- In airway epithelium, a viral protein caused mislocalization of ZO-1 from apical junctions while E-cadherin remained at lateral membranes. TEER dropped and paracellular dye penetration increased, but cells remained in a continuous sheet. Which conclusion is most consistent with the affected junction component?
Answer: Disrupting tight junction scaffolding impairs barrier function without necessarily abolishing cell–cell adhesion
This question tests understanding of cell–cell junctions and ECM in cellular organization (Foundational Concept 2). Cell–cell junctions like tight junctions regulate permeability, while ECM provides structural support and signaling cues. In this vignette, the impact of ZO-1 mislocalization on airway epithelial barrier function is examined. Choice A is correct because it accurately describes how disrupting tight junction scaffolding impairs barrier function without abolishing adhesion, as TEER drops but the sheet remains continuous. Choice B is incorrect as it confuses ZO-1 with integrins, a common misconception since ZO-1 scaffolds tight junctions, not ECM adhesion. Ensure understanding of specific junction functions and ECM roles in cellular processes; apply this to predict effects of their disruption, such as in viral infections affecting barriers.
- Endothelial cells were exposed to inflammatory cytokines that increased vascular permeability. Imaging showed internalization of VE-cadherin from cell borders, while tight junction proteins were unchanged in abundance but appeared more fragmented. Which statement best describes how the altered cell–cell junction interaction most likely contributes to increased permeability?
Answer: Reduced adherens junction adhesion can create intercellular gaps and destabilize barrier architecture, increasing leakage
This question tests understanding of cell–cell junctions and ECM in cellular organization (Foundational Concept 2). Cell–cell junctions like tight junctions regulate permeability, while ECM provides structural support and signaling cues. In this vignette, the impact of VE-cadherin internalization on endothelial permeability is examined. Choice D is correct because it accurately describes how reduced adherens junction adhesion creates gaps and destabilizes barriers, increasing leakage despite unchanged tight junction proteins. Choice C is incorrect as it confuses adherens with gap junctions, a common misconception since adherens provide adhesion, not ion flow. Ensure understanding of specific junction functions and ECM roles in cellular processes; apply this to predict effects of their disruption, such as edema in inflammation.
- Keratinocytes were engineered to express a dominant-negative desmoglein that reduces desmosome assembly. When subjected to cyclic mechanical stretch, the monolayer developed frequent intercellular tears, but transepithelial electrical resistance remained near control values. What effect would be expected if this change in junctional organization occurs?
Answer: Reduced mechanical resilience of the tissue due to impaired intermediate filament anchoring at cell–cell contacts
This question tests understanding of cell–cell junctions and ECM in cellular organization (Foundational Concept 2). Cell–cell junctions like tight junctions regulate permeability, while ECM provides structural support and signaling cues. In this vignette, desmoglein mutation impairs desmosomes, reducing mechanical strength in keratinocytes under stretch. Choice B is correct because it accurately describes reduced resilience from poor intermediate filament anchoring, consistent with tears but stable resistance. Choice A is incorrect as it confuses desmosomes with tight junctions, a common misconception in mechanical vs. barrier functions. Ensure understanding of specific junction functions and ECM roles in cellular processes; apply this to predict effects of their disruption in tissues under mechanical stress.
- Cardiomyocytes in culture were treated with a connexin43 inhibitor. Action potential propagation velocity across the monolayer decreased, while cell morphology and desmosomal marker localization were unchanged. Which statement best describes how the affected junction type influences cellular behavior in this system?
Answer: Gap junctions provide low-resistance pathways for ionic current between cells, supporting electrical conduction
This question tests understanding of cell–cell junctions and ECM in cellular organization (Foundational Concept 2). Cell–cell junctions like tight junctions regulate permeability, while ECM provides structural support and signaling cues. In this vignette, connexin inhibition affects electrical conduction in cardiomyocytes via gap junctions. Choice A is correct because it accurately describes gap junctions enabling ionic current for conduction, consistent with slowed propagation velocity. Choice B is incorrect as it confuses gap junctions with tight junctions, a common misconception in electrical coupling. Ensure understanding of specific junction functions and ECM roles in cellular processes; apply this to predict effects of their disruption in excitable tissues like heart.
- A lab studies wound closure in a confluent epithelial sheet. Cells express normal integrins and deposit fibronectin, but a dominant-negative form of a focal adhesion adaptor prevents efficient coupling of integrins to actin. In a scratch assay, cells at the wound edge extend protrusions but frequently retract and show reduced forward displacement; cell–cell junction markers remain continuous in the bulk sheet. What effect would be expected if this change in ECM-related coupling occurs?
