Admin: 1 версия импортирована

2025-11-13T18:01:36Z

1 версия импортирована

← Предыдущая версия		Версия от 18:01, 13 ноября 2025
(нет различий)

ru>Marksimon3: /* growthexperiments-addlink-summary-summary:3|0|0 */

2025-10-03T03:54:58Z

growthexperiments-addlink-summary-summary:3|0|0

Новая страница

{{Short description|Transposable element system in maize}}
{{cs1 config|name-list-style=vanc}}
'''Ac/Ds transposable controlling elements''' was the first [[transposable element]] system recognized in [[maize]]. The ''Ac Activator'' element is autonomous, whereas the ''Ds Dissociation'' element requires an ''Activator'' element to transpose.<ref name=":0">{{cite book|title=Encyclopedia of Genetics, Genomics, Proteomics and Informatics|url=https://archive.org/details/encyclopediagene12gred|url-access=limited|date=2008|publisher=Springer | location = Netherlands|isbn=9781402067532|pages=[https://archive.org/details/encyclopediagene12gred/page/n16 8]–9|doi=10.1007/978-1-4020-6754-9_76|chapter = Ac—Ds (Activator-Dissociator) }}</ref> ''Ac'' was initially discovered as enabling a ''Ds'' element to break [[chromosome]]s. Both ''Ac'' and ''Ds'' can also insert into genes, causing [[Mutation|mutant]]s that may revert to normal on excision of the element.<ref name="McClintock50">{{cite journal | vauthors = McClintock B | title = The origin and behavior of mutable loci in maize | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 36 | issue = 6 | pages = 344–55 | date = June 1950 | pmid = 15430309 | pmc = 1063197 | doi = 10.1073/pnas.36.6.344 | bibcode = 1950PNAS...36..344M | doi-access = free }}</ref> The phenotypic consequence of ''Ac''/''Ds'' transposable element includes [https://static-content.springer.com/image/prt%3A978-1-4020-6754-9%2F1/MediaObjects/978-1-4020-6754-9_1_Part_Fig1-76_HTML.jpg mosaic colors in kernels and leaves in maize].

== Discovery ==
Its discovery was based on studying its genetic behavior, i.e., "jumping genes" in maize and published by [[Barbara McClintock]],<ref name="McClintock47">{{cite journal|last=McClintock|first=Barbara |year=1947|title=Cytogenetic studies of maize and Neurospora|journal=Carnegie Inst. Washington Year Book|volume=46|pages=146–152}}</ref><ref name="McClintock49">{{cite journal|last=McClintock|first=Barbara |year=1949|title=Mutable loci in maize.|journal=Carnegie Inst. Washington Year Book|volume=48|pages=142–154}}</ref> leading to her 1983 [[List of Nobel laureates in Physiology or Medicine|Nobel Prize in Medicine]]. The Ac/Ds transposable elements were first isolated and sequenced By Fedoroff et al. 1983 <ref name="Federoff83">{{cite journal | vauthors = Fedoroff N, Wessler S, Shure M | title = Isolation of the transposable maize controlling elements Ac and Ds | journal = Cell | volume = 35 | issue = 1 | pages = 235–42 | date = November 1983 | pmid = 6313225 | doi = 10.1016/0092-8674(83)90226-x | doi-access = free }}</ref> using insertions of ''Ac'' and ''Ds'' into the well-studied [[Waxy corn|Waxy(Wx1)]] gene. The elements have been shown to function in other plants, including tobacco,<ref name="Baker87">{{cite journal | vauthors = Baker B, Coupland G, Fedoroff N, Starlinger P, Schell J | title = Phenotypic assay for excision of the maize controlling element Ac in tobacco | journal = The EMBO Journal | volume = 6 | issue = 6 | pages = 1547–54 | date = June 1987 | pmid = 16453771 | pmc = 553523 | doi=10.1002/j.1460-2075.1987.tb02399.x}}</ref> Arabidopsis,<ref name="VanSluys87">{{cite journal | vauthors = Van Sluys MA, Tempé J, Fedoroff N | title = Studies on the introduction and mobility of the maize Activator element in Arabidopsis thaliana and Daucus carota | journal = The EMBO Journal | volume = 6 | issue = 13 | pages = 3881–9 | date = December 1987 | pmid = 2832144 | pmc = 553865 | doi=10.1002/j.1460-2075.1987.tb02728.x}}</ref>) and rice.<ref name="Murai91">{{cite journal | vauthors = Murai N, Li ZJ, Kawagoe Y, Hayashimoto A | title = Transposition of the maize activator element in transgenic rice plants | journal = Nucleic Acids Research | volume = 19 | issue = 3 | pages = 617–22 | date = February 1991 | pmid = 1849265 | pmc = 333657 | doi = 10.1093/nar/19.3.617 }}</ref>

