How are different types of RNAs used in various applications?
Summary:
- RNAs are a diverse group of molecules that exist ubiquitously in nature. They may possess varying biological functions and can be utilised for varying therapeutic goals.
- The function of RNA is driven by its sequence.
- CRISPR sgRNA and mRNA vaccines consist of different sequences and act differently.
- CRISPR sgRNA binds to its target genome sequence and Cas9 protein in order to allow Cas9 to cut the DNA.
- mRNA vaccines produce antigens by engaging the proteins production machinery.
In the XXI century, medicine has rapidly expanded its therapeutic repertoire beyond proteins (e.g. monoclonal antibodies (monoclonal antibody), cytokines, interferons) or small molecules (such as aspirin, antihistamine, insulin) by employing RNA in a broad array of applications [1]. RNAs are naturally occurring molecules that serve essential functions in all organisms and scientists take advantage of them in various research and therapeutic areas. Two such technologies have been described previously by our team – mRNA-based vaccines and CRISPR-Cas9 system (article 1, article 2). The development has not stopped on the aforementioned two [1]. In fact, there are multiple other applications of RNAs in disease treatment/prevention. Our team presented the most relevant information about the discussed biologics but, just like the whole field of molecular biology, the topic may still be confusing. Recently, our team has received questions about the potential of RNA in mRNA vaccines to change the human genome like RNA in CRISPR/Cas9 method does. The aim of this article is to present a small commentary on the diversity in the RNA world and use this knowledge to clarify the raised concerns.
Most people have heard about DNA and have a rough idea about its function. DNA and RNA are similar molecules that are capable of information storage and propagation. However, RNAs are an even more diverse set of molecules with varying functions [2]. The most well-known group of RNAs is messenger RNA – mRNA (an edited copy of a DNA fragment) that delivers information about a future protein to the cellular production machinery, the ribosomes. Interestingly, ribosomes include other RNAs – rRNA or ribosomal (ribosome) RNA that possess enzymatic activity [3]. Such RNAs are called ribozymes (ribonucleic acid + enzymes) and participate in protein production, RNA biosynthesis and processing, and viral replication [4]. Another group of RNAs is the one that regulates the production of macromolecules or battle viral genomes [5]. The groups are highly diverse and can be further divided into multiple subgroups.
It may be surprising to many that RNAs have quite diverse roles in biology. To understand it, let us use a linguistic analogy. There is a limited amount of letters (building blocks) in our languages but they are capable of generating a much broader set of words. Even the same set of letters may create many different words/sentences and meanings as in anagrams (e.g. “listen” and “silent” or “William Shakespeare” and “I am a weakish speller”). The same can be applied to RNA. However, the order of the building blocks (sequence) is not the only important factor – the 3D structure also is. Importantly, the 3D structure is also a result of the instructions in the sequence; the building blocks of DNA and RNA are called nucleotides that can be modified in post-production that may then fold into 3D structures.
Such a lengthy introduction should be then used to analyse the concern from the first paragraph. mRNA vaccines use mRNA molecules to deliver the building instruction about an antigen. This instruction is then used by our cells to produce the antigen, which in turn notifies and trains our immune system against a pathogen (e.g. SARS-CoV-2) [6]. The mRNA must contain features that allow this, which include the sequence of the Spike antigen to be read by the protein production machinery. Other elements that are included are essential for the binding of the machinery and the stability of the mRNA itself. The mRNA from the vaccines does not possess other elements that would allow genome-altering activities, nor is it in close contact with our genome. Conversely, the sgRNA, used in the CRISPR/Cas9 system, contains a sequence to guide the Cas9 protein to a target genome sequence to be edited. Importantly, Cas9 protein is the one that performs the editing, not the sgRNA [7]. To know more about the CRISPR/Cas9 system, please check our previous articles (article 1, article 2).
In this short commentary, one can appreciate that RNAs can be very diverse. From a limited amount of available building blocks, nature or scientists generate multitudes of different molecules with varying functions. While some activities may overlap, there is a strong difference between mRNAs, as in mRNA vaccines, and RNAs from CRISPR technology. The medical applications for RNA are as many as there are kinds of RNAs. The understanding of RNA biology did not explode overnight in 2020 with the invention of anti-SARS-CoV-2 mRNA vaccines, but has been accumulated for almost a century [8]. This will possibly lead to the expansion of RNA-based therapeutics in medicine. It is therefore important for potential patients – us – to understand the concepts related to RNA biology and technologies.
References:
- Damase TR, Sukhovershin R, Boada C, Taraballi F, Pettigrew RI, Cooke JP. The Limitless Future of RNA Therapeutics. Front Bioeng Biotechnol. 2021;9:628137.
- Cech TR, Steitz JA. The noncoding RNA revolution-trashing old rules to forge new ones. Cell. 2014;157(1):77-94.
- Petrov AS, Gulen B, Norris AM, Kovacs NA, Bernier CR, Lanier KA, et al. History of the ribosome and the origin of translation. Proc Natl Acad Sci U S A. 2015;112(50):15396-401.
- Doherty EA, Doudna JA. Ribozyme structures and mechanisms. Annu Rev Biophys Biomol Struct. 2001;30:457-75.
- Kaikkonen MU, Lam MTY, Glass CK. Non-coding RNAs as regulators of gene expression and epigenetics. Cardiovasc Res. 2011;90(3):430-40.
- Vogel AB, Kanevsky I, Che Y, Swanson KA, Muik A, Vormehr M, et al. BNT162b vaccines protect rhesus macaques from SARS-CoV-2. Nature. 2021;592(7853):283-9.
- Adli M. The CRISPR tool kit for genome editing and beyond. Nat Commun. 2018;9(1):1911.
- Caspersson T, Schultz J (1939). “Pentose nucleotides in the cytoplasm of growing tissues”. Nature. 143 (3623): 602–03.