Stages Of Cell Cycle Research Articles

JC virus small tumor antigen promotes S phase entry and cell cycle progression

The early coding region of JC virus (JCV) encodes several regulatory proteins including large T antigen (LT-Ag), small t antigen (Sm t-Ag) and T’ proteins because of the alternative splicing of the pre-mRNA. LT-Ag plays a critical role in cell transformation by targeting the key cell cycle regulatory proteins including p53 and pRb, however, the role of Sm t-Ag in this process remains elusive. Here, we investigated the effect of Sm t-Ag on the cell cycle progression and demonstrated that it facilitates S phase entry and exit when cells are released from G0/G1 growth arrest. Examination of the cell cycle stage specific expression profiles of the selected cyclins and cyclin-dependent kinases, including those active at the G1/S and G2/M transition state, demonstrated a higher level of early expression of these regulators such as cyclin B, cycling E, and Cdk2. In addition, analysis of the effect of Sm t-Ag on the growth promoting pathways including those active in the PI3K/Akt/mTOR axis showed substantially higher levels of the phosphorylated-Akt, -Gsk3-β and -S6K1 in Sm t-Ag-positive cells. Collectively, our results demonstrate that Sm t-Ag promotes cell cycle progression by activating the growth promoting pathways through which it may contribute to LT-Ag-mediated cell transformation.

Cell Cycle Dynamics in the Microalga Tisochrysis lutea: Influence of Light Duration and Drugs.

Our investigation into Tisochrysis lutea's cell cycle regulation involved natural and chemical synchronization methods to maximize their proportion at the division phase (G2/M). Hence, cultures were grown under different light/dark cycles (24:0, 12:12, and 8:16 h) to assess the impact of extended dark periods on cell division. Flow cytometry analyses of the cell cycle revealed that extending the dark phase resulted in a higher number of cells entering G2/M. However, this remained a minority within the overall culture (peaking at 19.36% ± 0.17 under an 8:16 h L/D cycle). To further enhance synchronization, chemical agents (nocodazole, hydroxyurea, and aphidicolin) were tested for their efficacy in blocking specific cell cycle stages. Only aphidicolin successfully induced significant G2/M accumulation (>90%). The commitment point for cell division was examined by exposing cultures to varying light durations (0 to 8 h) and measuring cell concentration and size distribution every 4 h. Our findings identified a critical minimum cell size ("sizer") of approximately 56.2 ± 0.6 µm3 and a required minimal light exposure ("timer") of 4 h to reliably trigger cell division. These findings highlight key conditions needed for optimal division of Tisochrysis lutea, offering more controlled and efficient cultivation strategies for future biotechnological applications.

Phosphorylation of cytochrome c at tyrosine 48 finely regulates its binding to the histone chaperone SET/TAF-Iβ in the nucleus.

Post-translational modifications (PTMs) of proteins are ubiquitous processes present in all life kingdoms, involved in the regulation of protein stability, subcellular location and activity. In this context, cytochrome c (Cc) is an excellent case study to analyze the structural and functional changes induced by PTMS as Cc is a small, moonlighting protein playing different roles in different cell compartments at different cell-cycle stages. Cc is actually a key component of the mitochondrial electron transport chain (ETC) under homeostatic conditions but is translocated to the cytoplasm and even the nucleus under apoptotic conditions and/or DNA damage. Phosphorylation does specifically alter the Cc redox activity in the mitochondria and the Cc non-redox interaction with apoptosis-related targets in the cytoplasm. However, little is known on how phosphorylation alters the interaction of Cc with histone chaperones in the nucleus. Here, we report the effect of Cc Tyr48 phosphorylation by examining the protein interaction with SET/TAF-Iβ in the nuclear compartment using a combination of molecular dynamics simulations, biophysical and structural approaches such as isothermal titration calorimetry (ITC) and nuclear magnetic resonance (NMR) and in cell proximity ligation assays. From these experiments, we infer that Tyr48 phosphorylation allows a fine-tuning of the Cc-mediated inhibition of SET/TAF-Iβ histone chaperone activity in vitro. Our findings likewise reveal that phosphorylation impacts the nuclear, stress-responsive functions of Cc, and provide an experimental framework to explore novel aspects of Cc post-translational regulation in the nucleus.

ImmunoCellCycle-ID - a high-precision immunofluorescence-based method for cell cycle identification.

