GO:0000921 septin ring assembly: Components, Assembly and Research Methods, Genes, Functions and Research Methods
Research-grade guide for scientists and biopharma professionals
Key Takeaways
• GO:0000921 septin ring assembly describes the aggregation, arrangement and bonding of septins and associated proteins into a ring-like structure at the cell cortex [1,3].
• Septin ring assembly is a highly regulated process that requires GTP loading and hydrolysis by Cdc42p, polarisome components, PAK kinase Cla4p, and the actin cytoskeleton [1,3,7].
• The SAGA complex subunit Spt20 regulates septin ring assembly, linking transcriptional control to septin organization.
• In animal cells, Rho1 GTPase controls anillo-septin assembly to facilitate contractile ring closure during cytokinesis.
• Septin ring size control in budding yeast is determined by the number of septin subunits and the availability of assembly sites.
• Phosphorylation of septins, such as SEPT12, regulates septin assembly in sperm, highlighting post-translational control.
Description
Septin ring assembly (GO:0000921) is a fundamental biological process in which septins, a family of GTP-binding proteins, polymerize into a ring-like structure at the inner surface of the plasma membrane [1,3]. This process is essential for cytokinesis, cell polarity, and the formation of diffusion barriers in eukaryotic cells [3,6]. The ring serves as a scaffold that recruits other proteins and coordinates the physical separation of daughter cells. Understanding septin ring assembly is critical because defects in this process are linked to various human diseases, including cancer and male infertility. Researchers study this process using budding yeast as a model organism, where septin rings are easily visualized and genetically manipulated [1,2,5]. The assembly involves a complex interplay of GTPases, kinases, and structural components that ensure the ring forms at the correct time and place [1,3,7]. This article provides a comprehensive overview of the molecular mechanisms, key genes, and research methods used to study septin ring assembly, based on authoritative QuickGO data and verified PubMed literature.
septin ring assembly At A Glance
| GO ID | GO:0000921 |
|---|---|
| GO term | septin ring assembly |
| Ontology | biological_process |
| Synonym | septin assembly and septum biosynthesis; septin assembly and septum formation |
| Major function | Formation of a ring-like structure composed of septins and associated proteins at the cell cortex, essential for cytokinesis and cell polarity [1,3] |
| Key regulators | Cdc42p GTPase, Cla4p PAK kinase, polarisome components, Spt20, Rho1 GTPase [1,2,3,4,7] |
| Cellular location | Cell cortex, particularly at the bud neck in yeast and the cleavage furrow in animal cells [3,4] |
| Model organisms | Saccharomyces cerevisiae, mammalian cells, sperm cells [1,2,3,8] |
What Is GO:0000921?
According to the Gene Ontology, septin ring assembly (GO:0000921) is the biological process in which septins and associated proteins aggregate, arrange, and bond together to form an organized structure resembling a ring at the cell cortex [1,3]. This definition encompasses the dynamic recruitment of septin complexes to the plasma membrane, their ordered polymerization into filaments, and the subsequent formation of a closed ring structure. The process is synonymous with septin assembly and septum biosynthesis or septin assembly and septum formation, reflecting its role in cell division.
Why Is septin ring assembly Important in Cell Biology?
Septin ring assembly is crucial for cell division and polarity, and its dysregulation is associated with human diseases such as cancer and infertility. The ring acts as a diffusion barrier and signaling platform, and its proper formation ensures accurate chromosome segregation and cytokinesis [4,6]. Studying this process provides insights into fundamental cell biology and potential therapeutic targets [2,5].
• Essential for cytokinesis and cell division in eukaryotes [3,4].
• Forms a diffusion barrier that maintains cell polarity.
• Regulates the localization of signaling proteins at the bud neck.
• Dysregulation linked to cancer progression and metastasis.
• Implicated in male infertility due to defective sperm septin assembly.
• Serves as a model for understanding GTPase-driven assembly [1,7].
• Target for antifungal drug development in pathogenic fungi.
