GO:1902896 terminal web assembly: Components, Assembly and Research Methods, Genes, Functions and Research Methods
Research-grade guide for scientists and biopharma professionals
Key Takeaways
• GO:1902896 terminal web assembly is the biological process of aggregating, arranging and bonding components to form a terminal web, a specialized apical cytoskeletal structure in polarized epithelial cells.
• The terminal web is a dense apical meshwork of intermediate filaments, actin and associated proteins that supports microvilli and maintains epithelial polarity.
• Plastin 1 (PLS1) binds keratin and is required for terminal web assembly in the intestinal epithelium, linking actin and intermediate filament systems.
• In Caenorhabditis elegans, LET-413 maintains the apical disposition of the intestinal terminal web, revealing conserved mechanisms of apical polarity.
• Intermediate filaments, particularly keratins, are core structural components of the terminal web and are essential for its assembly and function.
• Disruption of terminal web assembly is linked to epithelial barrier defects and diseases such as inflammatory bowel disease and cancer.
Description
The terminal web is a specialized cytoskeletal structure located at the apical pole of polarized epithelial cells, where it forms a dense meshwork that anchors microvilli and provides mechanical support. The process by which this structure is assembled is termed terminal web assembly, and it is annotated with the Gene Ontology term GO:1902896 (terminal web assembly). This process involves the aggregation, arrangement and bonding together of a set of components, including actin filaments, intermediate filaments and associated proteins, to form the terminal web. Understanding terminal web assembly is crucial for researchers studying epithelial cell polarity, barrier function and tissue morphogenesis, as defects in this process can lead to compromised epithelial integrity and disease. The assembly of the terminal web is a dynamic and regulated process that requires the coordinated action of multiple cytoskeletal elements and accessory proteins. In this article, we explore the molecular mechanisms, key genes and research methods used to study terminal web assembly, based on authoritative QuickGO data and published literature.
terminal web assembly At A Glance
| GO ID | GO:1902896 |
|---|---|
| GO term | terminal web assembly |
| Ontology | biological_process |
| Synonym | terminal web formation |
| Major function | Assembly of a specialized apical cytoskeletal structure in epithelial cells |
| Key components | Actin filaments, intermediate filaments (keratins), plastin 1, LET-413 |
| Related processes | Epithelial cell polarity, microvilli formation, cytoskeletal organization |
| Research relevance | Epithelial barrier function, inflammatory bowel disease, cancer |
What Is GO:1902896?
Terminal web assembly (GO:1902896) is the biological process in which a set of components aggregate, arrange and bond together to form a terminal web. The terminal web is a specialized apical cytoskeletal structure found in polarized epithelial cells, composed of a dense network of actin filaments, intermediate filaments and associated proteins. This process is essential for the formation and maintenance of the apical domain and for epithelial barrier function.
Why Is terminal web assembly Important in Cell Biology?
Terminal web assembly is fundamental to the architecture and function of polarized epithelial cells, which line the surfaces of organs such as the intestine, kidney and lung. The terminal web provides mechanical support to microvilli and serves as a scaffold for proteins that regulate apical transport and signaling. Defects in terminal web assembly can disrupt epithelial polarity and barrier function, contributing to diseases such as inflammatory bowel disease and cancer. Moreover, the terminal web is a model system for studying cytoskeletal cross-talk between actin and intermediate filaments, as it requires the coordinated assembly of both filament systems. Research on terminal web assembly also sheds light on conserved mechanisms of apical polarity across species, as studies in Caenorhabditis elegans have identified key regulators such as LET-413. Thus, understanding terminal web assembly has broad implications for cell biology, developmental biology and medicine.
• Maintains epithelial barrier function by anchoring microvilli and sealing the apical surface.
• Required for proper epithelial cell polarity and morphogenesis.
• Involved in intestinal homeostasis and nutrient absorption.
• Dysregulation is associated with inflammatory bowel disease and colorectal cancer.
• Provides a model for studying actin-intermediate filament cross-talk.
• Conserved mechanisms revealed by C. elegans studies.
• Potential target for therapies aimed at restoring epithelial integrity.
• Key to understanding apical transport and signaling.
• Relevant to tissue engineering and regenerative medicine.
• Implications for developmental defects and cancer progression.
What Happens During terminal web assembly?
Initiation and Nucleation
In simple terms: The cell starts building the terminal web by setting up initial anchor points.
Terminal web assembly begins with the nucleation of actin filaments and the recruitment of intermediate filaments to the apical domain. Plastin 1 (PLS1), an actin-bundling protein, binds to keratin and is required for this initial step in intestinal epithelial cells. The apical disposition of the terminal web is maintained by LET-413, a conserved protein that regulates apical polarity. This initiation phase establishes the framework for subsequent assembly steps.
