The nuclear Cajal bodies (CBs) are small subnuclear membraneless organelles present either free in the nucleoplasm and/or physically associated to specific regions of chromatin. CBs contain newly assembled small nuclear ribonucleoproteins (snRNPs) and small nucleolar ribonucleoproteins (snoRNPs) particles, which are involved in pre-mRNA splicing and in ribosomal RNA processing, respectively. Mammalian nucleus in interphase, show 2-6 CBs, as irregular, punctuate structures, which vary in size and shape and which are often juxtaposed to nucleoli. At the electronic-microscope level, they are composed of heterogeneous mixture of electro-dense particles with diameters ranging from 20-25 nm and are called coiled body. Structures similar to CBs have been identified in the amphibian oocyte nucleus (called sphere organelles) and in insect (called endobodies). CBs are motile and dynamic structures. Both their protein and RNA-protein components can cycle continuously between CBs and other nuclear locations depending on the transcriptional state of the cell.

› Cellular component

› Cajal body [ GO:0015030 ]