Introduction
Gene silencing is the regulation of gene expression in a cell to prevent the expression of a certain gene. Gene silencing can occur during either transcription or translation and is often used in research. Methods used to silence genes are being increasingly used to produce therapeutics to combat cancer and other diseases, such as infectious diseases and neurodegenerative disorders.
Gene silencing is nearly similar to gene knockout, in gene silencing the expression of the gene was suppresed, whereas in gene knockout the gene was completely erased. Even though it's said to be similar because of the methods used for gene silencing which can reduce the expression by at least 70% not completely erase.
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Gene silencing is better than gene knockout because it helps the researchers to study particular gene without removing the other genes. More than that it gives clear cut about the diseases due to suppression of a gene.
History of gene silencing
Gene silencing was discovered in 1998 by Andrew fire and Craig Mello. They won the noble prize for their discovery in 2006. They discovered the RNA interference gene silencing by ds-RNA in C.elegans.
TYPES OF GENE SILENCING
There are three major types of gene silencing;
- Transcriptional
- Post-transcriptional
- Meiotic
Transcriptional involves:
- Genomic Imprinting
- Paramutation
- Transposon silencing
- Transgene silencing
- Position effect
- RNA-directed DNA methylation
Post-transcriptional involves:
- RNA interference
- RNA silencing
- Nonsense mediated decay
Meiotic involves:
- Transvection
- Meiotic silencing of unpaired DNA
APPLICATION
- Gene silencing techniques have been widely used by researchers to study genes associated with disorders include cancer, infectious diseases, respiratory diseases, etc.
- Gene silencing is also currently being used in drug discovery efforts, such as synthetic lethality, high-throughput screening, and miniaturized RNAi screens.
- RNA interference has been used to silence genes associated with several cancers.
- Ribozymes, antisense oligonucleotides, and more recently RNAi have been used to target mRNA molecules involved in asthma.
- Huntington's disease is incurable and known to cause motor, cognitive, and behavioral deficits. Researchers have been looking to gene silencing as a potential therapeutic for HD.
- Gene silencing has been used to knock down the SOD1 mutant that is characteristic of ALS.In specific, siRNA molecules have been successfully used to target the SOD1 mutant gene and reduce its expression through allele-specific gene silencing.
Therapeutic challenges of gene silencing
There are several challenges associated with gene silencing therapies, including delivery and specificity for targeted cells. For treatment of neurodegenerative disorders, molecules for a prospective gene silencing therapy must be delivered to the brain. The blood-brain barrier makes it difficult to deliver molecules into the brain through the bloodstream by preventing the passage of the majority of molecules that are injected or absorbed into the blood. Thus, researchers have found that they must directly inject the molecules or implant pumps that push them into the brain.
Gene silencing in food
Arctic Apples are a suite of trademarked apples that contain a nonbrowning trait created by using gene silencing to reduce the expression of polyphenol oxidase (PPO). It is the first approved food product to use this technique.
Recent studies on gene silencing
Recent advances in reversal of gene silencing during X chromosome reactivation:
Dosage compensation between XX female and XY male cells is achieved by a process referred to as X chromosome inactivation (XCI) in mammals. Initially, XCI is developed earlier in female cells and later it is stably maintained in most of the somatic cells.
Despite its stability, the robust transcriptional silencing of XCI is reversible, within the embryo and also during a number of reprogramming settings. However, XCI has been intensively studied, the dynamics, factors, and mechanisms of X chromosome reactivation (XCR) remain unknown. This research, tells us about how new sequencing technologies and reprogramming approaches have enabled recent advances that exposed the timing of transcriptional activation during XCR.
In addition to it also discuss the factors and chromatin features which may be important to know the dynamics and mechanisms of the erasure of transcriptional gene silencing on the inactive X chromosome (Xi).
Concluding results
Collectively, recent studies that built upon the newest technological advances like scRNA-seq, allele-resolution transcriptomics and epigenomics, also as cellular reprogramming, have revealed that XCR may be a gradual process. The timing of X-linked gene reactivation involves the combinatorial effects of multiple pathways including pluripotency and other TFs, chromatin modifications, histone writers and erasers also as chromatin organization and lncRNAs. it'll now be interesting to dissect how these layers interplay to regulate the kinetics of XCR. The enrichment of pluripotency TF binding on multiple X-linked genes suggests that these and other TFs could play an immediate role in transcriptional activation.
