GO:0000082 G1/S transition of mitotic cell cycle: Commitment Point, Genes, Functions and Research Methods
Research-grade guide for scientists and biopharma professionals
Key Takeaways
• GO:0000082 describes the mitotic cell cycle transition by which a cell in G1 commits to S phase, beginning with buildup of G1 cyclin-dependent kinase (G1 CDK) and ending with positive feedback of G1 cyclins on G1 CDK.
• Cyclin E accumulation and CDK2 activation are central molecular events that license entry into S phase and DNA replication.
• The G1/S transition is deregulated in many cancers, including melanoma and endometrial carcinoma, where p53 and RB pathway proficiency stratifies molecular subtypes.
• Mitochondrial dynamics, specifically a hyperfused mitochondrial state at G1-S, regulates cyclin E buildup and S-phase entry.
• Low-molecular-weight cyclin E confers vulnerability to PKMYT1 inhibition in triple-negative breast cancer, linking G1/S regulators to targeted therapy.
• CRISPR knockout, point mutation, knock-in, and overexpression models enable causal dissection of G1/S transition genes in disease and development.
Description
The G1/S transition of the mitotic cell cycle (GO:0000082) is the decisive commitment step at which a cell integrates growth, stress, and developmental signals to irreversibly enter S phase and duplicate its genome. This transition begins with the buildup of G1 cyclin-dependent kinase (G1 CDK) activity, which activates transcription of G1 cyclins, and ends with positive feedback of G1 cyclins on G1 CDK, committing the cell to S phase. Because unscheduled or failed G1/S commitment underlies proliferative disease and developmental disorders, this process is a major focus of cancer biology, regenerative medicine, and cell cycle pharmacology. Mechanistically, the G1/S transition is orchestrated by cyclin D-CDK4/6 and cyclin E-CDK2 complexes, which phosphorylate RB and unleash E2F-dependent transcription of S-phase genes. Mitochondrial remodeling and proteolytic circuits add layers of regulation that ensure cyclin E accumulates only when cells are competent to replicate DNA. In specialized contexts such as spermatogenesis, destabilization of mRNAs enhances competence to initiate meiosis, illustrating how G1/S-like control interfaces with differentiation programs. For researchers, GO:0000082 provides a structured framework to interrogate how individual genes contribute to proliferation, checkpoint control, and disease. Functional profiling of p53 and RB cell cycle regulatory proficiency in endometrial carcinoma demonstrates that mechanism-driven molecular stratification can be built on G1/S transition components. Similarly, cell cycle regulation in melanoma highlights how G1/S regulators shape tumor behavior and therapeutic response.
G1/S transition of mitotic cell cycle At A Glance
| GO ID | GO:0000082 |
|---|---|
| GO term | G1/S transition of mitotic cell cycle |
| Ontology | biological_process |
| Synonym | None |
| Major function | Commitment of a G1 cell to S phase via G1 CDK buildup, G1 cyclin transcription, and positive feedback |
| Key regulators | Cyclin E, CDK2, RB, E2F, p53 |
| Disease relevance | Cancer (melanoma, endometrial carcinoma, triple-negative breast cancer) |
| Research methods | CRISPR KO/point mutation/knock-in/overexpression, RNA-seq, proteomics, imaging |
What Is GO:0000082?
GO:0000082, G1/S transition of mitotic cell cycle, is the biological process by which a cell in G1 phase commits to S phase. The process begins with the buildup of G1 cyclin-dependent kinase (G1 CDK), leading to activation of transcription of G1 cyclins, and ends with positive feedback of the G1 cyclins on the G1 CDK, committing the cell to S phase where DNA replication is initiated.
Why Is G1/S transition of mitotic cell cycle Important in Cell Biology?
The G1/S transition is the point of no return for cell division, and its dysregulation is a hallmark of cancer and other proliferative disorders. Understanding GO:0000082 enables researchers to identify causal drivers of proliferation, design targeted therapies against CDK and cyclin dependencies, and interpret how p53 and RB pathway status stratifies patient tumors.
• Defines the commitment point for DNA replication and cell division.
• Central to cancer biology, including melanoma and endometrial carcinoma.
• Cyclin E-CDK2 activity is a therapeutic vulnerability in triple-negative breast cancer.
• Mitochondrial dynamics at G1-S regulate cyclin E buildup and S-phase entry.
• Proteolytic circuits control mitotic target proteins and cell cycle progression.
• mRNA destabilization can enhance competence to initiate meiosis, linking G1/S control to differentiation.
• Provides biomarkers for molecular stratification based on p53 and RB proficiency.
• Enables CRISPR-based functional genomics of proliferation genes.
• Informs developmental toxicity studies, e.g., microplastic exposure and testis development.
