Editing Nucleoplasm

{{Short description|Protoplasm that permeates a cell's nucleus}}
[[Image:Diagram human cell nucleus.svg|thumb|300px|The [[protoplasm]]ic material of the nucleus including the [[nucleolus]] labelled as nucleoplasm.]]
The '''nucleoplasm''', also known as '''karyoplasm''',<ref name="Collins_karyoplasm">{{cite web |title=karyoplasm |url=https://www.collinsdictionary.com/dictionary/english/karyoplasm |website=Collins English Dictionary |access-date=2 December 2022}}</ref> is the type of [[protoplasm]] that makes up the [[cell nucleus]], the most prominent [[organelle]] of the [[eukaryotic cell]]. It is enclosed by the [[nuclear envelope]], also known as the nuclear membrane.<ref name="proteinatlas_nucleoplasm">{{Cite web|title=The human cell in nucleoplasm|url=https://www.proteinatlas.org/humanproteome/subcellular/nucleoplasm|website=[[Human Protein Atlas]]|access-date=2025-01-08|url-status=live|archive-url=https://web.archive.org/web/20240915080037/https://www.proteinatlas.org/humanproteome/subcellular/nucleoplasm|archive-date=2024-09-15}}</ref> The nucleoplasm resembles the [[cytoplasm]] of a eukaryotic cell in that it is a gel-like substance found within a membrane, although the nucleoplasm only fills out the space in the nucleus and has its own unique functions. The nucleoplasm suspends structures within the nucleus that are not membrane-bound and is responsible for maintaining the shape of the nucleus.<ref name="proteinatlas_nucleoplasm"/> The structures suspended in the nucleoplasm include [[chromosome]]s, various [[protein]]s, [[nuclear bodies]], the [[nucleolus]], [[nucleoporin]]s, [[nucleotides]], and [[nuclear speckle]]s.<ref name="proteinatlas_nucleoplasm"/>

The soluble, liquid portion of the nucleoplasm is called the '''karyolymph'''<ref name="Collins_karyolymph">{{cite web |title=karyolymph |url=https://www.collinsdictionary.com/dictionary/english/karyolymph |website=Collins English Dictionary |access-date=2 December 2022}}</ref> '''nucleosol''',<ref name="PloS">{{cite journal |last1=Kühn |first1=T |last2=Ihalainen |first2=TO |last3=Hyväluoma |first3=J |last4=Dross |first4=N |last5=Willman |first5=SF |last6=Langowski |first6=J |last7=Vihinen-Ranta |first7=M |last8=Timonen |first8=J |title=Protein diffusion in mammalian cell cytoplasm. |journal=PLOS ONE |date=2011 |volume=6 |issue=8 |pages=e22962 |doi=10.1371/journal.pone.0022962 |pmid=21886771|pmc=3158749 |doi-access=free }}</ref> or '''nuclear hyaloplasm'''.

== History ==
[[File:Plate_03_Professor_E._Strassburger,_Photograph_album_of_German_and_Austrian_scientists_(cropped).png|thumb|alt=alt text|[[Poland|Polish]]-[[Germany|German]] [[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 [[Leeuwenhoek]] and was later described and drawn by [[Franz Bauer]].<ref name="Harris">{{cite book | vauthors = Harris H | title =The Birth of the Cell | year =1999 | publisher =Yale University Press | location =New Haven | isbn =978-0-300-07384-3 | url-access =registration | url =https://archive.org/details/birthofcell0000harr }}</ref> However, the cell nucleus was not named and described in detail until [[Robert Brown (Scottish botanist from Montrose)|Robert Brown's]] presentation to the [[Linnean Society]] in 1831.<ref name="Robert Brown">{{cite journal | last =Brown | first = Robert | name-list-style = vanc | title = On the Organs and Mode of Fecundation of Orchidex and Asclepiadea | journal = Miscellaneous Botanical Works I | pages = 511–514 | year = 1866}}</ref> 
The nucleoplasm, while described by Bauer and Brown, was not specifically isolated as a separate entity until its naming in 1882 by [[Poland|Polish]]-[[Germany|German]] scientist [[Eduard Strasburger]], one of the most famous [[botanist]]s of the 19th century, and the first person to discover [[mitosis]] in plants.<ref>{{cite web |url=https://universalium.en-academic.com/289156/Strasburger%2C_Eduard_Adolf |title=Strasburger, Eduard Adolf |date=2010 |website=Universalium |access-date=October 31, 2022}}</ref>

