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'''Q-system''' is a [[Genetics|genetic]] tool that allows to [[Gene expression|express]] [[transgenes]] in a living [[organism]].<ref name="Riabinina2016book">{{cite book | vauthors = Riabinina O, Potter CJ | title = Drosophila | chapter = The Q-System: A Versatile Expression System for Drosophila | series = Methods in Molecular Biology | volume = 1478 | pages = 53–78 | year = 2016 | pmid = 27730575 | pmc = 5270762 | doi = 10.1007/978-1-4939-6371-3_3 | isbn = 978-1-4939-6369-0 }}</ref> Originally the Q-system was developed <ref name="Potter2010">{{cite journal | vauthors = Potter CJ, Tasic B, Russler EV, Liang L, Luo L | title = The Q system: a repressible binary system for transgene expression, lineage tracing, and mosaic analysis | journal = Cell | volume = 141 | issue = 3 | pages = 536–48 | date = April 2010 | pmid = 20434990 | pmc = 2883883 | doi = 10.1016/j.cell.2010.02.025 }}</ref><ref name="Riabinina2015">{{cite journal | vauthors = Riabinina O, Luginbuhl D, Marr E, Liu S, Wu MN, Luo L, Potter CJ | title = Improved and expanded Q-system reagents for genetic manipulations | journal = Nature Methods | volume = 12 | issue = 3 | pages = 219–22, 5 p following 222 | date = March 2015 | pmid = 25581800 | pmc = 4344399 | doi = 10.1038/nmeth.3250 }}</ref> for use in the [[vinegar fly]] ''Drosophila melanogaster'', and was rapidly adapted for use in cultured [[Cell culture|mammalian cells]],<ref name="Potter2010" /> [[zebrafish]],<ref name="Subedi2014">{{cite journal | vauthors = Subedi A, Macurak M, Gee ST, Monge E, Goll MG, Potter CJ, Parsons MJ, Halpern ME | title = Adoption of the Q transcriptional regulatory system for zebrafish transgenesis | journal = Methods | volume = 66 | issue = 3 | pages = 433–40 | date = April 2014 | pmid = 23792917 | pmc = 3883888 | doi = 10.1016/j.ymeth.2013.06.012 }}</ref> [[Caenorhabditis elegans|nematodes]]<ref name="Wei2010">{{cite journal | vauthors = Wei X, Potter CJ, Luo L, Shen K | title = Controlling gene expression with the Q repressible binary expression system in Caenorhabditis elegans | journal = Nature Methods | volume = 9 | issue = 4 | pages = 391–5 | date = March 2012 | pmid = 22406855 | pmc = 3846601 | doi = 10.1038/nmeth.1929 }}</ref> and [[Anopheles gambiae|mosquitoes]].<ref name="Riabinina2016">{{cite journal | vauthors = Riabinina O, Task D, Marr E, Lin CC, Alford R, O'Brochta DA, Potter CJ | title = Organization of olfactory centres in the malaria mosquito Anopheles gambiae | journal = Nature Communications | volume = 7 | article-number = 13010 | date = October 2016 | pmid = 27694947 | pmc = 5063964 | doi = 10.1038/ncomms13010 | bibcode = 2016NatCo...713010R }}</ref> The Q-system utilizes [[genes]] from the ''qa'' cluster<ref name="Giles1991">{{cite journal | vauthors = Giles NH, Geever RF, Asch DK, Avalos J, Case ME | title = The Wilhelmine E. Key 1989 invitational lecture. Organization and regulation of the qa (quinic acid) genes in Neurospora crassa and other fungi | journal = The Journal of Heredity | volume = 82 | issue = 1 | pages = 1–7 | year = 1991 | pmid = 1825499 | doi = 10.1093/jhered/82.1.1 }}</ref> of the [[Neurospora crassa|bread fungus]] ''Neurospora crassa'', and consists of four components: the [[transcriptional activator]] (QF/QF2/QF2w), the [[Enhancer (genetics)|enhancer]] QUAS, the [[repressor]] QS, and the chemical de-repressor [[quinic acid]]. Similarly to [[GAL4/UAS system|GAL4/UAS]]<ref name="Brandt1993">{{cite journal | vauthors = Brand AH, Perrimon N | title = Targeted gene expression as a means of altering cell fates and generating dominant phenotypes | journal = Development | volume = 118 | issue = 2 | pages = 401–15 | date = June 1993 | doi = 10.1242/dev.118.2.401 | pmid = 8223268 | url = http://dev.biologists.org/content/118/2/401.long | url-access = subscription }}</ref> and LexA/LexAop,<ref name="Lai2006">{{cite journal | vauthors = Lai SL, Lee T | title = Genetic mosaic with dual binary transcriptional systems in Drosophila | journal = Nature Neuroscience | volume = 9 | issue = 5 | pages = 703–9 | date = May 2006 | pmid = 16582903 | doi = 10.1038/nn1681 | s2cid = 10780729 }}</ref> the Q-system is a binary expression system that allows to express [[Reporter gene|reporters]] or effectors (e.g. [[Green fluorescent protein|fluorescent proteins]], [[ion channels]], [[toxins]] and other genes) in a defined subpopulation of [[cell (biology)|cells]] with the purpose of visualising these cells or altering their function. In addition, GAL4/UAS, LexA/LexAop and the Q-system function independently of each other and can be used simultaneously to achieve a desired pattern of reporter expression, or to express several reporters in different subsets of cells.