Answer: Reduced traction generation at the leading edge due to impaired integrin–actin linkage, decreasing effective migration without directly disrupting cell–cell junction continuity
This question tests understanding of cell–cell junctions and ECM in cellular organization (Foundational Concept 2). Focal adhesions link integrins to the actin cytoskeleton through adaptor proteins, and this coupling is essential for generating traction forces that drive cell migration on ECM substrates. In this vignette, a dominant-negative focal adhesion adaptor prevents efficient integrin-actin coupling, specifically affecting migration mechanics. Choice D is correct because impaired integrin-actin linkage prevents cells from generating effective traction at focal adhesions, causing protrusions to retract rather than pull the cell forward, while cell-cell junctions in the sheet remain unaffected. Choice B is incorrect as the defect is in cell-ECM mechanics, not tight junction permeability, and continuous junction markers confirm barrier integrity. The specific phenotype of protrusion extension followed by retraction indicates a failure in force transmission rather than adhesion formation, highlighting the importance of mechanical coupling in migration.
- Keratinocytes were engineered to express a dominant-negative desmoglein that reduces desmosome assembly. In a cyclic stretching assay, monolayers maintained TEER but developed frequent intercellular tears and increased cell loss under mechanical stress. What effect would be expected from this junction alteration?
Answer: Decreased mechanical resilience of the sheet due to weakened intermediate filament coupling between neighboring cells
This question tests understanding of cell–cell junctions and ECM in cellular organization (Foundational Concept 2). Cell–cell junctions like tight junctions regulate permeability, while ECM provides structural support and signaling cues. In this vignette, the role of desmosomes in providing mechanical strength to keratinocyte monolayers is examined. Choice D is correct because it accurately describes how desmosome disruption decreases mechanical resilience due to weakened intermediate filament coupling, leading to tears under stress while TEER is maintained. Choice B is incorrect as it confuses desmosomes with tight junctions, a common misconception since desmosomes do not form diffusion barriers. Ensure understanding of specific junction functions and ECM roles in cellular processes; apply this to predict effects of their disruption, such as increased fragility in skin disorders like pemphigus.
- In an intestinal epithelial model, a cytokine exposure causes internalization of occludin and claudins from the apical junctional complex. TEER decreases, but the rate of endocytosis of a labeled nutrient transporter at the apical membrane is unchanged. Based on the vignette, which conclusion is most consistent with the affected cellular process?
Answer: Paracellular barrier function is compromised while transcellular transporter trafficking can remain intact, indicating selective disruption of tight junctions
This question tests understanding of cell–cell junctions and ECM in cellular organization (Foundational Concept 2). Tight junctions create paracellular barriers through transmembrane proteins like occludin and claudins, while transcellular transport occurs through specific transporters and is regulated independently. In this vignette, cytokine-induced internalization of tight junction proteins reduces barrier function without affecting transporter endocytosis. Choice A is correct because tight junction disruption specifically compromises the paracellular barrier (decreased TEER) while transcellular transport mechanisms remain functional, as evidenced by unchanged nutrient transporter trafficking. Choice B is incorrect as tight junction proteins form paracellular barriers, not nutrient transporter pores, and transcellular transport uses distinct membrane proteins. Understanding that paracellular and transcellular pathways are independently regulated helps predict how specific perturbations affect epithelial function.
- In a polarized epithelial monolayer cultured on Transwell filters, researchers used CRISPR to delete claudin-1 while leaving E-cadherin intact. Cells formed a confluent sheet with normal morphology, but transepithelial electrical resistance (TEER) fell by 70% and apical-to-basolateral flux of a 4-kDa fluorescent tracer increased. Which conclusion is most consistent with these findings regarding the affected cellular interaction?
Answer: Loss of claudin-1 primarily disrupts tight junction sealing, increasing paracellular permeability without preventing cell–cell adhesion
This question tests understanding of cell–cell junctions and ECM in cellular organization (Foundational Concept 2). Cell–cell junctions like tight junctions regulate permeability, while ECM provides structural support and signaling cues. In this vignette, the role of claudin-1 in tight junction function within a polarized epithelial monolayer is examined. Choice B is correct because it accurately describes how loss of claudin-1 disrupts tight junction sealing, leading to increased paracellular permeability as evidenced by decreased TEER and increased tracer flux, while E-cadherin maintains cell–cell adhesion. Choice A is incorrect as it confuses the function of claudin-1 with adherens junctions, a common misconception since adherens junctions involve cadherins, not claudins. Ensure understanding of specific junction functions and ECM roles in cellular processes; apply this to predict effects of their disruption, such as how tight junction defects might lead to barrier dysfunction in tissues like the intestine.