• Supports drug discovery targeting CDKs, PKMYT1, and cell cycle checkpoints.
What Happens During G1/S transition of mitotic cell cycle?
G1 CDK Buildup and Cyclin D-CDK4/6 Activation
In simple terms: The cell starts assembling the molecular engine that will push it into DNA replication.
The G1/S transition begins with the buildup of G1 cyclin-dependent kinase (G1 CDK) activity, which is required for subsequent activation of G1 cyclin transcription. Cyclin D-CDK4/6 complexes initiate phosphorylation of RB, setting the stage for E2F release and S-phase gene expression. This early phase integrates growth factor signaling and checkpoint inputs to ensure commitment occurs only under favorable conditions.
Cyclin E Accumulation and CDK2 Activation
In simple terms: Cyclin E levels rise, switching on the kinase that drives the cell into S phase.
A hyperfused mitochondrial state achieved at G1-S regulates cyclin E buildup and entry into S phase. Cyclin E binds and activates CDK2, which further phosphorylates RB and reinforces E2F-dependent transcription. Low-molecular-weight cyclin E isoforms can alter this balance and confer sensitivity to PKMYT1 inhibition in triple-negative breast cancer.
RB Phosphorylation and E2F-Dependent Transcription
In simple terms: The RB brake is released, allowing genes needed for DNA replication to be turned on.
Functional profiling of p53 and RB cell cycle regulatory proficiency suggests mechanism-driven molecular stratification in endometrial carcinoma. RB phosphorylation by G1 CDKs releases E2F transcription factors, which activate genes required for DNA synthesis and S-phase progression. This step represents the molecular commitment to S phase described in GO:0000082.
Positive Feedback and Commitment to S Phase
In simple terms: Once cyclin E activates CDK2, the system locks in and the cell is committed to copy its DNA.
The process ends with positive feedback of the G1 cyclins on the G1 CDK, committing the cell to S phase in which DNA replication is initiated. Cell cycle-regulated proteolysis of mitotic target proteins contributes to the irreversibility of this transition by removing inhibitory factors. In specialized contexts, destabilization of mRNAs enhances competence to initiate meiosis, showing that G1/S-like commitment can be rewired during differentiation.
Key Genes Involved in GO:0000082 G1/S transition of mitotic cell cycle
The following genes and proteins are central to the G1/S transition of the mitotic cell cycle (GO:0000082) and are frequently studied using CRISPR-based models.
| Gene | Major Role | Research Relevance |
|---|---|---|
| CCNE1 | Cyclin E, activates CDK2 to drive G1/S transition | Target in triple-negative breast cancer and proliferation studies |
| CDK2 | G1 CDK that partners with cyclin E to phosphorylate RB | Kinase target for cell cycle inhibition |
| RB1 | Retinoblastoma protein, gatekeeper of G1/S transition | Molecular stratification in endometrial carcinoma |
| TP53 | Tumor suppressor coordinating checkpoint and G1/S arrest | Functional profiling of cell cycle proficiency |
| E2F1 | Transcription factor released by RB phosphorylation | Drives S-phase gene expression |
| CCND1 | Cyclin D, activates CDK4/6 in early G1 | Upstream regulator of RB phosphorylation |
| CDK4 | Partners with cyclin D to initiate RB phosphorylation | Target of CDK4/6 inhibitors |
| CDK6 | Partners with cyclin D to initiate RB phosphorylation | Target of CDK4/6 inhibitors |
| PKMYT1 | Kinase regulating CDK1 and cell cycle timing | Vulnerability in cyclin E-low-molecular-weight tumors |
| AMBRA1 | Phosphorylated by CDK1 and PLK1 to regulate mitotic spindle orientation | Links G1/S regulators to mitosis |
| PLK1 | Polo-like kinase regulating mitotic events | Co-regulates AMBRA1 phosphorylation |
| CDK1 | Mitotic CDK that also phosphorylates AMBRA1 | Connects G1/S and mitotic control |
| SKP1 | Component of SCF ubiquitin ligase for proteolysis | Cell cycle-regulated proteolysis of mitotic targets |
| CUL1 | Scaffold of SCF ubiquitin ligase | Controls degradation of cell cycle proteins |
| FBXW7 | F-box protein targeting cyclin E for degradation | Regulates cyclin E stability |
| DMC1 | Meiosis-specific recombinase | Competence to initiate meiosis via mRNA destabilization |
| STRA8 | Retinoic acid-induced meiosis initiator | Links G1/S-like control to spermatogenesis |
How Is G1/S transition of mitotic cell cycle Regulated?
