We often hear that oligos (primers) are a simple product, and they should work every single time. From a producer’s point of view, oligos are arguably the most complicated products among common molecular biology reagents, at least in terms of the number of chemical steps required. DNA synthesis starts from the 3’ end to the 5’ end (opposite to DNA polymerases) on a solid support (e.g. CPG beads). For the addition of each base, the process begins by removing a protection group via “Deblocking”; then activating the last base for coupling with an “Activator”, adding the current nucleotide in the chemical form of a phosphoramidite (4 times in our protocol), blocking un-reacted openings with “Capping A and B solutions” (again 4 times each), forming bonds between bases by oxidization with Iodine, then looping all the way back to the beginning of the cycle. Many of these chemicals are either highly sensitive to moisture or have a short shelf life (can go bad any time).
Coming back from a seminar, sitting at the lab desk, you know you have a new idea and some cloning to do, and of course, it must be done tomorrow. The first thing you do is to send in some oligo sequences online to a local synthesis company late in the afternoon after looking at some maps and sequences. Around noon the next day, the oligos will be delivered in person to your hands. Most times everything will just work out fine as far as experiments involving primers are concerned; others you get stuck here and there along the way of cloning. Chances are you have run into problems with primers not giving PCR signals or clones with mistakes in the primer regions at some points in your research career. Even if this has only happened a few times, the memory, as well as the dissatisfaction and anger, can last for quite some time.
Between ordering and delivering, oligos are made overnight; they are then post-synthesis processed (requiring several hours starting in the early morning), OD’ed, and concentration adjusted. Given that the machine completes the run without any problems (power or computer related), and none of the chemicals run out, the best quick indicator of a good run is a color change from the protection group removed by Deblock at the last base. If there is visible amount of blocking group at the end of the synthesis, as reflected by an orange color from a Trityl group, it is likely that the synthesis was efficient till the end. Unfortunately, the efficiency of adding each base is never 100%–accumulations of missing or, at a lower percentage, mistaken bases will add up, especially in long oligos. Purification will remove some of the oligos with deletions, but not all of the bad oligos. MASS analysis will help determine the approximate percentage of bad oligos, but it will require time and cost not typically chosen by customers. It is our hope that understanding how oligos are made will help with more effective use of oligos when you order oligos, conduct experiments using oligos, or clone with oligos.
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Off-target effects are a major problem when using RNA interference (RNAi) to silence genes in mammalian systems. One potential source of off-target effects, by either transfected siRNA duplexes or transcriptionally expressed shRNAs, is the inadvertent activation of the interferon response. There are several steps that can be taken to deal with this problem.
Interferon response is more likely when high levels of siRNA are used; it is important to transfect the minimum amount of the siRNA duplex that gives rise to a specific RNAi response, as assessed by the level of expression of the target mRNA and/or protein. The level of stable shRNA expression achieved by using lentiviral or retroviral vectors is comparatively modest. Unless very high levels of shRNA expression are achieved, for example, by using highly transfectable cells and a very efficient shRNA expression plasmid, nonspecific activation of the innate immune response are less likely to be induced.
Previous work has shown that the interferon response is induced by dsRNAs of ?30 bp in length and that perfect dsRNAs of as little as 11 bp in length can produce a weak induction. One possible approach to solving the problem of nonspecific activation of the cellular interferon response is to design the siRNA duplex or shRNA precursor so that it does not contain any stretches of perfect dsRNA of ?11 bp.
If activation of the interferon response remains a concern, it is possible to routinely check for this effect during the course of an RNAi experiment. Analyzing the level of expression of an interferon-response gene, such as oligoadenylate synthase-1 (OAS1), interferon-stimulated gene-54 (ISG54), and guanylate-binding protein (GBP), in the transfected or transduced cells by northern blot or RT- PCR assays are commonly used.
Can there be any more convenient alternative method for checking interferon response? One potentially useful product could be HiTiter™ pre-packaged lentiviruses that would have a fluorescent protein (mTFP1, mWasabi, or the brightest FP in lanYFP) under the control of an ISRE (IFN-stimulated response element) or GAS (IFN gamma-activating sequence)*. This could be another group of Product-on-Demand type of reagents, meaning that we will have the design ready, but only to produce them upon ordering. This way the cost to us and the price to customers can be kept at minimum.
