Cell Cycle Analysis by Flow Cytometry

Understanding the Cell Cycle and Flow Cytometry

Overview of the Cell Cycle

• The cell cycle is a series of steps from cell formation to reproduction, resulting in two daughter cells.

• Eukaryotic cells undergo two main phases: interphase (DNA replication) and mitotic phase (DNA separation).

Phases of Interphase

• Interphase consists of three phases: G1 (first gap), S (synthesis), and G2 (second gap).

• G1 Phase: The cell grows in size and copies organelles to prepare for DNA synthesis.

• S Phase: The cell synthesizes DNA, leading to elevated DNA levels within the cell.

• G2 Phase: Further growth occurs, with protein and organelle production in preparation for mitosis.

Introduction to Flow Cytometry

Principles of Flow Cytometry

• Flow cytometry is a laser-based technology that measures fluorescence intensity for cell analysis.

• Cells pass through a laser in single file, allowing for counting and sorting based on surface and intracellular molecule expression.

Use of Fluorescent Dyes

• A DNA fluorescent dye binds to DNA; when excited by a laser, it emits a signal proportional to the amount of DNA present.

• Propidium iodide (PI) will be used for staining; it requires permeabilization since it cannot enter intact membranes.

Experimental Procedure Overview

Day One: Plating Cells

• Cells are plated in six-well plates following established protocols for detaching them from flasks using trypsinization.

• After achieving a single-cell suspension, cells are counted using trypan blue exclusion method before incubation.

Day Two: Treatment Application

• Compounds and controls are added as duplicates across five concentrations after 24 hours of incubation for analysis.

Harvesting Cells for Analysis

Cell Collection Steps

• Supernatant containing floating cells is collected into labeled tubes post-treatment to capture those undergoing mitosis or dying after treatment.

• Trypsin is used again to detach cells from wells, followed by media addition to stop trypsin activity before transferring cells into tubes.

Preparing Samples for Flow Cytometry

Centrifugation and Washing Steps

• After centrifugation at 1200 rpm, supernatant is discarded carefully while ensuring the pellet remains intact; cold PBS washes away excess media.

Fixation and Permeabilization

• Cells are fixed with 70% ethanol while vortexing to prevent aggregation; this step allows PI access into the cells' membranes for effective staining during analysis.

Finalizing Sample Preparation

Staining with Propidium Iodide

• PI solution containing RNase is added post-fixation; this ensures RNA degradation so that PI can bind primarily to DNA during incubation periods under low light conditions due to PI's sensitivity.

Resuspension Before Analysis

• Following another round of centrifugation, samples are resuspended in PBS before being transferred into suitable tubes for flow cytometer analysis where histograms will represent different stages of the cell cycle based on PI fluorescence intensity levels observed during testing procedures .