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Somatic cell

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See also:Somatic (biology)

Incellular biology,asomatic cell(fromAncient Greekσῶμα(sôma)'body'), orvegetal cell,is anybiological cellforming the body of amulticellular organismother than agamete,germ cell,gametocyteor undifferentiatedstem cell.[1]Somatic cells compose the body of an organism and divide throughmitosis.

In contrast,gametesderive frommeiosiswithin thegerm cellsof thegermlineand they fuse duringsexual reproduction.Stem cellsalso can divide throughmitosis,but are different from somatic in that theydifferentiateinto diverse specialized cell types.

Inmammals,somatic cells make up all the internal organs, skin, bones, blood andconnective tissue,while mammalian germ cells give rise tospermatozoaandovawhich fuse duringfertilizationto produce a cell called azygote,which divides and differentiates into the cells of anembryo.There are approximately 220 types of somatic cell in the human body.[1]

Theoretically, these cells are not germ cells (the source of gametes); they transmit theirmutations,to their cellular descendants (if they have any), but not to the organism's descendants. However, insponges,non-differentiated somatic cells form the germ line and, inCnidaria,differentiated somatic cells are the source of the germline. Mitotic cell division is only seen indiploidsomatic cells. Only some cells like germ cells take part in reproduction.[2]

Evolution

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Asmulticellularitywas theorized to be evolved many times,[3]so did sterile somatic cells.[citation needed]The evolution of an immortalgermlineproducing specialized somatic cells involved the emergence ofmortality,and can be viewed in its simplest version involvocinealgae.[4]Those species with a separation between sterile somatic cells and a germline are calledWeismannists.Weismannist development is relatively rare (e.g.,vertebrates,arthropods,Volvox), as many species have the capacity forsomatic embryogenesis(e.g.,land plants,mostalgae,and numerousinvertebrates).[5][6]

Genetics and chromosomes

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Like all cells, somatic cells containDNAarranged inchromosomes.If a somatic cell contains chromosomes arranged in pairs, it is calleddiploidand the organism is called a diploid organism. The gametes of diploid organisms contain only single unpaired chromosomes and are calledhaploid.Each pair of chromosomes comprises one chromosome inherited from the father and one inherited from the mother. In humans, somatic cells contain 46chromosomesorganized 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 azygote.Due to the fusion of the two gametes, a human zygote contains 46 chromosomes (i.e. 23 pairs).[citation needed]

A large number ofspecieshave 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 ofwheat,Triticum aestivum L.,a hexaploid species whose somatic cells contain six copies of everychromatid.[citation needed]

The frequency of spontaneousmutationsis significantly lower in advanced malegerm cellsthan in somatic cell types from the same individual.[7]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.[8]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 ofDNA repairenzymes that ameliorate most potentially mutagenicDNA damages.[8]

Cloning

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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 ofcloningwhole 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 thenucleusfrom 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 anovumof the same species which has had its own genetic material removed.[9]The ovum now no longer needs to be fertilized, because it contains the correct amount of genetic material (adiploidnumber ofchromosomes). In theory, the ovum can be implanted into theuterusof 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 anymitochondrialDNA 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 asDolly the Sheep(July 5, 1996 - February 14, 2003)[10]and, more recently,Snuppy(April 24, 2005 - May 2015), the first cloneddog.[11]

Biobanking

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Somatic cells have also been collected in the practice of biobanking. Thecryoconservation of animal genetic resourcesis a means of conserving animal genetic material in response to decreasing ecological biodiversity.[12]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.[13]

Genetic modifications

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Schematic of CRISPR based gene editing technique

Development ofbiotechnologyhas allowed for the genetic manipulation of somatic cells, whether for the modelling of chronic disease or for the prevention of malaise conditions.[14][15]Two current means of gene editing are the use oftranscription activator-like effector nucleases(TALENs) orclustered regularly interspaced short palindromic repeats(CRISPR).[citation needed]

Genetic engineering of somatic cells has resulted in somecontroversies,[16]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.[17]

Cellular aging

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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 inDNA repaircapability.[18][19][20]This reduction may be an evolutionary adaptation permitting the diversion of cellular resources that were earlier used for DNA repair, as well as forDNA replicationandcell division,to higher priority neuronal and muscular functions. An effect of these reductions is to allow increased accumulation ofDNA damagelikely contributing to cellular aging.