*The expression of the interferon-stimulated genes (ISGs) is induced by the type I interferons IFN-alpha and IFN-beta. A cis-acting element (TAGTTTCACTTTCCC, nucleotides -101 to -87) has been identified in its promoter of one of these genes, ISG54. This element is responsible for the inducible expression of the ISG54 gene and is referred to as IFN-stimulated response element. The human guanylate-binding (GBP) gene is induced by INF-gamma in fibroblasts within 15 minutes of treatment. An IFN gamma-activating sequence (GAS) has been identified in the GBP promoter (nucleotides -123 to -103). To create the interferon reporters, we would insert five direct repeats of this ISRE and/or four direct repeats of this GAS upstream of the basic promoter element (TATA box) and mWasabi GFP gene of the Allele’s patented pLico lentiviral plasmid backbone.
It should be noted, however, that simple transfection of cells with expression plasmids can induce low-level activation of the interferon response, presumably owing to the presence of cryptic convergent promoters that cause the expression of low levels of dsRNA. In general, very low-level activation of the interferon response, that is, activation that exerts a global inhibitory effect on protein translation of less than twofold, is unlikely to be a problem as long as the specificity of any observed phenotype is fully confirmed.
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RNA interference (RNAi) has been demonstrated to be a powerful tool to silence gene expression. Therapies based on RNAi are being developed in numerous application areas at fast paces. Although in basic research both expressed and synthetic double-stranded RNA molecules are broadly used to induce gene silencing, synthetic small interfering RNAs (siRNAs) are deemed easier to deliver in preclinical and clinical studies. Compared to synthetic siRNAs, DNA cassettes that express small hairpin RNA (shRNA), microRNA (miRNA), or strands of siRNAs have advantages of prolonged effects.
RNAi-expressing DNA cassettes have been incorporated into viral and non-viral vectors for delivery. Viral vectors for RNAi carry the same risks as those for gene therapies, and are currently not the method of choice for human therapies. Non-viral DNA molecules, often in the form of plasmids, can be easily created and reproduced, but their efficacy is hindered by delivery barriers at the tissue, cell, and the nucleus levels. These difficulties are in part due to the plasmids’ large size, presence of antibiotic resistance genes, and immuresponse-generating CpG islands created in bacteria during propagation.
One way to alleviate these difficulties with non-viral DNA vectors for RNAi is to use linear DNA cassettes. Linear DNAs traverse nucleopores efficiently. The DNA molecules can be conveniently produced by PCR reactions without going through production in bacteria, avoiding DNA modifications such as CpG motifs and the need for replication origin or drug-resistance genes. Linear DNA encompassing a promoter, coding region, and poly(A) signals has been used for protein production. Similarly, by incorporating a miRNA cassette into linear transcription unit driven by a Pol II promoter was used to express RNAi for inhibiting HBV (Chattopadhyay et al. (2009). There are now available technologies and commercial services (e.g. Vandalia Research, Inc.) to produce therapeutic grade linear DNA by specialized PCR reactions.
Allele Biotech’s patents on DNA-expressed RNAi provide a platform for highly express shRNA or siRNA from a DNA molecule as short as fewer than 200 basepairs, potentially more suitable for large scale production, and even more efficient transduction trough tissue, cell membrane, and nuclear pores than the large linear cassettes used by Chattopadhyay et al. A set of experiments similar to the cited HBV studies could quickly lead to the validation of a possibly the most effect way yet for RNAi therapeutics.
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Allele Biotechnology & Pharmaceuticals, a San Diego based private company with associate offices and laboratories in China and distribution channels in 30 countries, was granted a major landmark patent in China in the field of RNA interference (RNAi). The patent CN02828345.7, issued on January 20, 2010, covers compositions of DNA molecules that can be transcribed into RNAi-mediating RNA molecules, including the commonly used shRNA and miRNA-like designs. The patent also grants Allele Biotech rights to the process of introducing such DNA molecules into cells. To induce gene silencing by RNA interference, researchers often bring DNA molecules that encode interfering RNAs into cells via plasmid or viral vectors. The rights to use related technologies for the purposes of completely or partially abolishing gene functions through the mechanism of RNAi are granted to Allele Biotech.
Additional claims include methods of studying gene functions using DNA-encoded RNAi agents, or modifying gene expression profile by introducing gene expression-altering DNA molecules that will induce RNAi. The patent further protects the use of DNA-mediated RNAi in creating cell, animal models, and for curing human diseases. According to a Nov 2009 CreditSuisse analysis on the pharmaceutical market in China (and a number of other reports by JP Morgan as well as Morgan Stanley research, etc.), the drug market in China will double by 2015 and the expected revenues for major pharmaceutical companies are in the billion US dollar range each. Many large drug developers have opened research centers in China. For instance, Novartis just announced a 1.25 billion US dollar investment in Chinese R&D centers, making Shanghai one of its top three global research centers. Roche, Pfizer, JNJ, AZN, Bayer, and LLY also have substantial investments in R&D there. Some of their research teams have plans to use the virus-carried shRNA technologies in oncology and other areas, either as screening/validation tools or as therapeutic candidates. Such activities in China are now under the Allele’s recently granted RNAi patent.
