Nucleoplasm

Source: Wikipedia, the free encyclopedia.
The protoplasmic material of the nucleus including the nucleolus labelled as nucleoplasm.

The nucleoplasm, also known as karyoplasm,

nuclear speckles.[2]

The soluble, liquid portion of the nucleoplasm is called the karyolymph[3] nucleosol,[4] or nuclear hyaloplasm.

History

botanist and namer of nucleoplasm, Eduard Strasburger
.

The existence of the nucleus, including the nucleoplasm, was first documented as early as 1682 by the Dutch microscopist

Linnean Society in 1831.[6]
The nucleoplasm, while described by Bauer and Brown, was not specifically isolated as a separate entity until its naming in 1882 by
botanists of the 19th century, and the first person to discover mitosis in plants.[7]

Role

Many important cell functions take place in the nucleus, more specifically in the nucleoplasm. The main function of the nucleoplasm is to provide the proper environment for essential processes that take place in the nucleus, serving as the suspension substance for all organelles inside the nucleus, and storing the structures that are used in these processes.

gene regulation in the nucleoplasm.[2] Proteins located in the nucleoplasm are involved in the activation of genes that are used in the cell cycle.[8] Some nucleoporins which typically make up the nuclear pore, can be mobile and participate in the regulation of gene expression in the nucleoplasm.[8][9] The nuclear pore is where molecules travel from inside the nucleoplasm to the cytoplasm and vice versa.[9] The nucleoplasm is also a route for many molecules to travel through.[9] Smaller molecules are able to pass freely through the nuclear pore to get into and out of the nucleoplasm, while larger proteins need the help of receptors on the surface of the nuclear envelope.[9]
The nuclear matrix is also believed to be contained in the nucleoplasm where it functions to maintain the size and shape of the nucleus, in a role similar to that of the cytoskeleton found in the cytoplasm.[10] However, the existence and the exact function of the nuclear matrix remain unclear and heavily debated.

Composition

The nucleoplasm is a highly viscous liquid that is enveloped by the nuclear membrane and consists mainly of water, proteins, dissolved ions, and a variety of other substances including nucleic acids and minerals.

Proteins

Nearly a third of the human protein-coding genes (6784 genes)[2] have been found to localize to the nucleoplasm via targeting by a nuclear localization sequence (NLS). Cytosolic proteins, known as importins, act as receptors for the NLS, escorting the protein to a nuclear pore complex to be transported into the nucleoplasm.[11] Proteins in the nucleoplasm are mainly tasked with participating in and regulating cellular functions that are DNA-dependent, including transcription, RNA splicing, DNA repair, DNA replication, and a variety of metabolic processes.[2] These proteins are divided into histone proteins, a class of proteins that bind to DNA and give chromosomes their shape and regulate gene activity,[12] and non-histone proteins.

The nucleoplasm contains many enzymes that are instrumental in the synthesis of DNA and RNA, including

pyruvate along with the phosphorylation of adenosine diphosphate (ADP) to ATP.[14] Importantly, the nucleoplasm contains co-factors and co-enzymes, including acetyl-CoA, which plays a vital role in the citric acid cycle,[15]
and ATP, which is involved in energy storage and transfer.

Ions

sodium-potassium pump, a P-type ATPase, which controls the ionic gradient across the cell membrane and the nuclear envelope as well as the ionic makeup of the nucleoplasm through the selective pumping of sodium and potassium ions
.

The ionic composition of the nucleoplasm is crucial in maintaining

plasma membrane protein, its presence has been recorded in the nuclear envelope, controlling the ionic gradient between the cytoplasm and nucleoplasm of the cell and contributing to the homeostasis of calcium within the cell.[17] These ions also determine the concentration gradient that exists between the cytoplasm and nucleoplasm, serving to control the flow of ions across the nuclear envelope.[18]
They are important in maintaining the osmolarity of the nucleoplasm which in turn provides structural integrity to the nuclear envelope as well as the organelles suspended in the dense nucleoplasm.

Similarity to cytoplasm

Nucleoplasm is quite similar to the cytoplasm, with the main difference being that nucleoplasm is found inside the nucleus while the cytoplasm is located inside the cell, outside of the nucleus. Their ionic compositions are nearly identical due to the ion pumps and permeability of the nuclear envelope, however, the proteins in these two fluids differ greatly. Proteins in the cytoplasm are termed cytosolic proteins which are produced by free

secretory pathway. These proteins also differ in function, as proteins that localize to the nucleoplasm are largely involved in DNA-dependent processes including cell division and gene regulation, while cytosolic proteins are mainly involved in protein modification, mRNA degradation, metabolic processes, signal transduction, and cell death.[19]

The cytoplasm and the nucleoplasm are both highly gelatinous structures enclosed by membranous structures- the plasma membrane and the nuclear envelope, respectively. However, while the cytoplasm is contained by a single lipid bilayer membrane, the nuclear envelope that compartmentalizes the nucleoplasm consists of two separate lipid bilayers- an outer membrane and an inner membrane.[20] The cytoplasm is also found in all known cells while nucleoplasm is only found in eukaryotic cells, as

prokaryotic cells lack a well-defined nucleus and membrane-bound organelles. Additionally, during cell division, the cytoplasm divides during cytokinesis
, while the nucleoplasm is released with the dissolution of the nuclear envelope, refilling only after the nuclear envelope reforms.

The organelles and other structures within the cytoplasm and nucleoplasm are organized by protein filaments within their respective compartments. The cytoplasm contains the cytoskeleton, a network of protein filaments found in all cells, while the nucleoplasm is believed to contain the nuclear matrix, a hypothetically analogous network of filaments that organizes the organelles and genetic information within the nucleus. While the structure and function of the cytoskeleton have been well documented, the exact function, and even the presence, of the nuclear matrix is disputed.[21] While the exact composition of the nuclear matrix has not been confirmed, type V intermediate filaments, known as nuclear lamins, have been documented in the nucleoplasm, functioning in the structural support of the nucleus as well as the regulation of DNA replication, transcription, and chromatin organization.[22] Cytoplasmic streaming, the circular flow of cytoplasm driven by the cytoskeleton, has been well documented in the cytoplasm, aiding in intracellular transport, but this process has not been documented in the nucleoplasm.

References

  1. ^ "karyoplasm". Collins English Dictionary. Retrieved 2 December 2022.
  2. ^ a b c d e f g h "The human cell in nucleoplasm". Human Protein Atlas.
  3. ^ "karyolymph". Collins English Dictionary. Retrieved 2 December 2022.
  4. PMID 21886771
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  5. ISBN 978-0-300-07384-3
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  6. ^ Brown R (1866). "On the Organs and Mode of Fecundation of Orchidex and Asclepiadea". Miscellaneous Botanical Works I: 511–514.
  7. ^ "Strasburger, Eduard Adolf". Universalium. 2010. Retrieved October 31, 2022.
  8. ^
    S2CID 17260209
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  9. ^
    PMID 32308628
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  10. ^ Hed, Greer (October 6, 2022). "What is Nucleoplasm?". wisegeek. Retrieved October 28, 2022.
  11. ISBN 978-0-12-801394-6
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  12. S2CID 20285491
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  13. PMID 20007326
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  14. PMID 26277545
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  15. PMID 19618123
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  16. doi:10.2210/rcsb_pdb/mom_2009_10
    . Retrieved October 30, 2022.
  17. PMID 23077175
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  18. PMID 35180215
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  19. ^ "The human cell in cytoplasm". Human Protein Atlas.
  20. ^ "Nuclear Membrane". National Human Genome Research Institute.
  21. PMID 10712500
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  22. PMID 20826548
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