Editing Cell nucleus (section)

===Cajal bodies and gems===
[[File:Cajal-Body-Overview.svg|thumb|Cajal body]]
A nucleus typically contains between one and ten compact structures called [[Cajal body|Cajal bodies]] or coiled bodies (CB), whose diameter measures between 0.2&nbsp;μm and 2.0&nbsp;μm depending on the cell type and species.<ref name="Cioce" /> When seen under an electron microscope, they resemble balls of tangled thread<ref name="Pollard" /> and are dense foci of distribution for the protein [[coilin]].<ref name="MateraFrey">{{cite journal | vauthors = Matera AG, Frey MR | title = Coiled bodies and gems: Janus or gemini? | journal = American Journal of Human Genetics | volume = 63 | issue = 2 | pages = 317–21 | date = August 1998 | pmid = 9683623 | pmc = 1377332 | doi = 10.1086/301992 | department = Review }}</ref> CBs are involved in a number of different roles relating to RNA processing, specifically [[snoRNA|small nucleolar RNA]] (snoRNA) and [[small nuclear RNA]] (snRNA) maturation, and histone mRNA modification.<ref name="Cioce" />

Similar to Cajal bodies are Gemini of Cajal bodies, or gems, whose name is derived from the [[Gemini (constellation)|Gemini constellation]] in reference to their close "twin" relationship with CBs. Gems are similar in size and shape to CBs, and in fact are virtually indistinguishable under the microscope.<ref name="MateraFrey" /> Unlike CBs, gems do not contain [[snRNP|small nuclear ribonucleoproteins]] (snRNPs), but do contain a protein called [[survival of motor neuron protein|survival of motor neuron]] (SMN) whose function relates to snRNP biogenesis. Gems are believed to assist CBs in snRNP biogenesis,<ref name="Matera">{{cite journal | vauthors = Matera AG | title = Of coiled bodies, gems, and salmon | journal = Journal of Cellular Biochemistry | volume = 70 | issue = 2 | pages = 181–92 | date = August 1998 | pmid = 9671224 | doi = 10.1002/(sici)1097-4644(19980801)70:2<181::aid-jcb4>3.0.co;2-k | s2cid = 44941483 | department = Review }}</ref> though it has also been suggested from microscopy evidence that CBs and gems are different manifestations of the same structure.<ref name="MateraFrey" /> Later ultrastructural studies have shown gems to be twins of Cajal bodies with the difference being in the coilin component; Cajal bodies are SMN positive and coilin positive, and gems are SMN positive and coilin negative.<ref name="Navascues">{{cite journal | vauthors = Navascues J, Berciano MT, Tucker KE, Lafarga M, Matera AG | title = Targeting SMN to Cajal bodies and nuclear gems during neuritogenesis | journal = Chromosoma | volume = 112 | issue = 8 | pages = 398–409 | date = June 2004 | pmid = 15164213 | pmc = 1592132 | doi = 10.1007/s00412-004-0285-5 | department = Primary }}</ref>