Cross-linking and Bundling
In simple terms: Proteins tie the filaments together into a dense mesh.
Following nucleation, actin filaments are cross-linked into bundles by actin-bundling proteins such as plastin 1, while intermediate filaments are integrated into the network. The interaction between plastin 1 and keratin is critical for the formation of a cohesive terminal web. This cross-linking provides mechanical strength and stability to the apical cytoskeleton.
Anchoring to the Apical Membrane
In simple terms: The mesh is secured to the cell membrane at the top of the cell.
The terminal web is anchored to the apical plasma membrane through interactions with transmembrane proteins and adaptors. LET-413 in C. elegans is essential for maintaining the apical localization of the terminal web, likely by regulating vesicle trafficking and membrane domain identity. This anchoring ensures that the terminal web remains properly positioned to support microvilli and maintain polarity.
Maturation and Stabilization
In simple terms: The structure matures and becomes a stable part of the cell.
Once assembled, the terminal web undergoes maturation, which involves further cross-linking and stabilization by additional proteins. Intermediate filaments, particularly keratins, contribute to the long-term stability of the terminal web. The mature terminal web is a dynamic structure that can be remodeled in response to cellular signals, but its core architecture is maintained by the interactions established during assembly.
Key Genes Involved in GO:1902896 terminal web assembly
The following genes and proteins are key players in terminal web assembly, as identified in published literature.
| Gene | Major Role | Research Relevance |
|---|---|---|
| PLS1 | Actin-bundling protein that binds keratin; required for terminal web assembly in intestinal epithelium | Knockout studies in mice and cell lines; link to epithelial barrier defects |
| KRT8 | Type II keratin; structural component of intermediate filaments in the terminal web | Mutations linked to liver disease and colitis; model for intermediate filament assembly |
| KRT18 | Type I keratin; partners with KRT8 in intermediate filaments | Knockout mice show epithelial fragility; used to study filament cross-talk |
| LET-413 | Conserved protein maintaining apical disposition of terminal web in C. elegans | Genetic screens in C. elegans; regulator of apical polarity |
| ACTB | Beta-actin; major component of actin filaments in the terminal web | Essential for cell motility and structure; knockout is lethal |
| ACTG1 | Gamma-actin; component of actin filaments | Mutations cause deafness; role in cytoskeletal dynamics |
| VIL1 | Villin; actin-binding protein that bundles filaments in microvilli and terminal web | Knockout mice show microvillar defects; marker of epithelial differentiation |
| EZR | Ezrin; links actin filaments to the plasma membrane | Phosphorylation regulates activity; involved in apical transport |
| RDX | Radixin; similar to ezrin, links actin to membrane | Knockout mice show liver and intestinal defects |
| MSN | Moesin; actin-membrane linker | Role in immune cell polarity; potential model for apical anchoring |
| CDH1 | E-cadherin; adherens junction protein that indirectly influences terminal web assembly | Loss promotes epithelial-mesenchymal transition and cancer |
| CTNNB1 | Beta-catenin; links cadherins to actin cytoskeleton | Mutations in cancer; affects cell polarity |
| MYO5B | Myosin Vb; motor protein involved in apical transport | Mutations cause microvillus inclusion disease; affects terminal web |
| STX3 | Syntaxin 3; t-SNARE for apical vesicle fusion | Required for apical protein delivery; knockout models |
| RAB8A | Rab GTPase; regulates apical vesicle trafficking | Knockdown affects apical transport and terminal web |
| RAB11A | Rab GTPase; regulates recycling endosomes to apical membrane | Involved in microvilli formation; potential regulator |
| EPB41 | Protein 4.1R; links spectrin-actin network to membrane | Role in red blood cell membrane; may have analogous function in terminal web |
| SPTBN1 | Beta-spectrin; component of membrane skeleton | Mutations cause liver disease; interacts with actin |
How Is terminal web assembly Regulated?
Terminal web assembly is regulated by multiple signaling pathways and proteins. In C. elegans, LET-413 is a key regulator that maintains the apical disposition of the terminal web, likely through its role in vesicle trafficking and apical polarity. In intestinal epithelial cells, plastin 1 (PLS1) is required for terminal web assembly, and its expression is regulated during differentiation. The assembly process is also influenced by the availability of actin and intermediate filament subunits, which are controlled by transcriptional and post-translational mechanisms. Additionally, small GTPases such as RAB8A and RAB11A regulate the trafficking of membrane and cytoskeletal components to the apical domain, thereby impacting terminal web formation. Phosphorylation of ezrin/radixin/moesin proteins regulates their ability to link actin to the membrane, which is critical for anchoring the terminal web. Overall, terminal web assembly is a highly regulated process that integrates signals from cell polarity, vesicle trafficking and cytoskeletal dynamics.
