A nuclear organelle first identified in 1903 by the Spanish neurobiologist Santiago Ramon y Cajal in mammalian neurons and called by him the accessory body. In 1969 A. Monneron and W. Bernhard rediscovered these organelles within the interphase nuclei of mammalian liver cells and named them coiled bodies on the basis of their appearance in electron micrographs. Cajal bodies are now generally identified by immunofluorescence with specific antibodies against the protein coilin (q.v.), which is concentrated in them. The giant nucleus of amphibian oocytes (the germinal vesicle) contains 50 to 100 large Cajal bodies. All three eukaryotic RNA polymerases are found in oocyte Cajal bodies, along with many factors involved in transcription and processing of all types of RNA (pre-mRNA, pre-rRNA, tRNA, etc.). Based on studies of oocytes, Gall et al. have suggested that Cajal bodies are sites for preassembly of the transcription machinery of the nucleus, much as nucleoli are sites for preassembly of the translation machinery (ribosomes). See Chronology, 1999, Gall et al.; nucleolus, posttranscriptional processing, snurposomes, transcriptosomes.
Subjects: Genetics and Genomics.