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[[File:Telomere mediated minichromosome production.jpg|thumb|Through the insertion of multiple genes and telomeres, a shortened minichromosome is produced, which can then be inserted into a host cell]]

A '''minichromosome''' is a small [[chromatin]]-like structure resembling a [[chromosome]] that contains [[centromere]]s, [[telomere]]s, and [[replication origin]]s,<ref name=XuYu2009>{{cite journal |last1=Xu |first1=Chunhui |last2=Yu |first2=Weichang |year=2009 |title=Engineered minichromosomes in plants |journal=AccessScience |publisher=McGraw-Hill Education |doi=10.1036/1097-8542.YB090068 }}</ref> but relatively little additional genetic material. They replicate autonomously in the cell during [[cellular division]].<ref name="Goyal et al 2009">{{cite journal |first1=Aakash |last1=Goyal |first2=Pankaj Kumar |last2=Bhowmik |first3=Saikat Kumar |last3=Basu |title=Minichromosomes: The second generation genetic engineering tool |journal=Plant Omics Journal |year=2009 |volume=2 |issue=1 |pages=1–8 |url=https://www.pomics.com/Saikat_January2009_2_1_1_8.pdf }}</ref> Minichromosomes may be created by natural processes as chromosomal aberrations or by [[genetic engineering]].<ref name=XuYu2009/>

==Structure==

Minichromosomes can be either linear or circular pieces of [[DNA]].<ref name="Goyal et al 2009"/> By minimizing the amount of unnecessary genetic information on the chromosome and including the basic components necessary for [[DNA replication]] (centromere, telomeres, and replication sequences), molecular biologists aim to construct a chromosomal platform which can be utilized to insert or present new [[gene]]s into a [[host (biology)|host cell]].<ref name="Goyal et al 2009"/>

==Production==

Producing minichromosomes by genetic engineering techniques involves two primary methods, the ''[[:wikt:de novo|de novo]]'' (bottom-up) and the top-down approach.<ref name=XuYu2009/>

===''De novo''===

The minimum constituent parts of a chromosome (centromere, telomeres, and DNA replication sequences) are assembled<ref>{{cite web|title=Minichromosomes: The Next Generation Technology for Plant Engineering|url=http://www.isb.vt.edu/articles/aug0703.htm|accessdate=11 April 2012|author=Yu, Weichang|author2=Birchler, James|date=August 2007}}</ref> by using [[molecular cloning]] techniques to construct the desired chromosomal contents ''in vitro''. Next, the desired contents of the minichromosome must be [[Transformation (genetics)|transformed]] into a host which is capable of assembling the components (typically yeast or mammalian cells<ref name="Yu et al 2015">{{cite journal |doi=10.1111/pbi.12466 |pmid=26369910 |title=Plant artificial chromosome technology and its potential application in genetic engineering |journal=Plant Biotechnology Journal |volume=14 |issue=5 |pages=1175–82 |year=2016 |last1=Yu |first1=Weichang |last2=Yau |first2=Yuan-Yeu |last3=Birchler |first3=James A. |doi-access=free |pmc=11389009 }}</ref>) into a functional chromosome. This approach has been attempted for the introduction of minichromosomes into [[maize]] for the possibility of genetic engineering, but success has been limited and questionable.<ref name="Carlson et al 2007">{{cite journal |doi=10.1371/journal.pgen.0030179 |pmid=17953486 |pmc=2041994 |title=Meiotic Transmission of an in Vitro–Assembled Autonomous Maize Minichromosome |journal=PLOS Genetics |volume=3 |issue=10 |pages=1965–74 |year=2007 |last1=Carlson |first1=Shawn R. |last2=Rudgers |first2=Gary W. |last3=Zieler |first3=Helge |last4=Mach |first4=Jennifer M. |last5=Luo |first5=Song |last6=Grunden |first6=Eric |last7=Krol |first7=Cheryl |last8=Copenhaver |first8=Gregory P. |last9=Preuss |first9=Daphne |doi-access=free }}</ref> In general, the ''de novo'' approach is more difficult than the top-down method due to species incompatibility issues and the [[heterochromatin|heterochromatic]] nature of centromeric regions.<ref name="Yu et al 2015"/>