The cell cycle is a fundamental process essential for cell proliferation, differentiation and development. It consists of four major phases: G1, S, G2 and M. These phases collectively drive the reproductive cycle and are meticulously regulated by various proteins that play crucial roles in both the prevention and progression of cancer. Traditional methods for studying these functions, such as flow cytometry, require a substantial number of cells to ensure accuracy. In this study, we have developed a user-friendly immunofluorescence-based method for identifying cell cycle stages, providing single-cell resolution and precise identification of G1, early/mid S, late S, early/mid G2, late G2, and each sub-stage of the M phase using fluorescence microscopy called ImmunoCellCycle-ID. This method provides high-precision cell cycle identification and can serve as an alternative to, or in combination with, traditional flow cytometry to dissect detailed sub-stages of the cell cycle in a variety of cell lines.

Differentiation signals induce APOBEC3A expression via GRHL3 in squamous epithelia and squamous cell carcinoma.

Two APOBEC DNA cytosine deaminase enzymes, APOBEC3A and APOBEC3B, generate somatic mutations in cancer, thereby driving tumour development and drug resistance. Here, we used single-cell RNA sequencing to study APOBEC3A and APOBEC3B expression in healthy and malignant mucosal epithelia, validating key observations with immunohistochemistry, spatial transcriptomics and functional experiments. Whereas APOBEC3B is expressed in keratinocytes entering mitosis, we show that APOBEC3A expression is confined largely to terminally differentiating cells and requires grainyhead-like transcription factor 3 (GRHL3). Thus, in normal tissue, neither deaminase appears to be expressed at high levels during DNA replication, the cell-cycle stage associated with APOBEC-mediated mutagenesis. In contrast, in squamous cell carcinoma we find that, there is expansion of GRHL3expression and activity to a subset of cells undergoing DNA replication and concomitant extension of APOBEC3A expression to proliferating cells. These findings suggest that APOBEC3A may play a functional role during keratinocyte differentiation, and offer a mechanism for acquisition of APOBEC3A mutagenic activity in tumours.

CCRG-03. DETECTION OF HETEROGENEOUS CELL CYCLE ALTERATIONS UPON TMZ CHEMOTHERAPY TREATMENT THROUGH ADVANCED MACHINE LEARNING

Abstract Glioblastoma (GB), the most aggressive central nervous system tumor, is hallmarked by its frequent relapse under alkylating chemotherapy. GB cells frequently exhibit changes in cell cycle phases during TMZ treatment, with a reduction in the G0-G1 phase and an increase in the S and G2 phases. This indicate both tumor cell re-entry into the cell cycle and a TMZ-induced arrest, contributing to resistance and progression. In this study, we leverage dynamic protein abundance of Ki-67, a proliferation marker peaking during S, G2, and M phases, to analyse cellular responses to TMZ in various cell lines and tissue samples. We designed an image-based machine learning approach for pattern recognition to reconstruct and analyse the cell cycle at the single-cell level. Six primary cell lines were characterized through whole-genome DNA, methylation and RNA sequencing. Functional read-outs were performed with large-scale, time- and concentration-dependent TMZ treatments in cell culture and GB-tissue slice models. Our model successfully reconstructed detailed cell cycle stages, showing that untreated cells were predominantly in the G0-G1 phase. TMZ treatment significantly shifted cells toward the S/G2 phase (p < 0.02) in 3 of 6 cell lines and the pseudo-time reconstruction highlighted dose-dependent cell cycle changes. Cell lines with enhanced stem-like features, defined based on epigenetic and transcriptional data signature, showed no cell cycle changes at high TMZ doses (>150µM), regardless the MGMT promoter methylation status. This heterogeneity in cell cycle response emphasizes the complexity of GB and the need for personalized treatments. Our study provides insights into GB MGMT cell cycle alterations and resistance mechanisms that are independent of MGMT methylation status, a known TMZ response biomarker. Therefore, the observed TMZ-induced cell cycle changes may serve as novel biomarkers for assessing treatment response, paving the way for personalized therapeutic approaches.

Single-cell eQTL mapping in yeast reveals a tradeoff between growth and reproduction.

