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Nuclear bodies (also known as nuclear domains or nuclear dots) are biomolecular condensates, membraneless structures found in the Cell nucleus of eukaryote cells. Nuclear bodies include Cajal body, the nucleolus, nuclear speckles (also called splicing speckles), histone locus bodies, and promyelocytic leukemia protein (PML) nuclear bodies (also called PML oncogenic dots). Nuclear bodies also include ND10s. ND stands for nuclear domain, and 10 refers to the number of dots seen. Additionally, a nuclear body subtype is a clastosome suggested to be a site of protein degradation.
While biomolecular condensate is a term often used interchangeably with nuclear bodies, the term "condensates" implies the thermodynamic properties of the body are known. Thus, nuclear body (and sometimes nuclear compartment) is a term that is more general and encompasses structures where either the biophysical property is not a condensate or is currently untested.
Nuclear bodies were first seen as prominent interchromatin structures in the nuclei of malignant or hyperstimulated animal cells identified using anti-sp100 autoantibodies from primary biliary cirrhosis and subsequently the promyelocytic leukemia (PML) factor, but appear also to be elevated in many autoimmune and cancerous diseases. Nuclear dots are metabolically stable and resistant to nuclease digestion and salt extraction.
One hypothesized function of the dots is as a 'nuclear dump' or 'storage depot'. The nuclear bodies may not all perform the same function. Sp140 associates with certain bodies and appears to be involved in transcriptional activation.
ND10 nuclear bodies have been shown to play a major role in chromatin regulation.
Nuclear bodies have been suggested to be involved in multiple aspects of gene regulation. By concentrating substrates and enzymes in these defined territories (i.e., pre-ribosomal RNA and associated ribosome biogenesis protein within the nucleolus), it is hypothesized that this may help increase the efficiency of the enzymatic reactions associated with the particular nuclear body. For example, nuclear speckles, once thought to be storage depots of splicing factors, have been now shown to concentrate splicing-promoting factors (e.g., components of the major and minor spliceosome) and pre-mRNA substrate molecules to boost the kinetic efficiency of the splicing reaction. Thus future studies will show whether other nuclear bodies play functional roles in various aspects of gene regulation, such as transcription, RNA modifications, ribosome biogenesis, and other nuclear processes.
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