See also

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References

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  1. ^abCampbell NA, Reece JB, Urry LA, Cain ML, Wasserman SA, Minorsky PV, Jackson RB (2009).Biology(9th ed.). Pearson Benjamin Cummings. p.229.ISBN978-0-8053-6844-4.
  2. ^Chernis PJ (1985)."Petrographic analysis of URL-2 and URL-6 special thermal conductivity samples".Department Cf Energy, Mines, and Resources. Earth Physics Branch, Report.8:20.doi:10.4095/315247.
  3. ^Grosberg, Richard K.; Strathmann, Richard R. (2007-12-01)."The Evolution of Multicellularity: A Minor Major Transition?".Annual Review of Ecology, Evolution, and Systematics.38(1): 621–654.doi:10.1146/annurev.ecolsys.36.102403.114735.ISSN1543-592X.
  4. ^Hallmann A (June 2011)."Evolution of reproductive development in the volvocine algae".Sexual Plant Reproduction.24(2): 97–112.doi:10.1007/s00497-010-0158-4.PMC3098969.PMID21174128.
  5. ^Ridley M (2004) Evolution, 3rd edition. Blackwell Publishing, p. 29-297.
  6. ^Niklas, K. J. (2014)The evolutionary-developmental origins of multicellularity.
  7. ^Walter CA, Intano GW, McCarrey JR, McMahan CA, Walter RB (August 1998)."Mutation frequency declines during spermatogenesis in young mice but increases in old mice".Proceedings of the National Academy of Sciences of the United States of America.95(17): 10015–10019.Bibcode:1998PNAS...9510015W.doi:10.1073/pnas.95.17.10015.PMC21453.PMID9707592.
  8. ^abMurphey P, McLean DJ, McMahan CA, Walter CA, McCarrey JR (January 2013)."Enhanced genetic integrity in mouse germ cells".Biology of Reproduction.88(1): 6.doi:10.1095/biolreprod.112.103481.PMC4434944.PMID23153565.
  9. ^Wilmut, Ian; Bai, Yu; Taylor, Jane (2015-10-19)."Somatic cell nuclear transfer: origins, the present position and future opportunities".Philosophical Transactions of the Royal Society B: Biological Sciences.370(1680): 20140366.doi:10.1098/rstb.2014.0366.ISSN0962-8436.PMC4633995.PMID26416677.
  10. ^"The Life of Dolly | Dolly the Sheep".Retrieved2023-12-09.
  11. ^Kim, Min Jung; Oh, Hyun Ju; Kim, Geon A; Setyawan, Erif Maha Nugraha; Choi, Yoo Bin; Lee, Seok Hee; Petersen-Jones, Simon M.; Ko, CheMyong J.; Lee, Byeong Chun (2017-11-10)."Birth of clones of the world's first cloned dog".Scientific Reports.7(1): 15235.Bibcode:2017NatSR...715235K.doi:10.1038/s41598-017-15328-2.ISSN2045-2322.PMC5681657.PMID29127382.
  12. ^Bolton, Rhiannon L; Mooney, Andrew; Pettit, Matt T; Bolton, Anthony E; Morgan, Lucy; Drake, Gabby J; Appeltant, Ruth; Walker, Susan L; Gillis, James D; Hvilsom, Christina (2022-07-01)."Resurrecting biodiversity: advanced assisted reproductive technologies and biobanking".Reproduction and Fertility.3(3): R121–R146.doi:10.1530/RAF-22-0005.ISSN2633-8386.PMC9346332.PMID35928671.
  13. ^Sun, Yanyan; Li, Yunlei; Zong, Yunhe; Mehaisen, Gamal M. K.; Chen, Jilan (2022-10-09)."Poultry genetic heritage cryopreservation and reconstruction: advancement and future challenges".Journal of Animal Science and Biotechnology.13(1): 115.doi:10.1186/s40104-022-00768-2.ISSN2049-1891.PMC9549680.PMID36210477.
  14. ^Jarrett KE, Lee CM, Yeh YH, Hsu RH, Gupta R, Zhang M, et al. (March 2017)."Somatic genome editing with CRISPR/Cas9 generates and corrects a metabolic disease".Scientific Reports.7:44624.Bibcode:2017NatSR...744624J.doi:10.1038/srep44624.PMC5353616.PMID28300165.
  15. ^"NIH Commits $190M to Somatic Gene-Editing Tools/Tech Research".24 January 2018.Retrieved5 July2018.
  16. ^Singh, Amarendra N. (2021-04-01)."Ethical Controversies and Challenges in Human Genome Editing. | International Medical Journal | EBSCOhost".openurl.ebsco.Retrieved2024-06-20.
  17. ^"Why Treat Gene Editing Differently In Two Types Of Human Cells?".8 December 2015.Retrieved5 July2018.
  18. ^Gensler HL (1981). "Low level of U.V.-induced unscheduled DNA synthesis in postmitotic brain cells of hamsters: possible relevance to aging".Exp. Geronont.16(2): 199–207.doi:10.1016/0531-5565(81)90046-2.
  19. ^Karran P, Moscona A, Strauss B (July 1977)."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".J Cell Biol.74(1): 274–86.doi:10.1083/jcb.74.1.274.PMC2109876.PMID559680.
  20. ^Lampidis TJ, Schaiberger GE (December 1975). "Age-related loss of DNA repair synthesis in isolated rat myocardial cells".Exp Cell Res.96(2): 412–6.doi:10.1016/0014-4827(75)90276-1.PMID1193184.
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