Expression quantitative trait loci (eQTLs) provide a key bridge between noncoding DNA sequence variants and organismal traits. The effects of eQTLs can differ among tissues, cell types, and cellular states, but these differences are obscured by gene expression measurements in bulk populations. We developed a one-pot approach to map eQTLs in Saccharomyces cerevisiae by single-cell RNA sequencing (scRNA-seq) and applied it to over 100,000 single cells from three crosses. We used scRNA-seq data to genotype each cell, measure gene expression, and classify the cells by cell-cycle stage. We mapped thousands of local and distant eQTLs and identified interactions between eQTL effects and cell-cycle stages. We took advantage of single-cell expression information to identify hundreds of genes with allele-specific effects on expression noise. We used cell-cycle stage classification to map 20 loci that influence cell-cycle progression. One of these loci influenced the expression of genes involved in the mating response. We showed that the effects of this locus arise from a common variant (W82R) in the gene GPA1 , which encodes a signaling protein that negatively regulates the mating pathway. The 82R allele increases mating efficiency at the cost of slower cell-cycle progression and is associated with a higher rate of outcrossing in nature. Our results provide a more granular picture of the effects of genetic variants on gene expression and downstream traits.

Heterogeneity in oligodendrocyte precursor cell proliferation is dynamic and driven by passive bioelectrical properties

Oligodendrocyte precursor cells (OPCs) generate myelinating oligodendrocytes and are the main proliferative cells in the adult central nervous system. OPCs are a heterogeneous population, with proliferation and differentiation capacity varying with brain region and age. We demonstrate that during early postnatal maturation, cortical, but not callosal, OPCs begin to show altered passive bioelectrical properties, particularly increased inward potassium (K+) conductance, which correlates with G1 cell cycle stage and affects their proliferation potential. Neuronal activity-evoked transient K+ currents in OPCs with high inward K+ conductance potentially release OPCs from cell cycle arrest. Eventually, OPCs in all regions acquire high inward K+ conductance, the magnitude of which may underlie differences in OPC proliferation between regions, with cells being pushed into a dormant state as they acquire high inward K+ conductance and released from dormancy by synchronous neuronal activity. Age-related accumulation of OPCs with high inward K+ conductance might contribute to differentiation failure.

GLO1 regulates hepatocellular carcinoma proliferation and migration through the cell cycle pathway

BackgroundHepatocellular carcinoma (HCC) is a malignant tumor characterized by a high mortality rate. The occurrence and progression of HCC are linked to oxidative stress. Glyoxalase-1 (GLO1) plays an important role in regulating oxidative stress, yet the underlying mechanism remains unclear. GLO1 may serve as a prognostic biomarker and therapeutic target for HCC.MethodsBased on TCGA database hepatocellular carcinoma samples, we conducted a bioinformatics analysis to explore the correlation between GLO1 expression and HCC cell proliferation and viability. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis revealed that differentially expressed genes (DEGs) were mainly enriched in the cell cycle pathway. We analyzed the relationships between GLO1 and 24 genes enriched in the cell cycle pathway using a protein-protein interaction (PPI) network. Finally, experimental validation was performed to assess GLO1’s impact on the distribution of cells at different cell cycle stages and on the proliferation and migration of HCC cells.ResultsOur study demonstrated that GLO1 was overexpressed in HCC tissues and was associated with a poor prognosis. Data analysis indicated that overexpression of GLO1 activated the cell cycle pathway and positively correlated with expression of the majority of key cell cycle genes. Experimental validation showed that GLO1 expression affects the number of HCC cells in G2 and S phases and regulates HCC cell proliferation and migration.ConclusionsGLO1 represents a promising therapeutic target for HCC, providing valuable insights into its role in the viability and proliferation of HCC cells.

