What is siRNA and RNA Interference (RNAi)?

[ATGC2001]

RNA stands for ribonucleic acids. "si" stands for small interference. RNA interference (RNAi) is a process by which living cells control genes, at what level these genes are expressed, and how active they become. Small interfering RNA (siRNA) is also sometimes known as silencing RNA, or short interfering RNA. siRNA is made up of long double-stranded RNA molecules that may create interference pathways, or in other words - interfere with the expression of a specific gene or certain gene process.

The structure of siRNA comprises of a 20-to 28-nucleotide long double-stranded RNA molecules, these molecules can be synthesized in laboratory and introduced into cells utilizing molecular biology technique called transfection. Researchers can modulate nucleic acid sequence of siRNA in a way that it could be targeted against specific gene (any human gene out of ~30,000 genes in human genome, or any gene of other species). Inactivation of specific gene in such directed manner (scientists often focus on oncogenes, or other genes causing various diseases) hold promise for development of new generation of medicined (also known as targeted therapeutics).

Induction of RNAi in cells or tissues is known as gene knockdown (or gene silencing). It's usually a temporary phase and will only work well with rapidly dividing cells. Scientists have attempted to overcome the limitations of such processes by modifying siRNA (shRNA) to be expressed from a vector such as plasmid DNA (stable shRNA expressing cell lines). However, inadequate introduction, structure, or size of siRNA (or other small RNA molecule) can initiate undesirable immune responses.

To date, scientists are looking for more efficient methods to deliver siRNA molecules into cells (invivo and invitro). Also, depending on cell type - cells can induce differential responce, the mechanism of which is not yet understood. Several Phase 1 trials are underway for therapeutic use of siRNA molecules for medical conditions such as age-related macular degeneration, diabetes, and cancer. And in the near future, small RNA (including microRNA) molecules and siRNAs may create new classes of drugs for the treatment of many human immunodeficiency viruses.

RNA Interference and siRNA will continue to be studied in biological and medical research field, as well as pharmaceutical and biotechnology industries that will help scientists and researchers better understand gene silencing (RNAi) mechanism and apply it to develop new medicines and therapeutics.

[biologist]

Also, stable cell line generation offers the ability to transform cell lines that can stably express an RNAi “knockdown” sequence and target specific genes on a long-term basis. This homogenous cell population can be utilized for many experiments, including inducible expression studies and differentiation studies. See another post for details - http://www.transfection.ws/forum/viewtopic.php?f=25&t=297&sid=b075d20a3a6c21e88de64a9bbefde992

[transfection]

There are two general types of small RNA molecules, known as microRNA and small interfering RNA (siRNA). RNAi products are able to bind or bond with other types of RNAs leading to increase or decrease activities by preventing messenger RNA (mRNA) from producing various proteins. The process of RNA interference plays an essential role in the defense of cells against viruses.

[transfection]

MicroRNAs (miRNAs) are highly conserved, small RNA molecules, 21-23 nucleotides in length, that are encoded in the genomes of plants and animals. These endogenously expressed molecules regulate gene expression by binding to the 3'-untranslated regions (3'-UTR) of specific mRNAs. Over 600 microRNAs have been identified, some of which are known to play important regulatory roles in animals by targeting specific messages of protein-coding genes, resulting in translational repression. Misregulation of miRNA expression plays an important role in the development of cancer, and perhaps many other diseases.

[invivo]

siRNA consist of short segments of double-stranded RNA that exhibit gene silencing activity within a cell’s cytoplasm. Such phenomana occurs via a mechanism known as RNA Interference (RNAi) where siRNA prevent specific mRNA molecules from being translated into functional proteins in sequence-specific manner. Therapeutic applications of siRNA (and recently - microRNA) demonstrated useful gene silencing capability for medical applications, and is currently being utilized by large pharmaceutical companies to develop new treatments for genetic diseases. Due to their sequence-based highly specific nature, siRNA capable to provide potent gene inhibition at the level of single-nucleotide polymorphisms. However, while great potential from these siRNAs exist - a challenge arises from the delivery and stability of siRNAs in vivo.