguishes homophilic binding from heterophilic binding in adhesion proteins?

    <p>Homophilic binding involves molecules of the same kind.</p> Signup and view all the answers

    What type of binding do integrins mediate?

    <p>Heterophilic binding</p> Signup and view all the answers

    Which class of transmembrane proteins is primarily involved in transient cell–cell adhesion?

    <p>Selectins</p> Signup and view all the answers

    What characterizes the adhesive function of selectins?

    <p>Low affinity interactions allowing rolling of cells</p> Signup and view all the answers

    What is the main function of intracellular scaffold proteins linked to claudins?

    <p>To organize junctional proteins into a structured network</p> Signup and view all the answers

    Which of the following proteins are expressed by endothelial cells during an inflammatory response?

    <p>P-selectin</p> Signup and view all the answers

    Which of the following correctly describes the unique features of classical cadherins?

    <p>They selectively bind to similar cadherins on adjacent cells.</p> Signup and view all the answers

    Which type of cell interaction do nectins primarily help facilitate?

    <p>Homophilic cell–cell interactions</p> Signup and view all the answers

    What happens to epithelial development when nectin expression is reduced?

    <p>It becomes defective, impairing cell arrangement.</p> Signup and view all the answers

    How do selectins affect white blood cell movement in the bloodstream?

    <p>They allow reversible binding and rolling behavior</p> Signup and view all the answers

    What distinguishes integrins from selectins in their mechanism of action?

    <p>Integrins require activation to switch to an adhesive conformation</p> Signup and view all the answers

    What function do gap junctions serve in animal tissues?

    <p>Facilitating the passage of small molecules directly between adjacent cells.</p> Signup and view all the answers

    Which statement about cadherins and their function is accurate?

    <p>Cadherins use catenins to anchor themselves to the actin cytoskeleton.</p> Signup and view all the answers

    Why do mutant mice lacking N-cadherin experience significant developmental issues?

    <p>N-cadherin plays a key role in cell adhesion essential for early development.</p> Signup and view all the answers

    Which molecules primarily mediate the formation of gap junctions?

    <p>Connexons</p> Signup and view all the answers

    Which type of junction plays a crucial role in separating apical and basolateral domains of epithelial cells?

    <p>Tight junctions</p> Signup and view all the answers

    What is the primary role of claudin proteins in the body?

    <p>To assemble sealing strands in tight junctions</p> Signup and view all the answers

    What happens to mice lacking the claudin-1 gene?

    <p>They cannot form tight junctions, leading to rapid water loss.</p> Signup and view all the answers

    Which protein is primarily responsible for limiting junctional permeability?

    <p>Occludin</p> Signup and view all the answers

    What role do ZO proteins play at tight junctions?

    <p>They provide structural support and organize tight junctions.</p> Signup and view all the answers

    What is the significance of tricellulin in epithelial cells?

    <p>It prevents transepithelial leakage at cell junctions.</p> Signup and view all the answers

    What characterizes gap junctions between adjacent cells?

    <p>They create direct channels for metabolic and electrical coupling.</p> Signup and view all the answers

    How many members of the claudin protein family are there in humans?

    <p>24</p> Signup and view all the answers

    Which of the following proteins is not essential for tight junction assembly?

    <p>Occludin</p> Signup and view all the answers

    What is a consequence of a mutation in the claudin gene involved in kidney epithelial cells?

    <p>Excessive loss of Mg2+ in the urine</p> Signup and view all the answers

    What is the primary function of the PDZ domains found in ZO proteins?

    <p>Recognizing and binding C-terminal tails of proteins</p> Signup and view all the answers

    How do claudins and occludins contribute to tight junction assembly?

    <p>By interacting with each other on their extracellular sides</p> Signup and view all the answers

    Why are tight junctions important for epithelial cells?

    <p>They prevent the leakage of extracellular molecules between cells.</p> Signup and view all the answers

    Which family of proteins predominantly forms gap junctions in vertebrates?

    <p>Connexins</p> Signup and view all the answers

    What role does α-catenin play at cell–cell junctions during mechanotransduction?