== 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.<ref name="proteinatlas_nucleoplasm"/> 34% of [[protein]]s encoded in the [[human genome]] are ones that localize to the nucleoplasm.<ref name="proteinatlas_nucleoplasm"/> These proteins take part in [[RNA transcription]] and [[gene regulation]] in the nucleoplasm.<ref name="proteinatlas_nucleoplasm"/> Proteins located in the nucleoplasm are involved in the activation of genes that are used in the cell cycle.<ref name=":1">{{Cite journal|last1=Kalverda|first1=Bernike|last2=Pickersgill|first2=Helen|last3=Shloma|first3=Victor V. |last4=Fornerod|first4=Maarten|date=2010|title=Nucleoporins Directly Stimulate Expression of Developmental and Cell-Cycle Genes Inside the Nucleoplasm|journal= Cell|volume=140|issue=3|pages=306-383<!--web version says 360-371?-->|doi=10.1016/j.cell.2010.01.011|pmid=20144760|s2cid=17260209|doi-access=free}}</ref> Some nucleoporins which typically make up the [[nuclear pore]], can be mobile and participate in the regulation of gene expression in the nucleoplasm.<ref name=":1" /><ref name=":2">{{Cite journal|last1=Khan|first1=Asmat Ullah|last2=Qu|first2=Rongmei|last3=Ouyang|first3=Jun|last4=Dai|first4=Jingxing|date=2020-04-03|title=Role of Nucleoporins and Transport Receptors in Cell Differentiation|journal=Frontiers in Physiology|volume=11|page=239|doi=10.3389/fphys.2020.00239|pmid=32308628|pmc=7145948|doi-access=free}}</ref> The nuclear pore is where molecules travel from inside the nucleoplasm to the cytoplasm and vice versa.<ref name=":2" /> The nucleoplasm is also a route for many molecules to travel through.<ref name=":2" /> 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.<ref name=":2" />
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.<ref>{{cite web |url=https://www.wise-geek.com/what-is-nucleoplasm.htm |title=What is Nucleoplasm? |last=Hed |first=Greer |date=October 6, 2022 |website=wisegeek |access-date=October 28, 2022}}</ref> 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 ===
There are around 20,000 [[protein-coding genes]] in humans,<ref name="Genome">{{cite web |title=Gene |url=https://www.genome.gov/genetics-glossary/Gene#:~:text=And%20genes%20are%20the%20part,of%20the%20entire%20human%20genome. |website=www.genome.gov |access-date=7 January 2025 |language=en}}</ref> and nearly a third of these have been found to  localize to the nucleoplasm via targeting by a [[nuclear localization sequence]] (NLS).<ref name="proteinatlas_nucleoplasm"/> Cytosolic proteins, known as [[importin]]s, act as receptors for the NLS, escorting the protein to a nuclear pore complex to be transported into the nucleoplasm.<ref name=":3">{{cite book |last=Casem|first=Merri Lynn|date=2016 |title=Case Studies in Cell Biology |publisher=Elsevier|pages=73–103 |isbn=978-0-12-801394-6}}</ref> 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.<ref name="proteinatlas_nucleoplasm"/> These proteins are divided into histone proteins, a class of proteins that bind to DNA and give chromosomes their shape and regulate gene activity,<ref>{{cite journal |last1=Stein |last2=Thrall |first2=C.L. |date=1973|title=Evidence for the presence of nonhistone chromosomal proteins in the nucleoplasm of HeLa S3 cells |journal=FEBS Letters |volume=32 |issue=1 |pages=41–45 |doi=10.1016/0014-5793(73)80732-X|pmid=4715686 |s2cid=20285491 |doi-access=free }}</ref> and non-histone proteins.

The nucleoplasm contains many enzymes that are instrumental in the synthesis of DNA and RNA, including [[DNA polymerase]] and [[RNA polymerase]] which function in DNA replication and RNA transcription, respectively. Additionally, the nucleoplasm is host to many of the enzymes that play essential roles in [[cellular metabolism]]. [[NAD+ synthase]] is stored in the nucleoplasm and functions in electron transport and [[redox reaction]]s involved with the [[electron transport chain]] and synthesis of [[adenosine triphosphate]] (ATP).<ref>{{cite journal |last1= Houtkooper |last2= Cantó |first2=C. |last3=Wanders |first3=R.J. |last4= Auwerx |first4=J. |date=2010|title=The Secret Life of NAD+: An Old Metabolite Controlling New Metabolic Signaling Pathways |journal= Endocrine Reviews|volume=31 |issue=2 |pages=194–223 |doi=10.1210/er.2009-0026|pmid= 20007326 |pmc= 2852209 }}</ref> [[Pyruvate kinase]] is also found in the nucleoplasm in significant quantities; this enzyme is involved in the final step of [[glycolysis]], catalyzing the conversion of [[phosphoenolpyruvate]] (PEP) to [[pyruvate]] along with the phosphorylation of [[adenosine diphosphate]] (ADP) to ATP.<ref>{{cite journal |last1= Israelsen |last2= Vander Heiden |first2=M.G. |date=2015|title=Pyruvate kinase: Function, regulation and role in cancer |journal=Seminars in Cell & Developmental Biology |volume=43 |pages=43–51 |doi=10.1016/j.semcdb.2015.08.004|pmid= 26277545 |pmc= 4662905 }}</ref> Importantly, the nucleoplasm contains [[Cofactor (biochemistry)|co-factor]]s and co-enzymes, including [[acetyl-CoA]], which plays a vital role in the [[citric acid cycle]],<ref>{{cite journal |last1=Falcón |last2=Chen |first2=S. |last3=Wood |first3=M.S. |last4=Aris |first4=J.P.|date=2010 |title=Acetyl-coenzyme A synthetase 2 is a nuclear protein required for replicative longevity in Saccharomyces cerevisiae |journal=Molecular and Cellular Biochemistry |volume=333 |issue=1–2 |pages=99–108 |doi=10.1007/s11010-009-0209-z|pmid=19618123 |pmc=3618671 }}</ref> and ATP, which is involved in energy storage and transfer.

