Cells grow and divide through a tightly regulated process known as the cell cycle. 

This cycle plays a critical role in tissue development, maintenance, and regeneration, and is essential for repairing damaged structures in living organisms.

A clear understanding of cell cycle progression and regulation is crucial for designing and analyzing experiments, and is fundamental in fields such as cancer research, tissue regeneration, and drug efficacy testing.

In this article, we outline the key stages and regulatory mechanisms of the cell cycle. We also present observation examples that capture dynamic morphological changes in real time, specifically focusing on mitotic (M phase) progression in two different cell types using live-cell imaging.

Table of Contents

 

1. Phases of the Cell Cycle
2. Cell Cycle Regulation
3. Observation Examples

1. Phases of the Cell Cycle

The cell cycle consists of four main stages—G1 (Gap 1), S (Synthesis), G2 (Gap 2), and M (Mitosis)—with some cells entering an additional phase called G0.

G1 Phase

The cell grows and prepares the necessary proteins and energy for DNA synthesis.

S Phase

The cell duplicates its DNA so that each new cell receives an exact copy of genetic information.

G2 Phase

The cell checks for DNA damage and synthesizes additional components needed for mitosis.

These three phases (G1, S, G2) are collectively referred to as interphase, during which the cell prepares for division.

M Phase

The duplicated chromosomes are separated, followed by cytokinesis, resulting in two daughter cells.

The M phase consists of five substages — prophase, prometaphase, metaphase, anaphase, and telophase — and is the most dynamic and visually distinct phase, especially in live-cell imaging.

G0 Phase

Some cells exit the cycle into a quiescent state where they remain metabolically active but non-proliferative.

This phase is typical of differentiated cells that no longer need to divide.

2. Cell Cycle Regulation

Although the cell cycle progresses in a defined sequence, this progression is tightly regulated and not automatic.

To ensure genomic stability and accurate division, cells utilize internal checkpoints that monitor readiness before transitioning to the next phase.

When errors are detected, these checkpoints function as quality control systems, pausing the cycle to allow for repair. If regulation fails, uncontrolled proliferation may result — a key hallmark of cancer.

Key checkpoints include:

G1/S Checkpoint

Assesses whether the cell is ready to enter the S phase. It verifies cell size, nutrient availability, and DNA integrity before allowing DNA replication. If this checkpoint fails, cells with damaged or incomplete DNA may continue dividing, increasing the risk of mutations and cancer development.

G2/M Checkpoint

Ensures that DNA replication is complete and error-free before the cell proceeds to mitosis. Failure at this point can lead to the transmission of genetic errors, contributing to genomic instability.

Spindle Assembly Checkpoint

During mitosis, confirms that chromosomes are properly attached to spindle fibers before segregation. Failure at this stage can cause chromosome missegregation and result in aneuploidy.

These checkpoints serve as critical safeguards against abnormal cell proliferation. When damage cannot be repaired, the cell cycle halts and apoptosis(programmed cell death) is triggered.

3. Observation Example:

To illustrate how U2OS cells progress through the cell cycle in real time, we monitored tFucci(CA)5-transfected cells using the Celloger® Pro. The Fucci system enables clear visualization of phase-specific fluorescence, allowing continuous tracking of individual cells throughout division.

U2OS cells expressing the tFucci(CA)5 construct display distinct fluorescence patterns as they move through the cell cycle.
 

Green fluorescence marks S/G2 phases, shifting to yellow as cells enter early mitosis, followed by red fluorescence in G1 after division. Morphological changes such as cell rounding, chromatin condensation, chromosome segregation, and cleavage furrow formation are clearly captured throughout mitosis.

These results were acquired using Celloger® Pro, a live-cell imaging system designed to monitor dynamic cellular processes over extended periods.

👉 Learn more about Celloger® Pro on our product page.

In this article, we explored the phases and regulation of the cell cycle. In addition, we demonstrated how live-cell imaging with Celloger® captures the dynamic morphological changes of cells in real time.

Live-cell imaging opens new perspectives in cellular dynamics research. Curiosis provides advanced imaging solutions like Celloger®, supporting researchers in their studies. Learn more about our technology and products on this website.