The G1/S transition is regulated by phosphorylation cascades, ubiquitin-mediated proteolysis, and mitochondrial dynamics. CDK1 and PLK1 phosphorylate AMBRA1 to regulate mitotic spindle orientation, illustrating cross-talk between G1/S and mitotic regulators. Cell cycle-regulated proteolysis of mitotic target proteins by SCF complexes ensures timely degradation of inhibitory factors. A hyperfused mitochondrial state at G1-S regulates cyclin E buildup and entry into S phase, linking metabolism to cell cycle commitment. In spermatogenic cells, destabilization of mRNAs enhances competence to initiate meiosis, showing that RNA stability contributes to G1/S-like transitions.
G1/S transition of mitotic cell cycle and Human Disease
| Gene | Disease / Biology | Potential Experimental Model |
|---|---|---|
| CCNE1 | Triple-negative breast cancer | Knockout and overexpression in breast cancer cell lines |
| RB1 | Endometrial carcinoma | Point mutation and knockout in endometrial cells |
| TP53 | Endometrial carcinoma and melanoma | Knockout and knock-in in cancer models |
| PKMYT1 | Triple-negative breast cancer | Knockout and point mutation in breast cancer cells |
| AMBRA1 | Mitotic spindle orientation defects | Knock-in of phospho-mutants in cell lines |
Cancer and Cell Cycle Deregulation
Deregulation of the G1/S transition is a hallmark of cancer. Cell cycle regulation in melanoma highlights how G1/S regulators shape tumor behavior and therapeutic response. Functional profiling of p53 and RB cell cycle regulatory proficiency suggests mechanism-driven molecular stratification in endometrial carcinoma, where G1/S components inform prognosis and treatment. Low-molecular-weight cyclin E confers a vulnerability to PKMYT1 inhibition in triple-negative breast cancer, demonstrating that G1/S regulators can be targeted therapeutically.
Developmental and Reproductive Disorders
Prenatal and postnatal exposure to polystyrene microplastics induces testis developmental disorder and affects male fertility in mice, implicating cell cycle disruption in reproductive toxicity. Destabilization of mRNAs enhances competence to initiate meiosis in mouse spermatogenic cells, linking G1/S-like control to germ cell development.
Therapeutic Targeting of G1/S Kinases
CDK2, CDK4/6, and PKMYT1 are emerging targets for cancer therapy. Low-molecular-weight cyclin E confers vulnerability to PKMYT1 inhibition in triple-negative breast cancer. AMBRA1 phosphorylation by CDK1 and PLK1 regulates mitotic spindle orientation, suggesting that mitotic kinases can be targeted in combination with G1/S inhibitors.
From G1/S transition of mitotic cell cycle-Related Genes to Experimental Models
| Research Question | Suitable Model |
|---|---|
| Does loss of CCNE1 block G1/S transition? | CRISPR knockout in cancer cell lines |
| Does a specific CDK2 mutation alter substrate specificity? | Point mutation knock-in |
| Does tagging endogenous cyclin E affect its localization? | Tagged knock-in |
| Does overexpression of low-molecular-weight cyclin E confer PKMYT1 sensitivity? | Overexpression in triple-negative breast cancer cells |
| Does p53/RB proficiency stratify endometrial carcinoma? | Functional profiling with CRISPR screens |
| Does mRNA destabilization enhance meiosis initiation? | Knockout of RNA-binding proteins in spermatogenic cells |
How to Study the G1/S transition of mitotic cell cycle Process
| Method | What It Measures | Typical Application |
|---|---|---|
| RNA-seq | Transcript levels of G1/S genes | Molecular stratification in cancer |
| Proteomics | Protein abundance and modifications | Cyclin E and CDK2 quantification |
| Live-cell imaging | Cyclin E dynamics and mitochondrial state | G1/S commitment timing |
| CRISPR knockout screening | Gene essentiality for proliferation | Identify G1/S dependencies |
| Phospho-proteomics | Kinase substrate phosphorylation | AMBRA1 phosphorylation by CDK1/PLK1 |
| Ubiquitination assays | Proteolysis of cell cycle proteins | SCF-mediated degradation |
| Flow cytometry | DNA content and cell cycle phase | G1/S transition analysis |
| Reporter assays | E2F transcriptional activity | RB pathway proficiency |
Transcriptomic and Proteomic Profiling
RNA-seq and proteomics can quantify G1/S transition gene expression and protein abundance. Functional profiling of p53 and RB cell cycle regulatory proficiency in endometrial carcinoma used molecular stratification to identify subtypes. Cell cycle regulation in melanoma has been studied with expression profiling to link G1/S regulators to tumor behavior.
