Editing Somatic cell

{{short description|Any biological cell forming the body of an organism}}
{{see also|Somatic (biology)}}
In [[cellular biology]], a '''somatic cell''' ({{ety|grc|''σῶμα'' (sôma)|body}}), or '''vegetal cell''', is any [[cell (biology)|biological cell]] forming the body of a [[multicellular organism]] other than a [[gamete]], [[germ cell]], [[gametocyte]] or undifferentiated [[stem cell]].<ref name="campbell229">{{Cite book |url=https://archive.org/details/biologynastaedit00camp_302 |title=Biology |vauthors=Campbell NA, Reece JB, Urry LA, Cain ML, Wasserman SA, Minorsky PV, Jackson RB |publisher=Pearson Benjamin Cummings |year=2009 |isbn=978-0-8053-6844-4 |edition=9th |page=[https://archive.org/details/biologynastaedit00camp_302/page/n275 229] |url-access=limited}}</ref> Somatic cells compose the body of an organism and divide through [[mitosis]].

In contrast, [[gametes]] derive from [[meiosis]] within the [[germ cell]]s of the [[germline]] and they fuse during [[sexual reproduction]]. [[Stem cells]] also can divide through [[mitosis]], but are different from somatic in that they [[Cellular differentiation|differentiate]] into diverse specialized cell types.

In [[mammal]]s, somatic cells make up all the internal organs, skin, bones, blood and [[connective tissue]], while mammalian germ cells give rise to [[spermatozoa]] and [[ovum|ova]] which fuse during [[fertilization]] to produce a cell called a [[zygote]], which divides and differentiates into the cells of an [[embryo]]. There are approximately 220 types of somatic cell in the human body.<ref name="campbell229" />

Theoretically, these cells are not germ cells (the source of gametes); they transmit their [[mutations]], to their cellular descendants (if they have any), but not to the organism's descendants. However, in [[sponge]]s, non-differentiated somatic cells form the germ line and, in [[Cnidaria]], differentiated somatic cells are the source of the germline. Mitotic cell division is only seen in [[diploid]] somatic cells. Only some cells like germ cells take part in reproduction.<ref>{{Cite journal |vauthors=Chernis PJ |date=1985 |title=Petrographic analysis of URL-2 and URL-6 special thermal conductivity samples. |journal=Department Cf Energy, Mines, and Resources. Earth Physics Branch, Report. |volume=8 |page=20 |doi=10.4095/315247 |doi-access=free}}</ref>

==Evolution==
As [[multicellularity]] was theorized to be evolved many times,<ref>{{Cite journal |last=Grosberg |first=Richard K. |last2=Strathmann |first2=Richard R. |date=2007-12-01 |title=The Evolution of Multicellularity: A Minor Major Transition? |url=https://www.annualreviews.org/doi/10.1146/annurev.ecolsys.36.102403.114735 |journal=Annual Review of Ecology, Evolution, and Systematics |language=en |volume=38 |issue=1 |pages=621–654 |doi=10.1146/annurev.ecolsys.36.102403.114735 |issn=1543-592X|url-access=subscription }}</ref> so did sterile somatic cells.{{CN|date=August 2020}} The evolution of an immortal [[germline]] producing specialized somatic cells involved the emergence of [[Death#In biology|mortality]], and can be viewed in its simplest version in [[Volvocales|volvocine]] algae.<ref>{{Cite journal |vauthors=Hallmann A |date=June 2011 |title=Evolution of reproductive development in the volvocine algae |journal=Sexual Plant Reproduction |volume=24 |issue=2 |pages=97–112 |doi=10.1007/s00497-010-0158-4 |pmc=3098969 |pmid=21174128}}</ref> Those species with a separation between sterile somatic cells and a germline are called [[Weismann barrier|Weismannists]]. Weismannist development is relatively rare (e.g., [[vertebrate]]s, [[arthropod]]s, ''[[Volvox]]''), as many species have the capacity for [[somatic embryogenesis]] (e.g., [[land plant]]s, most [[algae]], and numerous [[invertebrates]]).<ref>Ridley M (2004) Evolution, 3rd edition. Blackwell Publishing, p. 29-297.</ref><ref>Niklas, K. J. (2014) [https://web.archive.org/web/20170327213452/http://www.amjbot.org/content/101/1/6.long The evolutionary-developmental origins of multicellularity].</ref>