=== Ions ===
[[File:NaKpompe2.jpg|thumb|alt=alt text|An example of the [[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]] [[ion]]s.]]
The ionic composition of the nucleoplasm is crucial in maintaining [[homeostasis]] within the cell and the organism as a whole. Ions that have been documented in the nucleoplasm include [[sodium]], [[potassium]], [[calcium]], [[phosphorus]], and [[magnesium]]. These ions are key players in a variety of biological functions. Sodium and potassium play key roles in the [[sodium-potassium pump]], a [[transmembrane]] [[ATPase]] that pumps three sodium ions out of the cell for every two potassium ions it pumps into the cell, creating an ionic gradient.<ref>{{cite journal |url=https://pdb101.rcsb.org/motm/118 |title=Molecule of the Month: Sodium-Potassium Pump |last=Goodsell |first=David |date=October 2009 |website=PDB-101 |access-date=October 30, 2022 |doi=10.2210/rcsb_pdb/mom_2009_10|url-access=subscription }}</ref> While this pump is generally considered to be a [[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.<ref>{{cite journal |last1=Galva |first1=Charitha |last2=Artigas |first2=Pablo |last3=Gatto |first3=Craig |date= December 2012|title=Nuclear Na+/K+-ATPase plays an active role in nucleoplasmic Ca2+ homeostasis |journal= Journal of Cell Science|volume=125 |issue=24 |pages=6137–6147 |doi=10.1242/jcs.114959|pmid=23077175 |pmc=3585523 }}</ref> 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.<ref>{{cite journal |last1=Wu |first1= Yufei |last2=Pegoraro |first2=Adrian |last3=Weitz |first3=David |last4=Janmey |first4=Paul|last5=Sun|first5=Sean|date= February 2022|title=The correlation between cell and nucleus size is explained by an eukaryotic cell growth model |journal= PLOS Computational Biology|volume=18 |issue=2 |pages= e1009400 |doi=10.1371/journal.pcbi.1009400|pmid= 35180215 |pmc= 8893647 |doi-access= free }}</ref> 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 [[ribosome]]s while proteins that localize to the nucleoplasm must undergo processing in the [[endoplasmic reticulum]] and [[golgi apparatus]] before being delivered to the nucleoplasm as part of the [[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.<ref>{{Cite web|title=The human cell in cytoplasm|url=https://www.proteinatlas.org/humanproteome/subcellular/cytosol|website=[[Human Protein Atlas]]}}</ref>

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.<ref>{{Cite web|title=Nuclear Membrane|url=https://www.genome.gov/genetics-glossary/Nuclear-Membrane|website=[[National Human Genome Research Institute]]}}</ref> 
The cytoplasm is also found in all known cells while nucleoplasm is only found in eukaryotic cells, as [[prokaryotic cell]]s 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 filament]]s 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.<ref>{{cite journal |last1=Pederson |first1=Thoru |date= March 2000|title=Half a Century of "The Nuclear Matrix" |journal= Molecular Biology of the Cell|volume=11 |issue=3 |pages=799–805 |doi= 10.1091/mbc.11.3.799|pmid=10712500 |pmc=14811 }}</ref> While the exact composition of the nuclear matrix has not been confirmed, type V [[intermediate filament]]s, 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.<ref>{{cite journal |last1=Dechat |first1=Thomas |last2=Adam |first2=Stephen A. |last3=Taimen |first3=Pekka |last4=Shimi |first4=Takeshi |last5=Goldman |first5=Robert D. |date= November 2010|title=Nuclear Lamins |journal= Cold Spring Harbor Perspectives in Biology |volume=2 |issue=11 |pages=a000547 |doi=10.1101/cshperspect.a000547|pmid=20826548 |pmc=2964183 }}</ref> [[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==
{{Reflist}}
{{Commons category|Nucleoplasm}}

{{Nucleus}}

[[Category:Cell anatomy]]
[[Category:Nuclear substructures]]