Cajal bodies (CBs), alsocoiled bodies, are sphericalnuclear bodies of 0.3–1.0 μm in diameter found in thenucleus of proliferativecells likeembryonic cells andtumor cells, or metabolically active cells likeneurons. CBs are membrane-lessorganelles and largely consist ofproteins andRNA. They were first reported bySantiago Ramón y Cajal in 1903, who called themnucleolar accessory bodies due to their association with thenucleoli in neuronal cells.[1] They were rediscovered with the use of theelectron microscope (EM) and namedcoiled bodies, according to their appearance as coiled threads on EM images, and later renamed after their discoverer.[2] Research on CBs was accelerated after discovery andcloning of the marker proteinp80/Coilin.[3] CBs have been implicated in RNA-related metabolic processes such as the biogenesis, maturation and recycling ofsnRNPs,histone mRNA processing andtelomere maintenance. CBs assemble RNA which is used bytelomerase to addnucleotides to the ends of telomeres.[4]
CBs were initially discovered by neurobiologistSantiago Ramón y Cajal in 1903 as smallargyrophilic (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 themnucleolar 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 400–600Å. 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 ofribonucleoproteins since treatment of cells withprotease andRNase together, but not alone, caused dramatic changes to the structure of CBs.[5]
Cajal bodies are found in all eukaryotes that have been carefully studied.[6]The cells in which Cajal bodies are most apparent usually demonstrate high levels of transcriptional activity, and are often dividing rapidly.[7]
They are about 0.1–2.0micrometres 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 thetranscription machinery of the nucleus.[8]
CBs are bound to thenucleolus bycoilin proteins. P80-coilin is a specific marker for coiled bodies,[9] 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 theRNA component of telomerase (TERC). TCAB1 recognizes the CAB sequence in both and recruits telomerase to the CBs.[citation needed]
CBs contain high concentrations ofsplicing small nuclear ribonucleoproteins (snRNPs), possibly indicating that they function to modify RNA after it has beentranscribed from DNA.[10] Experimental evidence indicates that CBs contribute to the biogenesis of enzymetelomerase, and assist in subsequent transport of telomerase totelomeres.[11][12]