==Genetics and chromosomes==
Like all cells, somatic cells contain [[DNA]] arranged in [[chromosome]]s. If a somatic cell contains chromosomes arranged in pairs, it is called [[diploid]] and the organism is called a diploid organism. The gametes of diploid organisms contain only single unpaired chromosomes and are called [[haploid]]. Each pair of chromosomes comprises one chromosome inherited from the father and one inherited from the mother. In humans, somatic cells contain 46 [[chromosomes]] organized into 23 pairs. By contrast, gametes of diploid organisms contain only half as many chromosomes. In humans, this is 23 unpaired chromosomes. When two gametes (i.e. a spermatozoon and an ovum) meet during conception, they fuse together, creating a [[zygote]]. Due to the fusion of the two gametes, a human zygote contains 46 chromosomes (i.e. 23 pairs).{{cn|date=June 2024}}

A large number of [[species]] have the chromosomes in their somatic cells arranged in fours ("[[tetraploid]]") or even sixes ("[[hexaploid]]"). Thus, they can have diploid or even triploid germline cells. An example of this is the modern cultivated species of [[wheat]], ''Triticum aestivum L.'', a hexaploid species whose somatic cells contain six copies of every [[chromatid]].{{cn|date=June 2024}}

The frequency of spontaneous [[mutation]]s is significantly lower in advanced male [[germ cell]]s than in somatic cell types from the same individual.<ref name="pmid9707592">{{Cite journal |vauthors=Walter CA, Intano GW, McCarrey JR, McMahan CA, Walter RB |date=August 1998 |title=Mutation frequency declines during spermatogenesis in young mice but increases in old mice |journal=Proceedings of the National Academy of Sciences of the United States of America |volume=95 |issue=17 |pages=10015–10019 |bibcode=1998PNAS...9510015W |doi=10.1073/pnas.95.17.10015 |pmc=21453 |pmid=9707592 |doi-access=free}}</ref> Female germ cells also show a mutation frequency that is lower than that in corresponding somatic cells and similar to that in male germ cells.<ref name="pmid23153565">{{Cite journal |vauthors=Murphey P, McLean DJ, McMahan CA, Walter CA, McCarrey JR |date=January 2013 |title=Enhanced genetic integrity in mouse germ cells |journal=Biology of Reproduction |volume=88 |issue=1 |pages=6 |doi=10.1095/biolreprod.112.103481 |pmc=4434944 |pmid=23153565}}</ref> These findings appear to reflect employment of more effective mechanisms to limit the initial occurrence of spontaneous mutations in germ cells than in somatic cells. Such mechanisms likely include elevated levels of [[DNA repair]] enzymes that ameliorate most potentially mutagenic [[DNA damage (naturally occurring)|DNA damages]].<ref name="pmid23153565" />