- An epithelial monolayer expresses normal levels of tight junction proteins but is engineered to overexpress a protease that degrades pericellular hyaluronan, reducing the thickness of the glycocalyx-like pericellular matrix. Under identical fluid shear, these cells show increased activation of a membrane mechanosensor and increased downstream inflammatory gene expression compared with control. Which conclusion is most consistent with the role of the extracellular matrix in this context?
Answer: Pericellular matrix depletion reduces mechanical buffering at the cell surface, increasing force transmission to mechanosensors and signaling.
This question tests understanding of cell-cell junctions and ECM in cellular organization (Foundational Concept 2). The pericellular matrix, including glycocalyx components like hyaluronan, forms a protective layer that modulates mechanical forces experienced by cells. In this vignette, degrading pericellular hyaluronan increases mechanosensor activation under identical shear conditions. Choice A is correct because the pericellular matrix acts as a mechanical buffer that dampens forces reaching the cell membrane; its depletion allows greater force transmission to membrane mechanosensors, triggering inflammatory signaling. Choice B is incorrect as it incorrectly links pericellular matrix to tight junction formation rather than mechanical buffering. Understanding mechanosensing requires recognizing that ECM components can modulate force transmission before it reaches cellular sensors.
- Fibroblasts were seeded onto 2D hydrogels coated with identical amounts of fibronectin but differing in stiffness (soft: 1 kPa; stiff: 20 kPa). After 6 hours, cells on stiff gels showed larger spread area and increased nuclear localization of a mechanosensitive transcription coactivator compared to cells on soft gels. Integrin-blocking antibodies eliminated both effects without changing fibronectin coating density. Which statement best describes how the extracellular matrix influences cellular behavior in this experiment?
Answer: ECM stiffness alters integrin-mediated adhesion forces that are transduced into cytoskeletal tension and nuclear signaling
This question tests understanding of cell–cell junctions and ECM in cellular organization (Foundational Concept 2). Cell–cell junctions like tight junctions regulate permeability, while ECM provides structural support and signaling cues. In this vignette, the ECM's role in mechanosensing via stiffness influences fibroblast spreading and signaling. Choice D is correct because it accurately describes how ECM stiffness modulates integrin-mediated forces and nuclear signaling, consistent with the observed effects blocked by antibodies. Choice B is incorrect as it confuses stiffness with ligand diffusion, a common misconception in adhesion-independent signaling. Ensure understanding of specific junction functions and ECM roles in cellular processes; apply this to predict effects of their disruption in mechanotransduction pathways.
- To assess epithelial polarity, investigators misexpressed an apical tight junction protein along the entire lateral membrane. Cells retained E-cadherin contacts but showed mislocalized apical transporters and reduced vectorial transport across the monolayer. Which conclusion is most consistent with these observations?
Answer: Tight junction positioning helps define apical–basolateral membrane domains required for directional transport
This question tests understanding of cell–cell junctions and ECM in cellular organization (Foundational Concept 2). Cell–cell junctions like tight junctions regulate permeability, while ECM provides structural support and signaling cues. In this vignette, the role of tight junction positioning in establishing epithelial polarity is examined. Choice C is correct because it accurately describes how tight junctions define apical–basolateral domains for directional transport, as misexpression leads to mislocalized transporters. Choice B is incorrect as it underestimates tight junctions' role, a common misconception since adherens provide cues but tight junctions fence domains. Ensure understanding of specific junction functions and ECM roles in cellular processes; apply this to predict effects of their disruption, such as transport defects in kidney tubules.
- Endothelial cells were engineered to express a dominant-negative form of VE-cadherin that reaches the plasma membrane but cannot bind catenins. In a shear-flow chamber, these cells maintain contact with neighbors but show increased formation of intercellular gaps and elevated permeability to albumin compared with wild-type. Which conclusion is most consistent with the role of this junctional complex in the observed behavior?
Answer: VE-cadherin–catenin coupling stabilizes actin-linked adherens junctions that resist gap formation under shear.
This question tests understanding of cell-cell junctions and ECM in cellular organization (Foundational Concept 2). Adherens junctions in endothelial cells use VE-cadherin linked to the actin cytoskeleton via catenins to maintain barrier function and resist mechanical forces. In this vignette, dominant-negative VE-cadherin disrupts the cadherin-catenin-actin linkage while maintaining membrane localization. Choice D is correct because VE-cadherin-catenin coupling is essential for stabilizing adherens junctions that resist shear-induced gap formation; without this linkage, junctions cannot withstand mechanical stress, leading to increased permeability. Choice B is incorrect as cadherins form adhesive junctions, not pores for transport. This demonstrates that functional adherens junctions require both cadherin trans-binding and cytoskeletal anchoring for barrier integrity.