The Contract Research Organization (CRO) industry in Shanghai, Suzhou, and Beijing has seen significant growth in the past few years, benefiting from R&D cost cutting in Western countries and the flow of Western-trained researchers back into China. The focus of the CRO business also shifted from chemical synthesis towards one-stop service, including functional screening and animal testing. The clarification of the RNAi patent landscape by the current granting should make the relevant CRO applications of RNAi more mature. It should also provide both the service and the customer companies with a clear route to licensing and/or collaboration.
Most major biomedical research tool and reagent companies have established themselves in the Chinese market and seen fast-growing revenues due to large funding increases to biomedical research in China. For example, Life Technologies, Promega, Millipore, Thermo Scientific, and Sigma-Aldrich all sell RNAi kits that use DNA template for expressing shRNA in mammalian cells, either by viral infection or DNA transfection. In addition, there are many local companies in China that provide reagent kits as well as services.
The Allele patent specifically states claims on reagent kits that contain shRNA-encoding DNA molecules. While being the first in China’s RNAi market, Allele Biotech manufactures in the United States and sells world-wide a set of RNAi kits in the form of retroviral or lentiviral vectors, plasmids, and linear DNA—all of which have superior design for precise shRNA production. As a matter of fact, Allele Biotech helped introduce the RNAi concept through a series of workshops in major universities in China for 3 consecutive years since 2002, at a time when most biologists had just heard of RNAi.
Allele Biotech intends to fully realize the value of this broad patent by providing opportunities to R&D centers, service providers, and reagent sellers to license at reasonable fees, so that this great technology will continue to be widely used and further developed through original research and investment. Allele Biotech intends to set licensing fees on a sliding scale in several aspects:
–the closer a drug gets to market, the higher the fees;
–the smaller the company, the lower the fees;
–the earlier the license is negotiated within an industry sector, the lower the fees.
Allele’s attorneys in China have already been contacted to start drafting plans for licensing deals and patent rights execution. “While stressing wide access, limiting the number of licenses in China is not completely out of the question. In general we want to grant all-application, non-exclusive, low-cost licenses to many companies to keep the costs affordable.” says Dr. Jiwu Wang, Allele’s CEO and the inventor of the patents. “However, if a dominant player in a particular application area is more interested in some exclusivity, a co-exclusive or conditional exclusive license may be negotiated”.
A brief background about RNAi patents:
–The original Fire and Mello patent claimed double-stranded RNAs longer than 25, eliminating use in most mammalian cells.
–The few other RNAi patents granted in the US, Europe, Japan and other markets so far mostly concern chemically synthesized siRNAs.
–The Tuschl I and II patents, with the latter being frequently mentioned in the news because it has generated hundreds of millions of dollars in licensing fees, concern siRNAs suitable for mammalian cells, but they are either chemically synthesized or processed in cell lysate.
–The Allele patent family includes 3 issued US patents on using RNA polymerase III promoter (e.g., commonly used U6 promoter) for generating RNAi. The core of the Allele patents describes making siRNAs that can be of 19 to 25 basepairs long, which are not covered by the Fire and Mello patent. Further, these transcribed siRNA are not chemically synthesized; therefore, they do not conflict with the Tuschl patents. The Allele patent in China has an even broader field of granted rights, covering any DNA-based gene silencing using double-stranded RNA as intermediates.
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RNAi refers to dsRNA-induced gene silencing, a cellular process that degrades RNA homologous to one strand of the dsRNA [1, 2]. The intermediates of long dsRNA-initiated RNAi are double-stranded small interfering RNAs (siRNA), typically 21-23 nucleotide (nt) long. The siRNAs, when introduced into cells, can be used to silence genes in mammalian systems where long dsRNAs prompt protein kinase R (PKR), RNase L, and interferon activities that result in non-specific RNA degradation and general shutdown of protein synthesis . siRNAs can either be chemically synthesized then directly transfected into cells or can be generated inside the cell by introducing vectors that express short-hairpin RNA (shRNA) precursors of siRNAs. The process of shRNA into functional siRNA involves cellular RNAi machinery that naturally process genome encoded microRNAs (miRNA) that are responsible for cellular regulation of gene expression by modulating mRNA stability, translation, and chromatin structures .