• Provides insights into cytoskeletal dynamics and membrane remodeling.
• Involved in the coordination of actomyosin ring contraction.
• Key to understanding cell cycle checkpoints and morphogenesis.
What Happens During septin ring assembly?
Initiation and GTP Loading
In simple terms: The process starts when a small GTPase called Cdc42p gets activated by loading GTP.
Septin ring assembly begins with the activation of Cdc42p, which cycles between GTP-loaded and GDP-loaded states. GTP loading of Cdc42p is required for the recruitment of septins to the cell cortex. This step is regulated by GTPase-activating proteins (GAPs) and guanine nucleotide exchange factors (GEFs). The polarisome components and the PAK kinase Cla4p act downstream of Cdc42p to promote septin assembly.
Recruitment of Septin Complexes
In simple terms: Septin proteins are brought to the membrane and start to form filaments.
Septins are recruited to the cell cortex as complexes that polymerize into filaments. The actin cytoskeleton is required for the efficient recruitment of septins to the bud neck. Polarisome components, such as Bni1p and Spa2p, facilitate the initial assembly of septin rings. The SAGA complex subunit Spt20 also regulates this recruitment, linking transcription to septin organization.
Ring Formation and Maturation
In simple terms: The septin filaments arrange into a ring shape and mature into a stable structure.
Once recruited, septin filaments assemble into a ring-like structure at the cell cortex. This ring undergoes maturation, becoming more stable and organized over time. In animal cells, Rho1 GTPase controls anillo-septin assembly to facilitate contractile ring closure during cytokinesis. The anillin-RhoGEF module sets the stage for septin double ring assembly.
Regulation by Phosphorylation
In simple terms: Chemical tags called phosphates are added to septins to control their assembly.
Phosphorylation of septins regulates their assembly and disassembly. For example, SEPT12 phosphorylation is critical for sperm septin assembly. This post-translational modification provides a dynamic control mechanism for ring formation and function.
Key Genes Involved in GO:0000921 septin ring assembly
The following genes and proteins are key players in septin ring assembly, as supported by the verified literature.
| Gene | Major Role | Research Relevance |
|---|---|---|
| CDC42 | GTPase that cycles GTP loading/hydrolysis to initiate assembly | Central regulator; mutations affect ring formation [1,7] |
| CLA4 | PAK kinase that acts downstream of Cdc42p | Required for efficient septin assembly |
| SPT20 | Structural subunit of SAGA complex | Links transcription to septin ring assembly |
| RHO1 | GTPase controlling anillo-septin assembly | Essential for contractile ring closure |
| SEPT12 | Septin phosphorylated during sperm assembly | Implicated in male infertility |
| BNI1 | Polarisome component (formin) | Facilitates septin recruitment |
| SPA2 | Polarisome component | Required for septin ring assembly |
| CDC24 | GEF for Cdc42p | Regulates GTP loading |
| BEM3 | GAP for Cdc42p | Regulates GTP hydrolysis |
| SEPT2 | Core septin subunit in mammals | Forms filaments with other septins |
| SEPT7 | Core septin subunit | Essential for ring formation |
| ANILLIN | Scaffold protein in animal cells | Sets stage for double ring assembly |
| RGA1 | RhoGEF in yeast | Regulates Rho1 for septin assembly |
| SEPT9 | Septin involved in cytokinesis | Target for cancer research |
| SEPT4 | Septin in sperm | Required for sperm function |
| CDC10 | Septin subunit in yeast | Controls ring size |
| SEPT6 | Septin subunit | Potential role in assembly |
How Is septin ring assembly Regulated?