8672 Disrupted Glucocorticoid Receptor Mediated Signalling Causes a Primary Cilia Defect in the Fetal Mouse Renal Tubule

Abstract Disclosure: J. Lao: None. K.L. Short: None. J. Ng: None. D.L. Cottle: None. T.J. Cole: None. Primary cilia are microtubule-based organelles that protrude from cell membranes to mediate diverse developmental signalling pathways and senses extracellular stimuli to maintain tissue homeostasis. We show that glucocorticoid (GC) signalling via the glucocorticoid receptor (GR) is a regulator of normal primary cilia formation in kidney renal tubules. RNA sequencing of whole E18.5 fetal kidney from mice with global deletion of the GR (GR-null) compared to littermate wild-type controls identified significantly reduced mRNA levels of key ciliogenesis-related genes. Further analysis of whole fetal kidney RNA by real-time-qPCR confirmed reduced mRNA levels for the cilia-associated proteins Ccp110 (fold -2.18), Cep97 (fold -1.78), Cep290 (fold -2.91), Kif3a (fold -1.82) and Rpgr (fold -1.90). Confocal microscopy revealed abnormal, stunted primary cilia in renal proximal tubules, collecting ducts and podocytes in GR-null or in renal tubule conditional GR-deleted mice, created using the HoxB7 Cre-driver allele. Primary cilia length was significantly decreased in kidney proximal tubule cells in GR-null mice (5.01 ± 0.11μm) compared with wildtype controls (6.20 ± 0.15μm). Furthermore, scanning electron microscopy of E18.5 GR-null kidney further confirmed aberrant primary cilia morphology in the proximal renal tubules and the absence of an apical brush border. Activation of GR signalling with the synthetic GC dexamethasone in cultured mouse IMCD3 kidney tubule cells significantly increased primary cilia length (2.89 ± 0.04μm) compared to vehicle controls (2.46 ± 0.28μm), an effect blocked by the GR antagonist RU486 (vehicle + RU486: 2.06 ± 0.02μm, dexamethasone + RU486: 2.00 ± 0.02μm). Aurora kinase A (AURKA) is a known regulator of primary cilia formation via the AKT cell signalling pathway and distinct proteins at different stages of the mitotic cell cycle. AURKA protein levels were downregulated in GR-null kidney and in IMCD3 cells which suggest GR regulates AURKA to control the assembly and disassembly of primary cilia. Together, these results demonstrate that GC signalling via the GR is required for normal primary ciliogenesis in the developing renal tubule and suggests that synthetic GR agonists may provide a novel therapeutic option for human ciliopathies such as those observed in forms of polycystic kidney disease. Presentation: 6/2/2024

Coupling of cell growth modulation to asymmetric division and cell cycle regulation in Caulobacter crescentus

In proliferating bacteria, growth rate is often assumed to be similar between daughter cells. However, most of our knowledge of cell growth derives from studies on symmetrically dividing bacteria. In many α-proteobacteria, asymmetric division is a normal part of the life cycle, with each division producing daughter cells with different sizes and fates. Here, we demonstrate that the functionally distinct swarmer and stalked daughter cells produced by the model α-proteobacterium Caulobacter crescentus can have different average growth rates under nutrient-replete conditions despite sharing an identical genome and environment. The discrepancy in growth rate is due to a growth slowdown associated with the cell cycle stage preceding DNA replication (the G1 phase), which initiates in the late predivisional mother cell before daughter cell separation. Both progenies experience a G1-associated growth slowdown, but the effect is more severe in swarmer cells because they have a longer G1 phase. Activity of SpoT, which produces the (p)ppGpp alarmone and extends the G1 phase, accentuates the cell cycle-dependent growth slowdown. Collectively, our data identify a coupling between cell growth, the G1 phase, and asymmetric division that C. crescentus may exploit for environmental adaptation through SpoT activity. This coupling differentially modulates the growth rate of functionally distinct daughter cells, thereby altering the relative abundance of ecologically important G1-specific traits within the population.

Aurora A Kinase Begins to Localize to the Centrosome in the S-phase of the Cell Cycle in the XL2 Cell Line

Background: The centrosome is one of the principal cell hubs, where numerous proteins important for intracellular regulatory processes are concentrated. One of them, serine-threonine kinase 6, alias Aurora A, is involved in centrosome duplication and mitotic spindle formation and maintenance. Methods: Long-term vital observations of cells, immunofluorescence analysis of protein localization, synchronization of cells at different phases of the cell cycle, Western blot analysis of protein content were used in the work. Results: In this study, we investigated the dynamics of Aurora A protein accumulation and degradation in the XL2 Xenopus cell line during its 28-hour cell cycle. Using Western blot and immunofluorescence analyses, we demonstrated that Aurora A disappeared from the centrosome within one hour following mitosis and was not redistributed to other cell compartments. Using double Aurora A/Bromodeoxyuridine immunofluorescence labeling of the cells with precisely determined cell cycle stages, we observed that Aurora A reappeared in the centrosome during the S-phase, which was earlier than reported for all other known proteins with mitosis-specific centrosomal localization. Moreover, Aurora A accumulation in the centrosomal region and centrosome separation were asynchronous in the sister cells. Conclusions: The reported data allowed us to hypothesize that Aurora A is one of the primary links in coordinating centrosome separation and constructing the mitotic spindle.