Chemically synthesized siRNA is the simplest format for RNAi. One of the biggest hurdles for achieving effective RNAi with siRNA is that many cells are difficult to transfect. An RNAi experiment is typically considered successful when the target gene expression is reduced by >70%, a threshold not reachable by many types of cells due to their low transfection efficiency. Another drawback of using synthetic siRNA is the limited duration of post-transfection effects, typically with gene silencing activities peaking around 24 hours, and diminishing within 48 hours . Chemical synthesis of siRNA, which is a service Allele Biotech and Orbigen (now merged under the Allele brand) pioneered and still provides, is expensive on a per transfection basis relative to DNA vector based reagents.
shRNA can be introduced by DNA plasmid, linear template, or packaged retroviral/lentiviral vectors. Using any form of DNA construct, except the PCR template format such as Allele’s LineSilence platform, requires creating DNA constructs and sequence verification; a taxing work load if multiple genes need to be studied. However, once the constructs are made, they can be reproduced easily and inexpensively. It is difficult to directly compare the effectiveness of siRNA versus shRNA on a per molecule basis because RNA polymerase III (Pol III) promoters such as U6 or H1 commonly used to express shRNAs can make thousands of copies of shRNA from a single DNA template. However when both siRNA and shRNA are produced the same way, e.g. synthesized chemically, shRNA is reported to be somewhat more effective [6, 7]. For the goals of this research, the most important advantage using shRNA can provide over siRNA is that it can be carried on a lentiviral vector and introduced into a wide variety of cells.
Similar to the comparison between siRNA versus shRNA, it is also difficult to rank the efficiency of shRNA versus miRNA from published data, partly due to different results from different experimental systems. There have been several reports that showed shRNA can cause significant cell toxicity, especially in vivo such as after injection into mouse brain. It was originally reasoned that highly efficient expression from Pol III promoters might overwhelm the cellular machinery that is needed to execute endogenous RNAi functions such as transporting miRNA from the nucleus to the cytoplasm. It was later found out that even using Pol III promoter to create miRNA could still mitigate the toxic effects of shRNA . Since shRNA and miRNA are processed by endonuclease Dicer before being incorporated into RNA induced silencing complex (RISC), the exact identity of siRNAs produced from a given shRNA or miRNA targeting the same region on the mRNA are not known in most of the earlier studies. By designing shRNA and miRNA to give exactly the same processed siRNAs, Boudreau et al. showed that shRNA is actually more potent than miRNA in various systems .
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1. Fire, A., S. Xu, M.K. Montgomery, S.A. Kostas, S.E. Driver, and C.C. Mello, Potent and specific genetic interference by double-stranded RNA in Caenorhabditis elegans. Nature, 1998. 391(6669): p. 806-11.
2. Hannon, G.J., RNA interference. Nature, 2002. 418(6894): p. 244-51.
3. McManus, M.T. and P.A. Sharp, Gene silencing in mammals by small interfering RNAs. Nat Rev Genet, 2002. 3(10): p. 737-47.
4. Hutvagner, G. and P.D. Zamore, A microRNA in a multiple-turnover RNAi enzyme complex. Science, 2002. 297(5589): p. 2056-60.
5. Rao, D.D., J.S. Vorhies, N. Senzer, and J. Nemunaitis, siRNA vs. shRNA: similarities and differences. Adv Drug Deliv Rev, 2009. 61(9): p. 746-59.
6. Vlassov, A.V., B. Korba, K. Farrar, S. Mukerjee, A.A. Seyhan, H. Ilves, R.L. Kaspar, D. Leake, S.A. Kazakov, and B.H. Johnston, shRNAs targeting hepatitis C: effects of sequence and structural features, and comparision with siRNA. Oligonucleotides, 2007. 17(2): p. 223-36.
7. Siolas, D., C. Lerner, J. Burchard, W. Ge, P.S. Linsley, P.J. Paddison, G.J. Hannon, and M.A. Cleary, Synthetic shRNAs as potent RNAi triggers. Nat Biotechnol, 2005. 23(2): p. 227-31.
8. McBride, J.L., R.L. Boudreau, S.Q. Harper, P.D. Staber, A.M. Monteys, I. Martins, B.L. Gilmore, H. Burstein, R.W. Peluso, B. Polisky, B.J. Carter, and B.L. Davidson, Artificial miRNAs mitigate shRNA-mediated toxicity in the brain: implications for the therapeutic development of RNAi. Proc Natl Acad Sci U S A, 2008. 105(15): p. 5868-73.
9. Boudreau, R.L., A.M. Monteys, and B.L. Davidson, Minimizing variables among hairpin-based RNAi vectors reveals the potency of shRNAs. Rna, 2008. 14(9): p. 1834-44.
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