The first instance of RNA silencing in animals was documented in , when Guo and Kemphues observed that, by introducing sense and antisense RNA to par-1 mRNA in Caenorhabditis elegans caused degradation of the par-1 message. RNAi could potentially be used to treat viruses ,  bacterial diseases ,  parasites ,  maladaptive genetic mutations ,  control drug consumption ,  provide pain relief ,  and even modulate sleep.
Antiviral treatment is one of the earliest proposed RNAi-based medical applications, and two different types have been developed. The first type is to target viral RNAs. While traditional chemotherapy can effectively kill cancer cells, lack of specificity for discriminating normal cells and cancer cells in these treatments usually cause severe side effects. Numerous studies have demonstrated that RNAi can provide a more specific approach to inhibit tumor growth by targeting cancer-related genes i. RNAi strategies also show potential for treating neurodegenerative diseases. Studies in cells and in mouse have shown that specifically targeting Amyloid beta -producing genes e.
However, there are various barriers that must be fixed before it can be used clinically. For example, "Naked" siRNA is susceptible to several obstacles that reduce its therapeutic efficacy. Therefore, artificial or nanoparticle encapsulated siRNA must be used. However, transporting siRNA across the cell membrane still has its own unique challenges.
If siRNA is transferred across the cell membrane, unintended toxicities can occur if therapeutic doses are not optimized, and siRNAs can exhibit off-target effects e. As previously described, parts of the vector that transports dsRNA can also have regulatory effects. Therefore, unspecific side effects should be considered and controlled.
Common assays for identifying immune response genes
Compared with chemotherapy or other anti-cancer drugs, there are a lot of advantages of siRNA drug. RNAi drugs treat cancer by silencing certain cancer promoting genes. The human immune system is divided into two separate branches: the innate immune system and the adaptive immune system. The challenge between old pathogens and new has helped create a system of guarded cells and particles that are called safe framework. Clinical Phase I and II studies of siRNA therapies conducted between and have demonstrated potent and durable gene knockdown in the liver , with some signs of clinical improvement and without unacceptable toxicity.
The nanoparticle delivery system shows the most promise yet this method presents additional challenges in the scale-up of the manufacturing process, such as the need for tightly controlled mixing processes to achieve consistent quality of the drug product. RNA interference has been used for applications in biotechnology and is nearing commercialization in other fields. RNAi has resulted in the invention of novel crops such as nicotine-free tobacco, decaffeinated coffee, nutrient fortified vegetation, and hypoallergenic crops.
The genetically-engineered Arctic apples received FDA approval in PPO-silenced apples are unable to convert chlorogenic acid into the standard quinone product. There are several opportunities for the applications of RNAi in crop science for its improvement such as stress tolerance and enhanced nutritional level.
RNAi will prove its potential for inhibition of photorespiration to enhance the productivity of C3 plants. This knockdown technology may be useful in inducing early flowering, delayed ripening, delayed senescence, breaking dormancy, stress-free plants, overcoming self-sterility, etc. RNAi has been used to genetically engineer plants to produce lower levels of natural plant toxins.
Such techniques take advantage of the stable and heritable RNAi phenotype in plant stocks. Cotton seeds are rich in dietary protein but naturally contain the toxic terpenoid product gossypol , making them unsuitable for human consumption. RNAi has been used to produce cotton stocks whose seeds contain reduced levels of delta-cadinene synthase , a key enzyme in gossypol production, without affecting the enzyme's production in other parts of the plant, where gossypol is itself important in preventing damage from plant pests. No plant products that use RNAi-based genetic engineering have yet exited the experimental stage.
Development efforts have successfully reduced the levels of allergens in tomato plants  and fortification of plants such as tomatoes with dietary antioxidants. Another effort decreased the precursors of likely carcinogens in tobacco plants. RNAi is under development as an insecticide , employing multiple approaches, including genetic engineering and topical application.
Endogenous retroviruses in the human genome can regulate genes involved in innate immune responses.
Animals exposed to RNAi at doses millions of times higher than anticipated human exposure levels show no adverse effects. RNAi has varying effects in different species of Lepidoptera butterflies and moths. To develop resistance to RNAi, the western corn rootworm would have to change the genetic sequence of its Snf7 gene at multiple sites. Combining multiple strategies, such as engineering the protein Cry, derived from a bacterium called Bacillus thuringiensis Bt , and RNAi in one plant delay the onset of resistance. Transgenic crops have been made to express dsRNA, carefully chosen to silence crucial genes in target pests.
These dsRNAs are designed to affect only insects that express specific gene sequences. As a proof of principle , in a study showed RNAs that could kill any one of four fruit fly species while not harming the other three. The International Potato Center in Lima, Peru is looking for genes to target in the sweet potato weevil, a beetle whose larvae ravage sweet potatoes globally. Other researchers are trying to silence genes in ants, caterpillars and pollen beetles.
Monsanto will likely be first to market, with a transgenic corn seed that expresses dsRNA based on gene Snf7 from the western corn rootworm , a beetle whose larvae annually cause one billion dollars in damage in the United States alone. A paper showed that silencing Snf7 stunts larval growth, killing them within days.
RNA interference - Wikipedia
In the same team showed that the RNA affects very few other species. Alternatively dsRNA can be supplied without genetic engineering. One approach is to add them to irrigation water. The molecules are absorbed into the plants' vascular system and poison insects feeding on them. Another approach involves spraying dsRNA like a conventional pesticide. This would allow faster adaptation to resistance. Such approaches would require low cost sources of dsRNAs that do not currently exist. RNAi HTS technology allows genome-wide loss-of-function screening and is broadly used in the identification of genes associated with specific phenotypes.
This technology has been hailed as a potential second genomics wave, following the first genomics wave of gene expression microarray and single nucleotide polymorphism discovery platforms. With the ability to generate a large amount of data per experiment, genome-scale RNAi screening has led to an explosion of data generation rates. The process of RNAi was referred to as "co-suppression" and "quelling" when observed prior to the knowledge of an RNA-related mechanism.
The discovery of RNAi was preceded first by observations of transcriptional inhibition by antisense RNA expressed in transgenic plants,  and more directly by reports of unexpected outcomes in experiments performed by plant scientists in the United States and the Netherlands in the early s. The overexpressed gene was expected to result in darker flowers, but instead caused some flowers to have less visible purple pigment, sometimes in variegated patterns, indicating that the activity of chalcone synthase had been substantially decreased or became suppressed in a context-specific manner.
This would later be explained as the result of the transgene being inserted adjacent to promoters in the opposite direction in various positions throughout the genomes of some transformants, thus leading to expression of antisense transcripts and gene silencing when these promoters are active.
Another early observation of RNAi was came from a study of the fungus Neurospora crassa ,  although it was not immediately recognized as related. Further investigation of the phenomenon in plants indicated that the downregulation was due to post-transcriptional inhibition of gene expression via an increased rate of mRNA degradation. Not long after, plant virologists working on improving plant resistance to viral diseases observed a similar unexpected phenomenon.
While it was known that plants expressing virus-specific proteins showed enhanced tolerance or resistance to viral infection, it was not expected that plants carrying only short, non-coding regions of viral RNA sequences would show similar levels of protection. Researchers believed that viral RNA produced by transgenes could also inhibit viral replication.
After these initial observations in plants, laboratories searched for this phenomenon in other organisms. As a result of this work, they coined the term RNAi. This discovery represented the first identification of the causative agent for the phenomenon.
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From Wikipedia, the free encyclopedia. A biological process in which RNA molecules inhibit gene expression or translation, by neutralizing targeted mRNA molecules.
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