Cell Adhesion: L19

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Questions and Answers

What role does Ca2+ play in cadherin function?

It activates GPI anchors.

It facilitates transmembrane transport.

It strengthens desmosome junctions.

It mediates cell-cell adhesion. (correct)

How can the role of Ca2+ in cell adhesion be demonstrated experimentally?

By exposing cells to high oxygen concentrations.

By increasing the temperature of the environment.

By using a GPI anchor.

By adding a chelating agent like EDTA. (correct)

Which of the following are types of classical cadherins?

N-cadherin and Desmocollin

Claudin and ZO-1

N-cadherin and P-cadherin (correct)

E-cadherin and R-cadherin

What is a major characteristic of cadherins in terms of their structure?

They tend to form homodimers. Signup and view all the answers

Which of the following statements about non-classical cadherins is true?

They form junctions without a transmembrane domain. Signup and view all the answers

Why are cadherins considered vital during embryogenesis?

They help cells stick together. Signup and view all the answers

What is the function of desmocollin?

To form desmosome junctions. Signup and view all the answers

What is a common misconception about cadherin binding strength?

Cadherin binding is based on a single strong link. Signup and view all the answers

What is the role of Fascicilin3 in synapse formation?

It allows synapse formation with muscle. Signup and view all the answers

Which components are involved in holding pre- and postsynaptic membranes together?

Cadherins, Ig superfamily members, neuroligins, and neurexins. Signup and view all the answers

What role do pectins play in cell adhesion?

They form a hydrated gel in the cell wall. Signup and view all the answers

What is a primary function of the plant cell wall?

To provide structural and mechanical support. Signup and view all the answers

Which of the following is a type of pectin domain?

Rhamnogalacturonan I. Signup and view all the answers

What challenges are posed by ectopic Fascicilin3 expression?

It can lead to abnormal synapses. Signup and view all the answers

What is a significant characteristic of the middle lamella in plant cells?

It is rich in pectin and facilitates cell adhesion. Signup and view all the answers

Why is the synthesis of cell wall components, particularly pectins, complex?

There is limited knowledge about the enzymes needed for pectin synthesis. Signup and view all the answers

What characterizes the inactive state of integrins?

α and β chains are close and adhere Signup and view all the answers

Which process describes the activation of integrins by intracellular regulatory molecules?

Inside-out activation Signup and view all the answers

What can result from defects in integrin subunits?

Genetic disorders Signup and view all the answers

What type of binding do selectins facilitate?

Heterophilic binding Signup and view all the answers

Which selectin is found on white blood cells?

L-selectin Signup and view all the answers

Which CAMs are known for homophilic binding?

NCAMs Signup and view all the answers

How are multiple forms of NCAM generated?

Alternative splicing Signup and view all the answers

What role do Cadherins play compared to NCAMs?

Stronger adhesion properties Signup and view all the answers

What is an important function of Fascicilin3?

Mediating recognition of target tissue Signup and view all the answers

What characterizes the binding of ICAMs and VCAMs?

Heterophilic binding Signup and view all the answers

What is the primary function of cadherins in cell adhesion?

Facilitate cell-cell attachments Signup and view all the answers

Which of the following describes the function of integrins?

Mediate cell-matrix attachments Signup and view all the answers

Which proteins are characteristic of tight junctions?

Immunoglobulin superfamily members and ZO proteins Signup and view all the answers

What is a common feature of junction complexes?

Intracellular link to the cytoskeleton Signup and view all the answers

In which organisms are cadherins not found?

All of the above Signup and view all the answers

Which type of junctions is associated with cadherins linking to actin?

Adherens junctions Signup and view all the answers

Which of the following provides extracellular links to outside structures in junction complexes?

Transmembrane adhesion proteins Signup and view all the answers

What advantage do choanoflagellates have in terms of cell arrangement?

Formation of colonies Signup and view all the answers

What is the consequence of Ca2+ binding to the flexible hinge regions of cadherins?

It prevents the hinge from flexing. Signup and view all the answers

Which type of cadherin is lost when the neural tube separates from the ectoderm?

E-cadherin. Signup and view all the answers

What is the function of β-catenin in the context of adherens junctions?

It acts as a transcriptional regulator in Wnt signalling. Signup and view all the answers

How do integrins contribute to dynamic cell adhesion?

Through allosteric regulation that switches between active and inactive states. Signup and view all the answers

In cadherins, what happens when the intracellular domain is absent?

Cell adhesion is weakened. Signup and view all the answers

What is the role of vascular endothelial cadherin (VE-cadherin)?

It is critical for endothelial cell survival. Signup and view all the answers

What happens to β-catenin in the absence of the Wnt signal?

It is degraded. Signup and view all the answers

What is likely to be the function of Flamingo due to its 7TM structure?

It acts as a G-protein coupled receptor (GPCR). Signup and view all the answers

Which protein typically links integrins to the actin cytoskeleton?

Talin. Signup and view all the answers

How does the binding of VEGF to its receptor affect endothelial cells?