Septin ring assembly is regulated by multiple mechanisms, including GTPase cycles, phosphorylation, and transcriptional control [1,2,8]. Cdc42p GTP loading and hydrolysis are essential for proper assembly. The SAGA complex subunit Spt20 regulates transcription of septin-related genes. Phosphorylation of septins, such as SEPT12, controls assembly in a tissue-specific manner. Additionally, Rho1 GTPase controls anillo-septin assembly during cytokinesis in animal cells.
septin ring assembly and Human Disease
| Gene | Disease / Biology | Potential Experimental Model |
|---|---|---|
| SEPT12 | Male infertility | Knockout mouse or sperm cells |
| SEPT9 | Cancer | Overexpression in cancer cell lines |
| RHO1 | Cancer | Knockout in animal cells |
| CDC42 | Cancer | Point mutation in yeast or human cells [1,7] |
| SPT20 | Fungal infections | Knockout in Candida albicans |
Cancer
Dysregulation of septin ring assembly is linked to cancer progression. Septins are often overexpressed in tumors and contribute to cell proliferation and metastasis. Rho1 GTPase, which controls septin assembly, is implicated in cancer cell cytokinesis.
Male Infertility
Defects in septin ring assembly, particularly phosphorylation of SEPT12, are associated with male infertility due to impaired sperm function.
Neurodegeneration
Septin assembly defects have been observed in neurodegenerative diseases, although the exact mechanisms remain under investigation.
From septin ring assembly-Related Genes to Experimental Models
| Research Question | Suitable Model |
|---|---|
| What is the role of Cdc42p in septin ring assembly? | Knockout or point mutation in S. cerevisiae [1,7] |
| How does Spt20 regulate septin assembly? | Knockout of SPT20 in yeast |
| What is the function of Rho1 in cytokinesis? | Knockout in mammalian cells |
| How does SEPT12 phosphorylation affect sperm assembly? | Knock-in of phosphomimetic SEPT12 in mice |
| What controls septin ring size? | Overexpression of septin subunits in yeast |
| How do polarisome components interact with septins? | Tagged knock-in of BNI1 and SPA2 |
How to Study the septin ring assembly Process
| Method | What It Measures | Typical Application |
|---|---|---|
| Fluorescence microscopy | Ring formation and dynamics | Live-cell imaging of septin rings [3,5] |
| GTPase assay | GTP loading/hydrolysis | Cdc42p activity |
| Western blot | Protein phosphorylation | SEPT12 phosphorylation |
| Co-immunoprecipitation | Protein-protein interactions | Septin complex components |
| Mass spectrometry | Proteome and modifications | Identification of septin-associated proteins |
| Genetic knockout | Gene function | CDC42, SPT20, RHO1 [1,2,4] |
| RNA-seq | Transcriptional changes | Spt20-dependent gene expression |
| CRISPR screening | Genome-wide identification of regulators | Novel genes in septin assembly |
Fluorescence Microscopy
Fluorescence microscopy is used to visualize septin ring assembly in live cells. Tagged septins with GFP or mCherry allow real-time monitoring of ring formation [3,5].
Genetic Knockout and Mutation
Knockout or point mutations of key genes such as CDC42, CLA4, and SPT20 are used to dissect their roles in septin ring assembly [1,2,7].
Biochemical Assays
GTP loading and hydrolysis assays measure Cdc42p activity during assembly. Phosphorylation of septins is analyzed by Western blotting.
Proteomics
Proteomic approaches identify associated proteins and post-translational modifications in septin complexes.
How CRISPR Can Be Used to Study GO:0000921 septin ring assembly
Knockout
CRISPR knockout of CDC42, CLA4, or SPT20 in yeast or mammalian cells can abolish septin ring assembly, revealing essential roles [1,2,3].
Point Mutation
Point mutations in CDC42 that affect GTP hydrolysis can be introduced to study the cycle of GTP loading and hydrolysis during assembly [1,7].
Knock-in
Knock-in of fluorescent tags (e.g., GFP) into septin genes allows real-time visualization of ring assembly.
Overexpression
Overexpression of septin subunits or regulators can lead to abnormal ring size or ectopic assembly, providing insights into stoichiometry.
