History

Theodor Boveri

Theodor Boveri

-External links:* Fritz Baltzer. . excerpt from . University of California Press, Berkeley; pp. 85–97....

 originally observed the fact that abnormal nuclear morphologies commonly occurred in cancer

Cancer

Cancer , known medically as a malignant neoplasm, is a large group of different diseases, all involving unregulated cell growth. In cancer, cells divide and grow uncontrollably, forming malignant tumors, and invade nearby parts of the body. The cancer may also spread to more distant parts of the...

. Micronuclei are also referred to Howell-Jolly bodies; founded by hematologists William Henry Howell

William Henry Howell

William Henry Howell, Ph.D., M.D., LL.D., Sc.D. was an American physiologist. He pioneered the use of heparin as a blood anti-coagulant....

 and Justin Marie Jolly

Justin Marie Jolly

Justin Marie Jolly was a French hematologist and histologist born in Melun, Seine-et-Marne. He was a pioneer in the field of hematology as it pertained to the study of living tissue....

 in erythrocytes. Micronuclei induction by a chemical was first reported in Ehrlich ascites tumor cells treated with colchicine. The affect of environmental stressors on the expression of micronuclei was first analyzed in root tip cells under ionizing radiation

Ionizing radiation

Ionizing radiation is radiation composed of particles that individually have sufficient energy to remove an electron from an atom or molecule. This ionization produces free radicals, which are atoms or molecules containing unpaired electrons...

. It can be inferred that nuclear abnormalities are a result of various molecular mechanisms. These events can ultimately lead to cell death.

Characteristics

Micronuclei are characterized in the cells that have some sort of DNA

DNA

Deoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...

damage. This includes damage caused by radiation

Radiation

In physics, radiation is a process in which energetic particles or energetic waves travel through a medium or space. There are two distinct types of radiation; ionizing and non-ionizing...

, harmful chemicals, and random mutations that occur throughout the genome

Genome

In modern molecular biology and genetics, the genome is the entirety of an organism's hereditary information. It is encoded either in DNA or, for many types of virus, in RNA. The genome includes both the genes and the non-coding sequences of the DNA/RNA....

. Micronuclei are small bodies that can be seen budding off of a newly divided daughter cell. Micronuclei can contain a whole chromosome

Chromosome

A chromosome is an organized structure of DNA and protein found in cells. It is a single piece of coiled DNA containing many genes, regulatory elements and other nucleotide sequences. Chromosomes also contain DNA-bound proteins, which serve to package the DNA and control its functions.Chromosomes...

 or part of a chromatid

Chromatid

A chromatid is one of the two identical copies of DNA making up a duplicated chromosome, which are joined at their centromeres, for the process of cell division . They are called sister chromatids so long as they are joined by the centromeres...

. The increased formation of micronuclei is usually an indication of increased DNA

DNA

Deoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...

 damage or mutation

Mutation

In molecular biology and genetics, mutations are changes in a genomic sequence: the DNA sequence of a cell's genome or the DNA or RNA sequence of a virus. They can be defined as sudden and spontaneous changes in the cell. Mutations are caused by radiation, viruses, transposons and mutagenic...

. It is characteristically found in cancer

Cancer

Cancer , known medically as a malignant neoplasm, is a large group of different diseases, all involving unregulated cell growth. In cancer, cells divide and grow uncontrollably, forming malignant tumors, and invade nearby parts of the body. The cancer may also spread to more distant parts of the...

 cells, or cells that have been exposed to increased risk factors.

Formation

Micronuclei are small, extranuclear bodies that are formed during mitosis from lagging chromosomes. In anaphase

Anaphase

Anaphase, from the ancient Greek ἀνά and φάσις , is the stage of mitosis or meiosis when chromosomes move to opposite poles of the cell....

, the microtubules are not attached properly to the chromosomes, which can cause pulling in a different direction. This results in parts of the chromatids or chromosomes being broken off and enveloped as an extra nucleus

Cell nucleus

In cell biology, the nucleus is a membrane-enclosed organelle found in eukaryotic cells. It contains most of the cell's genetic material, organized as multiple long linear DNA molecules in complex with a large variety of proteins, such as histones, to form chromosomes. The genes within these...

 in one of the daughter cells. This is the main way that micronuclei are formed.
Micronuclei can also be spontaneously formed as a byproduct of cellular defense. If the cell senses extra chromosomes, the cell can attempt to remove the extra chromosome

Chromosome

A chromosome is an organized structure of DNA and protein found in cells. It is a single piece of coiled DNA containing many genes, regulatory elements and other nucleotide sequences. Chromosomes also contain DNA-bound proteins, which serve to package the DNA and control its functions.Chromosomes...

 in another cell membrane

Cell membrane

The cell membrane or plasma membrane is a biological membrane that separates the interior of all cells from the outside environment. The cell membrane is selectively permeable to ions and organic molecules and controls the movement of substances in and out of cells. It basically protects the cell...

, separate from the other normal chromosome

Chromosome

A chromosome is an organized structure of DNA and protein found in cells. It is a single piece of coiled DNA containing many genes, regulatory elements and other nucleotide sequences. Chromosomes also contain DNA-bound proteins, which serve to package the DNA and control its functions.Chromosomes...

. Another mechanism to micronuclei formation is by a double-strand break in the DNA

DNA

Deoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...

, creating a separate linear fragment. Furthermore, the breaking of an anaphase bridge could also lead to formation of a micronucleus.

Role in Cancer

Micronuclei are often overlooked in cancer

Cancer

Cancer , known medically as a malignant neoplasm, is a large group of different diseases, all involving unregulated cell growth. In cancer, cells divide and grow uncontrollably, forming malignant tumors, and invade nearby parts of the body. The cancer may also spread to more distant parts of the...

. If observed under a microscope

Microscope

A microscope is an instrument used to see objects that are too small for the naked eye. The science of investigating small objects using such an instrument is called microscopy...

, they are viewable and often next to other larger nuclei

Cell nucleus

In cell biology, the nucleus is a membrane-enclosed organelle found in eukaryotic cells. It contains most of the cell's genetic material, organized as multiple long linear DNA molecules in complex with a large variety of proteins, such as histones, to form chromosomes. The genes within these...

. Based on the structure of a Micronucleus, or the function of a cell, it provides support in the central apparatus within the cell. Micronuclei are under investigation and research regarding whether or not they can be used to predict future cancer risks. They are easy to analyze compared to chromosome

Chromosome

A chromosome is an organized structure of DNA and protein found in cells. It is a single piece of coiled DNA containing many genes, regulatory elements and other nucleotide sequences. Chromosomes also contain DNA-bound proteins, which serve to package the DNA and control its functions.Chromosomes...

aberrations.