Retta - L6 part 2

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Questions and Answers

What is the role of SARC kinase in relation to beta cadherin?

It activates integrins at the cell surface.

It enhances the stability of cell junctions.

It promotes the disassembly of junctions through phosphorylation. (correct)

It prevents the remodeling of the actin cytoskeleton.

Which small GTPase is primarily responsible for the formation of filopodia?

RHO

CDC42 (correct)

ARF

RAC

What impact do mutations in genes regulating actin dynamics have on immune cells?

They promote abnormal signaling but normal proliferation.

They enhance the motility of the cells.

They can lead to primary immunodeficiencies. (correct)

They have no effect on cell signaling.

How does integrin involvement with the extracellular matrix influence intracellular signaling?

It recruits motor proteins for enhanced adhesion. Signup and view all the answers

What structural component is primarily affected during endocytosis related to actin dynamics?

Actin cytoskeleton. Signup and view all the answers

What role do fimbrin and alpha-actinin play in regard to actin filaments?

They create parallel bundles that help in the formation of filopodia. Signup and view all the answers

What is a primary difference between stress fibers and the structures found in filopodia?

Stress fibers are contractile bundles, whereas filopodia are composed of parallel bundles. Signup and view all the answers

How does filamin contribute to cellular structure?

By crosslinking actin filaments at right angles to form gel-like networks. Signup and view all the answers

Which type of microscopy can be used to detect alpha-actinin molecules?

Molecular microscopy. Signup and view all the answers

What genetic mutation is specifically linked to malformation in neuronal migration?

Mutation in the filamin A gene. Signup and view all the answers

What cellular structure is primarily supportive and involves actin filaments?

Filopodia with parallel bundles. Signup and view all the answers

In terms of structure, what distinguishes a contractile bundle from a parallel bundle?

Parallel bundles are less dense and do not allow myosin-2 entry. Signup and view all the answers

What combination of techniques reveals the presence of crosslinked actin networks?

Fluorescent and electron microscopy. Signup and view all the answers

What primarily facilitates the connection between the extracellular matrix and the cytoskeleton within a cell?

Integrins Signup and view all the answers

Which of the following accurately describes the role of stress fibers?

They play a role in cell adhesion and contraction. Signup and view all the answers

How is the strength of focal adhesions increased?

By recruiting more adhesive proteins. Signup and view all the answers

What structural components are essential for the formation of contractile stress fibers?

Actin and myosin Signup and view all the answers

What does the term "nascent adhesion" refer to?

An initial, weak point of cell attachment. Signup and view all the answers

Which statements about integrins is correct?

They act as protein bridges connecting extracellular matrix and cytoskeletal elements. Signup and view all the answers

What is the role of the Arp2/3 complex in cell migration?

To promote the branching and elongation of actin filaments. Signup and view all the answers

What key function do focal adhesions serve in relation to immune cells?

They enable the migration of immune cells towards infection sites. Signup and view all the answers

Which statement best describes focal adhesions?

They are discrete points of strong adhesion between cells and the extracellular matrix. Signup and view all the answers

What is indicated by the presence of alpha-actinin in stress fibers?

Indicates parallel organization of actin filaments. Signup and view all the answers

What is the primary role of gelsolin in relation to cell motility and metastasis?

Promotes cell migration and motility when inactive. Signup and view all the answers

Which protein is essential for the attachment of actin filaments to the plasma membrane in microvilli?

Villin Signup and view all the answers

What mechanism allows cadherin-based adherens junctions to establish stable cell-cell adhesion?

Linking cadherins to the actin cytoskeleton via adaptor proteins. Signup and view all the answers

What triggers the transient disassembly of adhesion junctions in epithelial cells?

Signal-induced phosphorylation of adaptor proteins. Signup and view all the answers

What change must occur for new cell junctions to form after cells have separated?

Dephosphorylation of adaptor proteins. Signup and view all the answers

In the context of epithelial cells, what is the function of adhesion belts?

To mediate stable interactions between adjacent cells. Signup and view all the answers

How do signals affect the dynamics of focal adhesion structures?

They can either promote or inhibit the assembly of the structures. Signup and view all the answers

What type of proteins mediate cell-cell interactions within adhesion belts?

Cadherins Signup and view all the answers

What effect does the loss of gelsolin suppressive function have on a tumor's characteristics?

It enhances cell migration and may increase metastasis. Signup and view all the answers

Which of the following statements correctly describes the role of actin filaments in epithelial cells?

They provide structural support and assist in cell-cell adhesion. Signup and view all the answers

What drives the forward movement during the extension stage of cell crawling?

Polymerization of actin filaments Signup and view all the answers

How does the actin cytoskeleton contribute to the motility of a cancer cell compared to a normal cell?

Abnormal activation of gelsolin increases actin turnover. Signup and view all the answers

What role do integrins play during the cell migration process?

They help form new anchorage points in the lamellipod. Signup and view all the answers

What happens to the rear edge of the cell during migration after the cell body translocates?

It releases from adhesion sites and retracts. Signup and view all the answers

What is the primary function of the Arp2/3 complex in cell migration?