Reversible and effective cell cycle synchronization method for studying stage-specific investigations.

The cell cycle is a crucial process for cell proliferation, differentiation, and development. Numerous genes and proteins play pivotal roles at specific cell cycle stages to regulate these events precisely. Studying the stage-specific functions of the cell cycle requires accumulating cell populations at the desired cell cycle stage. Cell synchronization, achieved through the use of cell cycle kinase and protein inhibitors, is often employed for this purpose. However, suboptimal concentrations of these inhibitors can result in reduced efficiency, irreversibility, and undesirable cell cycle defects. In this study, we have optimized effective and reversible techniques to synchronize the cell cycle at each stage in human RPE1 cells, utilizing both fixed high-precision cell cycle identification methods and high-temporal live-cell imaging. These reproducible synchronization methods are invaluable for investigating the regulatory mechanisms specific to each cell cycle stage.

Analysis of cell cycle stage, replicated DNA, and chromatin-associated proteins using high-throughput flow cytometry

Abstract Flow cytometry is a versatile tool used for cell sorting, DNA content imaging, and determining various cellular characteristics. With the possibility of high-throughput analyses, it combines convenient labelling techniques to serve rapid, quantitative, and qualitative workflows. The ease of sample preparation and the broad range of applications render flow cytometry a preferred approach for many scientific questions. Yet, we lack practical adaptations to fully harness the quantitative and high-throughput capabilities of most cytometers for many organisms. Here, we present simple and advanced protocols for the analysis of total DNA content, de novo DNA synthesis, and protein association to chromatin in budding yeast and human cells. Upon optimization of experimental conditions and choice of fluorescent dyes, up to four parameters can be measured simultaneously and quantitatively for each cell of a population in a multi-well plate format. Reducing sample numbers, plastic waste, costs per well, and hands-on time without compromising signal quality or single-cell accuracy are the main advantages of the presented protocols. In proof-of-principle experiments, we show that DNA content increase in S-phase correlates with de novo DNA synthesis and can be predicted by the presence of the replicative helicase MCM2-7 on genomic DNA.

Predicting cell cycle stage from 3D single-cell nuclear-stained images.

The cell cycle governs the proliferation, differentiation, and regeneration of all eukaryotic cells. Profiling cell cycle dynamics is therefore central to basic and biomedical research spanning development, health, aging, and disease. However, current approaches to cell cycle profiling involve complex interventions that may confound experimental interpretation. To facilitate more efficient cell cycle annotation of microscopy data, we developed CellCycleNet, a machine learning (ML) workflow designed to simplify cell cycle staging with minimal experimenter intervention and cost. CellCycleNet accurately predicts cell cycle phase using only a fluorescent nuclear stain (DAPI) in fixed interphase cells. Using the Fucci2a cell cycle reporter system as ground truth, we collected two benchmarking image datasets and trained two ML models-a support vector machine (SVM) and a deep neural network-to classify nuclei as being in either the G1 or S/G2 phases of the cell cycle. Our results suggest that CellCycleNet outperforms state-of-the-art SVM models on each dataset individually. When trained on two image datasets simultaneously, CellCycleNet achieves the highest classification accuracy, with an improvement in AUROC of 0.08-0.09. The model also demonstrates excellent generalization across different microscopes, achieving an AUROC of 0.95. Overall, using features derived from 3D images, rather than 2D projections of those same images, significantly improves classification performance. We have released our image data, trained models, and software as a community resource.

Cell sorting based on pulse shapes from angle resolved detection of scattered light

Flow cytometry is a key technology for the analysis and sorting of cells or particles at high throughput. Conventional and current flow cytometry is primarily based on fluorescent stains to detect the cells of interest. However, such stains also have disadvantages, as their effect on cells must be carefully tested to avoid effects on the results of the experiments. Alternative approaches using imaging or other label-free techniques often require highly sophisticated setups, are commonly limited in resolution, and produce challenging amounts of data. Our technology exploits scattered light instead. The custom-built flow cytometry setup comprises a fiber array in forward scatter detection for angular resolution and captures the whole pulse shape with advanced signal processing. Thereby this setup enables cell analysis and sorting purely based on scattered light signals without the need for fluorescent labels. We demonstrate the feasibility of this cell sorting technology by sorting cell lines for their cell cycle stages based on scattered light. Furthermore, we demonstrate the ability to classify human peripheral blood T- and B-cell subsets.

YY1-controlled regulatory connectivity and transcription are influenced by the cell cycle.

