GO:0044732 mitotic spindle pole body: Components, Assembly and Research Methods
Research-grade guide for scientists and biopharma professionals
Key Takeaways
• GO:0044732 (mitotic spindle pole body) is the fungal microtubule-organizing center that assembles during the mitotic cell cycle and is functionally homologous to the animal centrosome.
• The spindle pole body is embedded in the nuclear envelope and nucleates both cytoplasmic and nuclear microtubules, making it the central organizer of mitotic spindle assembly in fungi.
• Its duplication is tightly coupled to the cell cycle, ensuring exactly one new spindle pole body per division cycle.
• The spindle pole body coordinates mitotic commitment and late mitotic events, linking cell cycle progression to spindle function.
• KASH-domain proteins such as Kms2 connect the spindle pole body to the nuclear envelope and coordinate its mitotic remodeling.
• Dysregulation of spindle pole body components has been linked to cancer biology, including prostate cancer crosstalk with tumor-associated macrophages.
Description
The mitotic spindle pole body (SPB) is the principal microtubule-organizing center (MTOC) of fungal cells, defined by the Gene Ontology term GO:0044732 as the microtubule organizing center that forms as part of the mitotic cell cycle and is functionally homologous to the animal cell centrosome. Unlike the centrosome, which is a cytoplasmic organelle, the SPB is embedded in the nuclear envelope, allowing it to nucleate both cytoplasmic microtubules that position the nucleus and nuclear microtubules that form the mitotic spindle. This dual-nucleation capacity makes the SPB essential for accurate chromosome segregation and for coupling spindle assembly to cell cycle progression. Because the SPB is the fungal counterpart of the centrosome, it has become a powerful model for understanding how MTOCs duplicate once per cell cycle, how they insert into the nuclear envelope, and how they coordinate mitotic commitment. Studies in fission yeast Schizosaccharomyces pombe and budding yeast Saccharomyces cerevisiae have revealed that SPB components are conserved in structure and function, and that their regulation is intimately tied to cyclin-dependent kinase (CDK) activity and nuclear envelope remodeling. For researchers, GO:0044732 provides a precise annotation for genes and proteins that localize to or function at the mitotic SPB. Understanding this term is critical for interpreting genome-wide screens, for designing CRISPR models of fungal MTOC biology, and for translating findings from yeast to human centrosome-related diseases such as cancer.
mitotic spindle pole body At A Glance
| GO ID | GO:0044732 |
|---|---|
| GO term | mitotic spindle pole body |
| Ontology | cellular_component |
| Synonym | none |
| Major function | Microtubule organizing center that nucleates cytoplasmic and nuclear microtubules during mitosis; functionally homologous to the animal centrosome |
| Organism context | Fungal cells, including Schizosaccharomyces pombe and Saccharomyces cerevisiae |
| Cell cycle timing | Forms and duplicates once per cell cycle; coordinates mitotic commitment and late mitotic events |
| Structural hallmark | Embedded in the nuclear envelope; contains a central plaque, inner and outer plaques, and a half-bridge |
| Related disease relevance | SPB component 25 (SPBC25) has been implicated in prostate cancer crosstalk with tumor-associated macrophages |
What Is GO:0044732?
GO:0044732 (mitotic spindle pole body) is a cellular component term describing the microtubule-organizing center that forms as part of the mitotic cell cycle. It is functionally homologous to the animal cell centrosome but is structurally distinct, being embedded in the nuclear envelope of fungal cells. The SPB nucleates both cytoplasmic and nuclear microtubules and serves as the primary site of spindle assembly during mitosis.
Why Is mitotic spindle pole body Important in Cell Biology?
The mitotic spindle pole body is essential for faithful chromosome segregation in fungi and serves as the evolutionary counterpart of the human centrosome, making it a key model for understanding MTOC biology and its links to disease. Because SPB duplication and function are tightly coordinated with the cell cycle, defects in SPB components can lead to spindle defects, aneuploidy, and cell cycle arrest. In addition, SPB proteins such as SPBC25 have been detected in human cancer contexts, suggesting that fungal MTOC studies may inform cancer biology.
• The SPB is the primary microtubule-organizing center in fungi and is required for mitotic spindle assembly and chromosome segregation.
• SPB duplication is coupled to the cell cycle, ensuring one SPB per division and preventing aneuploidy.
• The SPB coordinates mitotic commitment, linking cell cycle progression to spindle function.
• SPB components regulate late mitotic events, including spindle disassembly and cytokinesis.
• KASH-domain proteins such as Kms2 connect the SPB to the nuclear envelope and coordinate its mitotic remodeling.
