The Power of Cas

Precise engineering of the genomes of higher eukaryotes can enable a variety of biological and medical applications. Targeted gene disruption, editing, and insertion can translate into the much desired freedom to generate cells or organisms bearing a desired genetic change. Recent developments in the stem cell field have created even more excitement for genetically modifying genomes because it enables delivering more beneficial stem cell-derived therapeutic cells to patients. For instance, by correcting a gene mutation known to be critical to Parkinson’s disease, LRRK2 G2019S, in patient-specific iPSCs (induced pluripotent stem cells), researchers were able to rescue neurodegenerative phenotypes [1].

Cumbersome reagent development and high costs have been major barriers to targeted genome modification using the current technologies, which include the zinc finger nuclease (ZFN) and transcription activator-like effector nuclease (TALEN). Unlike the ZFN and TALEN systems, CRISPR/cas does not require assembly of DNA pieces that encode the functional proteins every time a new sequence is to be targeted. Instead, it uses a guide RNA to direct the traffic of a nuclease complex. Five recent publications of modifying eukaryotic chromosomes showed the importance of the CRISPR/cas system [2-6], they also hinted at the ease of adapting this system in eukaryotes given that the functions of cas and the small guide RNA were described in bacteria merely few months ago [7].

The concern that the bacterial CRISPR/cas system would not access the chromatin structures of eukaryotic genome was muted as a result of recent publications; it also seems that the cas9 protein is as powerful an enzyme as one could have hoped in an endonuclease. As a matter of fact, cas9 from S. pyogenes contains 2 different single-stranded DNAse domains independent of each other, and can be mutated to change from a double-stranded DNA endonuclease to a single-strand cutter, or a non-cutting block. That’s not all, a more recent Nature publication further showed that cas9 (from another species, F. novicida), can bind to yet another small RNA and, instead of cutting chromosomal DNA, it degrades RNA, apparently through a direct cas9/RNA binding mechanism [8]. It may be chromosomal modification and RNAi rolled in one (cas9 from different genera are quite different though). One has to admire the powerful cas!

1. Reinhardt, P., et al., Genetic Correction of a LRRK2 Mutation in Human iPSCs Links Parkinsonian Neurodegeneration to ERK-Dependent Changes in Gene Expression. Cell Stem Cell, 2013. 12(3): p. 354-67.
2. Qi, L.S., et al., Repurposing CRISPR as an RNA-Guided Platform for Sequence-Specific Control of Gene Expression. Cell, 2013. 152(5): p. 1173-83.
3. Mali, P., et al., RNA-guided human genome engineering via Cas9. Science, 2013. 339(6121): p. 823-6.
4. Cong, L., et al., Multiplex genome engineering using CRISPR/Cas systems. Science, 2013. 339(6121): p. 819-23.
5. Cho, S.W., S. Kim, J.M. Kim, and J.S. Kim, Targeted genome engineering in human cells with the Cas9 RNA-guided endonuclease. Nat Biotechnol, 2013. 31(3): p. 230-2.
6. Hwang, W.Y., et al., Efficient genome editing in zebrafish using a CRISPR-Cas system. Nat Biotechnol, 2013. 31(3): p. 227-9.
7. Jinek, M., et al., A Programmable Dual-RNA-Guided DNA Endonuclease in Adaptive Bacterial Immunity. Science, 2012.
8. Sampson, T.R., et al., A CRISPR/Cas system mediates bacterial innate immune evasion and virulence. Nature, 2013.

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NIDA Branch Chief, Jonathan D. Pollock, Ph.D., Encourages SBIR/STTR Grants on Reagent Kits Including iPSC

“We’re interested in areas of genetics, in terms of smoking cessation, pharmacogenomics, treatment of substance abuse, and particularly right now, issues related to prescription substance abuse,” Jonathan D. Pollock, Ph.D., chief of the Genetics and Molecular Neurobiology Research Branch at NIDA’s Division of Basic Neuroscience and Behavioral Research, told GEN.

In addition to that solicitation, Dr. Pollock said, the branch is interested in supporting commercialization and development of products, resources, and services through SBIR/STTR relevant to brain research. They include protein capture reagents, proteomics, genomics, pharmacogenomics, molecular diagnostics, nanotechnology, gene delivery and viral vectors, identification of RNA and DNA sequences in formalin fixed nervous tissue, shRNA, microfluidics, epigenetics diagnostics, therapeutics, and tools to detect epigenetic modifications.

The branch is also looking to support commercialization and development of biomarkers, optogenetics, reagents for iPS and neural stem cells, technologies to uniquely barcode cell types, improved super resolution microscopy methods, in vivo gene expression imaging, automated sectioning, image acquisition and 3D reconstruction of electron micrographic sections, genetically encoded markers for electron microscopy, and “big” genomic and proteomic data, including data visualization, data contextualization, and data analysis.

“What we’re really looking for is products that you could basically commercialize coming out of research. These can be things that are either products or services. I think that there are opportunities, particularly for groups of individuals that have an idea, IP, and want to have a startup company.”

SBIR/STTR grants account for 2.8% of NIDA’s roughly $1 billion annual budget. NIDA spent $26.679 million on SBIR and STTR in fiscal year 2012, which ended September 30—up from $26.497 million in FY 2011. The number of SBIR/STTR research projects grants rose to 56 in FY 2012 from 44 a year earlier, according to the GEN article.

Allele Biotech’s CEO, Jiwu Wang, Ph.D., has worked with Dr. Pollock on a previous, VHH nanobody-related project under the NIDA SBIR program. He has just submitted a SBIR grant application based on Allele’s recently published mRNA-based reprogramming technology, after discussion with Dr. Pollock.

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Thursday, December 6th, 2012 NIH Budget and You No Comments

How do you make shRNA-expressing viruses for function screening?

