Cajal bodies (CBs) also coiled bodies, are spherical

nuclear bodies Nuclear bodies (also known as nuclear domains, or nuclear dots) are membraneless structures found in the cell nuclei of eukaryotic cells. Nuclear bodies include Cajal bodies, the nucleolus, and promyelocytic leukemia protein (PML) nuclear b ...

of 0.3–1.0 µm in diameter found in the

nucleus Nucleus ( : nuclei) is a Latin word for the seed inside a fruit. It most often refers to: *Atomic nucleus, the very dense central region of an atom * Cell nucleus, a central organelle of a eukaryotic cell, containing most of the cell's DNA Nucl ...

of proliferative cells like

embryonic cell In biology, a blastomere is a type of cell produced by cell division (cleavage) of the zygote after fertilization; blastomeres are an essential part of blastula formation, and blastocyst formation in mammals. Human blastomere characteristics In h ...

s and tumor cells, or metabolically active cells like

neuron A neuron, neurone, or nerve cell is an membrane potential#Cell excitability, electrically excitable cell (biology), cell that communicates with other cells via specialized connections called synapses. The neuron is the main component of nervous ...

s. CBs are membrane-less

organelle In cell biology, an organelle is a specialized subunit, usually within a cell, that has a specific function. The name ''organelle'' comes from the idea that these structures are parts of cells, as organs are to the body, hence ''organelle,'' t ...

s and largely consist of

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respon ...

s and

RNA Ribonucleic acid (RNA) is a polymeric molecule essential in various biological roles in coding, decoding, regulation and expression of genes. RNA and deoxyribonucleic acid ( DNA) are nucleic acids. Along with lipids, proteins, and carbohydra ...

. They were first reported by Santiago Ramón y Cajal in 1903, who called them ''nucleolar accessory bodies'' due to their association with the nucleoli in neuronal cells. They were rediscovered with the use of the

electron microscope An electron microscope is a microscope that uses a beam of accelerated electrons as a source of illumination. As the wavelength of an electron can be up to 100,000 times shorter than that of visible light photons, electron microscopes have a ...

(EM) and named ''coiled bodies'', according to their appearance as coiled threads on EM images, and later renamed after their discoverer. Research on CBs was accelerated after discovery and

cloning Cloning is the process of producing individual organisms with identical or virtually identical DNA, either by natural or artificial means. In nature, some organisms produce clones through asexual reproduction. In the field of biotechnology, c ...

of the marker protein p80/Coilin. CBs have been implicated in RNA-related metabolic processes such as the biogenesis, maturation and recycling of

snRNP snRNPs (pronounced "snurps"), 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 pr ...

histone In biology, histones are highly basic proteins abundant in lysine and arginine residues that are found in eukaryotic cell nuclei. They act as spools around which DNA winds to create structural units called nucleosomes. Nucleosomes in turn ar ...

mRNA processing and

telomere A telomere (; ) is a region of repetitive nucleotide sequences associated with specialized proteins at the ends of linear chromosomes. Although there are different architectures, telomeres, in a broad sense, are a widespread genetic feature mo ...

maintenance. CBs assemble RNA which is used by

telomerase Telomerase, also called terminal transferase, is a ribonucleoprotein that adds a species-dependent telomere repeat sequence to the 3' end of telomeres. A telomere is a region of repetitive sequences at each end of the chromosomes of most e ...

to add

nucleotide Nucleotides are organic molecules consisting of a nucleoside and a phosphate. They serve as monomeric units of the nucleic acid polymers – deoxyribonucleic acid (DNA) and ribonucleic acid (RNA), both of which are essential biomolecul ...

s to the ends of telomeres.

History

CBs were initially discovered by neurobiologist Santiago Ramón y Cajal in 1903 as small argyrophilic (readily stained by silver salts, literally "silver loving") spots in the 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 "sphere organelles", "Binnenkörper", "nucleolar 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. 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 A protease (also called a peptidase, proteinase, or proteolytic enzyme) is an enzyme that catalyzes (increases reaction rate or "speeds up") proteolysis, breaking down proteins into smaller polypeptides or single amino acids, and spurring the form ...

and

RNase Ribonuclease (commonly abbreviated RNase) is a type of nuclease that catalyzes the degradation of RNA into smaller components. Ribonucleases can be divided into endoribonucleases and exoribonucleases, and comprise several sub-classes within th ...

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 in which Cajal bodies are most apparent usually demonstrate high levels of transcriptional activity, and are often dividing rapidly.

Cell cycle

They are about 0.1–2.0

micrometre The micrometre ( international spelling as used by the International Bureau of Weights and Measures; SI symbol: μm) or micrometer ( American spelling), also commonly known as a micron, is a unit of length in the International System of ...

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 machinery of the nucleus.

Functions

CBs are bound to the

nucleolus The nucleolus (, plural: nucleoli ) is the largest structure in the nucleus of eukaryotic cells. It is best known as the site of ribosome biogenesis, which is the synthesis of ribosomes. The nucleolus also participates in the formation of s ...

by coilin 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. CBs are associated with telomerase assembly and recruitment via a CAB-RNA sequence common in both CB RNAs ( scaRNAs) and the

RNA component of telomerase Telomerase RNA component, also known as TR, TER or TERC, is an ncRNA found in eukaryotes that is a component of telomerase, the enzyme used to extend telomeres. TERC serves as a template for telomere replication (reverse transcription) by tel ...

(TERC). TCAB1 recognizes the CAB sequence in both and recruits telomerase to the CBs. CBs contain high concentrations of splicing small nuclear ribonucleoproteins (

s), possibly indicating that they function to modify RNA after it has been transcribed from DNA. Experimental evidence indicates that CBs contribute to the

biogenesis Spontaneous generation is a superseded scientific theory that held that living creatures could arise from nonliving matter and that such processes were commonplace and regular. It was hypothesized that certain forms, such as fleas, could arise ...

of enzyme

, and assist in subsequent transport of telomerase to

References

{{Nucleus Organelles S Cell nucleus Cell anatomy Telomeres