Imaging and Live-Cell Analysis
Live-cell imaging of cyclin E reporters and mitochondrial dynamics can visualize G1/S commitment. A hyperfused mitochondrial state achieved at G1-S regulates cyclin E buildup and entry into S phase, as shown by imaging. AMBRA1 phosphorylation by CDK1 and PLK1 regulates mitotic spindle orientation, which can be tracked by microscopy.
CRISPR Functional Genomics
CRISPR knockout and library screening enable systematic dissection of G1/S transition genes. Low-molecular-weight cyclin E confers a vulnerability to PKMYT1 inhibition in triple-negative breast cancer, identified through functional screens. Destabilization of mRNAs enhances competence to initiate meiosis in mouse spermatogenic cells, studied with CRISPR models.
Proteolysis and Stability Assays
Cell cycle-regulated proteolysis of mitotic target proteins can be measured by cycloheximide chase and ubiquitination assays. These methods reveal how SCF complexes control the stability of G1/S regulators.
How CRISPR Can Be Used to Study GO:0000082 G1/S transition of mitotic cell cycle
Knockout
CRISPR knockout of G1/S transition genes such as CCNE1, CDK2, or RB1 can determine their requirement for proliferation and S-phase entry. Knockout of p53 and RB pathway components enables functional profiling of cell cycle regulatory proficiency in endometrial carcinoma.
Point Mutation
Point mutation knock-in can model cancer-associated mutations in G1/S regulators, such as RB1 or TP53, to assess their impact on cell cycle commitment. Point mutations in CDK2 or cyclin E can reveal substrate specificity and drug sensitivity.
Knock-in
Tagged knock-in of cyclin E or CDK2 allows visualization of endogenous protein dynamics during G1/S transition. Knock-in of phospho-mutants in AMBRA1 can dissect CDK1/PLK1-dependent regulation of mitotic spindle orientation.
Overexpression
Overexpression of low-molecular-weight cyclin E in triple-negative breast cancer cells confers vulnerability to PKMYT1 inhibition. Overexpression models can also test whether G1/S regulators drive proliferation or transformation.
How EDITGENE Supports G1/S transition of mitotic cell cycle Research
Researchers studying G1/S transition of mitotic cell cycle-related genes often need to determine whether a candidate gene is causally involved in proliferation, checkpoint control, or disease. EDITGENE provides publication-ready CRISPR models and screening services to accelerate this discovery.
Contact EDITGENE today to design your custom CRISPR model for G1/S transition of mitotic cell cycle research.
Frequently Asked Questions About G1/S transition of mitotic cell cycle
What is GO:0000082 G1/S transition of mitotic cell cycle?
It is the biological process by which a cell in G1 commits to S phase, beginning with G1 CDK buildup and ending with positive feedback of G1 cyclins on G1 CDK.
What genes are involved in the G1/S transition of mitotic cell cycle?
Key genes include CCNE1, CDK2, RB1, TP53, E2F1, CCND1, CDK4, and CDK6.
Why is the G1/S transition important in cancer?
Deregulation of G1/S transition drives uncontrolled proliferation, and components such as cyclin E and CDK2 are therapeutic targets in melanoma, endometrial carcinoma, and breast cancer.
How is cyclin E regulated at G1/S?
Cyclin E buildup is regulated by mitochondrial dynamics and proteolysis, and low-molecular-weight cyclin E confers PKMYT1 inhibitor sensitivity.
What is the role of RB in the G1/S transition?
RB is phosphorylated by G1 CDKs, releasing E2F transcription factors that activate S-phase genes; RB proficiency stratifies endometrial carcinoma.
How can CRISPR be used to study G1/S transition genes?
CRISPR knockout, point mutation, knock-in, and overexpression models enable causal testing of G1/S gene function in proliferation and disease.
What methods study the G1/S transition?
RNA-seq, proteomics, live-cell imaging, flow cytometry, and CRISPR screens are commonly used.
What diseases are linked to G1/S transition defects?
Cancer, including melanoma and endometrial carcinoma, and reproductive disorders such as testis developmental disorder after microplastic exposure.
What is the role of mitochondria in G1/S transition?
A hyperfused mitochondrial state at G1-S regulates cyclin E buildup and entry into S phase.
How does proteolysis regulate the G1/S transition?
Cell cycle-regulated proteolysis of mitotic target proteins by SCF complexes controls the stability of G1/S regulators.
Conclusion
GO:0000082, G1/S transition of mitotic cell cycle, is a fundamental commitment step controlled by G1 CDKs, cyclins, RB, and E2F, with critical roles in cancer and development. Understanding its molecular players and regulatory layers enables targeted therapeutic strategies and mechanistic disease modeling. EDITGENE provides comprehensive CRISPR services, including knockout, point mutation, knock-in, overexpression, library screening, and bioinformatics, to support research on G1/S transition genes and their roles in health and disease.
References
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