==Cloning==
[[File:Cloning diagram english.svg|thumb|Schematic model of somatic cell nuclear transfer. This technique has been used to create clones of an organism or in therapeutic medicine.]]
In recent years, the technique of [[cloning]] whole organisms has been developed in mammals, allowing almost identical genetic clones of an animal to be produced. One method of doing this is called "[[somatic cell nuclear transfer]]" and involves removing the [[cell nucleus|nucleus]] from a somatic cell, usually a skin cell. This nucleus contains all of the genetic information needed to produce the organism it was removed from. This nucleus is then injected into an [[ovum]] of the same species which has had its own genetic material removed.<ref>{{Cite journal |last=Wilmut |first=Ian |last2=Bai |first2=Yu |last3=Taylor |first3=Jane |date=2015-10-19 |title=Somatic cell nuclear transfer: origins, the present position and future opportunities |journal=Philosophical Transactions of the Royal Society B: Biological Sciences |language=en |volume=370 |issue=1680 |pages=20140366 |doi=10.1098/rstb.2014.0366 |issn=0962-8436 |pmc=4633995 |pmid=26416677}}</ref> The ovum now no longer needs to be fertilized, because it contains the correct amount of genetic material (a [[diploid]] number of [[chromosomes]]). In theory, the ovum can be implanted into the [[uterus]] of a same-species animal and allowed to develop. The resulting animal will be a nearly genetically identical clone to the animal from which the nucleus was taken. The only difference is caused by any [[mitochondria]]l DNA that is retained in the ovum, which is different from the cell that donated the nucleus. In practice, this technique has so far been problematic, although there have been a few high-profile successes, such as [[Dolly the Sheep]] (July 5, 1996 - February 14, 2003)<ref>{{Cite web |title=The Life of Dolly {{!}} Dolly the Sheep |url=https://dolly.roslin.ed.ac.uk/facts/the-life-of-dolly/index.html |access-date=2023-12-09 |language=en-US}}</ref> and, more recently, [[Snuppy]] (April 24, 2005 - May 2015), the first cloned [[dog]].<ref>{{Cite journal |last=Kim |first=Min Jung |last2=Oh |first2=Hyun Ju |last3=Kim |first3=Geon A |last4=Setyawan |first4=Erif Maha Nugraha |last5=Choi |first5=Yoo Bin |last6=Lee |first6=Seok Hee |last7=Petersen-Jones |first7=Simon M. |last8=Ko |first8=CheMyong J. |last9=Lee |first9=Byeong Chun |date=2017-11-10 |title=Birth of clones of the world's first cloned dog |journal=Scientific Reports |language=en |volume=7 |issue=1 |page=15235 |bibcode=2017NatSR...715235K |doi=10.1038/s41598-017-15328-2 |issn=2045-2322 |pmc=5681657 |pmid=29127382}}</ref>

== Biobanking ==
Somatic cells have also been collected in the practice of biobanking. The [[cryoconservation of animal genetic resources]] is a means of conserving animal genetic material in response to decreasing ecological biodiversity.<ref>{{Cite journal |last=Bolton |first=Rhiannon L |last2=Mooney |first2=Andrew |last3=Pettit |first3=Matt T |last4=Bolton |first4=Anthony E |last5=Morgan |first5=Lucy |last6=Drake |first6=Gabby J |last7=Appeltant |first7=Ruth |last8=Walker |first8=Susan L |last9=Gillis |first9=James D |last10=Hvilsom |first10=Christina |date=2022-07-01 |title=Resurrecting biodiversity: advanced assisted reproductive technologies and biobanking |url=https://raf.bioscientifica.com/view/journals/raf/3/3/RAF-22-0005.xml |journal=Reproduction and Fertility |volume=3 |issue=3 |pages=R121–R146 |doi=10.1530/RAF-22-0005 |issn=2633-8386 |pmc=9346332 |pmid=35928671}}</ref> As populations of living organisms fall so does their genetic diversity. This places species long-term survivability at risk. Biobanking aims to preserve biologically viable cells through long-term storage for later use. Somatic cells have been stored with the hopes that they can be reprogrammed into induced pluripotent stem cells (iPSCs), which can then differentiate into viable reproductive cells.<ref>{{Cite journal |last=Sun |first=Yanyan |last2=Li |first2=Yunlei |last3=Zong |first3=Yunhe |last4=Mehaisen |first4=Gamal M. K. |last5=Chen |first5=Jilan |date=2022-10-09 |title=Poultry genetic heritage cryopreservation and reconstruction: advancement and future challenges |journal=Journal of Animal Science and Biotechnology |language=en |volume=13 |issue=1 |page=115 |doi=10.1186/s40104-022-00768-2 |issn=2049-1891 |pmc=9549680 |pmid=36210477 |doi-access=free}}</ref>

