Amitosis: Difference between revisions

'''[[Amitosis''']], also calledknown as '''karyostenosis''', '''direct cell division''', or '''[[Fission (biology)|binary fission''']], isrepresents a formmode of asexual [[cell division]] thatpredominantly occursobserved in most [[Prokaryote|prokaryotes]]. ItThis differsprocess is distinct from other forms of cell division (e.g.,mechanisms such as [[mitosis]], and [[meiosis]]), asprimarily because it doesbypasses notthe involvecomplexities associated with the [[Spindle apparatus|mitotic apparatus]], such as (spindle formation). orAdditionally, amitosis does not involve the condensation of [[chromatin]] into distinct [[chromosomeChromosome|chromosomes]]s priorbefore tothe division of the cell occurs, simplifying the process of [[DNA replication|cellular divisionreplication]].

Several instances of cell division formerly thought to be "non-mitotic", such as the division of some unicellular [[Eukaryote|eukaryotes]], [https://www.ncbi.nlm.nih.gov/pubmed/?term=19234477 may actually occur by the process of "closed mitosis"], which is different from open or semi-closed mitotic processes, all of which involve mitotic chromosomes and are classified by [[nuclear envelope]]. Amitosis can also effect on the distribution of human lactic acid [[dehydrogenase]] [[Isozyme|isoenzyme]] which is present in almost all body tissue. Example of amitosis is [[spermatogenesis]]. When in the process of amitosis the [[cell membrane]] will not divide.

There are two or more nuclei which are called dinucleated and multinucleated cells respectively. Sometimes it is also formed by fusion of the cell. Amitosis differs fundamentally from mitosis without [[cytokinesis]], yet still shares some similarities between amitosis and [[cell fusion]]. Amitosis can result in near [[Ploidy|haploid]] nuclei, which is not possible through mitosis or cell fusion.<ref>{{Cite journal |title=Amitosis and endocycles in early cultured mouse trophoblast |url=https://pubmed.ncbi.nlm.nih.gov/1754574/ |journal=Placenta|date=1991 |pmid=1754574 |last1=Kuhn |first1=E. M. |last2=Therman |first2=E. |last3=Susman |first3=B. |volume=12 |issue=3 |pages=251–261 |doi=10.1016/0143-4004(91)90006-2 }}</ref>

The mitotic index declines from 2.2% at day ten to 0.3% at day thirty during postnatal life. Delayed fixation yields degenerated [[prophase]] and [[telophase]] nuclei only. <ref>{{Cite journal |title=Amitosis: A Historical Misinterpretation? |date=1980 |pmid=7433237 |url=https://pubmed.ncbi.nlm.nih.gov/7433237/ |last1=Pfitzer |first1=P. |journal=Pathology, Research and Practice |volume=167 |issue=2–4 |pages=292–300 |doi=10.1016/S0344-0338(80)80059-8 }}</ref>