• SPB assembly can occur without insertion into the nuclear envelope in certain meiotic contexts, revealing flexibility in MTOC function.
• SPB component 25 (SPBC25) has been linked to prostate cancer crosstalk with tumor-associated macrophages, highlighting disease relevance.
• The SPB is a model for studying centrosome duplication and function, with implications for human ciliopathies and cancer.
• CRISPR-based models of SPB genes enable functional dissection of MTOC assembly and cell cycle control.
• Understanding SPB biology supports antifungal drug discovery and synthetic biology applications.
Core Biology of the Mitotic Spindle Pole Body
What Happens During mitotic spindle pole body Assembly?
In simple terms: The spindle pole body is built once per cell cycle, starting as a small structure that grows and inserts into the nuclear envelope to become the main microtubule organizer for mitosis.
The mitotic spindle pole body (SPB) assembles as part of the mitotic cell cycle and is functionally homologous to the animal centrosome. Its duplication is tightly coupled to the cell cycle, ensuring that exactly one new SPB forms per division cycle. In fission yeast, the SPB plays a key role in controlling mitotic commitment, acting as a signaling hub that integrates cell cycle cues with spindle assembly. The SPB also regulates late mitotic events, including spindle disassembly and cytokinesis, through its interaction with the nuclear envelope and microtubule networks. In certain meiotic contexts, spindle assembly can occur without SPB insertion into the nuclear envelope, demonstrating that the SPB can function in alternative configurations.
Structure and Composition of mitotic spindle pole body
In simple terms: The spindle pole body is a layered structure embedded in the nuclear envelope, with distinct plaques and a bridge that anchor it and help it duplicate.
The fungal SPB is a multilayered structure composed of a central plaque, inner and outer plaques, and a half-bridge that connects it to the nuclear envelope. The central plaque is embedded in the nuclear envelope and serves as the site of microtubule nucleation, while the outer plaque faces the cytoplasm and the inner plaque faces the nucleoplasm. The half-bridge is essential for SPB duplication and is the site where the new SPB assembles. KASH-domain proteins such as Kms2 localize to the SPB and coordinate its mitotic remodeling by linking it to the nuclear envelope. The SPB contains a conserved set of proteins, including Spc42, Spc110, and Cmd1 (calmodulin), which form the core structural scaffold.
Molecular Mechanism of mitotic spindle pole body Function
In simple terms: The spindle pole body works by nucleating microtubules from its plaques, using conserved proteins to anchor and organize the microtubule arrays that separate chromosomes.
The SPB nucleates microtubules through the action of gamma-tubulin complexes that are recruited to its plaques. The central plaque contains Spc42, which forms a lattice that recruits Spc110 and calmodulin (Cmd1) to establish the microtubule-nucleating sites. The outer plaque nucleates cytoplasmic microtubules that position the nucleus and spindle, while the inner plaque nucleates nuclear microtubules that form the mitotic spindle. SPB duplication requires the half-bridge protein Spc72 and the kinase Mps1, which regulate the assembly of a new SPB once per cell cycle. The KASH protein Kms2 interacts with the SPB to coordinate its remodeling during mitosis, ensuring proper nuclear envelope insertion and spindle function.
Regulation of mitotic spindle pole body Duplication and Function
In simple terms: The spindle pole body is controlled by cell cycle signals that ensure it duplicates only once and is ready for mitosis at the right time.
SPB duplication is regulated by cyclin-dependent kinase (CDK) activity, which triggers the assembly of a new SPB in late G1 and prevents re-duplication until the next cycle. In fission yeast, the SPB controls mitotic commitment by integrating CDK signals with the activation of the Polo-like kinase Plo1. The KASH protein Kms2 coordinates mitotic remodeling of the SPB, linking it to nuclear envelope dynamics and ensuring proper spindle assembly. Late mitotic events, including spindle disassembly, are also regulated by SPB components that recruit signaling molecules to the SPB. These regulatory mechanisms ensure that the SPB functions as a faithful MTOC and that chromosome segregation is accurate.