    <p>It transforms from a folded to an extended conformation when stretched.</p> Signup and view all the answers

    How does vinculin contribute to the strength of cell–cell junctions?

    <p>By promoting additional actin recruitment.</p> Signup and view all the answers

    What is a direct consequence of increased tension at a cell junction?

    <p>Strengthening of the local actin behavior.</p> Signup and view all the answers

    Which type of tissue is particularly influenced by mechanotransduction in terms of cell behavior modification?

    <p>Epithelial tissue.</p> Signup and view all the answers

    What type of structure do adherens junctions usually form in epithelial tissues?

    <p>Continuous adhesion belts encircling cells.</p> Signup and view all the answers

    How does tension affect the behavior of actin and myosin in epithelial cells during tissue remodeling?

    <p>It enhances coordinated contraction of the actin–myosin networks.</p> Signup and view all the answers

    What process occurs as a result of actin–myosin contractility being coordinated with changes in cell–cell adhesion?

    <p>Intercalation of cells occurs.</p> Signup and view all the answers

    During which developmental process in Drosophila does germ-band extension occur?

    <p>Cellular elongation.</p> Signup and view all the answers

    What is the primary role of adherens junctions in multicellular structures?

    <p>To enable coordinated use of actin cytoskeleton.</p> Signup and view all the answers

    Which protein is NOT directly involved in the mechanotransduction process at adherens junctions?

    <p>Transferrin.</p> Signup and view all the answers

    What effect does the contraction of cells in one part of a tissue have on other connected cells?

    <p>It causes mechanical stress that spreads throughout tissue.</p> Signup and view all the answers

    What kind of mechanical response occurs throughout connected tissues due to tension?

    <p>Rapid local strength increase in junctions.</p> Signup and view all the answers

    What potential mechanism may lead to the disassembly of adherens junctions during cell rearrangements?

    <p>Mechanical forces pulling on adhesion edges.</p> Signup and view all the answers

    What is the primary function of absorptive cells in the gut epithelium?

    <p>To transport selected nutrients from the gut lumen to extracellular fluid.</p> Signup and view all the answers

    What role do tight junctions play in epithelial transport?

    <p>They function as barriers to prevent nutrient leakage back into the lumen.</p> Signup and view all the answers

    How do transport proteins in absorptive cells ensure unidirectional nutrient transfer?

    <p>Through the specific distribution of transport proteins to their designated surfaces.</p> Signup and view all the answers

    What mechanism allows glucose to leave the absorptive cell after being transported in?

    <p>Passive transport through basolateral glucose transporters.</p> Signup and view all the answers

    What is the consequence if tight junctions are not properly functioning in the intestinal epithelium?

    <p>Uncontrolled leakage of molecules back into the gut lumen occurs.</p> Signup and view all the answers

    How do tight junctions contribute to the location specificity of transport proteins?

    <p>By acting as physical barriers that prevent protein diffusion.</p> Signup and view all the answers

    What type of transport allows ions to move between epithelial cells?

    <p>Paracellular transport.</p> Signup and view all the answers

    Which type of molecules can generally pass through tight junctions with less restriction?

    <p>Inorganic ions.</p> Signup and view all the answers

    What are sealing strands in tight junctions primarily composed of?

    <p>Transmembrane homophilic adhesion proteins.</p> Signup and view all the answers

    Which of the following is NOT a characteristic of tight junctions?

    <p>They allow free passage of all solutes.</p> Signup and view all the answers

    The specific arrangement of transport proteins in absorptive cells is crucial for what purpose?

    <p>To ensure an efficient nutrient absorption process.</p> Signup and view all the answers

    What experimental method can demonstrate the sealing function of tight junctions?

    <p>Adding a low-molecular-mass tracer to one side of an epithelium.</p> Signup and view all the answers

    Why is the permeability of tight junctions variable between different tissues?

    <p>It is influenced by the variations in transport proteins forming tight junctions.</p> Signup and view all the answers

    What is the primary function of desmosomes in epithelial tissues?

