Cajal body
Encyclopedia
Cajal bodies are spherical sub-organelles of 0.3-1.0 µm in diameter found in the 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...

 of proliferative cell
Cell (biology)
The cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of life that is classified as a living thing, and is often called the building block of life. The Alberts text discusses how the "cellular building blocks" move to shape developing embryos....

s like embryonic cells and tumor cells, or metabolically active cells like neuron
Neuron
A neuron is an electrically excitable cell that processes and transmits information by electrical and chemical signaling. Chemical signaling occurs via synapses, specialized connections with other cells. Neurons connect to each other to form networks. Neurons are the core components of the nervous...

s. In contrast to cytoplasmic organelle
Organelle
In cell biology, an organelle is a specialized subunit within a cell that has a specific function, and is usually separately enclosed within its own lipid bilayer....

s, CBs lack any phospholipid membrane which would separate their content, largely consisting of proteins and RNA, from the surrounding nucleoplasm
Nucleoplasm
Similar to the cytoplasm of a cell, the nucleus contains nucleoplasm or karyoplasm. The nucleoplasm is one of the types of protoplasm, and it is enveloped by the nuclear membrane or nuclear envelope. The nucleoplasm is a highly viscous liquid that surrounds the chromosomes and nucleoli...

. They were first reported by Santiago Ramón y Cajal
Santiago Ramón y Cajal
Santiago Ramón y Cajal ForMemRS was a Spanish pathologist, histologist, neuroscientist, and Nobel laureate. His pioneering investigations of the microscopic structure of the brain were original: he is considered by many to be the father of modern neuroscience...

 in 1903, who called them nucleolar accessory bodies due to their association with the nucleoli
Nucleolus
The nucleolus is a non-membrane bound structure composed of proteins and nucleic acids found within the nucleus. Ribosomal RNA is transcribed and assembled within the nucleolus...

 in neuronal cells. These structures were forgotten and later rediscovered by electron microscopists and named coiled bodies according to their appearance as coiled threads on EM
Electron microscope
An electron microscope is a type of microscope that uses a beam of electrons to illuminate the specimen and produce a magnified image. Electron microscopes have a greater resolving power than a light-powered optical microscope, because electrons have wavelengths about 100,000 times shorter than...

 images. More recently, to simplify the nomenclature the coiled bodies were renamed after their discoverer. Research on CBs was accelerated after discovery and cloning
Molecular cloning
Molecular cloning refers to a set of experimental methods in molecular biology that are used to assemble recombinant DNA molecules and to direct their replication within host organisms...

 of the marker protein p80/Coilin
Coilin
Coilin is a protein that in humans is encoded by the COIL gene.Coilin protein is one of the main molecular components of Cajal bodies . Cajal bodies are nuclear suborganelles of varying number and composition that are involved in the post-transcriptional modification of small nuclear and small...

. So far, CBs were implicated in important RNA-related metabolic processes such as snRNP
SnRNP
snRNPs , or small nuclear ribonucleoproteins, are RNA-protein complexes that combine with unmodified pre-mRNA and various other proteins to form a spliceosome, a large RNA-protein molecular complex upon which splicing of pre-mRNA occurs...

s biogenesis, maturation and recycling, histone
Histone
In biology, histones are highly alkaline proteins found in eukaryotic cell nuclei that package and order the DNA into structural units called nucleosomes. They are the chief protein components of chromatin, acting as spools around which DNA winds, and play a role in gene regulation...

 mRNA processing and telomere maintenance. With regard to CB's role in telomere maintenance, researchers at UT Southwestern Medical Centre showed that CBs assemble RNA which telomerase in turn uses to add nucleotides to the ends of telomeres.

History

CBs were initially discovered by neurobiologist Santiago Ramón y Cajal in 1903 as small argyrophilic spots in nuclei of silver-stained neuronal cells. Because of their close association with nucleoli he named them nucleolar accessory bodies. Later on, they were forgotten and rediscovered multiple times independently which led to a state where scientists from different research fields used different names for the same structure. Names used for CBs included "spere organelles", "Binnenkörper", "nucelolar bodies" or "coiled bodies". The name coiled bodies comes from observation of electron microscopists Monneron and Bernhard. They described bodies as aggregates composed of coiled threads with thickness of 400-600 Å
Ångström
The angstrom or ångström, is a unit of length equal to 1/10,000,000,000 of a meter . Its symbol is the Swedish letter Å....

. When using higher magnification, they appear as tiny, 50 Å thick fibrils irregularly twisted along the axis of the threads. The bodies were even predicted to consist of ribonucleoproteins since treatment of cells with protease
Protease
A protease is any enzyme that conducts proteolysis, that is, begins protein catabolism by hydrolysis of the peptide bonds that link amino acids together in the polypeptide chain forming the protein....

 and RNase together, but not alone, caused dramatic changes to the structure of CBs.

Localization

Cajal bodies are only found in nuclei of plant, yeast, and animal cells. The cells are usually demonstrating high levels of transcriptional activity, including cells that are rapidly dividing.

CBs and cell cycle

They are about 0.1-2.0 micrometre
Micrometre
A micrometer , is by definition 1×10-6 of a meter .In plain English, it means one-millionth of a meter . Its unit symbol in the International System of Units is μm...

s and are found one to five per nucleus. The number varies in different types of cells and over the cell cycle. Maximum number is reached in mid G1 phase and towards G2 they become larger and their number decreases. CBs disassemble during the M phase and reappear again later in G1 phase. Cajal bodies are possibly sites of assembly or modification of the transcription
Transcription (genetics)
Transcription is the process of creating a complementary RNA copy of a sequence of DNA. Both RNA and DNA are nucleic acids, which use base pairs of nucleotides as a complementary language that can be converted back and forth from DNA to RNA by the action of the correct enzymes...

 machinery of the nucleus.

Functions

CBs are bound to the nucleolus
Nucleolus
The nucleolus is a non-membrane bound structure composed of proteins and nucleic acids found within the nucleus. Ribosomal RNA is transcribed and assembled within the nucleolus...

 by coilin
Coilin
Coilin is a protein that in humans is encoded by the COIL gene.Coilin protein is one of the main molecular components of Cajal bodies . Cajal bodies are nuclear suborganelles of varying number and composition that are involved in the post-transcriptional modification of small nuclear and small...

proteins. P80-coilin is a specific marker for coiled bodies, and demonstrates these bodies tend to be associated with the nucleolus when cells are not dividing.
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