===Top-down===

This method utilizes the mechanism of [[telomere]]-mediated chromosomal truncation (TMCT). This process is the generation of [https://www.ncbi.nlm.nih.gov/pubmed/21181527 truncation] by selective transformation of telomeric sequences into a host genome. This insertion causes the generation of more telomeric sequences and eventual truncation.<ref name="Goyal et al 2009"/> The newly synthesized truncated chromosome can then be altered through the insertion of new genes for desired traits. The top-down approach is generally considered as the more plausible means of generating extra-numerary chromosomes for the use of genetic engineering of plants. In particular it is useful because their stability during cell division has been demonstrated.<ref>{{cite journal |doi=10.1073/pnas.0700932104 |pmid=17502617 |pmc=1885604 |title=Construction and behavior of engineered minichromosomes in maize |journal=Proceedings of the National Academy of Sciences |volume=104 |issue=21 |pages=8924–9 |year=2007 |last1=Yu |first1=W. |last2=Han |first2=F. |last3=Gao |first3=Z. |last4=Vega |first4=J. M. |last5=Birchler |first5=J. A. |bibcode=2007PNAS..104.8924Y |doi-access=free }}</ref> The limitation of this approach is that it is labor-intensive.

==Role in genetic engineering==

Unlike traditional methods of genetic engineering, minichromosomes can be used to transfer and express multiple sets of genes onto one engineered chromosome package.<ref>{{cite journal |doi=10.1105/tpc.107.056622 |pmid=18223035 |pmc=2254918 |jstor=25224208 |title=Engineered Plant Minichromosomes: A Bottom-Up Success? |journal=The Plant Cell Online |volume=20 |issue=1 |pages=8–10 |year=2008 |last1=Houben |first1=Andreas |last2=Dawe |first2=R. Kelly |last3=Jiang |first3=Jiming |last4=Schubert |first4=Ingo }}</ref> Traditional methods which involve the insertion of novel genes into existing sequences may result in the disruption of endogenous genes<ref name=XuYu2009/> and thus negatively affect the host cell. Additionally, with traditional gene insertion methods, scientists have had less ability to control where the newly inserted genes are located on the host cell chromosomes,<ref>{{cite web|title=Researchers to study minichromosomes in maize with $1.9 million grant |url=http://rcp.missouri.edu/articles/birchler-minichromosomes-grant.html |accessdate=15 April 2012 |url-status=dead |archiveurl=https://web.archive.org/web/20100605103134/http://rcp.missouri.edu/articles/birchler-minichromosomes-grant.html |archivedate=June 5, 2010 }}</ref> which makes it difficult to predict inheritance of multiple genes from generation to generation. Minichromosome technology allows for the stacking of genes side-by-side on the same chromosome thus reducing likelihood of segregation of novel traits.

===Plants===

In 2006, scientists demonstrated the successful use of telomere truncation in maize plants to produce minichromosomes that could be utilized as a platform for inserting genes into the plant genome.<ref>{{cite journal |doi=10.1073/pnas.0605750103 |pmid=17085598 |pmc=1859930 |title=Telomere-mediated chromosomal truncation in maize |journal=Proceedings of the National Academy of Sciences |volume=103 |issue=46 |pages=17331–6 |year=2006 |last1=Yu |first1=W. |last2=Lamb |first2=J. C. |last3=Han |first3=F. |last4=Birchler |first4=J. A. |bibcode=2006PNAS..10317331Y |doi-access=free }}</ref> In plants, the telomere sequence is conserved, which implies that this strategy can be utilized to successfully construct additional minichromosomes in other plant species.<ref name=XuYu2009/>

In 2007, scientists reported success in assembling minichromosomes ''in vitro'' using the ''de novo'' method.<ref name="Carlson et al 2007"/>

The use of minichromosomes as a means for generating more desirable crop traits is actively being explored. Major advantages include the ability to introduce genetic information which is highly compatible with the host genome. This eliminates the risk of disrupting various important processes such as cell division and gene expression. With continued development, the future for use of minichromosomes may make a huge impact on the productivity of major crops.<ref>{{cite journal |doi=10.1111/j.1467-7652.2004.00113.x |pmid=17173615 |title=Gene stacking in transgenic plants - the challenge for 21st century plant biotechnology |journal=Plant Biotechnology Journal |volume=3 |issue=2 |pages=141–55 |year=2005 |last1=Halpin |first1=Claire |doi-access=free }}</ref>

===Other organisms===

Minichromosomes have also been successfully inserted into yeast and animal cells. These minichromosomes were constructed using the ''de novo'' approach.<ref name="Goyal et al 2009"/>

==See also==

* [[Mini Chromosome Maintenance|Minichromosome maintenance proteins]]
* [[Microchromosome]]
* [[Y chromosome#Degeneration|Y chromosome, §Degeneration]]

==References==

{{reflist}}

[[Category:Genetics]]

Minichromosome - История изменений

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