- Endothelial monolayers were exposed to an inflammatory cytokine that caused VE-cadherin to internalize from cell–cell borders. In parallel, permeability to albumin increased, but claudin-5 expression was unchanged. A small-molecule that stabilizes cortical actin at adherens junctions partially restored barrier function. Based on the vignette, which conclusion is most consistent with the observed permeability change?
Answer: Barrier disruption is best explained by weakened adherens junction–cytoskeleton coupling that increases intercellular gaps
This question tests understanding of cell–cell junctions and ECM in cellular organization (Foundational Concept 2). Cell–cell junctions like tight junctions regulate permeability, while ECM provides structural support and signaling cues. In this vignette, cytokine-induced VE-cadherin internalization disrupts endothelial barrier via adherens junctions. Choice B is correct because it accurately describes weakened junction-cytoskeleton coupling leading to gaps, consistent with restored function by actin stabilization. Choice A is incorrect as it confuses adherens junctions with gap junctions, a common misconception in permeability regulation. Ensure understanding of specific junction functions and ECM roles in cellular processes; apply this to predict effects of their disruption in inflammatory conditions.
- In a blood–brain barrier model, astrocyte-conditioned medium increased claudin-5 localization at endothelial tight junctions and increased TEER. Adding a claudin-5 blocking antibody returned TEER to baseline without changing VE-cadherin staining. What effect would be expected if claudin-5 function is inhibited in this model?
Answer: Increased paracellular permeability due to reduced tight junction sealing, even if adherens junctions remain present
This question tests understanding of cell–cell junctions and ECM in cellular organization (Foundational Concept 2). Cell–cell junctions like tight junctions regulate permeability, while ECM provides structural support and signaling cues. In this vignette, the role of claudin-5 in blood–brain barrier integrity is examined. Choice A is correct because it accurately describes how inhibiting claudin-5 increases permeability by reducing tight junction sealing, as TEER decreases without affecting VE-cadherin. Choice C is incorrect as it confuses claudin with integrins, a common misconception since claudins seal, not adhere to ECM. Ensure understanding of specific junction functions and ECM roles in cellular processes; apply this to predict effects of their disruption, such as in neurological disorders.
- A lab compared two epithelial lines: Line 1 expresses normal integrin α6β4, while Line 2 lacks α6β4 but expresses other integrins. Both form cell–cell junctions, but Line 2 detaches more readily from laminin-coated substrates under shear stress. What effect would be expected if α6β4 is absent?
Answer: Reduced stable attachment to basement membrane due to impaired hemidesmosome-mediated anchoring
This question tests understanding of cell–cell junctions and ECM in cellular organization (Foundational Concept 2). Cell–cell junctions like tight junctions regulate permeability, while ECM provides structural support and signaling cues. In this vignette, the role of α6β4 integrin in epithelial attachment to laminin is examined. Choice A is correct because it accurately describes how absence of α6β4 reduces stable attachment via hemidesmosomes, leading to detachment under shear. Choice D is incorrect as it confuses integrins with cadherins, a common misconception since α6β4 anchors to ECM, not cell–cell. Ensure understanding of specific junction functions and ECM roles in cellular processes; apply this to predict effects of their disruption, such as in junctional epidermolysis bullosa.
- In a mouse model with a mutation that reduces type IV collagen assembly in basement membranes, renal glomeruli developed increased protein in the urine and ultrastructural thinning of the filtration barrier. Podocyte foot processes remained present but appeared less firmly attached to the underlying matrix. What effect would be expected if basement membrane integrity is compromised in this way?
Answer: Increased leakage across the filtration interface due to weakened ECM scaffold supporting selective permeability
This question tests understanding of cell–cell junctions and ECM in cellular organization (Foundational Concept 2). Cell–cell junctions like tight junctions regulate permeability, while ECM provides structural support and signaling cues. In this vignette, the role of type IV collagen in maintaining glomerular filtration barrier integrity is examined. Choice D is correct because it accurately describes how compromised basement membrane leads to increased leakage due to weakened ECM scaffold, as evidenced by proteinuria and thinning. Choice C is incorrect as it confuses collagen with connexins, a common misconception since ECM provides structure, not channels. Ensure understanding of specific junction functions and ECM roles in cellular processes; apply this to predict effects of their disruption, such as in Alport syndrome.