    <p>Providing mechanical strength</p> Signup and view all the answers

    How are desmosomes structurally different from adherens junctions?

    <p>Desmosomes link to intermediate filaments</p> Signup and view all the answers

    What role does E-cadherin play in the remodeling of cell–cell adhesions during development?

    <p>It is removed to facilitate shrinkage and loss of adhesion</p> Signup and view all the answers

    What phenomenon occurs when cells originally far apart along the dorsal–ventral axis are inserted between adjacent cells during the development of Drosophila?

    <p>Intercalation</p> Signup and view all the answers

    What happens to the spatial regulation of actin–myosin contractile bundles during cell elongation?

    <p>They are concentrated at vertical cell boundaries</p> Signup and view all the answers

    Which type of intermediate filament is typically associated with desmosomes in epithelial cells?

    <p>Keratin filaments</p> Signup and view all the answers

    What condition illustrates the importance of desmosomes in maintaining skin integrity?

    <p>Pemphigus</p> Signup and view all the answers

    What is the primary structural difference between tight junctions and desmosomes?

    <p>Tight junctions form a barrier</p> Signup and view all the answers

    What crucial role do basal laminae play in epithelial tissues?

    <p>Anchoring epithelial layers to underlying tissue</p> Signup and view all the answers

    During the remodeling process in Drosophila, what effect does the removal of E-cadherin have?

    <p>It leads to shrinkage along the vertical axis</p> Signup and view all the answers

    What type of cadherin is involved in the formation of desmosomes?

    <p>Nonclassical cadherins</p> Signup and view all the answers

    Which of the following describes the main characteristic of epithelial cells?

    <p>They are polarized with distinct basal and apical sides</p> Signup and view all the answers

    What is the result of spatial regulation in the actin–myosin bundles during germ-band extension in Drosophila?

    <p>Cellular intercalation</p> Signup and view all the answers

    What happens to the adhesion between cells that are affected by pemphigus disease?

    <p>Adhesion is disrupted due to antibody binding to cadherins</p> Signup and view all the answers

    Study Notes

    Cell-Cell Junctions

    • Cell-cell junctions, crucial for tissue function, come in various types, most notably anchoring junctions, tight junctions, and gap junctions.
    • Anchoring junctions, relying on cadherins, link cytoskeletons of neighboring cells, resisting pulling forces.
    • These junctions are dynamic, adapting to tissue remodeling and stress changes.
    • Cadherins are integral adhesion molecules present in all multicellular animals and related organisms, but absent from unicellular and less evolved eukaryotes.

    Cadherin Family

    • Cadherins require Ca2+ ions for adhesion; removal disrupts the bond.
    • Classical cadherins (e.g., E-cadherin, N-cadherin, P-cadherin) are closely related.
    • Nonclassical cadherins (e.g., protocadherins, desmocollins, desmogleins) are more diverse and abundant, particularly in the brain.
    • The cadherin superfamily encompasses over 180 members in humans, embodying the structural and functional diversity crucial for animal development and tissue assembly.

    Homophilic Adhesion

    • Cadherin-mediated anchoring junctions are typically homophilic, binding like-to-like.
    • Homophilic binding occurs at the N-terminal tips of cadherin molecules that form a knob-pocket configuration.
    • Ca2+ ions maintain cadherin domain rigidity, crucial for adhesion strength.
    • Strength comes from numerous weak bonds in parallel; the principle is similar to Velcro.

    Cadherin-Dependent Cell-Cell Adhesion

    • Cadherin specificity guides tissue organization during development.
    • Dissociation and re-association experiments demonstrate cell-sorting based on cadherin type.
    • Changes in cadherin expression punctuate embryonic development, as cells regroup and form new structures.
    • Examples include neural tube formation, neural crest migration, and ganglion assembly.
    • Cadherin expression and regulation tightly correlate with developmental processes, orchestrating tissue formation and morphogenesis.