terminal web assembly and Human Disease
| Gene | Disease / Biology | Potential Experimental Model |
|---|---|---|
| PLS1 | Inflammatory bowel disease, epithelial barrier defects | Intestinal epithelial cell-specific knockout mice; Caco-2 cell line |
| KRT8/KRT18 | Liver disease, colitis, cancer | Knockout mice; hepatocyte and intestinal organoids |
| MYO5B | Microvillus inclusion disease | Patient-derived organoids; Myo5b knockout mice |
| LET-413 | Apical polarity defects (C. elegans model) | C. elegans genetic mutants; RNAi knockdown |
| CDH1 | Cancer, epithelial-mesenchymal transition | Knockout cell lines; mouse models |
Inflammatory Bowel Disease and Epithelial Barrier Defects
Disruption of terminal web assembly can compromise the intestinal epithelial barrier, leading to increased permeability and inflammation. Plastin 1 (PLS1) mutations or deficiency result in defective terminal web formation in the intestine, which is associated with inflammatory bowel disease (IBD). The terminal web is essential for maintaining the integrity of the apical junctional complex and for sealing the paracellular space. Therefore, defects in its assembly can contribute to the pathogenesis of IBD.
Colorectal Cancer and Epithelial-Mesenchymal Transition
Loss of terminal web components is often observed in colorectal cancer, where epithelial cells undergo dedifferentiation and lose their apical polarity. The terminal web is a marker of differentiated epithelial cells, and its disassembly is associated with epithelial-mesenchymal transition (EMT) and tumor progression. For example, reduced expression of plastin 1 and keratins has been reported in invasive carcinomas. Thus, terminal web assembly is relevant to cancer biology.
Microvillus Inclusion Disease
Microvillus inclusion disease (MVID) is a congenital disorder characterized by severe diarrhea and loss of microvilli. Mutations in MYO5B, a motor protein involved in apical transport, cause MVID and are associated with abnormal terminal web structure. This highlights the importance of terminal web assembly in intestinal function and disease.
From terminal web assembly-Related Genes to Experimental Models
| Research Question | Suitable Model |
|---|---|
| What is the role of PLS1 in terminal web assembly? | PLS1 knockout in intestinal epithelial cells (Caco-2, HT-29) and mouse models |
| How does LET-413 regulate apical disposition of the terminal web? | C. elegans let-413 mutants and RNAi |
| What is the function of keratins in terminal web stability? | KRT8/KRT18 knockout mice and cell lines |
| How do RAB GTPases regulate apical transport for terminal web assembly? | RAB8A/RAB11A knockdown or overexpression in polarized epithelial cells |
| What is the impact of MYO5B mutations on terminal web structure? | Patient-derived organoids and Myo5b knockout mice |
| Can overexpression of PLS1 rescue terminal web defects? | PLS1 overexpression in PLS1-deficient cells |
How to Study the terminal web assembly Process
| Method | What It Measures | Typical Application |
|---|---|---|
| Fluorescence microscopy | Localization and dynamics of terminal web proteins | Visualizing assembly in fixed and live cells |
| Live-cell imaging | Real-time assembly and remodeling | Tracking GFP-tagged components |
| Transmission electron microscopy | Ultrastructure of terminal web and microvilli | High-resolution structural analysis |
| Immunoelectron microscopy | Protein localization at ultrastructural level | Mapping specific components |
| Proteomics | Protein composition and modifications | Identifying novel terminal web components |
| CRISPR knockout screens | Genes required for assembly | Functional genomics in epithelial cells |
| RNAi screens | Gene knockdown effects | C. elegans polarity studies |
| Biochemical fractionation | Isolation of terminal web fractions | Biochemical characterization |
Fluorescence Microscopy and Live Imaging
Fluorescence microscopy is a primary method to visualize terminal web assembly. Antibodies against actin, keratins, plastin 1 and other components can reveal the localization and dynamics of the terminal web in fixed or live cells. Live imaging using GFP-tagged proteins allows tracking of assembly in real time.
Electron Microscopy
Transmission electron microscopy (TEM) provides ultrastructural details of the terminal web, including the organization of actin and intermediate filaments and their relationship to microvilli. Immunoelectron microscopy can localize specific proteins within the terminal web.
Biochemical Fractionation and Proteomics
Biochemical fractionation can isolate terminal web-enriched fractions for proteomic analysis to identify novel components and post-translational modifications. Mass spectrometry-based proteomics can quantify changes in protein composition during assembly.
