38 terms

CSB331 - Term Test 1 - Short Answer

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Which cell-cell adhesion event occurs prior to the emergence of neural crest cells from the dorsal surface of the neural tube in chick embryos? Which switch then promotes their migration to their final destination?
cadherin N > cadherin 6b > cadherin 7b
What structural similarity was revealed by TEM between "young" desmosomes and wounds?
Both lack a dense central stratum. The absence of the dense central stratum promotes keratinocyte cell migration.
Provide a potential mechanistic explanation why anti-desmoglein-1 and -3 antibodies lead to desmosome instability.
The cross-linking of the desmoglein-1 and -3 by IgGs prevents desmosome renewal following turnover.
What was the first evidence a barrier function claudin-1 during mammalian development?
Claudin-1 null mice die of dehydration 24 hours after birth.
How do claudins 16 and 19 promote the resorption of Ca2+ ions from the ascending limb of the Loop of Henle in kidneys?
They enable Na+ paracellular influx from the renal interstitium to the urinary lumen, creating an electropositive gradient that promotes paracellular Ca2+ flux into the interstitium.
Why was a mutation in the γ1 chain of laminin used to study the role of laminin on embryoid development?
It is most represented in laminin isoforms.
Why does the treatment of mouse embryos with CPE lead to the loss of the blastocoel cavity?
The binding of CPE to claudins 4 and 6 results in a loss in barrier function (or tight junctions), which in turn results in insufficient fluid accumulation within the blastocoel cavity.
Why does the ARP2/3 complex bind preferentially near the barbed end of microfilaments?
The ARP2/3 complex has a preferential affinity for ATP-form of microfilaments.
How would siRNA against Laminin 10/11-impact trophoblast cell behavior? What in vitro data supports your answer?
It would inhibit trophoblast invasion of the endometrium. When trophoblasts were plated on a medium containing (LN10/11 they migrated; laminin1 they didn't migrate)
Why does the presence of whiskers on some members of the formin family accelerate actin nucleation?
The whiskers concentrate profilin G-actin near the site of nucleation.
How is force generated at the leading edge of a migrating cell?
By the elastic recoil force of the actin filament
How does non-muscle myosin II promote a pulling force during cell migration?
By re-orienting the actin filaments perpendicular to the direction of migration (or parallel to the leading edge) at the rear of the cell
When ovarian cancer cells were seeded on FITC-labeled collagen I, what activity was noted that is consistent with the invasive behavior these cells?
The aggressive cells were able to pull on the collagen I matrix
Certain cell attachments are strengthened in response to moderate amounts of mechanical stress. Give a specific example to briefly explain how the strengthening is accomplished.
In adherens junctions a-catenin is stretched to expose a cryptic vinculin binding site. Vinculin binds and provides additional bridges to the actin cytoskeleton.
What specific interaction within the EC-1 domain of classical cadherins is predicted to be de-stabilized when cadherins are in the Ca2+ bound form?
Tryptophan binding to the hydrophobic pocket of its own EC-1 domain.
p120 catenin expression is often downregulated in cancer cells. Would this stabilize or destabilize E-cadherin junctions?
Destabilize, because p120 protects E-cadherin from endocytosis.
Name two actin-binding proteins that have different preferences for ATP- vs. ADP- bound F-actin and whose activities contribute to ensuring actin polymerization at the leading edge (treadmilling)
cofilin & Arp2/3
What regulatory mechanism is used in the activation of both actin nucleators by Rho family GTPases?
Relief of autoinhibitory loop.
Name the two cell junctions whose failure results in skin/epidermal blistering diseases.
Desmosomes & hemidesmosomes
Intracellularly, what is the common denominator between desmosomes and hemidesmosomes that accounts for their important role in resisting mechanical strength?
Intermediate filaments
Which molecule provides a link between adherens junctions and Wnt signaling?
b-catenin
How does the fence function of tight junctions contribute to the formation of the blastocyst's blastocoel cavity?
Keeps Na+/K+ pump on basolateral side of cells
You mix two different types of cells together and observe that they form a single sphere, with cell type A sorting to the inside and cell type B sorting to the outside. What two pieces of information are you able to conclude about the cell-cell adhesion molecules they express?
They express a common classical cadherin & cell type A expresses higher levels of classical cadherins
You have two cell culture dishes with keratinocytes. The cells in plate A have been recently seeded in their dish. The cells in plate B have been growing there for many days. You need to release them to subculture them, so you add EDTA (a Ca2+ chelator). Cells in plate A are successfully released, but the cells in plate B remain attached. What is the hypothesis for the behaviour of cells in plate B? How could you verify this visually with equipment?
Desmosomal junctions of cells in plate B have become hyperadhesive. Use electron microscopy to check for dense central stratum in desmosomes of plate B cells.
What important role does laminin 1 (α1β1γ1) play in regulating trophoblast migration during embryonic implantation?
Inhibits migration of trophoblast cells into embryo.
Listeria monocytogenes bacteria hijack the cell's actin polymerization machinery for intracellular propulsion. What protein is mimicked in their coat? What nucleator becomes activated?
N-WASP & Arp2/3
Describe two ways that ROCK can affect tight junction permeability.
Phosphorylation of claudins and occludins. Activation of the myosin II motor by phosphorylation of myosin light chains.
How does IP3 indirectly activate PKC?
It binds to calcium channels on the ER, triggering the release of calcium ions which then bind to PKC.
How does an occludin deficiency affect the tight junction function of embryonic stem cells?
It does not.
When amphibian embryonic cells are allowed to re-associate in the presence of Ca2+, the cells reassemble into structures resembling their original positions in the embryo. Why?
Qualitative and quantitative differences in cadherin-dependent cell sorting.
How does ROCK promote the inactivation of Rac? When is RhoA inactivated at the leading edge of cells during their spreading on fibronectin?
By phosphorylating Rac GAPs. During the initial stages of adhesion to fibronectin.
In addition to the binding of αLβ2 to I-CAM, what other transmembrane receptor was found to promote leukocyte extravasation at the sites of infection? How was this demonstrated?
JAM-1. With the addition of anti-JAM1 antiserum to the tissue culture medium.
How is profilin bound to plasma membranes? Following the displacement of thymosin β4 from G-actin, what event does profilin promote before the addition of G-actin to the (+) end occurs?
Via PIP2. Conversion of ADP-G-actin to ATP-G-actin.
What effect would substituting α-actinin with fimbrin in actin stress fibers have on the interaction of actin with myosin II?
The myosin motor wouldn't have space to bind to the actin filaments.
What is a major difference between occludin-deficiency vs. a claudin-deficiency in epithelial cells?
The absence of occludin doesn't affect barrier function.
Why are neonates protected against pemphigus foliaceus?
Because desmoglein-3 is distributed throughout the neonate epidermis.
Which event during mammalian gastrulation involves the transmigration of cells? Where are the migrating cells derived from?
Mesoderm formation. Ectoderm.
How does absence of afadin affect the distribution of nectin-2 in the endoderm of embryoid bodies?
Nectin-2 is no longer restricted apically.