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Tight Junctions

Tight Junctions

Tight junctions are molecular seals between cells that prevent the leaking of fluids, ions, and other small solutes across cavities and compartments in multicellular organisms. They are mainly composed of claudin and occludin transmembrane proteins, and other proteins such as tricellulin and JAM (junctional adhesion molecule). All these proteins are 4-pass transmembrane proteins, except JAM, which is a single-pass transmembrane protein belonging to the immunoglobulin superfamily. The...

Adherens Junctions

Adherens Junctions

Strong contact points between adjacent cells anchor them to each other, forming tissues. Such anchoring junctions are of two types – adherens junctions and desmosomes. Adherens junctions are abundant in tissues such as epithelium and endothelium, forming a continuous zone of adhesion called the adhesion belt. In other tissues, such as heart muscle, they appear as clusters, linking the cells to produce coordinated heart muscle contraction.
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Cadherins in Tissue Organization

Cadherins in Tissue Organization

The cadherins are a superfamily of cell adhesion molecules comprising over 180 variants, with specific tissues expressing a particular combination of cadherin types. Cadherins generally exhibit homophilic binding; i.e., cadherins on one cell bind to cadherins of the same or closely related type on another cell. Thus, cells of the same type have a specific affinity to bind to each other and sort themselves into clusters to form tissues.
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Anchoring Junctions

Anchoring Junctions

Anchoring junctions are multiprotein complexes that help cells connect to other cells and the extracellular matrix. Anchoring junctions are present on the lateral and basal surfaces of cells, providing strong and flexible connections. Focal adhesions are often formed due to cell interactions with the ECM substrata, which initiate signal transduction via kinase cascades and other mechanisms. Together, they provide stability and tissue integrity. There are three types of anchoring junctions:...

Cell Polarization by Rho Proteins

Cell Polarization by Rho Proteins

Cell polarity is the asymmetric distribution of cellular and membrane components, making one side of the cell different from the other. This polarity is essential to many processes such as embryogenesis, axon migration, glucose transport across epithelial cells, and directional cell migration. A migrating cell responds to intracellular or extracellular signals via molecular cascades that reorganize the actin cytoskeleton to establish this polarity. In these cells, the Rho family proteins Cdc42,...

Intracellular Signaling Affects Focal Adhesions

Intracellular Signaling Affects Focal Adhesions

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Related Experiment Video

Updated: May 28, 2026

The C. elegans Intestine As a Model for Intercellular Lumen Morphogenesis and In Vivo Polarized Membrane Biogenesis at the Single-cell Level: Labeling by Antibody Staining, RNAi Loss-of-function Analysis and Imaging

The C. elegans Intestine As a Model for Intercellular Lumen Morphogenesis and In Vivo Polarized Membrane Biogenesis at the Single-cell Level: Labeling by Antibody Staining, RNAi Loss-of-function Analysis and Imaging

Published on: October 3, 2017

RalA and RalB differentially regulate development of epithelial tight junctions.

C Clayton Hazelett¹, David Sheff, Charles Yeaman

¹Department of Anatomy and Cell Biology, Carver College of Medicine, University of Iowa, Iowa City, IA 52242, USA.

Molecular Biology of the Cell

|October 21, 2011

Summary

Ral GTPases regulate tight junction (TJ) formation. RalA depletion disrupts TJs, while RalB depletion enhances them, both via the exocyst complex, impacting epithelial barrier function.

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Functional Assessment of Intestinal Tight Junction Barrier and Ion Permeability in Native Tissue by Ussing Chamber Technique

Functional Assessment of Intestinal Tight Junction Barrier and Ion Permeability in Native Tissue by Ussing Chamber Technique

Published on: May 26, 2021

Area of Science:

Cell Biology
Epithelial Biology
Molecular Cell Biology

Background:

Tight junctions (TJs) are crucial for epithelial cell function, controlling paracellular diffusion and maintaining cell polarity.
The precise mechanisms governing the establishment and regulation of specific TJ functions remain incompletely understood.

Purpose of the Study:

To investigate the roles of Ral GTPases and their effector, the exocyst complex, in the formation of nascent tight junctions.
To elucidate how Ral GTPases influence TJ development and epithelial barrier function.

Main Methods:

Utilized RNA interference (RNAi) to suppress the expression of RalA and RalB.
Assessed changes in paracellular permeability and the incorporation of TJ components.
Investigated the involvement of the exocyst complex in Ral GTPase-mediated TJ regulation.

Main Results:

Suppression of RalA led to increased paracellular permeability and reduced TJ component incorporation.
Suppression of RalB resulted in decreased paracellular permeability and enhanced TJ component incorporation.
Both RalA and RalB activities were found to be mediated through the exocyst complex.
TJ-mediated separation of apical-basal membrane domains precedes barrier function equilibration and is independent of Ral activity.

Conclusions:

Ral GTPases play opposing and critical roles in the formation and regulation of tight junctions.
The exocyst complex acts as a common effector for Ral GTPases in TJ development.
Epithelial barrier function and membrane domain separation are distinct processes regulated differently during TJ formation.