==Genetic modifications==
[[File:DNA Repair-colourfriendly.png|thumb|Schematic of CRISPR based gene editing technique]]
Development of [[biotechnology]] has allowed for the genetic manipulation of somatic cells, whether for the modelling of chronic disease or for the prevention of malaise conditions.<ref>{{Cite journal |display-authors=6 |vauthors=Jarrett KE, Lee CM, Yeh YH, Hsu RH, Gupta R, Zhang M, Rodriguez PJ, Lee CS, Gillard BK, Bissig KD, Pownall HJ, Martin JF, Bao G, Lagor WR |date=March 2017 |title=Somatic genome editing with CRISPR/Cas9 generates and corrects a metabolic disease |journal=Scientific Reports |volume=7 |pages=44624 |bibcode=2017NatSR...744624J |doi=10.1038/srep44624 |pmc=5353616 |pmid=28300165}}</ref><ref>{{Cite web |date=24 January 2018 |title=NIH Commits $190M to Somatic Gene-Editing Tools/Tech Research |url=https://www.genengnews.com/gen-news-highlights/nih-commits-190m-to-somatic-gene-editing-toolstech-research/81255414 |access-date=5 July 2018}}</ref> Two current means of gene editing are the use of [[transcription activator-like effector nuclease]]s (TALENs) or [[CRISPR gene editing|clustered regularly interspaced short palindromic repeats]] (CRISPR).{{cn|date=June 2024}}

Genetic engineering of somatic cells has resulted in some [[Human genetic engineering#Controversy|controversies]],<ref>{{Cite web |last=Singh |first=Amarendra N. |date=2021-04-01 |title=Ethical Controversies and Challenges in Human Genome Editing. {{!}} International Medical Journal {{!}} EBSCOhost |url=https://openurl.ebsco.com/contentitem/gcd:149537843?sid=ebsco:plink:crawler&id=ebsco:gcd:149537843 |access-date=2024-06-20 |website=openurl.ebsco.com |language=en}}</ref> although the International Summit on Human Gene Editing has released a statement in support of genetic modification of somatic cells, as the modifications thereof are not passed on to offspring.<ref>{{Cite web |date=8 December 2015 |title=Why Treat Gene Editing Differently In Two Types Of Human Cells? |url=http://www.iflscience.com/health-and-medicine/why-treat-gene-editing-differently-two-types-human-cells/ |access-date=5 July 2018}}</ref>

==Cellular aging==

In mammals a high level of repair and maintenance of cellular DNA appears to be beneficial early in life.  However, some types of cell, such as those of the brain and muscle, undergo a transition from mitotic cell division to a post-mitotic (non-dividing) condition during early development, and this transition is accompanied by a reduction in [[DNA repair]] capability.<ref>{{Cite journal |vauthors=Gensler HL |date=1981 |title=Low level of U.V.-induced unscheduled DNA synthesis in postmitotic brain cells of hamsters: possible relevance to aging |journal=Exp. Geronont. |volume=16 |issue=2 |pages=199–207 |doi=10.1016/0531-5565(81)90046-2}}</ref><ref>{{Cite journal |vauthors=Karran P, Moscona A, Strauss B |date=July 1977 |title=Developmental decline in DNA repair in neural retina cells of chick embryos. Persistent deficiency of repair competence in a cell line derived from late embryos |journal=J Cell Biol |volume=74 |issue=1 |pages=274–86 |doi=10.1083/jcb.74.1.274 |pmc=2109876 |pmid=559680}}</ref><ref>{{Cite journal |vauthors=Lampidis TJ, Schaiberger GE |date=December 1975 |title=Age-related loss of DNA repair synthesis in isolated rat myocardial cells |journal=Exp Cell Res |volume=96 |issue=2 |pages=412–6 |doi=10.1016/0014-4827(75)90276-1 |pmid=1193184}}</ref> This reduction may be an evolutionary adaptation permitting the diversion of cellular resources that were earlier used for DNA repair, as well as for [[DNA replication]] and [[cell division]], to higher priority neuronal and muscular functions.  An effect of these reductions is to allow increased accumulation of [[DNA damage (naturally occurring)|DNA damage]] likely contributing to cellular aging.

== See also ==
* [[Somatic cell count]]
* [[List of biological development disorders]]
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== References ==
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{{DEFAULTSORT:Somatic Cell}}
[[Category:Cloning]]
[[Category:Cells]]
[[Category:Developmental biology]]