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What is RNAi? All You Need to Know

RNA interference (RNAi), also referred to as Post-Transcriptional Gene Silencing (PTGS), is the process by which RNA molecules silence genes in response to double-stranded RNA. This article discusses RNAi, the various types of RNAi, its mechanism of action and RNAi therapeutics.

What is RNA Interference?

Gene silencing can be accomplished through a variety of mechanisms, including DNA methylation, histone modification, and RNAi. RNAi is a biological process in which RNA molecules are used to silence or degrade genes. It can be used to regulate gene expression in a variety of ways, including through the destruction of mRNA, the prevention of protein synthesis, and the alteration of chromatin structure. It is the process of inhibiting gene expression, typically at the level of transcription or translation.

RNA (Ribonucleic Acid) Structure

RNAi is a mechanism for post transcriptional gene silencing first observed in plants in 1998. Since then, it has been found to play a role in a wide range of biological processes in both plants and animals. RNAi has emerged as a powerful tool for researchers studying gene function and disease pathogenesis.

The basis for RNAi is the production of small interfering RNAs (siRNAs), which are double-stranded RNA molecules that bind to complementary sequences in target mRNA and silence gene expression. siRNAs can be produced naturally or through the use of synthetic oligonucleotides.

RNA interference is a powerful tool for studying gene function and disease pathogenesis. It can be used to silence genes in a variety of ways, including through the destruction of mRNA, the prevention of protein synthesis, and the alteration of chromatin structure. RNAi is also being explored as a potential therapeutic strategy for a wide range of diseases.

Forms of RNAi

miRNA (Micro RNASs), piRNA (Piwi-interacting RNAs), shRNA (short-hairpin RNAs) and smRNA (small modulatory RNAs) are all forms of RNAi, as well as the most natural occuring type - siRNA (Small interfering RNAs).

  • miRNA - miRNA are single stranded, non-coding RNAs which are expressed in eukaryotes. Within the cell cytoplasm, the miRNA controls gene expression as it binds with messenger RNA (mRNA).
  • piRNA - piRNA forms RNA-induced silencing complex (RISC) in the process of RNA silencing. They then interact with proteins from the Argonautes family called piwi proteins. Piwi protiens use the piRNA to regulate mRNAs at a post-transcriptional level.
  • shRNA - shRNA are an artificial form of RNA that can be used through RNAi to silence target gene expression. This type of RNA can be processed within the cell to form the most common form of RNAi - siRNA.

siRNA VS miRNA

siRNAs and miRNAs are both small RNA molecules that play a role in gene silencing. However, there are some key differences between the two.

  • SiRNAs are synthetic oligonucleotides that are designed to silence specific genes, while miRNAs are naturally occurring RNA molecules that silence genes in a more general way.
  • SiRNAs are double-stranded RNA molecules, while miRNAs are single-stranded RNA molecules.
  • SiRNAs bind to mRNA and prevent translation, while miRNAs bind to mRNA and degrade it.
  • SiRNAs are more specific than miRNAs and have fewer off-target effects.

RNAi Mechanisms

The mechanism of RNA interference is complex and not fully understood. However, it is known that small RNAs play a key role in mediating RNAi. Small RNAs are thought to bind to complementary sequences in target mRNA, causing degradation of the mRNA or preventing translation.

The RNA interference pathway is initiated by the production of small interfering RNAs (siRNAs). These siRNAs are then loaded into an RNA-induced silencing complex (RISC), which cleaves complementary mRNA. This results in the destruction of the mRNA or the prevention of protein synthesis.

Schematic of RNA interference mechanism

Types of RNAi Mechanisms

There are three main types of RNAi mechanisms: transcriptional, post-transcriptional, and epigenetic

  • Transcriptional RNA interference (TRI): This is where small RNAs bind to the promoter regions of target genes and prevent transcription. TRI can be used to silence genes that are involved in disease pathogenesis or to prevent the expression of genes that are involved in disease progression.
  • Post-transcriptional RNA interference (PTR): This is where small RNAs attach to mRNA and inhibit translation. PTR can be used to silence genes that are involved in disease pathogenesis or to prevent the expression of genes that are involved in disease progression.
  • Epigenetic RNA interference (ERI): This is where small RNAs bind to chromatin and alter the structure of DNA, preventing gene expression. ERI can be used to silence genes that are involved in disease pathogenesis or to prevent the expression of genes that are involved in disease progression.

RNAi VS CRISPR

RNAi and CRISPR are both powerful tools for gene silencing. However, there are some key differences between the two.

  • RNAi is a natural process that occurs in all cells, whereas CRISPR is a man-made technology.
  • RNAi is reversible, while CRISPR is not.
  • RNAi can be used to silence multiple genes at once, while CRISPR can only target one gene at a time.
  • RNAi is more specific than CRISPR and has fewer off-target effects.

RNAi's Role in Disease

While RNAi is a powerful tool for studying gene function, it also has the potential to be used as a therapeutic strategy for a wide range of diseases. RNAi is a promising therapeutic strategy for a wide range of diseases, including Alzheimer's disease, Huntington's disease, and cancer.

RNAi can be used to boost the expression of protective genes. For example, siRNAs that target the Huntington gene have been shown to increase levels of brain-derived neurotrophic factor (BDNF), a protein that protects neurons from death. In cancer, RNAi may be used to silence genes that promote tumor growth. For example, siRNAs that target the oncogene Bcl-2 have been shown to induce apoptosis in cancer cells. RNAi is also being explored as a treatment for viral infections. siRNAs that target viral mRNA can prevent the synthesis of new viruses and help the body clear existing infections.

RNAi Therapeutics

The way in which genes are regulated naturally in cells is referred to as RNAi therapeutics. RNAi therapeutics offer powerful methods for identifying both potent and specific inhibitors of disease targets from every molecular class.

There are many benefits to RNAi therapeutics. There include the ability to target a gene of interest easily. Another benefit it is a stable method of gene silencing which includes high efficiency of gene knockdown.

RNAi has also been seen as very beneficial in cancer therapy. They are highly specific and effective on suppressing the growth of even advanced stage tumors. It is also a relatively low cost cancer therapy.

Related Products

Product Name Sensitivity Range

Human RNASE3/ECP (Ribonuclease A3/ Eosinophil Cationic Protein) ELISA Kit

23.44pg/ml

39.06-2500pg/mL

Human WEGF ELISA Kit

18.75pg/ml

31.25-2000pg/mL

Human GAPDH ELISA Kit

0.094ng/ml

0.156-10ng/mL

Future of RNAi

At present, most studies use RNAi as a tool for identification of gene function. These are not the only applications that RNAi can be used for. Disease control (viruses; bacterial diseases; parasites; genetic tumors), production of animals of commercial interest and production of animal models for research use are just some of the other areas that RNAi is used. Other possible future applications include: control of drug consumption, pain relief, modulation of sleep, among many others.

Between 2014 and 2019, the global RNAi drug delivery market has increased by 7% with it expected to continue to grow over the next 5-10 years. The demand for RNAi drug delivery technologies has increased since the spread of COVID-19 also.

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4th Aug 2022 Niamh Murphy MSc

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