Genomic analysis of maize show that these elements, which share terminal 11 bp imperfect [[inverted repeat]] sequences, have much sequence heterogeneity, both in length and content. They also include a class of DNA elements that do not transpose in the presence of the Ac element (Du et al. 2011). The chromosome breaking property has been shown to come from pairs of closely positioned elements.<ref name="Huang08">{{cite journal | vauthors = Huang JT, Dooner HK | title = Macrotransposition and other complex chromosomal restructuring in maize by closely linked transposons in direct orientation | journal = The Plant Cell | volume = 20 | issue = 8 | pages = 2019–32 | date = August 2008 | pmid = 18708475 | pmc = 2553603 | doi = 10.1105/tpc.108.060582 }}</ref>

== Toolkits ==
Researchers use mutant phenotypes to discover gene functions. Ac/Ds prefer to transpose to nearby genes, affording a way to mutagenize those regions of the genome, and by subsequent genetic crosses, remove the Ac that causes new mutants and instability of a Ds mutant. Collections of Ac/Ds elements that cover the genome and are useful for generating mutants.<ref name="Vollbrecht_2010">{{cite journal | vauthors = Vollbrecht E, Duvick J, Schares JP, Ahern KR, Deewatthanawong P, Xu L, Conrad LJ, Kikuchi K, Kubinec TA, Hall BD, Weeks R, Unger-Wallace E, Muszynski M, Brendel VP, Brutnell TP | title = Genome-wide distribution of transposed Dissociation elements in maize | journal = The Plant Cell | volume = 22 | issue = 6 | pages = 1667–85 | date = June 2010 | pmid = 20581308 | pmc = 2910982 | doi = 10.1105/tpc.109.073452 }}</ref> Application of Ac/Ds toolkits has also been applied to other species like arabidopsis, yeast, and even zebrafish.<ref name=":0" />

== In corn ==
Activator (Ac)/ Dissociation (Ds) transposable elements were discovered by Barbara McClintock when she was studying the maize genomic composition of the short arm of [[chromosome 9]]. She noticed that when chromosome 9 had been exposed to drastic structural modifications, the progeny had changes such as multiple copies of the short arm or lacking one or more of its parts, as well as other changes. She believed that these changes were due to transposition of “mutable loci” into the genome and that these spontaneous translocations were not random due to where the breaks occurred and where they fused.<ref name="McClintock50" />

Ac/Ds elements have been observed to insert into gene rich regions of the maize genome, they alter the [[regulation of gene expression]] and may create unstable insertion alleles, stable derivatives, or excision alleles due to insertion of a transposable element into a gene.<ref name="Bai_2011">{{cite journal | vauthors = Bai L, Brutnell TP | title = The activator/dissociation transposable elements comprise a two-component gene regulatory switch that controls endogenous gene expression in maize | journal = Genetics | volume = 187 | issue = 3 | pages = 749–59 | date = March 2011 | pmid = 21196519 | pmc = 3063669 | doi = 10.1534/genetics.110.124149 }}</ref> Transposable elements residing at or near a gene prevent gene expression and can also result in a mutation that causes exhibition of the recessive phenotype.<ref name="Döring_1983">{{cite journal | vauthors = Döring HP, Starlinger P | title = Barbara McClintock's controlling elements: now at the DNA level | journal = Cell | volume = 39 | issue = 2 Pt 1 | pages = 253–9 | date = December 1984 | pmid = 6094008 | doi = 10.1016/0092-8674(84)90002-3 | doi-access = free }}</ref> Removal of transposable element locus results in restoration of the gene organization and activity.<ref name="McClintock50" /> Ac is 4565 base pairs long and codes for a 3.5 kb [[open reading frame]] that synthesizes an 807 amino acid long transposase enzyme.<ref name="Bai_2011" /> Ac elements are autonomous and their movement results in a 4.3 kb insertion.<ref name="Fedoroff_1983">{{cite journal | vauthors = Fedoroff N, Wessler S, Shure M | title = Isolation of the transposable maize controlling elements Ac and Ds | journal = Cell | volume = 35 | issue = 1 | pages = 235–42 | date = November 1983 | pmid = 6313225 | doi = 10.1016/0092-8674(83)90226-X | doi-access = free }}</ref> Ds elements are not autonomous because they cannot produce the transposase needed for transposition, and can only transpose when it is provided by the Ac element.<ref name="Fedoroff_1983" /> Ds elements have shown to cause a 4.1kB and 2.0 kB insertions.<ref name="Fedoroff_1983" /> The transposable elements were seen in progeny of plants that had undergone stress, and mutations caused by the insertion are like those caused by x-rays, UV light, or chemicals causing events like chromosome breakage and fusion.<ref name="McClintock50" />

There are distinct families of transposon controlling elements that are made up of a combination of elements some that can, and some that cannot, transpose. The families differ in their developmental timing and transposition frequency, as well other types of genetic rearrangements.<ref name="Fedoroff_1983" /> Ac or Ds element insertion near a locus causes unstable mutations. Ds elements are considered non-autonomous because they cannot transpose without the presence of the Ac element, since they themselves cannot produce the enzyme transposase needed for transposition. However, since Ds elements can utilize the transposase enzyme produced by the Ac elements, it shows that they have the structural information needed for transposition and only lack the information needed to produce the enzyme. Ds elements were identified at the site of a chromosome breakage.<ref name="McClintock50" /> Ac and Ds elements are structurally related because insertion of either element brings about similar mutations. They are also similar because their restriction endonuclease cleavage site maps are indistinguishable from each other.<ref name="Fedoroff_1983" />