Genetic and CRISPR Screens
CRISPR knockout screens in polarized epithelial cells can identify genes required for terminal web assembly. Candidate genes can be validated by imaging and biochemical assays. RNAi screens in C. elegans have also been used to discover regulators of apical polarity.
How CRISPR Can Be Used to Study GO:1902896 terminal web assembly
Knockout
CRISPR knockout of genes such as PLS1, KRT8, KRT18 or LET-413 orthologs can abolish terminal web assembly, providing causal evidence for their requirement. Knockout cell lines and mouse models are valuable for studying the consequences of terminal web loss on epithelial polarity and barrier function.
Point Mutation
Introducing point mutations in genes like PLS1 or keratins can mimic human disease variants and reveal structure-function relationships. For example, mutations in the actin-binding domain of PLS1 can be tested for their ability to support terminal web assembly.
Knock-in
Knock-in of fluorescent tags (e.g., GFP) into endogenous loci allows real-time visualization of terminal web components without overexpression artifacts. Tagged knock-in of PLS1 or keratins can be used to track assembly dynamics in live cells.
Overexpression
Overexpression of terminal web components such as PLS1 or LET-413 can rescue assembly defects or induce ectopic terminal web formation. This approach helps to establish sufficiency and to study dose-dependent effects.
How EDITGENE Supports terminal web assembly Research
Researchers studying terminal web assembly-related genes often need to determine whether a candidate gene is causally involved in the assembly process or is merely correlated with it. CRISPR-based genome editing provides the gold standard for establishing causality by enabling precise knockout, point mutation, knock-in and overexpression models in relevant epithelial cell types.
Contact EDITGENE today to design your custom CRISPR model for terminal web assembly research.
Frequently Asked Questions About terminal web assembly
What is terminal web assembly?
Terminal web assembly (GO:1902896) is the biological process of aggregating, arranging and bonding components to form the terminal web, a specialized apical cytoskeletal structure in polarized epithelial cells.
What genes are involved in terminal web assembly?
Key genes include PLS1, KRT8, KRT18, LET-413, ACTB, VIL1, EZR and MYO5B, among others.
Where is the terminal web located?
The terminal web is located at the apical pole of polarized epithelial cells, just beneath the microvilli.
What is the function of the terminal web?
It provides mechanical support to microvilli, anchors the apical cytoskeleton and helps maintain epithelial polarity and barrier function.
How is terminal web assembly regulated?
It is regulated by proteins such as LET-413, plastin 1, and small GTPases like RAB8A and RAB11A, as well as by phosphorylation of ezrin/radixin/moesin.
What diseases are associated with defective terminal web assembly?
Defects are linked to inflammatory bowel disease, colorectal cancer and microvillus inclusion disease.
What methods are used to study terminal web assembly?
Fluorescence microscopy, electron microscopy, proteomics, CRISPR screens and biochemical fractionation are commonly used.
Can CRISPR be used to study terminal web assembly?
Yes, CRISPR knockout, point mutation, knock-in and overexpression models are powerful tools to dissect gene function in terminal web assembly.
What is the role of plastin 1 in terminal web assembly?
Plastin 1 binds to keratin and is required for terminal web assembly in the intestinal epithelium.
How does LET-413 affect the terminal web?
LET-413 maintains the apical disposition of the terminal web in C. elegans, likely by regulating apical polarity and vesicle trafficking.
Conclusion
Terminal web assembly (GO:1902896) is a critical biological process for the formation of a specialized apical cytoskeletal structure in polarized epithelial cells. It requires the coordinated assembly of actin filaments, intermediate filaments and associated proteins, and is regulated by key factors such as plastin 1 and LET-413. Defects in terminal web assembly contribute to epithelial barrier dysfunction and diseases including inflammatory bowel disease and cancer. Understanding the molecular mechanisms and genes involved is essential for developing therapeutic strategies. EDITGENE provides comprehensive CRISPR services to facilitate research on terminal web assembly and its related genes.
References
- 2. Grimm-Günter EM et al.. 2009. Plastin 1 binds to keratin and is required for terminal web assembly in the intestinal epithelium.. Mol Biol Cell 20(10):2549-62 PMID: 19321664
- 3. Bossinger O et al.. 2004. The apical disposition of the Caenorhabditis elegans intestinal terminal web is maintained by LET-413.. Dev Biol 268(2):448-56 PMID: 15063180
- 5. Carberry K et al.. 2009. Intermediate filaments in Caenorhabditis elegans.. Cell Motil Cytoskeleton 66(10):852-64 PMID: 19437512
- 7. Fath KR et al.. 1993. The cytoskeleton in development of epithelial cell polarity.. J Cell Sci Suppl 17:65-73 PMID: 7511618