Key Genes Involved in GO:0044732 mitotic spindle pole body
The following genes and proteins are core components or regulators of the mitotic spindle pole body (GO:0044732) in fungal models such as Saccharomyces cerevisiae and Schizosaccharomyces pombe.
| Gene | Major Role | Research Relevance |
|---|---|---|
| SPC42 | Central plaque component; forms lattice for SPB assembly | Key structural marker for SPB duplication studies |
| SPC110 | Inner plaque component; recruits gamma-tubulin complexes | Essential for nuclear microtubule nucleation |
| CMD1 | Calmodulin; regulates SPB assembly and function | Calcium signaling in SPB regulation |
| SPC72 | Outer plaque component; anchors cytoplasmic microtubules | Required for SPB insertion and spindle positioning |
| MPS1 | Kinase; regulates SPB duplication | Cell cycle checkpoint control of SPB duplication |
| KMS2 | KASH-domain protein; coordinates SPB remodeling | Links SPB to nuclear envelope during mitosis |
| SPBC25 | SPB component 25; implicated in cancer crosstalk | Potential link between SPB and prostate cancer |
| PLO1 | Polo-like kinase; regulates mitotic commitment at SPB | Key regulator of SPB function in fission yeast |
| CDC31 | Calcium-binding protein; required for SPB duplication | Essential for half-bridge function |
| KAR1 | Half-bridge component; required for SPB duplication | Involved in SPB assembly and nuclear envelope insertion |
| NDC1 | Nuclear envelope protein; interacts with SPB | Links SPB to nuclear pore complex |
| BFR1 | SPB component; involved in spindle assembly | Required for bipolar spindle formation |
| SPC29 | Central plaque component; regulates SPB duplication | Phosphorylation target in SPB regulation |
| SPC98 | Gamma-tubulin complex component; nucleates microtubules | Essential for microtubule nucleation at SPB |
| TUB4 | Gamma-tubulin; core nucleation factor | Required for all SPB microtubule nucleation |
| SPC97 | Gamma-tubulin complex component | Required for SPB microtubule nucleation |
| MPS3 | Nuclear envelope protein; SPB insertion | Essential for SPB insertion into nuclear envelope |
How Is mitotic spindle pole body Regulated?
The mitotic spindle pole body (SPB) is regulated primarily by cell cycle kinases, including cyclin-dependent kinase (CDK) and Polo-like kinase (Plo1), which control the timing of SPB duplication and its mitotic remodeling. In fission yeast, the SPB acts as a signaling platform that integrates CDK activity with mitotic commitment, ensuring that spindle assembly begins only after DNA replication is complete. The KASH-domain protein Kms2 coordinates mitotic remodeling of the SPB by linking it to the nuclear envelope, a process that is essential for proper spindle function. Additionally, SPB duplication is restricted to once per cell cycle by a licensing mechanism involving the half-bridge proteins Kar1 and Cdc31, which prevent re-duplication until the next cycle. These regulatory layers ensure that the SPB functions as a faithful MTOC and that chromosome segregation is accurate.
mitotic spindle pole body and Human Disease
| Gene | Disease / Biology | Potential Experimental Model |
|---|---|---|
| SPBC25 | Prostate cancer crosstalk with tumor-associated macrophages | Knockout in prostate cancer cell lines; co-culture with macrophages |
| SPC42 | Fungal cell division; potential antifungal target | Point mutation in S. cerevisiae to disrupt SPB assembly |
| MPS1 | Cell cycle checkpoint; cancer drug target | Knock-in of kinase-dead MPS1 in yeast; human cancer cell lines |
| KMS2 | Nuclear envelope remodeling; potential link to laminopathies | Knockout in S. pombe; nuclear envelope integrity assays |
| TUB4 | Microtubule nucleation; potential antifungal target | Overexpression and knockout in yeast; microtubule imaging |
Spindle Pole Body Components and Cancer
Although the spindle pole body is a fungal-specific organelle, its components share functional homology with human centrosomal proteins, and some SPB proteins have been detected in human cancer contexts. For example, spindle pole body component 25 (SPBC25) has been shown to mediate crosstalk between tumor-associated macrophages and prostate cancer cells, suggesting that SPB-related proteins may influence tumor microenvironment interactions. This finding highlights the potential for fungal MTOC studies to inform cancer biology, particularly in understanding how centrosome-like structures contribute to tumor progression.
Centrosome Dysfunction and Human Disease
The human centrosome, which is functionally homologous to the fungal SPB, is implicated in a range of diseases including cancer, ciliopathies, and neurodevelopmental disorders. Because the SPB and centrosome share conserved components and regulatory mechanisms, studies of SPB duplication and function can provide insights into how centrosome amplification or dysfunction leads to disease. For instance, defects in centrosome duplication can cause aneuploidy, a hallmark of many cancers, and mutations in centrosomal genes are associated with microcephaly and other developmental disorders.
Fungal Pathogenesis and Antifungal Targets
The SPB is essential for fungal cell division, making it a potential target for antifungal drug development. Because the SPB is structurally distinct from the human centrosome, inhibitors that specifically target SPB components could selectively block fungal growth without affecting human cells. Understanding the molecular details of SPB assembly and function is therefore critical for identifying new antifungal targets, especially for pathogenic fungi that are resistant to current treatments.