Amitosis is the division of cells in the [[interphase]] state usually accomplished by a simple constriction into two sometimes unequal halves without any regular segregation of genetic material.<ref>{{Cite journal |last1=Tippit |first1=D. H. |last2=Pickett-Heaps |first2=J. D. |date=1976-07-01 |title=Apparent amitosis in the binucleate dinoflagellate ''Peridinium Balticum'' |url=https://doi.org/10.1242/jcs.21.2.273 |journal=Journal of Cell Science |volume=21 |issue=2 |pages=273–289 |doi=10.1242/jcs.21.2.273 |pmid=987046 |issn=0021-9533}}</ref> As a result, this process leads to random distribution of parental chromosomes in the subsequent daughter cells, in contrast to mitosis, which involves precise distribution of [[chromosomes]] in the resulting daughter cells. This phenomenon does not involve maximal condensation of [[chromatin]] into chromosomes, a molecular event that is observable by [[light microscopy]] when [[sister chromatids]] line up in pairs along the [[Metaphase|metaphase plate]]. While amitosis has been reported in [[Ciliate|ciliates]], its role in mammalian cell proliferation is still unconfirmed. The discovery of [[Copy-number variation|copy number variations]] (CNVs) in mammalian cells within an [[Organ (biology)|organ]]<ref>{{Cite journal|last1=O'Huallachain|first1=M.|last2=Karczewski|first2=K. J.|last3=Weissman|first3=S. M.|last4=Urban|first4=A. E.|last5=Snyder|first5=M. P.|date=2012-10-30|title=Extensive genetic variation in somatic human tissues|journal=Proceedings of the National Academy of Sciences|language=en|volume=109|issue=44|pages=18018–18023|doi=10.1073/pnas.1213736109|issn=0027-8424|pmc=3497787|pmid=23043118|bibcode=2012PNAS..10918018O|doi-access=free}}</ref> has challenged the assumption that every cell in an organism must inherit an exact copy of the parental [[genome]] to be functional. Instead of CNVs stemming from errors in mitosis, such variations could have arisen from amitosis, and may even be beneficial to the cells. Furthermore, [[Ciliate|ciliates]] possess a mechanism for adjusting copy numbers of individual [[Gene|genes]] during amitosis of the [[macronucleus]].<ref>{{Cite journal|last=Prescott|first=D. M.|date=June 1994|title=The DNA of ciliated protozoa|journal=Microbiological Reviews|volume=58|issue=2|pages=233–267|issn=0146-0749|pmc=372963|pmid=8078435|doi=10.1128/MMBR.58.2.233-267.1994}}</ref>