Most people use standard cloning procedures when trying to insert shRNA templates into lentiviral vectors, i.e. anneal a pair of long oligos with sticky ends and ligate the dsDNA into a linearized plasmid with compatible overhangs. However, since typical lentiviral vector plasmids have terminal repeats and are relatively large, when ligated to hairpin sequence-containing shRNA templates, recombination often occurs inside bacteria that results in smaller plasmids. This problem is common for cloning shRNA or other unstable DNA pieces into viral vectors. This cloning issue is further compounded by the fact that it is difficult to sequence any shRNA template region because the hairpin may block the progress of the DNA polymerase used in sequencing, sometimes requiring several repeats under different sequencing conditions, incurring high costs charged by sequencing service providers.

To deal with these aspects of the cloning difficulties, particularly for the purpose of increasing cloning efficiency RNAi-based screening, we compared three different strategies

First, we built a smaller shRNA cloning vector to clone and sequence shRNA templates prior to transferring to lentiviral vectors. This smaller vector does not have a severe recombination problem and is easier to sequence in the hairpin-containing region. After an initial round of cloning with this new vector, we further improved it by inserting an XbaI and a NheI site between the BamHI and SpeI insertion sites, so that any plasmid preparations can be screened for recombinants by a simple XbaI or NheI digest before sequencing. After cloning into this intermediate vector, the shRNA expression cassette can be transferred into the lentivirus vectors with some flanking viral sequences so that the insert size will be around 1kb.

Second, we developed a novel DNA preparation procedure after realizing that DNA damage during miniprep of vector plasmids and gel purification of vector fragment increased recombination of these constructs, which were already less stable than usual due to hairpin structures. This procedure of DNA preparation avoids UV or guanidium exposure, which can cause nicks on double-stranded DNA and facilitate recombination. This new procedure relies on purifying DNA through surface-binding to regular reaction tubes treated with a proprietary reagent (SurfaceBind Purification). The process simply requires adding a proprietary, guanidium-free binding buffer to the DNA, which has been processed in a specially coated tube (eppendorf or thin-wall PCR tube), and purifying directly in the same tube. Vectors prepared this way indeed provide more colony counts and a higher percentage of correct constructs as shown by our test runs. The procedure also requires less time and the purified DNA can be dissolved in volumes as small as a few microliters.

Third, to enable truly high throughput shRNA screening (i.e. looking for effective RNAi reagents), we further tested and adapted a ligationless cloning protocol that can be handled by a liquid handler almost entirely. In order to increase throughput, we designed a drastically different procedure that could bypass ligation and sequencing altogether before functional tests. Briefly, DNA molecules that would provide enhanced recombination were created by one round of PCR, purified directly in the surface bind PCR reaction tubes (any template DNA would be removed with DpnI enzyme that cuts non-PCR DNA), pooled, and transformed in bacteria directly. DNA plasmids from transformed bacteria can be used for lentivirus packaging, bypassing sequencing at the initial screening stage, and choose single colonies for sequencing only after a shRNA sequence shows promise in functional assays. This is based on the fact that such cloning rarely has any background colonies, and that among all oligos (if using the correct grade of oligos from validated suppliers) inserted this way, a good portion encodes the correct sequence.

New Products of the week: 100x 15mm EcoCulture Vented Dishes for better stem cell attachment and less plastic waste to the environment, APB-CS-114TC.

Promotion of the week: Buy 1 Stealth Express IPS Induction PCR Template Set, get 1 SurfaceBind RNA Purification Kit free. Use code FreePureRNA.

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Wednesday, November 16th, 2011 RNAi patent landscape No Comments

Our New Website is Complete, 10% off this week

We recently launched our new website, and to celebrate the launch, we’ll be offering a discount of 10 % on all our products and services from July 18th to July 22nd! Come explore a wide variety of products that Allele Biotech has to offer from viral expression to fluorescent proteins. Examples of services offered include custom lentiviral, retroviral, and baculoviral packaging along with cell production and cell line development. This is our effort to enhance your online shopping experience through our improved shopping cart system. Our mission remains the same; to increase accessibility to innovative molecular biology research tools by offering cutting edge products at a reasonable cost. Please visit http://www.allelebiotech.com and use the code NEWSITE to redeem the offer. We thank you for your support!
For more details click here

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State of the Biomedical Research–Not So Good for Pharma R&D

Exerpt from From Science News

Pfizer’s R&D budget, $9.3 billion in 2010, will drop to less than $8.5 billion this year and to between $6.5 billion and $7 billion in 2012, and the company will stop funding research in internal medicine, allergy and respiratory diseases, urology, and tissue repair.

In fact, the pharmaceutical industry as a whole faces financial pressures, as companies are producing fewer new drugs than in the past. In these conditions, even highly promising research has gotten the ax; in November, Roche cut its RNA interference research unit after spending $400 million over 3 years.

Drug companies also seem less wary nowadays about outsourcing. Among other examples, Eli Lilly began outsourcing animal toxicology studies in 2008, and Wyeth (purchased by Pfizer in 2009) began out sourcing data management for its clinical trials in 2003. In 2007, AstraZeneca even decided to move the production of many active pharmaceutical ingredients—perhaps the core activity of a drug company—to China.

These downsizing events are not particularly caused by still depressed economy, they have more to do with industry-specific patent expiration and productivity issues with large pharmas. What does it all mean to current graduate students and postdocs? Perhaps an even tighter job market than now for starting researchers for some years to come until the next round of sea change comes around. Be aware of what’s going on in smaller, more productive, and focused biotech companies.

New Product of the Week 020711-021311: Lentivirus expressing Luciferase 5 vial package

Promotion of the week 020711-021311: 10% off Luc Assays

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Thursday, February 10th, 2011 State of Research No Comments