From mitotic spindle pole body-Related Genes to Experimental Models
| Research Question | Suitable Model |
|---|---|
| What is the role of SPC42 in SPB duplication? | Knockout of SPC42 in S. cerevisiae; live-cell imaging of SPB markers |
| How does MPS1 regulate SPB duplication? | Point mutation of MPS1 kinase domain; cell cycle synchronization |
| Does KMS2 coordinate SPB remodeling with nuclear envelope? | Knock-in of tagged KMS2; fluorescence microscopy in S. pombe |
| Can SPB assembly occur without nuclear envelope insertion? | Knockout of insertion factors in fission yeast meiosis; electron microscopy |
| What is the role of SPBC25 in cancer crosstalk? | Overexpression of SPBC25 in prostate cancer cells; macrophage co-culture |
| How does CDK regulate SPB duplication timing? | Point mutation of CDK phosphorylation sites on SPB components; time-lapse imaging |
How to Study the mitotic spindle pole body Process
| Method | What It Measures | Typical Application |
|---|---|---|
| Live-cell fluorescence microscopy | SPB duplication, insertion, and spindle assembly dynamics | Tracking SPB markers in synchronized yeast cells |
| Electron microscopy | Ultrastructure of SPB plaques and nuclear envelope insertion | High-resolution structural analysis of SPB |
| CRISPR knockout library screening | Identification of genes required for SPB function | Genome-wide screens in S. cerevisiae |
| Affinity purification mass spectrometry | Protein-protein interactions within the SPB | Mapping SPB interactome |
| Proximity-dependent biotinylation (BioID) | Spatial interactome of SPB components | Identifying nuclear envelope proteins near SPB |
| Time-lapse imaging with cell cycle reporters | Timing of SPB duplication relative to cell cycle | Studying mitotic commitment |
| Fluorescence recovery after photobleaching (FRAP) | Turnover of SPB components | Measuring SPB dynamics |
| Genetic interaction screens | Synthetic lethality with SPB mutations | Identifying parallel pathways |
Live-Cell Imaging of SPB Dynamics
Live-cell fluorescence microscopy using GFP- or mCherry-tagged SPB components (e.g., Spc42, Spc110) allows real-time visualization of SPB duplication, insertion, and spindle assembly in fungal cells. Time-lapse imaging combined with cell cycle reporters can reveal the precise timing of SPB duplication relative to budding or septation. This method is essential for understanding how SPB components coordinate mitotic commitment and late mitotic events.
Electron Microscopy for SPB Ultrastructure
Electron microscopy (EM) provides high-resolution structural details of the SPB, including its plaques, half-bridge, and insertion site in the nuclear envelope. EM has been used to show that SPB assembly can occur without insertion into the nuclear envelope in certain meiotic contexts, revealing structural plasticity. Correlative light and electron microscopy (CLEM) can link dynamic SPB behavior with ultrastructural changes.
Genetic Screens and CRISPR Libraries
Genome-wide genetic screens in yeast, including CRISPR-based knockout libraries, can identify novel regulators of SPB duplication and function. These screens typically use SPB markers or spindle assembly defects as readouts, and can be coupled with next-generation sequencing to identify enriched mutations. Such approaches have uncovered conserved components like Mps1 and Kar1 that are essential for SPB duplication.
Proteomics and Interaction Mapping
Affinity purification coupled with mass spectrometry (AP-MS) can identify protein-protein interactions within the SPB, revealing the composition of its plaques and regulatory complexes. Proximity-dependent biotinylation (BioID) has been used to map the SPB interactome in living cells, providing spatial and temporal resolution. These methods are critical for understanding how SPB components assemble and communicate with the nuclear envelope.
How CRISPR Can Be Used to Study GO:0044732 mitotic spindle pole body
Knockout
CRISPR-Cas9 knockout of SPB component genes such as SPC42, SPC110, or TUB4 in fungal models can reveal essential functions in SPB assembly and microtubule nucleation. Knockout strains typically exhibit severe growth defects, spindle abnormalities, or cell cycle arrest, making them valuable for functional studies. In human cells, knockout of centrosomal homologs can model centrosome loss and its consequences for cell division.
Point Mutation
CRISPR-mediated point mutations can be used to dissect specific domains or phosphorylation sites within SPB proteins. For example, mutating the kinase domain of MPS1 can separate its role in SPB duplication from other functions. Point mutations in KMS2 can disrupt its KASH-domain interaction with the nuclear envelope, revealing its role in SPB remodeling. Such precise edits are essential for understanding molecular mechanisms without confounding effects of complete gene loss.
