(cell biology) An irregularly-shaped structure in the interchromatin space of nucleus in eukaryotic cell
In eukaryotic cell, the nucleus is the organelle responsible for maintaining the integrity of DNA and for controlling cellular activities such as metabolism, growth, and reproduction by regulating gene expression. It is a double-membraned organelle containing nuclear structures, e.g. chromatin and nuclear bodies. A nuclear body refers to any of the prominent non-membraned structures in the nucleus of the eukaryotic cell. Nuclear bodies are prominent structures of non-chromatinic fibrillary material and mostly proteinaceous. Examples of nuclear bodies are nucleolus, Cajal bodies and gems (Gemini of Cajal bodies), polymorphic interphase karyosomal association (PIKA) domains, promyelocytic leukaemia protein (PML) bodies, splicing speckles, paraspeckles, perichromatin fibrils, and clastosomes.
Paraspeckles are one of the nuclear bodies with a size approximately 0.2 to 1 μm. They can be found in the interchromatin space of the nucleus. The function is still unclear. They are first seen in HeLa cells. There are about 10 to 30 paraspeckles that are typically seen adjacent to splicing speckles, thus, the name. The proposed components of a paraspeckle include PSP1, PSP2, and p54nrb. These components have RNA recognition motifs. PSP1 and p54nrb have similar sequence. PSP1, though, was the protein that led to the discovery of paraspeckles (by Fox, et al.). Thus, it is used as a marker for paraspeckles. p54nrb is said to be involved in transcriptional regulation, splicing, unwinding of the DNA, viral RNA processing, circadian rhythm, regulation of cell proliferation, and nuclear retention of hyperedited dsRNA.  PSP2, in turn, is described to possibly be associated with RNA splicing and coactivating hormone receptors. Other suggested components are CFI(m)68 (Cleavage factor Im) and PSF. CFI(m)68 is proposed to be involved in pre-mRNA 3'end splicing.
Paraspeckles were observed to be present throughout the cell cycle except for telophase. During telophase, the paraspeckles seem to disappear. During this phase, the protein components were found to form a perinucleolar cap instead.
The function of the paraspeckles is not yet fully understood. Nevertheless, they are suggested to have a role in localizing its protein component and thus aid in directing their activity.
- Fox, A.; et al. (2002). "Paraspeckles: A Novel Nuclear Domain". Current Biology. 12 (1): 13–25. doi:10.1016/S0960-9822(01)00632-7
- Fox, A. and Bickmore, W. (1998). Nuclear Compartments: Paraspeckles. (2006, May 2). Retrieved from archive.is website: https://archive.is/20060502134554/http://npd.hgu.mrc.ac.uk/compartments/paraspeckles.html
- Fox, A. H., Bond, C. S., & Lamond, A. I. (November 2005). "P54nrb forms a heterodimer with PSP1 that localizes to paraspeckles in an RNA-dependent manner". Molecular Biology of the Cell. 16 (11): 5304–15. doi:10.1091/mbc.E05-06-0587
- Dettwiler, S., Aringhieri, C., Cardinale, S., Keller, W., & Barabino, S. M. (2004). "Distinct sequence motifs within the 68-kDa subunit of cleavage factor Im mediate RNA binding, protein-protein interactions, and subcellular localization". J. Biol. Chem. 279 (34): 35788–97. doi:10.1074/jbc.M403927200
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