- A carcinoma cell line is treated with an antibody that blocks $β$1-integrin binding to collagen I. In a 3D collagen matrix, treated cells show reduced migration and decreased phosphorylation of focal adhesion kinase (FAK), while E-cadherin levels at cell–cell contacts remain low and unchanged. Based on the vignette, which conclusion is best supported regarding the relevant cellular interaction?
Answer: Collagen-dependent migration in this setting is driven mainly by integrin-mediated cell–ECM adhesion that activates FAK signaling.
This question tests understanding of cell-cell junctions and ECM in cellular organization (Foundational Concept 2). Integrins mediate cell-ECM adhesion and activate intracellular signaling pathways like FAK that promote cell migration, particularly in 3D matrices. In this vignette, blocking β1-integrin reduces both migration and FAK phosphorylation in collagen matrices. Choice D is correct because β1-integrin is the primary collagen receptor that, upon binding, clusters to form focal adhesions and activates FAK signaling, which is essential for cell migration through ECM. Choice B is incorrect as it incorrectly attributes migration to tight junctions, which regulate barrier function, not ECM-based movement. This demonstrates that tumor cell migration through ECM requires integrin-mediated adhesion and downstream signaling activation.
- A patient-derived epithelial tumor line was found to have reduced expression of a basement membrane component, laminin-332, and forms invasive protrusions when cultured in 3D matrices. Reintroducing laminin-332 reduced invasion without changing proliferation rate. Which conclusion is most consistent with a role for the extracellular matrix in this pathological context?
Answer: Loss of laminin-332 likely weakens cell–matrix anchoring and alters integrin signaling, promoting invasive behavior
This question tests understanding of cell–cell junctions and ECM in cellular organization (Foundational Concept 2). Cell–cell junctions like tight junctions regulate permeability, while ECM provides structural support and signaling cues. In this vignette, loss of laminin-332 in the ECM promotes tumor cell invasion in 3D culture. Choice A is correct because it accurately describes how reduced ECM anchoring alters integrin signaling to enhance invasion, consistent with reversal upon reintroduction. Choice B is incorrect as it confuses ECM loss with gap junction effects, a common misconception in invasion mechanisms. Ensure understanding of specific junction functions and ECM roles in cellular processes; apply this to predict effects of their disruption in pathological contexts like cancer.
- Epithelial cells were treated with a calcium chelator that rapidly disrupts cadherin-dependent adhesion. Within minutes, lateral membranes separated and β-catenin redistributed from the membrane to the cytosol, while claudin staining at apical junctions became discontinuous. Based on the vignette, which conclusion is most consistent with the observed junction changes?
Answer: Disrupting cadherin adhesion destabilizes adherens junctions and secondarily impairs tight junction organization
This question tests understanding of cell–cell junctions and ECM in cellular organization (Foundational Concept 2). Cell–cell junctions like tight junctions regulate permeability, while ECM provides structural support and signaling cues. In this vignette, the interdependence of adherens and tight junctions in epithelial cells is examined. Choice A is correct because it accurately describes how disrupting cadherin adhesion destabilizes adherens junctions and impairs tight junction organization, as evidenced by β-catenin redistribution and discontinuous claudin staining. Choice C is incorrect as it mistakenly suggests calcium chelation strengthens tight junctions, a common misconception since calcium is required for cadherin function. Ensure understanding of specific junction functions and ECM roles in cellular processes; apply this to predict effects of their disruption, such as barrier defects in inflammatory conditions.
- In an experiment on epithelial wound closure, cells at the wound edge increased expression of a matrix metalloproteinase (MMP) and migrated into the gap. When an MMP inhibitor was added, cells maintained cell–cell contacts but migration slowed markedly, with cells appearing unable to advance over the underlying substrate. Based on the vignette, which conclusion is most consistent with the role of the ECM?
Answer: ECM remodeling facilitates migration by allowing cells to reorganize adhesion sites and clear a path through matrix constraints
This question tests understanding of cell–cell junctions and ECM in cellular organization (Foundational Concept 2). Cell–cell junctions like tight junctions regulate permeability, while ECM provides structural support and signaling cues. In this vignette, the role of ECM remodeling in epithelial wound closure is examined. Choice A is correct because it accurately describes how ECM remodeling facilitates migration by reorganizing adhesions and clearing paths, as MMP inhibition slows migration despite maintained contacts. Choice C is incorrect as it confuses remodeling with tight junctions, a common misconception since MMPs degrade ECM, not form junctions. Ensure understanding of specific junction functions and ECM roles in cellular processes; apply this to predict effects of their disruption, such as delayed healing in chronic wounds.