Knock-in
Knock-in of fluorescent tags (e.g., GFP, mCherry) at endogenous SPB gene loci allows real-time visualization of SPB dynamics in living cells. Knock-in of epitope tags (e.g., HA, FLAG) facilitates biochemical purification and interaction studies. These models are critical for tracking SPB duplication and insertion during the cell cycle.
Overexpression
CRISPR activation (CRISPRa) or plasmid-based overexpression of SPB components can test sufficiency for SPB assembly or identify dominant-negative phenotypes. Overexpression of SPBC25 in prostate cancer cells has been used to study its role in tumor-macrophage crosstalk. Overexpression of gamma-tubulin complex components can lead to ectopic microtubule nucleation, providing insights into SPB regulation.
How EDITGENE Supports mitotic spindle pole body Research
Researchers studying mitotic spindle pole body-related genes often need to determine whether a candidate gene is causally involved in SPB assembly, duplication, or function. Establishing causality requires precise genetic models that can knock out, mutate, tag, or overexpress the gene of interest in a controlled manner. EDITGENE provides a comprehensive suite of CRISPR services to accelerate this discovery process.
Contact EDITGENE today to design your custom CRISPR model for mitotic spindle pole body research.
Frequently Asked Questions About mitotic spindle pole body
What is the mitotic spindle pole body (GO:0044732)?
The mitotic spindle pole body is the microtubule-organizing center of fungal cells that forms during the mitotic cell cycle and is functionally homologous to the animal centrosome.
What genes are involved in the mitotic spindle pole body?
Key genes include SPC42, SPC110, CMD1, SPC72, MPS1, KMS2, and TUB4, which encode structural and regulatory components of the SPB.
How is the spindle pole body different from the centrosome?
The SPB is embedded in the nuclear envelope and nucleates both nuclear and cytoplasmic microtubules, whereas the centrosome is a cytoplasmic organelle that primarily nucleates cytoplasmic microtubules.
What is the function of the spindle pole body in mitosis?
The SPB nucleates microtubules that form the mitotic spindle, anchors the spindle to the nuclear envelope, and coordinates mitotic commitment and late mitotic events.
How does the spindle pole body duplicate?
SPB duplication is coupled to the cell cycle and requires the half-bridge proteins Kar1 and Cdc31, as well as the kinase Mps1, to assemble a new SPB once per cycle.
What diseases are associated with spindle pole body components?
SPB component 25 (SPBC25) has been linked to prostate cancer crosstalk with tumor-associated macrophages, and centrosomal homologs are implicated in cancer and ciliopathies.
Can CRISPR be used to study spindle pole body genes?
Yes, CRISPR knockout, point mutation, knock-in, and overexpression models are powerful tools for dissecting SPB gene function in fungal and human cells.
What methods are used to study the spindle pole body?
Common methods include live-cell fluorescence microscopy, electron microscopy, CRISPR screens, and proteomics to visualize and characterize SPB structure and dynamics.
What is the role of Kms2 in the spindle pole body?
Kms2 is a KASH-domain protein that coordinates mitotic remodeling of the SPB by linking it to the nuclear envelope.
How does the spindle pole body control mitotic commitment?
In fission yeast, the SPB acts as a signaling hub that integrates CDK activity with Polo-like kinase Plo1 to trigger mitotic commitment.
Conclusion
The mitotic spindle pole body (GO:0044732) is a structurally and functionally distinct microtubule-organizing center that is essential for fungal mitosis and serves as a model for understanding the human centrosome. Its duplication is tightly regulated to ensure one SPB per cell cycle, and its components coordinate mitotic commitment, spindle assembly, and late mitotic events. Dysregulation of SPB components has been linked to cancer and other diseases, highlighting the importance of continued research. Advances in CRISPR-based gene editing, live-cell imaging, and proteomics are accelerating the dissection of SPB biology. EDITGENE provides a comprehensive suite of services, including knockout, point mutation, knock-in, overexpression, and library screening, to support researchers in uncovering the molecular mechanisms of the mitotic spindle pole body and translating these findings into therapeutic insights.
References
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- 3. Pineda-Santaella A et al.. 2019. Spindle assembly without spindle pole body insertion into the nuclear envelope in fission yeast meiosis.. Chromosoma 128(3):267-277 PMID: 31152193
- 4. Wälde S et al.. 2014. The KASH protein Kms2 coordinates mitotic remodeling of the spindle pole body.. J Cell Sci 127(Pt 16):3625-40 PMID: 24963130
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