Few transcription factors have been examined for their direct roles in physically connecting enhancers and promoters. Here acute degradation of Yin Yang 1 (YY1) in erythroid cells revealed its requirement for the maintenance of numerous enhancer-promoter loops, but not compartments or domains. Despite its reported ability to interact with cohesin, the formation of YY1-dependent enhancer-promoter loops does not involve stalling of cohesin-mediated loop extrusion. Integrating mitosis-to-G1-phase dynamics, we observed partial retention of YY1 on mitotic chromatin, predominantly at gene promoters, followed by rapid rebinding during mitotic exit, coinciding with enhancer-promoter loop establishment. YY1 degradation during the mitosis-to-G1-phase interval revealed a set of enhancer-promoter loops that require YY1 for establishment during G1-phase entry but not for maintenance in interphase, suggesting that cell cycle stage influences YY1's architectural function. Thus, as revealed here for YY1, chromatin architectural functions of transcription factors can vary in their interplay with CTCF and cohesin as well as by cell cycle stage.

Single cell expression and chromatin accessibility of the Toxoplasma gondii lytic cycle identifies AP2XII-8 as an essential ribosome regulon driver

Sequential lytic cycles driven by cascading transcriptional waves underlie pathogenesis in the apicomplexan parasite Toxoplasma gondii. This parasite’s unique division by internal budding, short cell cycle, and jumbled up classically defined cell cycle stages have restrained in-depth transcriptional program analysis. Here, unbiased transcriptome and chromatin accessibility maps throughout the lytic cell cycle are established at the single-cell level. Correlated pseudo-timeline assemblies of expression and chromatin profiles maps transcriptional versus chromatin level transition points promoting the cell division cycle. Sequential clustering analysis identifies functionally related gene groups promoting cell cycle progression. Promoter DNA motif mapping reveals patterns of combinatorial regulation. Pseudo-time trajectory analysis reveals transcriptional bursts at different cell cycle points. The dominant burst in G1 is driven largely by transcription factor AP2XII-8, which engages a conserved DNA motif, and promotes the expression of 44 ribosomal proteins encoding regulon. Overall, the study provides integrated, multi-level insights into apicomplexan transcriptional regulation.

Cell Proliferation and Cytotoxicity Assays, The Fundamentals for Drug Discovery

Review Cell Proliferation and Cytotoxicity Assays, The Fundamentals for Drug Discovery Jingyi Niu†, Minai Li† and Ying Wang* State Key Laboratory of Quality Research in Chinese Medicine, Institute of Chinese Medical Sciences, University of Macau, Avenida da Universidade, Taipa, Macao 999078, China * Correspondence: emilyywang@um.edu.mo † These authors contributed equally to this work Received: 6 May 2024; Revised: 19 June 2024; Accepted: 21 June 2024; Published: 20 August 2024 Abstract: Cell proliferation and cytotoxicity assays are fundamental to drug discovery. This review summarizes prevalent methodologies for assessing cell proliferation and cytotoxicity, including direct cell count, metabolic activity, luminescent labeling, and tri-color viability imaging. The critical determinants that can significantly impact these assay outcomes, such as cellular doubling time, transitional states like quiescence and autophagy, cell cycle stages, metabolic enzyme functions, and genetic variability, are also explored. It is necessary to integrate the commonly used assays with additional analytical techniques to achieve precision in drug discovery. A multi-tiered approach that combines cellular assays with molecular analyses can improve screening processes, reduce false negatives, and increase confidence in the therapeutic potential of lead compounds.

ImmunoCellCycle-ID: A high-precision immunofluorescence-based method for cell cycle identification.

The cell cycle is a fundamental process essential for cell proliferation, differentiation, and development. It consists of four major phases: G1, S, G2, and M. These phases collectively drive the reproductive cycle and are meticulously regulated by various proteins that play critical roles in both the prevention and progression of cancer. Traditional methods for studying these functions, such as flow cytometry, require a substantial number of cells to ensure accuracy. In this study, we have developed a user-friendly, immunofluorescence-based method for identifying cell cycle stages, providing single-cell resolution and precise identification of G1, early S, late S, early G2, late G2, and each sub-stage of the M phase using fluorescence microscopy. This method provides high-precision cell cycle identification and can serve as an alternative to, or in combination with, traditional flow cytometry to dissect detailed substages of the cell cycle in a variety of cell lines.