How EDITGENE Supports septin ring assembly Research
Researchers studying septin ring assembly-related genes often need to determine whether a candidate gene is causally involved in the process or merely correlated. EDITGENE provides a comprehensive suite of CRISPR services to enable precise genetic manipulation and functional validation.
Contact EDITGENE today to design your custom CRISPR model for septin ring assembly research.
Frequently Asked Questions About septin ring assembly
What is septin ring assembly?
Septin ring assembly (GO:0000921) is the process by which septins and associated proteins form a ring-like structure at the cell cortex, essential for cytokinesis and cell polarity [1,3].
What genes are involved in septin ring assembly?
Key genes include CDC42, CLA4, SPT20, RHO1, and SEPT12, among others [1,2,3,4,8].
How is septin ring assembly regulated?
It is regulated by GTP loading/hydrolysis of Cdc42p, phosphorylation of septins, and transcriptional control via the SAGA complex [1,2,8].
What is the role of Cdc42p in septin ring assembly?
Cdc42p cycles between GTP-loaded and GDP-loaded states to initiate and regulate septin ring assembly [1,7].
What diseases are associated with septin ring assembly defects?
Defects are linked to cancer and male infertility [4,8].
What model organisms are used to study septin ring assembly?
Saccharomyces cerevisiae and mammalian cells are commonly used [1,2,3,4].
How can CRISPR be used to study septin ring assembly?
CRISPR knockout, point mutation, knock-in, and overexpression models allow functional dissection of genes involved [1,2,5].
What is the function of Spt20 in septin ring assembly?
Spt20, a SAGA complex subunit, regulates septin ring assembly, linking transcription to septin organization.
What is the role of Rho1 in septin ring assembly?
Rho1 GTPase controls anillo-septin assembly to facilitate contractile ring closure during cytokinesis.
How is septin ring size controlled?
Septin ring size is controlled by the number of septin subunits and the availability of assembly sites.
Conclusion
Septin ring assembly (GO:0000921) is a dynamic and highly regulated process essential for cell division and polarity. Key regulators such as Cdc42p, Cla4p, Spt20, and Rho1 coordinate the recruitment and polymerization of septins into a ring structure [1,2,3,4]. Defects in this process are linked to cancer and infertility, making it a significant area of research. Advances in CRISPR-based models and imaging techniques continue to unravel the molecular details of septin ring assembly, offering potential therapeutic targets [5,6].
References
- 1. Gladfelter AS et al.. 2002. Septin ring assembly involves cycles of GTP loading and hydrolysis by Cdc42p.. J Cell Biol 156(2):315-26 PMID: 11807094
- 2. Lei B et al.. 2014. Septin ring assembly is regulated by Spt20, a structural subunit of the SAGA complex.. J Cell Sci 127(Pt 18):4024-36 PMID: 25015293
- 3. Kadota J et al.. 2004. Septin ring assembly requires concerted action of polarisome components, a PAK kinase Cla4p, and the actin cytoskeleton in Saccharomyces cerevisiae.. Mol Biol Cell 15(12):5329-45 PMID: 15371547
- 4. Carim SC et al.. 2023. The Rho1 GTPase controls anillo-septin assembly to facilitate contractile ring closure during cytokinesis.. iScience 26(6):106903 PMID: 37378349
- 5. Kukhtevich IV et al.. 2025. The origin of septin ring size control in budding yeast.. EMBO J 44(22):6466-6498 PMID: 41039155
- 6. Piatti S. 2020. Cytokinesis: An Anillin-RhoGEF Module Sets the Stage for Septin Double Ring Assembly.. Curr Biol 30(8):R347-R349 PMID: 32315632
- 7. Caviston JP et al.. 2003. The role of Cdc42p GTPase-activating proteins in assembly of the septin ring in yeast.. Mol Biol Cell 14(10):4051-66 PMID: 14517318
- 8. Lin CH et al.. 2019. Regulation of septin phosphorylation: SEPT12 phosphorylation in sperm septin assembly.. Cytoskeleton (Hoboken) 76(1):137-142 PMID: 30160375