Promoting the branching of actin networks. Signup and view all the answers

How does the mutation of tumor suppressor proteins contribute to cancer cell migration?

By increasing gelsolin activity and actin turnover. Signup and view all the answers

Which structure is primarily responsible for the retraction of the cell's rear edge during migration?

Stress fibers Signup and view all the answers

What is the effect of strong adhesive points on a cell's migration speed?

It enhances speed by promoting more focal contacts. Signup and view all the answers

What is the lamellipod's primary characteristic in the context of a migrating cell?

It is a broad thin veil of cytoplasm at the front. Signup and view all the answers

Which protein is known to sever actin filaments and affect cell motility?

Gelsolin Signup and view all the answers

Study Notes

Comparison of Parallel Bundles and Contractile Bundles

Parallel bundles are formed by fimbrin, allowing filaments to be closer together, while alpha-actinin forms broader contractile bundles.
Contractile bundles enable the entry of myosin-2, promoting contractility, unlike parallel bundles found in filopodia, which are non-contractile.
Stress fibers are contractile structures, contrasting with the non-contractile nature of filopodia, which are supported by parallel bundles.

Role of Filamin in Cellular Structure

Filamin dimers crosslink actin filaments at right angles, contributing to gel-like networks that support the cell cortex and plasma membrane.
Mutations in the filamin A gene can cause periventricular heterotopia, a condition leading to neuronal migration malformations and associated seizures.

Stress Fibers and Focal Adhesions

Stress fibers are contractile structures attached to focal adhesions, which mediate cell attachment to the extracellular matrix through integrins.
Integrins are heterodimer proteins (alpha and beta subunits) that connect the cell's actin cytoskeleton to the extracellular matrix, allowing for stable adhesion.
Nascent adhesions are initial attachment points formed by a few adhesive proteins, which can grow stronger with additional protein recruitment.

Dynamics of Filopodia Growth

Arp2/3 complex promotes branching of actin filaments, pushing the plasma membrane and facilitating migration.
Focal adhesions can vary in size and strength based on the clustering of adhesive proteins at the plasma membrane.

Mechanisms of Cell Migration

Cell movement involves a sequence of stages: extension of the lamellipod, adhesion to the surface, translocation of the cell body, and retraction of the rear edge.
The actin cytoskeleton drives lamellipod extension, while contractile myosin structures facilitate the cell's retraction and movement.

Tumor Cell Migration and Metastasis

Abnormal activation of gelsolin can enhance motility and promote metastasis in cancer cells through increased actin turnover.
Tumor suppressor proteins play a critical role in regulating cell migration. Loss of function mutations can lead to unregulated cell movement and metastasis.

Microvilli and Absorptive Surface Area

Microvilli, supported by actin filaments, increase the absorptive surface area of epithelial cells, utilizing proteins like villin for stability.
Epithelial cells use adhesion belts, mediated by cadherins, for lateral cell-cell interactions, contributing to tissue integrity.

Regulation of Cell Adhesion

Dynamic cell adhesions, governed by receptor signaling (e.g., phosphorylation), allow for transient interactions necessary during cell division and migration.
Phosphorylation of adaptor proteins can regulate the assembly and disassembly of junctions, facilitating cell movement and tissue remodeling.

Importance of Research in Understanding Cell Dynamics

Discoveries regarding actin regulatory proteins and integrins have led to therapeutic insights for diseases, including cancer.
Understanding molecular mechanisms governing adhesion and motility can guide treatment strategies for conditions caused by mutations affecting these processes.### Endocytosis and Actin Cytoskeleton Remodeling
Remodeling of the actin cytoskeleton facilitates endocytosis, including phagocytosis.
Actin-induced invagination of the plasma membrane allows for the engulfment of substances like bacteria.
Specific regions in the plasma membrane undergo reorganization, promoting endocytosis through structural changes.

Role of Small GTPases in Cytoskeleton Dynamics

The Rho family of small GTPases, including RAC, CDC42, and RHO, plays significant roles in actin cytoskeleton organization.
Rho activation leads to the formation of stress fibers and focal adhesions, visible under microscopy.
RAC activation influences lamellipodia formation and actin networks at the cell's periphery, characterized by focal contacts.
CDC42 is critical for filopodia formation, inducing bundles of actin filaments and adhesion contacts.

Immuno-actinopathies and Human Diseases

Mutations in actin regulation genes cause immunodeficiencies known as immuno-actinopathies.
These mutations predominantly impact hematopoietic cells, leading to impaired immune cell functionality.
Alterations in the actin cytoskeleton affect motility, signaling, and overall cell proliferation.
Adhesion receptors like integrins and cadherins are involved in cell attachment and signal transduction.
Integrin engagement with the extracellular matrix activates signaling pathways, including those mediated by focal adhesion kinase (FAK).
The cytoskeleton's role in cell motility is essential for proper immune response functions.

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Description

Explore the distinctions between parallel bundles formed by fimbrin and contractile bundles formed by alpha-actinin. Understanding these differences is crucial for grasping how myosin-2 promotes contractility in muscle structures as opposed to non-contractile parallel arrangements.