An example of amitosis particularly suited to the formation of multiple differentiated nuclei in a reasonably short period of time has been shown to occur during the differentiation of fluid-enclosing hemispheres called domes from adherent Ishikawa endometrial monolayer cells during an approximately 20-hour period.<ref>{{Cite journal |last=Fleming |first=Honorée |date=1995 |title=Differentiation in human endometrial cells in monolayer culture: Dependence on a factor in fetal bovine serum |url=https://onlinelibrary.wiley.com/doi/10.1002/jcb.240570210 |journal=Journal of Cellular Biochemistry |language=en |volume=57 |issue=2 |pages=262–270 |doi=10.1002/jcb.240570210 |pmid=7759563 |s2cid=40483780 |issn=0730-2312}}</ref><ref>{{Cite journal |last=Fleming |first=Honoree |date=1999 |title=Structure and Function of Cultured Endometrial Epithelial Cells |url=http://www.thieme-connect.de/DOI/DOI?10.1055/s-2007-1016215 |journal=Seminars in Reproductive Medicine |language=en |volume=17 |issue=1 |pages=93–106 |doi=10.1055/s-2007-1016215 |pmid=10406079 |s2cid=9681391 |issn=1526-8004}}</ref> AggregatesDuring the initial stages of differentiation, particularly within the first 6 hours, aggregates of nuclei from monolayer syncytia undergo a unique process where they become enveloped in [[Mitochondrial membraneMitochondrion|mitochondrial membranes]],. These formingresulting structures, known as (mitonucleons), thatexperience becomean elevatedelevation asdue ato resultthe formation of vacuole[[Vacuole|vacuoles]] formationaround duringthem. theThis initialphenomenon 6indicates hoursa ofdistinct cellular organization and differentiation process, highlighting the complex interactions between cellular structures during development.<ref>{{Cite journal |last1=Fleming |first1=Honoree |last2=Condon |first2=Rebekah |last3=Peterson |first3=Genevieve |last4=Guck |first4=Ilse |last5=Prescott |first5=Elizabeth |last6=Chatfield |first6=Kathryn |last7=Duff |first7=Meghan |date=1998-12-01 |title=Role of biotin-containing membranes and nuclear distribution in differentiating human endometrial cells |url=https://onlinelibrary.wiley.com/doi/10.1002/(SICI)1097-4644(19981201)71:33.0.CO;2-W |journal=Journal of Cellular Biochemistry |language=en |volume=71 |issue=3 |pages=400–415 |doi=10.1002/(SICI)1097-4644(19981201)71:3<400::AID-JCB9>3.0.CO;2-W|pmid=9831077 |s2cid=19080155 }}</ref><ref>{{Cite report |url=https://peerj.com/preprints/1728 |title=Mitonucleons formed during differentiation of Ishikawa endometrial cells generate vacuoles that elevate monolayer syncytia: Differentiation of Ishikawa domes, Part 1 |last=Fleming |first=Honoree |date=2016-02-09 |publisher=PeerJ PrePrints |issue=e1728v1 |doi=10.7287/peerj.preprints.1728v1 |doi-access=free |language=en}}</ref> Over the next 4 to 5 hours, chromatin from these aggregated [[nuclei]] becomes increasingly [[Pyknosis|pycnotic]], eventually undergoing [[karyolysis]] and [[karyorrhexis]] in the now-elevated predome structures.<ref>{{Cite report |url=https://peerj.com/preprints/1729 |title=Pyknotic chromatin in mitonucleons elevating in syncytia undergo karyorhhexis and karyolysis before coalescing into an irregular chromatin mass: Differentiation of Ishikawa Domes, Part 2 |last=Fleming |first=Honoree |date=2016-02-09 |publisher=PeerJ PrePrints |issue=e1729v1 |doi=10.7287/peerj.preprints.1729v1 |doi-access=free |language=en}}</ref> In other systems, such changes accompany [[apoptosis]] but not in the differentiating Ishikawa cells, where the processes appear to accompany changes in DNA essential for the newly created, differentiated dome cells. Finally, the chromatin filaments emerging from these processes form a mass from which dozens of dome nuclei are amitotically generated<ref>{{Cite report |url=https://peerj.com/preprints/1730 |title=Chomatin mass from previously aggregated, pyknotic, and fragmented monolayer nuclei is a source for dome cell nuclei generated by amitosis: Differentiation of Ishikawa Domes, Part 3 |last=Fleming |first=Honoree |date=2016-02-09 |publisher=PeerJ PrePrints |issue=e1730v1 |doi=10.7287/peerj.preprints.1730v1 |doi-access=free |language=en}}</ref> over a period of approximately 3 hours with the apparent involvement of nuclear envelope-limited sheets.<ref>{{Cite journal|last1=Olins|first1=A. L.|last2=Buendia|first2=B.|last3=Herrmann|first3=H.|last4=Lichter|first4=P.|last5=Olins|first5=D. E.|date=1998-11-25|title=Retinoic acid induction of nuclear envelope-limited chromatin sheets in HL-60|journal=Experimental Cell Research|volume=245|issue=1|pages=91–104|doi=10.1006/excr.1998.4210|issn=0014-4827|pmid=9828104}}</ref>