==Origin==
[[File:Q-system shematic.png|thumb|Repressible Q binary expression system.]]
The Q-system is based on two out of the seven [[Gene|genes]] of the ''qa'' gene cluster of the [[Neurospora crassa|bread fungus]] ''Neurospora crassa''.<ref name="Giles1991" /> The genes of the ''qa'' cluster are responsible for the catabolism of quinic acid, which is used by the fungus as a carbon source in conditions of low glucose.<ref name="Giles1991" /> The cluster contains a transcriptional activator ''qa-1F'', a transcriptional repressor ''qa-1S'', and five structural genes. The ''qa-1F'' binds to a specific DNA sequence, found upstream of the ''qa'' genes. The presence of quinic acid disrupts interaction between ''qa-1F'' and ''qa-1S'', thus disinhibiting the transcriptional activity of ''qa-1F''.
Genes ''qa-1F'', ''qa-1S'' and the DNA binding sequence of ''qa-1F'' form the basis of the Q-system. The genes were renamed to simplify their use as follows: transcriptional activator ''qa-1F'' as QF, repressor ''qa-1S'' as QS, and the DNA binding sequence as QUAS.<ref name="Potter2010" /> The quinic acid represents the fourth component of the Q-system.
The original transactivator QF appeared to be toxic when expressed broadly in ''Drosophila''. To overcome this problem, two new transactivators were developed: QF2 and QF2w.<ref name="Riabinina2015" />

==Use in ''Drosophila''==

===Basic use===

The Q-system functions similarly to, and independently of, the GAL4/UAS<ref name="Brandt1993" /> and the LexA/LexAop <ref name="Lai2006" /> systems. QF, QF2 and QF2w are analogous to GAL4 and LexA, and their expression is usually under the control of cell-type specific promoter, such as ''nsyb'' (to target neurons) or ''tubulin'' (to target all cells). QUAS is analogous to UAS and LexAop, and is placed upstream of an effector gene, such as [[Green fluorescent protein|GFP]]. QS is analogous to GAL80, and may be driven by any promoter (e.g. ''tubulin-QS''). Quinic acid is a unique feature of the Q-system, and it must be fed to the flies or maggots in order to alleviate the QS-induced repression. In some ways, quinic acid is analogous to temperature in the case of GAL80ts.
In its basic form, two transgenic fly lines, one containing a QF transgene and the other one containing a QUAS transgene, are crossed together. Their progeny that had both a QF transgene and a QUAS transgene will be expressing a reporter gene in a subset of cells (e.g. ''nsyb-QF2, QUAS-GFP'' flies express GFP in all neurons). If a fly also expresses QS in some of the cells, the activity of QF will be repressed in these cells, but it may be restored of a fly is fed quinic acid (e.g. a ''nsyb-QF2, QUAS-GFP, tub-QS'' fly expresses no GFP when its diet doesn't contain quinic acid, and expresses GFP in its neurons when fed quinic acid).<ref name="Potter2010" /><ref name="Riabinina2015" /> The use of QS repressor and quinic acid allows to fine-tune the temporal control of transgene expression.