It requires VE-cadherin as a cofactor. Signup and view all the answers

Study Notes

Cell Adhesion and Communication

Lecture 19 covered cell adhesion and communication, from the cellular to tissue level.
Essential proteins for cell adhesion include cadherins, integrins, selectins, and immunoglobulin superfamily members.
Different methods of cell adhesion exist in animal and plant cells.
Junction complexes have transmembrane proteins that link to the cytoskeleton and structures outside cells.
Cadherins mediate cell-to-cell attachments while integrins mediate cell-to-matrix attachments.
Cadherins can form adherens junctions, linking to actin, or desmosome junctions, linking to intermediate filaments.
Tight junctions involve claudins, JAMs, and occludin, which are transmembrane proteins forming strands.
ZO proteins are scaffolding proteins supporting tight junctions (TJs).
Cadherins rely on Calcium (Ca2+) for cell-cell adhesion, essential for development.
Cadherins types are named based on the cell type they were discovered in.
Several cadherin types exist in different tissues and are crucial during embryogenesis.
Cadherins have diverse structures, with multiple copies of the extracellular cadherin domain and intracellular regions varying.
About 180 different cadherin types are found in humans.
Non-classical cadherins include desmosomal cadherins (desmocollins), fat-like cadherins, seven-pass transmembrane cadherins (flamingo), and T-cadherins.
Defects in cadherin proteins can result in developmental abnormalities, such as death at specific stages, abnormal organ development, and skin blistering.
Cadherin function relies on relatively weak individual bonds, but many links create stronger bonds for cells.
Flexible hinge regions between cadherin repeats need Calcium for strength and flexibility.
Cadherins play crucial roles in tissue organization, enabling cells to assemble based on type and form tissues.
Cadherins control neural tube development by changing their expression.
Additional proteins, like catenins and p120-catenin, connect cadherins to the cytoskeleton's actin filament.
The absence of intracellular cadherin domains weakens adhesion strength.
β-catenin is important for Wnt/Wingless signaling and cell adhesion.
Wnt signaling affects β-catenin phosphorylation and degradation, affecting its activity.
Other cadherins serve signaling roles, like Vascular Endothelial Cadherin (VE-Cadherin) and its role in cell survival, and response to Vascular Endothelial Growth Factor (VEGF).

Integrins

Integrins are transmembrane proteins composed of two subunits.
Integrins have a large extracellular N-terminal domain, binding extracellular matrix proteins or cell surface ligands.
Integrins play a role in hemidesmosomes.
Integrins are dynamic, switching between active and inactive states.
Allosteric regulation allows switching between active and inactive integrin states, influencing conformation and ligand binding.
Ligands like RGD peptides influence integrin conformation.
Outside-in activation occurs when ligands interact with extracellular domains, resulting in cytoskeleton connection.
Inside-out activation involves intracellular signals activating the integrin to bind extracellular ligands.
Integrin defects can lead to genetic disorders, impacting processes like blood vessel development, immune function, and skin development.

Selectins

Selectins mediate transient cell-cell adhesion in the bloodstream.
Selectins are carbohydrate-binding proteins (lectins).
Selectins are involved in controlling the interactions of white blood cells with endothelial cells.
Different selectins (e.g., P-selectin, E-selectin) are present depending on the trigger or specific step for interacting with the cellular surfaces.
The selectins' involvement is vital for white blood cell movement between bloodstream and tissues.
Various types of selectins exist, such as L-selectin on white blood cells (WBCs), P-selectin on activated platelets/endothelial cells (activated by an inflammatory response), and E-selectin on activated endothelial cells.

ICAMs, VCAMs, and NCAMS

These are members of the immunoglobulin (Ig) superfamily, having an extracellular domain resembling antibody domains.
ICAMs, VCAMs, and NCAMs support cell adhesion.
NCAMs and immunoglobulin superfamily members are present in the same cell types as cadherins, and often work together.
Different strengths of adhesion are a result of different types of interactions.
NCAMs are highly variable and can have a high level of sialic acid chains with negative charges, potentially inhibiting cell adhesion.

Plant Cell Walls

Plant cell adhesion involves polysaccharides, cellulose, hemicellulose, and pectins within the plant cell walls.
The middle lamella, rich in pectin, plays a role in cell adhesion.
Breakdown products of pectin, like oligogalacturonides, may act as signaling molecules.
Plant cell wall polysaccharides synthesis defects can lead to loss of cell adhesion.

Synapse formation

Synapse formation is complex and involves multiple interacting components.
Cadherins, Ig superfamily members, and other proteins (like neuroligins, and neurexins) help assemble presynaptic and postsynaptic membranes into a synapse.

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Description

This quiz focuses on the key concepts of cell adhesion and communication, as covered in Lecture 19. It delves into essential proteins like cadherins and integrins, their roles in junction complexes, and the differences between cell adhesion mechanisms in various organisms. Test your understanding of these critical biological processes and their implications in tissue structure and function.