Scientific literature not only affirms the involvement of amitosis in cell proliferation, but also explores the existence of more than one amitotic mechanism capable of producing "progeny nuclei" without the involvement of "mitotic chromosomes." A form of amitosis involves fissioning, a nucleus splitting in two without the involvement of chromosomes, which has been reported to occur in placental tissues and in cells grown from such tissues in rats,<ref>{{Cite journal |last1=Ferguson |first1=F. G. |last2=Palm |first2=J. |date=1976-02-15 |title=Histologic characteristics of cells cultured from rat placental tissue |journal=American Journal of Obstetrics and Gynecology |volume=124 |issue=4 |pages=415–420 |doi=10.1016/0002-9378(76)90103-4 |issn=0002-9378 |pmid=1251862}}</ref> as well as in human and mouse trophoblasts.<ref>{{Cite journal |last1=Cotte |first1=C. |last2=Easty |first2=G. C. |last3=Neville |first3=A. M. |last4=Monaghan |first4=P. |date=August 1980 |title=Preparation of highly purified cytotrophoblast from human placenta with subsequent modulation to form syncytiotrophoblast in monolayer cultures |journal=In Vitro |volume=16 |issue=8 |pages=639–646 |doi=10.1007/bf02619191 |issn=0073-5655 |pmid=7419234 |s2cid=20834295}}</ref><ref>{{Cite journal |last1=Kuhn |first1=E. M. |last2=Therman |first2=E. |last3=Susman |first3=B. |date=May 1991 |title=Amitosis and endocycles in early cultured mouse trophoblast |journal=Placenta |volume=12 |issue=3 |pages=251–261 |doi=10.1016/0143-4004(91)90006-2 |issn=0143-4004 |pmid=1754574}}</ref> Amitosis by fissioning has also been reported in mammalian liver cells<ref>{{Cite journal |last1=David |first1=H. |last2=Uerlings |first2=I. |date=September 1992 |title=[Ultrastructure of amitosis and mitosis of the liver] |journal=Zentralblatt für Pathologie |volume=138 |issue=4 |pages=278–283 |issn=0863-4106 |pmid=1420108}}</ref> and human adrenal cells.<ref>{{Cite journal |last1=Magalhães |first1=M. C. |last2=Pignatelli |first2=D. |last3=Magalhães |first3=M. M. |date=April 1991 |title=Amitosis in human adrenal cells |journal=Histology and Histopathology |volume=6 |issue=2 |pages=251–256 |issn=0213-3911 |pmid=1802124}}</ref> Chen and Wan<ref>{{Cite journal |last1=Chen |first1=Y. Q. |last2=Wan |first2=B. K. |date=1986 |title=A study on amitosis of the nucleus of the mammalian cell. I. A study under the light and transmission electron microscope |journal=Acta Anatomica |volume=127 |issue=1 |pages=69–76 |issn=0001-5180 |pmid=3788448}}</ref> reported amitosis in rat liver and presented a mechanism for a four-stage amitotic process whereby chromatin threads are reproduced and equally distributed to daughter cells as the nucleus splits in two. In Mac amitosis of [[Tetrahymena]] we required γ-tubulin-mediated MT assembly<ref>{{Cite journal |last=Kushida |first=Yasuharu |date=February 2011 |title=γ-tubulin-mediated MT |url=https://pubmed.ncbi.nlm.nih.gov/21246753/ |url-status=dead |journal=Cytoskeleton (Hoboken, N.j.)|volume=68 |issue=2 |pages=89–96 |doi=10.1002/cm.20496 |pmid=21246753 }}</ref>

In other studies, examination of fetal guts during development (5 to 7 weeks), colonic adenomas, and adenocarcinomas has revealed nuclei that appear as hollow bells encased in tubular [[Syncytium|syncytia]]. These structures can either divide symmetrically by an amitotic nuclear fission process, forming new "bells", or undergo fission asymmetrically, resulting in one of seven other nuclear [[Polymorphism (biology)|morphotypes]], five of which appear to be specific to development since they are rarely observed in adult organisms.<ref>{{Cite journal|last1=Gostjeva|first1=E. V.|last2=Zukerberg|first2=L.|last3=Chung|first3=D.|last4=Thilly|first4=W. G.|date=2006-01-01|title=Bell-shaped nuclei dividing by symmetrical and asymmetrical nuclear fission have qualities of stem cells in human colonic embryogenesis and carcinogenesis|journal=Cancer Genetics and Cytogenetics|volume=164|issue=1|pages=16–24|doi=10.1016/j.cancergencyto.2005.05.005|issn=0165-4608|pmid=16364758}}</ref>

When the intestinal [[Stem cell|stem cells]] (ISCs) in fruit flies' guts are seriously reduced, they use a cool trick called amitosis to fix the problem. Instead of the usual way cells divide, where a spindle structure helps split the cell, they do it differently. Cells in another part of the gut, called [[Enterocyte|enterocytes]], reduce their number of chromosomes without going through the normal division process. This helps replace the lost ISCs, keeping the gut functioning properly. It's like the gut has a backup plan to make sure everything stays in balance!