- 1 Tight Junctions
- 1.1 Introduction
- 1.2 History
- 1.3 Structure
- 1.4 Roles
- 1.5 Classification
- 1.6 Current associated research
- 1.7 Glossary
- 1.8 Further Information
- 1.9 Reference list
Before the arrival of electron microscopes,tight junctions were initially identified and thought as terminal bars between the
adjacent cells or junctional complexes bordering the apico-basolateral membrane in a variety of polarized simple epithelia and
playing an important role in barrier function.
After the arrival of electron microscopes and some other high resolution microscopes, tight junctions are found consisting of a
branching network of sealing strands of protein.Each strand is assembled from a series of transmembrane proteins(JAMs/Junctional
Adhesion Molecules,Claudins and Occludin) embedded in plasma membranes.The extracellular domains join each other in tight
junctions,whereas the intracellular domains are linked to peripheral membrane proteins,linking the transmembrane protein strands
to actin cytoskeleton to create a functional network that plays a role in cellular processes.Each strand functions as an
individual or linear barrie, therefore, the number of transmembrane protein strands is in relation with the degree of paracellular
electrical resistance and impedance to solute flux in tight junctions
Although other types of proteins are present at tight junctions, however, occludin and claudin are the major ones contributing to
the structure of tight junctions.
Associated molecular components of tight junctions,
Two groups of proteins:
- Transmembrane proteins
- Peripheral membrane proteins
Transmembrane proteins serve as important components of the tight junction that span across the junction, connecting two
adjacent cells and making a seal tight at the junction.The group has three members.
- Junctional Adhesion Molecules (JAMs)
- family of transmembrane proteins.
- the first tight junction associated transmembrane proteins and were identified in chicken liver.
- consists of four transmembrane domains,two extracellular loops and two intracellular domains.
- interacting directly with proteins zonula occludens,ZO-1 and ZO-2 and ZO-3 at the tight junction to localize occludins
- interacting indirectly with the actin cytoskeleton and junctional adhesion molecules(JAMs) via interacting with ZO proteins
- involving in cell-cell adhesion with extracellular domains of occludin
- vital in tight junction assembly in Xenopus embryo development
- regulating various signaling events initiating from the tight junction
- may involve in RhoA activation via a tight junction–associated guanine nucleotide exchange factor,GEF-H1/Lfc
- targeting TGF-ß receptors to tight junctions.
- family of transmembrane proteins that are also the main constituents of the tight junction intercellular strands
- claudin-1 and claudin-2 were the first claudin family members identified in a chicken liver fraction
- important for the barrier function of tight junctions.
- forming tight junction strands via interacting with each other between different tight junction strands or within individual strands in a homotypic and heterotypic manner 
- structural components are similar to occuldin.Four transmembrane domains, two extracellular loops, and two intracellular domains,however,it does not have sequence similarity to occludin 
- mediate calcium-independent cell-cell adhesion
- interacting directly with peripheral PDZ-domain-containing proteins(ZO-1, ZO-2, ZO-3,and protein associated with Lin seven 1
(PALS1)-associated tight junction protein (PATJ))
Junctional adhesion molecules (JAMs)
- immunoglobulin superfamily of proteins and are expressed in epithelial cells,leukocytes, endothelia, and platelets
- four members of the JAM protein family have been identified so far, JAM-A, JAM-B, JAM-C, and JAM4/JAML
- in epithelia, JAMs are directed to tight junctions, whereas,JAM-B exists along the lateral membrane
- have a single transmembrane domain, an extracellular domain containing two Ig-like motifs, and a cytoplasmic tail.
- may participate in cell adhesion via homophilic interactions
- interacting with each other. JAM-B interacts with JAM-C and integrins through heterophilic interactions
- forming intercellular junctions and epithelial barrier function.
Peripheral membrane proteins serve as intracellular binding sites for transmembrane proteins to allow transmembrane proteins to be organized in membrane and attached to the cytoskeleton to initiate cell signaling.The group has four members.
- Zonula occludens(ZOs)
- Membrane-associated guanylate kinase inverted(MAGI)
- tight junction proteins in the membrane-associated guanylate kinase (MAGUK) family of proteins
- contain a core structure consisting of one or more PDZ domains, an Src homology 3 (SH3) domain, and a guanylate kinase (GUK) domain
- three isoforms of ZO proteins: ZO-1, ZO-2, and ZO-3.
- serving as peripheral membrane scaffolding proteins
- interacting with many binding partners at the tight junction
- involving in the formation of tight junction.
Membrane-associated guanylate kinase inverted(MAGI)
- MAGUK family of proteins
- three features that distinguish them from all other members of the family:
(a) The GUK domain is located on the N terminus
(b) the SH3 domain is replaced by two WW domains and
(c) MAGI proteins contain five PDZ domains
- associating with ß-catenin in E-cadherin-based adherens junctions
- involving in the formation of adherens and tight junctions
- involving in the interaction involving junctional proteins during the polarization process
- playing role in actin-cytoskeleton dynamics within polarized epithelial cells
- involving in various signal transduction events
- a 140–160-kD protein localizes to the cytoplasmic surface of epithelial tight junctions
- was originally identified as a peripheral membrane protein at the tight junction in avian brush border cells
- has globular head and tail domains as well as a central a-helical rod domain.
- potential role in embryogenesis and epithelial maturation
- linking tight junction proteins to the actin cytoskeleton
- involving in transcriptional regulation and cell proliferation
- playing a role in cell-cycle progression.
ZO-1-associated nucleic acid–binding protein(ZONAB)
- was initially identified as a binding partner of ZO-1
- a Y-box transcription factor protein .
- interacting with cell division kinase 4 (CDK4) to regulate cell proliferation
- serving as a sensor of cell density.
- member of the small GTPase Rab family of proteins
- was first identified as a mammalian homolog of the yeast secretory protein, Sec4
- involving in the regulation of exocytic and endocytic pathways, including vesicle movement and fusion<pubmed>8294494</pubmed></ref>
- involving in early junctional formation .
Current associated research
- <pubmed>10772923 </pubmed>
Coordinator Comment to all Groups
I will add a general comment that will be the same to all groups under this heading.
Referencing Extension Problem
--Mark Hill 13:16, 3 May 2011 (EST) As mentioned in the lecture, I am aware of the referencing extension problem on your project pages. I have the following temporary solution, of removing the extension, so that groups can continue to add content to their project pages. I am also giving everyone a 1 week extension before the peer assessment.
This should only be done if your project page is not allowing you to save changes!
A. The Easy Way....
The following 4 steps can be done on the webpage or select all content in edit mode, copy and paste into a text editor. All steps must be completed before you attempt to save.
- In page edit mode, find all <pubmed> reference tags.
- Replace this tag with [http://www.ncbi.nlm.nih.gov/pubmed/ Note, there should be no spaces between the internet address and the pmid number.
- Now find all </pubmed> reference tags.
- Replace this second tag with ]
This will generate a numbered reference list that we can later fix up.
B. The Better Looking Result....
Whatever is between the <ref> </ref></pubmed> tags is what will appear in your reference list, so you can format the reference and link to appear in your reference list.
|2011 Projects: Synaptic Junctions | Gap Junctions | Tight Junctions | Desmosomes | Adherens Junctions | Neuromuscular Junction|