TFs like OCT4, NANOG, SOX2, PRDM14, and ESRRB could be directly involved in XCR and have also been implicated in Xist silencing (Navarro et al., 2008; Payer et al., 2013). Their binding to gene regulatory regions on the Xi, together of other TFs, could mediate the initiation, progression and completion of XCR. Histone modifications also appear to play a task in XCR by acting as barriers or mediators of transcriptional activation. So far, UTX and HDACs are implicated within the removal of repressive and active chromatin marks to market or oppose XCR, respectively.
Recent studies also suggested a possible influence of chromatin topology on the upkeep and reversal of Xist-induced silencing. Moreover, novel factors involved within the exit from pluripotency and early lineage commitment could potentially act as mediators of XCI or barriers of XCR. for instance , Polycomb targets which start to move after epiblast specification (pluripotency exit), the ubiquitin-ligase Rlim, whose expression correlates with XCI (Barakat et al., 2011), and therefore the refore the DNA methyltransferase Dnmt3a and the transcriptional repressor Zfp5J, which negatively correlates with XCI (Mohammed et al., 2017), might play a task in XCR. additionally , the invention of potential RNA interactors of Xist might shed light on XCR mechanisms. For this, techniques that enable to acknowledge interactions between two transcripts (e.g., Xist and potential RNA interactors) will got to be developed, almost like the one described in Quinodoz et al. (2018), where genome-wide detection of multiple, simultaneously occurring higher-order DNA interactions are detected. during this way, we'd discover unknown principles by which XCI is reversed.
Altogether, the dynamics of XCR is probably going the result of the combinatorial effect of lncRNAs, TFs, genome topology, and chromatin modifications. Understanding the reversal of gene silencing is vital for a minimum of three reasons. First, reactivation of silenced genes represents a possible therapy for diseases, like Rett Syndrome.
This strategy might reach targeted reactivation of silenced tumour suppressor genes in cancer. Second, it's likely that revealing mechanisms of XCR will uncover gene regulation principles that are generally applicable, because it has already repeatedly been wiped out the past (Pasque et al., 2011; Nora et al., 2012). Third, reactivation of X-linked genes may underlie the emergence and/or progression of specific human disorders. Many intriguing questions are still waiting to be addressed and can open new avenues to link fundamental research with diseases and therapies.
CONCLUSION
Gene silencing as a therapeutic technique is the active area for researches. This strategy will surely found solution for Huntington's disease because it able to reduce the expression of the protein. This highly helps researchers to identify the gene responsible for a disease. This method is popular than gene knockout technique. This could provide various solutions for the researchers for their future researches.
REFERENCE
- Red berry, Grace (2006). Gene silencing: new research. New York: Nova Science Publishers. ISBN 9781594548321.
- 'Gene Silencing'. National Center for Biotechnology Information. Retrieved 11 November 2013.
- Hood E (March 2004). 'RNAi: What's all the noise about gene silencing?'. Environmental Health Perspectives. 112 (4): A224–9. doi:10.1289/ehp.112-a224. PMC 1241909. PMID 15033605.
- Mocellin S, Provenzano M (November 2004). 'RNA interference: learning gene knock-down from cell physiology'. Journal of Translational Medicine. 2 (1): 39. doi:10.1186/1479-5876-2-39. PMC 534783. PMID 15555080.
- Kole R, Krainer AR, Altman S (February 2012). 'RNA therapeutics: beyond RNA interference and antisense oligonucleotides'. Nature Reviews. Drug Discovery. 11 (2): 125–40. doi:10.1038/nrd3625. PMC 4743652. PMID 22262036.
- Dias N, Stein CA (March 2002). 'Antisense oligonucleotides: basic concepts and mechanisms'. Molecular Cancer Therapeutics. 1 (5): 347–55. PMID 12489851.
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