Different mutants display different levels of gene expression, which largely depends on the presence or absence of the transposable element somewhere else in the genome.<ref name="Döring_1983" /> The different function of the elements are detected as altered temporal or spatial patterns of somatic reversions or reversible inactivation of the entire element.<ref name="Döring_1983" /> Some excision events of these elements restore gene function and can be detected as somatic reversions.<ref name="Döring_1983" /> If Ac or Ds insertions in an exon, and the transposable elements are excised leaving some of the duplicated base pairs behind, it alters the protein structure either by causing mutations such as frame shift mutations or the addition of amino acids.<ref name="Döring_1983" /> In some cases, unstable Ds or Ac induced mutant can give rise to a stable recessive mutant.<ref name="Döring_1983" /> Ac determines the mutation process and the mutable loci as well as their timing.<ref name="McClintock50" /> Ac transposase does not influence transcription initiation site selection, and large numbers of Ac elements may inhibit the expression of Ds by reducing the rate of transcription initiation instead of affecting the transcription site selection.<ref name="Bai_2011" /> Ac transposase is also capable of suppressing gene expression when Ac or Ds inserts in 5’ untranslated region using target sites.<ref name="Bai_2011" /> Ac or Ds element insertion sites have been characterized by the presence of different direct duplications of 6-10 base pairs prior to insertions, indicating that Ac transposase may have preference for short duplication as insertion sites.<ref name="Döring_1983" /> Transposition of both Ac and Ds occurs during development of a tissue and is under precise control which is determined by the number of Ac loci present, their organization, and their position in the chromosome complement.<ref name="McClintock50" /> The transposable elements not only entirely remove or alter the gene function via insertion, but can also exert a mutator activity when they leave the position where they had visited the chromosome.<ref name="Döring_1983" /> Induced disturbances in quantity and organization of the heterochromatic elements of the chromosome could give rise to a series of alterations in its structure, behavior, and in genic reactions that can alter phenotypic expression.<ref name="McClintock50" />

The Ac and Ds elements share two properties that are common for transposable elements.<ref name="Döring_1983" /> One is that at the site of their insertion, a short DNA sequence is 8 base pairs long, and is duplicated and borders exactly at the Ac or Ds sequence.<ref name="Döring_1983" /> Second, the sequences of several Ds elements terminate in an inverted repeat of the nucleotide sequence TAGGATGAAA.<ref name="Döring_1983" /> The Ds elements shows quite some degree of similarity with the Ac elements, such as the Ds9 element which is a complemental mutant of Ac and only differs in the open reading frame 1.<ref name="Döring_1983" /> Other Ds elements differ from the Ac element by internal deletions.<ref name="Döring_1983" />

As Ac copy number increases, the expression of genes flanking the Ds promoter insertion are negatively regulated, which is called the negative dosage effect.<ref name="Kunze_1987">{{cite journal | vauthors = Kunze R, Stochaj U, Laufs J, Starlinger P | title = Transcription of transposable element Activator (Ac) of Zea mays L | journal = The EMBO Journal | volume = 6 | issue = 6 | pages = 1555–63 | date = June 1987 | pmid = 16453772 | pmc = 553524 | doi=10.1002/j.1460-2075.1987.tb02400.x}}</ref> Ds flanking gene expression is inhibited in the presence of the autonomous Ac element.<ref name="Bai_2011" /> As the Ac element copy number increases, transposition events that require Ac occur at a later time during endosperm development.<ref name="Kunze_1987" /> Ac causes no or few chromosome breaks. In the absence of Ac, Ds caused mutations are stable.<ref name="Döring_1983" /> By identifying alleles that suppress the Ac element they could be used for functional genomics studies.<ref name="Bai_2011" /> The properties of transposable elements can also be altered in a clonally heritable fashion.<ref name="Döring_1983" /> Ds elements can be used as building blocks for complicated structures like the double Ds or the 30kb transposon-like insertion which is terminated by Ds elements.<ref name="Döring_1983" /> Ds elements can generate long direct inverted duplicates of a chromosome segment, indicating that Ds elements are able to mobilize DNA sequences unrelated to themselves, this can provide a mechanism for rearrangement of genetic information.<ref name="Döring_1983" /> Since small duplication of host DNA created by the insertion of the elements are left over in a slightly altered form after excision of the transposable element, they may indicate that plant transposable elements play a role in the evolution of genes.<ref name="Döring_1983" />

== References ==
{{reflist}}

{{DEFAULTSORT:Ac Ds Activator Dissociation Transposable Element}}
[[Category:Plant genes]]
[[Category:Plant genetics]]
[[Category:Genetics]]

Ac/Ds transposable controlling elements - История изменений

Admin: 1 версия импортирована

ru>Marksimon3: /* growthexperiments-addlink-summary-summary:3|0|0 */