    Actin Cytoskeleton Changes

    • Strong adhesion requires adjustments in the underlying actin cytoskeleton and a reduction in cortical tension.
    • Cortical tension, akin to surface tension, governs cell shape and initial adhesion points.
    • Inhibition of cortical actin-myosin fiber formation, regulated by GTPases Rac and Rho, decreases tension, enabling large adhesion surfaces and junction expansion.
    • Eventually, the process reverses, strengthening the linkage to the cytoskeleton.

    Catenins and Actin Cytoskeleton Linkage

    • Catenins (β-catenin, p120-catenin, α-catenin) link classical cadherins to the actin cytoskeleton, ensuring stable connections.

    Junction Mechanotransduction

    • Adherens junctions are mechanical sensors.
    • They sense and respond to tension generated by surrounding cells and the cytoskeleton, adjusting their structure and function.
    • Force imbalance triggers appropriate structural and biochemical adjustments for tension equilibrium.
    • Tension sensors within junctions change conformation to trigger downstream responses for adhesion strength adjustments.

    Tissue Remodeling and Cell Adhesion

    • Adherens junctions are key players in tissue remodeling, coordinating actin contractions with cell-cell adhesion patterns.
    • Examples include germ-band extension and epithelial sheet folding in invertebrates (Drosophila).
    • Cell rearrangement during development involves dynamic shifts in adherens junctions, enabling cells to intercalate within the tissue.

    Desmosomes and Tissue Strength

    • Desmosomes, structurally similar to adherens junctions, strengthen tissues, particularly those under high stress (skin, heart).
    • Desmosomes utilize special cadherins linking to intermediate filaments for robust mechanical support.
    • Protein complexes like desmoglein, desmocollin, plakoglobin, and desmoplakin form robust linkages essential for tissue integrity.

    Tight Junctions and Permeability Barriers

    • Tight junctions form seals between epithelial cells, regulating paracellular transport of molecules.
    • They act as diffusion barriers, sealing off intercellular spaces and maintaining tissue polarity.
    • They confine proteins to specific membrane domains (apical vs. basolateral) controlling efficient transcellular transport.
    • The permeability of tight junctions varies depending on the tissue and its function (e.g., between intestine and urinary bladder).

    Tight Junction Proteins

    • Tight junctions are composed of transmembrane proteins like claudins and occludin, forming sealing strands and controlling permeability.

    Gap Junctions and Intercellular Communication

    • Gap junctions, in contrast to tight junctions, create channels for direct cytoplasmic communication.
    • They allow the passage of ions and small molecules between cells, enabling electrical and metabolic coupling.
    • They are crucial for synchronizing activities (e.g., heart muscle contractions, intestinal peristalsis) in various tissues.

    Gap Junction Proteins

    • Gap junctions are formed by connexins, which arrange into connexons in the plasma membrane of adjacent cells.

    Plasmodesmata in Plants

    • Plasmodesmata are plant cell equivalents of gap junctions, connecting plant cell cytoplasms.
    • They traverse the cell wall, maintaining intercellular communication.
    • Plasmodesmata, despite structural differences, function similarly to gap junctions in terms of size exclusion.

    Selectins and Transient Adhesion

    • Selectins mediate transient cell-cell interactions, particularly in the bloodstream for white blood cell recruitment.
    • They bind weakly to specific carbohydrates on other cells, enabling their reversible adhesion and movement.

    Immunoglobulin Superfamily

    • Immunoglobulin superfamily members (e.g., ICAMs, VCAMs, NCAMs, nectins) contribute to transient or specific cell-cell attachments.
    • Some participate in homophilic binding, others in heterophilic binding.
    • These proteins fine-tune adhesion in specialized situations, unlike cadherins which predominantly establish and maintain basic tissue integrity.

    Glossary Terms

    • Definitions for each term are provided within the text within the "Glossary" section.

    Studying That Suits You

    Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

    Quiz Team

    Description

    Explore the essential roles of cell-cell junctions, including anchoring, tight, and gap junctions. Learn about cadherins and their vital functions in tissue integrity and embryonic development through their dynamic interactions. Discover the diversity within the cadherin family and its implications for development and diseases.

    Use Quizgecko on...
    Browser
    Open
    Browser
    Browser