What is the Difference Between Micronucleus and Comet Assay

The key difference between micronucleus and comet assay is that micronucleus assay is important to check chromosomal damage as a consequence of mutagen exposure, while comet assay is important to detect primary DNA damage in individual cells.

Genotoxicity assays help to assess the possibilities of mutations and chromosomal abnormalities. Genotoxins include chemical substances and radiation. Carcinogens, mutagens, and teratogens are the main categories of genotoxins. They cause various damages such as point mutations, deletions, single and double-strand breaks, chromosomal aberrations, micronuclei formations, DNA repair, and cell cycle interactions. Such conditions may lead to a wide variety of diseases, and genotoxicity assays prevent the potential damage from these conditions. Micronucleus assay and comet assay are two techniques under genotoxicity assays.

CONTENTS

1. Overview and Key Difference
2. What is Micronucleus Assay
3. What is Comet Assay
4. Similarities – Micronucleus and Comet Assay
5. Micronucleus vs Comet Assay in Tabular Form
6. Summary – Micronucleus vs Comet Assay

What is Micronucleus Assay?

Micronucleus assay is an assay to assess chromosomal damage as a consequence of mutagen exposure. It is important in screening chemicals that cause spindle formation and micronuclei. A micronucleus assay provides information on the stability of chemicals when interfering with chromosome structure and function. Many carcinogens test positive in micronucleus assays. The assay process involves a chemical treatment and measuring the frequency of micronucleated cells. If there is an abnormal increase in the number of micronuclei cells, it concludes that the chemical induces chromosomal damage.

A micronucleus assay is usually carried out on actively dividing cells. Therefore, erythrocytes and bone marrow stem cells produced through cell divisions are ideal candidates for such assays. They experience a constant and rapid turnover. Since erythrocytes have no true nuclei, it makes micronucleated cells more visible at the end of the assay.

Micronucleus assays are economical, faster, convenient, and require fewer skills to carry out. They reflect chromosomal aberrations rapidly in a reliable manner and are extremely useful to assess chromosomal damages quickly. A special and versatile type of micronucleus assay is the cytokinesis block micronucleus cytome (CBMNcyt) assay. It is the preferable assay to measure chromosomal damage and instability in cells. However, the main problem of using micronucleus assay is that it is unable to determine different types of chromosomal aberrations, and the assay has an influence on mitotic rate and proportion of cell death, causing the results to change.

What is Comet Assay?

Comet assay, which is also known as single gel electrophoresis assay, is a simple and sensitive technique to detect DNA damage. It measures the DNA breaks in eukaryotic cells and is a standard technique for biomonitoring and genotoxicity testing.

The comet assay is involved in the encapsulation of cells in low melting point agarose suspensions, lysis of cells in neutral or alkaline conditions, and electrophoresis of suspended lysed cells. During the encapsulation process, the cells are suspended in molten low melting point agarose, and the agarose forms a matrix of carbohydrate fibers to anchor them in place. Agarose is osmotically neutral; therefore, it enables the solutions to penetrate through the gel and affect the cells without disturbing and shifting them. The lysis solution is a highly concentrated aqueous salt solution and a detergent. This salt disrupts proteins and the bonding patterns within the cell while disrupting the RNA content of the cell. The cells destroy, and all proteins, RNA, cytoplasmic and nucleoplasmic constituents, disrupt and diffuse into the agarose matrix, leaving the DNA.

The electrophoresis solution is an alkaline solution where the DNA double helix denatures, and the nucleoid becomes single-stranded. During this process, an electric field is applied to analyze the images. The image analysis measures the overall intensity of the fluorescence for the DNA and nucleoid and compares the two. The overall structure resembles a comet with a circular head corresponding to the remaining undamaged DNA and a tail for the damaged DNA. The brighter and longer the tail due to stronger signals, the higher the level of damage.

What are the Similarities Between Micronucleus and Comet Assay?

• Micronucleus and the comet assay are economical, faster, convenient, and require fewer skills.
• They are mainly performed on DNA.
• Both assays help in assessing mutations and chromosomal abnormalities.
• Moreover, both techniques use chemicals to carry out the procedure.

What is the Difference Between Micronucleus and Comet Assay?

The micronucleus assay is important in checking chromosomal damage as a consequence of mutagen exposure, while comet assay is important in detecting primary DNA damage in individual cells. Thus, this is the key difference between micronucleus and comet assay. Also, the micronucleus assay is well established to detect clastogenicity and aneugenicity. The comet assay is used as a genotoxicity test to detect primary DNA damage in cells. Moreover, a micronucleus assay provides information on the stability of chemicals, while a comet assay is a single cell gel electrophoresis.

The below infographic presents the differences between micronucleus and comet assay in tabular form for side by side comparison.

Summary – Micronucleus vs Comet Assay

Genotoxicity assays help to assess the possibilities of mutations and chromosomal abnormalities. Micronucleus assay and comet assay are two techniques under genotoxicity assays. Micronucleus assay assesses chromosomal damage as a consequence of mutagen exposure. Comet assay is a simple and sensitive technique to detect DNA damage. So, this is the key difference between micronucleus and comet assay. Micronucleus assay is important in screening for chemicals that cause spindle formation and micronuclei. Comet assay is involved in the encapsulation of cells in low melting point agarose suspensions, lysis of cells in neutral or alkaline conditions, and electrophoresis of suspended lysed cells.

Reference:

1. “Comet Assay.” Sigmaaldrich.
2. “Micronucleus Test.” An Overview | ScienceDirect Topics.

Image Courtesy:

1. “Maskmaking for automatic detection of micronuclei” By Genomicintegrity – Own work (CC BY 4.0) via Commons Wikimedia
2. “Casplabapp” By Koncak – Own work (CC BY-SA 3.0) via Commons Wikimedia