===Chimeric transactivators===
Chimeric transactivators GAL4QF<ref name="Riabinina2015" /> and LexAQF<ref name="Riabinina2015" /> allow to combine the use of all three binary expression systems. GAL4QF binds to UAS, and may be repressed by QS while being unaffected by GAL80. Similarly, LexAQF binds to LexAop, and may be repressed by QS. LexAQF represents a useful extension of the LexA/LexAop system that doesn't have its own repressor.

===Intersectional expression===
[[File:G4QF-intersectionals.png|thumb|Intersectional expression patterns possible using GAL4 and QF binary expression systems.]]
A variety of expression patterns may be achieved by combination of the three binary expression systems and the FLP/FRT or other recombinases.<ref name="Bischof2008">{{cite book | vauthors = Bischof J, Basler K | title = Drosophila | chapter = Recombinases and Their Use in Gene Activation, Gene Inactivation, and Transgenesis | series = Methods in Molecular Biology | volume = 420 | pages = 175–95 | year = 2008 | pmid = 18641947 | doi = 10.1007/978-1-59745-583-1_10 | isbn = 978-1-58829-817-1 }}</ref> Expression patterns may be constructed as AND, OR, NOR etc. logic gates <ref name="Riabinina2016book" /><ref name="Potter2010" /> to e.g. narrow down expression patterns of available GAL4 lines. The resulting expression pattern somewhat depends on the developmental timing of activation of the transcription factors (discussed in <ref name="Riabinina2016book" />).

==Use in other organisms==
Q-system appeared to be working successfully in a variety of organisms. It has been used to drive expression of luciferase, as a proof of principle, in cultured [[Cell culture|mammalian cells]].<ref name="Potter2010" /> In [[zebrafish]]<ref name="Subedi2014" /> the Q-system has been successfully used with several tissue-specific promoters, and was shown to work independently of the GAL4/UAS system when expressed in the same cell. In [[Caenorhabditis elegans|C. elegans]]<ref name="Wei2010" /> the Q-system has been shown to work in muscles and in neuronal tissue. In 2016, the Q-system was used to target, for the first time, the olfactory neurons of malaria mosquitoes ''[[Anopheles gambiae]].''<ref name="Riabinina2016" /> In 2019, the Q-system in ''Anopheles'' mosquitoes was used to examine the functional responses of olfactory neurons to odors.<ref>{{cite journal | vauthors = Afify A, Betz JF, Riabinina O, Lahondère C, Potter CJ | title = Commonly Used Insect Repellents Hide Human Odors from Anopheles Mosquitoes | language = en | journal = Current Biology | date = October 2019 | volume = 29 | issue = 21 | pmid = 31630950 | doi = 10.1016/j.cub.2019.09.007 | pmc = 6832857 | pages = 3669–3680.e5 }}</ref> In 2019, the Q-system was introduced into the ''[[Aedes aegypti]]'' mosquito to capture tissue specific expression patterns.<ref>{{cite journal | vauthors = Matthews BJ, Younger MA, Vosshall LB | title = Aedes aegypti | journal = eLife | volume = 8 | article-number = e43963 | date = May 2019 | pmid = 31112133 | pmc = 6597239 | doi = 10.7554/eLife.43963 | doi-access = free }}</ref> These successes make the Q-system the system of choice when developing genetic tools for other organisms. Currently the main shortcoming of the Q-system is the low number of available transgenic lines, but it will be overcome as the scientific community creates and shares these resources, such as by the use of the GAL4>QF2 HACK system to convert existing GAL4 transgenic insertions to QF2.<ref>{{cite journal | vauthors = Lin CC, Potter CJ | title = Editing Transgenic DNA Components by Inducible Gene Replacement in Drosophila melanogaster | journal = Genetics | volume = 203 | issue = 4 | pages = 1613–28 | date = August 2016 | pmid = 27334272 | pmc = 4981265 | doi = 10.1534/genetics.116.191783 }}</ref> DNA binding domain of QF2 fused with VP16 transcriptional activator domain was successfully applied in ''Penicillium'' to gain control over the penicillin producing secondary metabolite gene cluster in a scalable manner.<ref>{{cite journal | vauthors = Mózsik L et al. | title = Synthetic control devices for gene regulation in Penicillium chrysogenum | journal = Microb Cell Fact | volume = 18 | issue = 203 | date = November 2019 | page = 203 | doi = 10.1186/s12934-019-1253-3 | pmid = 31739777 | pmc = 6859608 | doi-access = free }}</ref>

== References ==
{{reflist}}

[[Category:Genetics]]

Q-system (genetics) - История изменений

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