Monday, 2 April 2012

Non-coding RNAs are more important than we thought

It is only recently that we found the importance of non-protein-coding RNA (other than messenger and transfer RNAs). If DNA sequences didn’t code for proteins or the small fraction of RNA that are known (such as mRNA and tRNA) then the sequence of genetic information was thought to be relatively useless. However, near-past and current ongoing studies have discovered new types of RNA molecules; RNA molecules that play a crucial part in gene regulation through a process called “RNA interference” (RNAi).

RNA interference plays a large role in gene regulation. The process stops the production of faulty or possibly lethal proteins by getting rid of the mRNA molecules which code for these proteins. Basically, RNAi molecules called microRNA (miRNA) and small interfering RNA (siRNA) [1] attach to “Argonaut” proteins in the cytosol. This miRNA-protein complex travels to the target mRNA molecule and the protein degrades it into its monomer nucleotides. This is possible because the miRNA/siRNA strands are made of complimentary bases to the target mRNA [1][2], thus the complex can seek out the target mRNA and attach to it. A more in depth visualisation is available through this link: http://www.nature.com/nrg/multimedia/rnai/animation/index.html


Fig. 1: RNAi process (showing miRNAs) [1]
Although RNAi occurs naturally, scientists and researchers have taken full advantage of the recent discovery, leading to new technological developments in the biomedical field. SiRNAs are used to treat illnesses and diseases, and also stop the growth and reproduction of some harmful bacteria and viruses. Artificially synthesised siRNA molecules can be injected into a cell. These molecules will then attach to pre-existing argonaut proteins in the cell and carry out the degradation of the target mRNA. This prevents the production of the target proteins and thus will treat the illness caused by the protein, or kill off the bacteria that requires the protein.

Some biomedical firms have taken this RNAi process further by pairing it with recombinant DNA technology. The process is called DNA directed RNAi (ddRNAi) [3][4]. DdRNAi is a form of gene therapy: DNA (as part of plasmids) that codes for the transcription of siRNA molecules is inserted into the target cell. This DNA then forms part of the cell’s gene and thus siRNAs are continually produced [3][4]. This will be particularly effective at treating patients with chronic illnesses that continually require the breakdown of a certain protein.


 Fig. 2: Recombinant RNAi technology compared to inserting siRNA molecules [4]

The action of RNAi molecules is one of the leading research subjects in modern biotechnology. Naturally, these molecules help us survive through gene regulation and new technology has helped us to more clearly understand their potential.
References:
[1] Reece, J. B. et al., 2011. Campbell Biology. 9th (Australian Version) ed. Pearson Australia Group Pty.Ltd
[2] Nature Reviews 2012. Video Animation: RNA interference. 16/03/12. http://www.nature.com/nrg/multimedia/rnai/animation/index.html
[3] Carol Potera (GEN) 2012. Firm (Benitec) focuses operations on gene silencing. 20/03/2012. http://www.genengnews.com/gen-articles/firm-focuses-operations-on-gene-silencing/4004/
[4] Benitec Biopharma 2012. Technology. 20/03/12. http://www.benitec.com/technology.php

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