Introduction

By Zuoshang Xu, Department of Biochemistry and Molecular Pharmacology, University of Massachusetts Medical School, Worcester, MA 01605

Zuoshang Xu led this live discussion on 18 March 2003. Readers are invited to submit additional comments by using our Comments form at the bottom of the page.

Transcript:

Live Chat held 20 September 2002, featuring Zuoshang Xu, Department of Biochemistry and Molecular Pharmacology, University of Massachusetts Medical School, Worcester, MA.

Participants: Zuoshang Xu, University of Massachusetts Medical School, Worcester; Claudius Vincenz, University of Michigan; Dave Teplow, Brigham and Women's Hospital, Boston, Massachusetts; Natasha Caplen, Medical Genetics Branch, NHGRI, NIH; Victor Miller, University of Iowa; Gabrielle Strobel, Alzheimer Research Forum; Claudia Almeida, Cornell Medical College; Ramesh Tennore, ALS Therapy Development Foundation, Newton, Massachusetts; Jungsu Kim, Mayo Clinic; Amita, USF; Bert Tseng, UC Irvine

Note: The transcript has been edited for clarity and accuracy.

Gabrielle Strobel
Hello, everyone.

Dave Teplow
Hello, there!

Gabrielle Strobel
Hi Dave, hi Zuoshang! Welcome, everyone.

Claudius Vincenz
Is this discussion exclusively about the in-vivo application, or solving the nuts and bolts in cell culture first?

Gabrielle Strobel
Claudius, I think it is safe to say that all here probably feel a lot needs to be figured out in cell culture first. But work in animal models should go in parallel. Disagree, anyone?

Dave Teplow
So, Zuoshang, is RNAi the "cure" we've all been looking for in the Alzheimer's field?

Zuoshang Xu
It could be one of several. I think the key is the delivery.

Victor Miller
And safety: I don't know if long term triggering of the RNAi pathway will be tolerated.

Dave Teplow
Are you talking about tissue or intracellular or organellar delivery?

Zuoshang Xu
Right now, virus-mediated gene therapy appears to be the obvious way, but there is a long way to go before it can be applied.

Gabrielle Strobel
Presently, what seems like the best way to approach delivery?

Dave Teplow
How is this progressing with respect to delivery to hippocampal neurons, for example?

Zuoshang Xu
In cultured cells, the current protocols can mediate highly efficient transductions. But in vivo, how can we deliver widespread infection so that effective inhibition can be achieved in the CNS? I think that is one of the key obstacles.

Dave Teplow
What are some possibilities, Zuoshang?

Natasha Caplen
At present I don't think any of the in-vivo delivery vectors can mediate sufficient specificity to target a particular population of neurons.

Gabrielle Strobel
Zuoshang, based on current evidence, do you think lentiviruses are safe and effective?

Zuoshang Xu
Lentiviruses have potential, but controlling the integration site is the challenge. This is important because of the potential effects on surrounding gene expression.

Gabrielle Strobel
Zuoshang and Victor, and also Natasha, do you want to tell us briefly what you have done so far in animal models?

Victor Miller
We have so far done most of the work on specific disease genes in cell culture. We have shown that the viruses can knock out GFP in mouse brain. We are currently constructing viruses based on the cell culture work to test in SCA3 mouse models.

Ramesh Tennore
What applications of RNAi are closest to the clinic? I read that the first RNA-based molecule got FDA approval recently.

Gabrielle Strobel
Do you remember the application?

Ramesh Tennore
It's from ISIS. It's for CMV. Vitravene (fomivirsen).

Zuoshang Xu
Hi, Ramesh. I don't know the answer to your question.

Natasha Caplen
A number of molecules based on RNAs are undergoing clinical trials primarily using antisense approaches to block protein expression. The development of an RNAi-based drug for testing is likely to be some time away, but based on the experiences in the antisense field, and the current RNAi literature, it is most likely to be a cancer or virally related target.

Ramesh Tennore
Thanks for the summary.

Claudius Vincenz
What promoters seem to work in lenti?

Zuoshang Xu
Many promoters have been used. For the ubiquitous ones, CMV, ubiquitin. There are a few recently published.

Claudius Vincenz
These are polymerase II promoters, not U6 (polymerase III).

Zuoshang Xu
One use of lentiviruses is to make transgenic mice. This has been done by several groups. The promoters used for RNAi are U6 and H1. All show high efficiency in mediating RNAi in mice.

Zuoshang Xu
Is it possible to administer antisense or siRNA directly to CNS?

Gabrielle Strobel
Perhaps a look at recent history could be instructive, too. Antisense RNA also looked terribly promising, but then big efforts in biotech failed to make it work, as far as I can tell. Does anyone know if RNAi stands a better chance, or is the use of antisense RNA bearing fruit now?

Claudius Vincenz
At least in cell culture, the specificity of RNAi is remarkable.

Zuoshang Xu
One advantage RNAi has is that it can be put in viral vectors. I think this is a big advantage.

Natasha Caplen
RNAi appears to be at least as specific as antisense, and probably much more so. With respect to delivery, antisense oligos have proven problematic because they have to be heavily modified to lengthen their half-life. Initial in-vivo experiments suggest that siRNA can be injected into the bloodstream, but the resulting RNAi is transient. This should be the advantage of viral delivery of siRNA.

Gabrielle Strobel
It seemed to me that specificity of integration and possible disruption of other gene expression was a problem. You think not, Claudius? I also found the specificity to single-nucleotide mutants, described by Zuoshang and Victor, to be remarkable....

Claudius Vincenz
I agree that is still potentially a problem; however, antisense was plagued by that and much more.

Zuoshang Xu
Both disruption or activation of a gene could be a problem. For example, if you disrupt a tumor suppressor or activate a cell proliferator, either could cause tumors.

Victor Miller
It is worth noting that the single nucleotide specificity took some "engineering" of the siRNAs to achieve. It may not always be sufficient to simply identify a mutation or SNP and then design an effective and specific siRNA. Several siRNA designs may need to be tried.

Claudius Vincenz
I'm having difficulties knocking down a new gene in cell culture. Does anybody have experience with the system that uses in-vitro Dicer digestion to produce 21bp oligos that cover the whole gene sequence?

Gabrielle Strobel
I am afraid some questions got drowned out. Let me repeat Zuoshang's: Is it possible to deliver antisense or siRNA directly to the CNS?

Zuoshang Xu
The answer to the question whether siRNA can be delivered directly is not known. It needs to be tested. Currently, it has been tested in liver, but I am not aware of it being tried on other cell types in vivo.

Ramesh Tennore
What lessons have we learned from the antisense RNA field that are applicable to RNAi regarding specificity and delivery? Sorry if this question is too broad.

Zuoshang Xu
One possible application is to use RNAi to generate "knockout" mice. It will be much easier to do than the conventional KO method. The question is whether it can be achieved. Does anyone know anything about using RNAi to achieve KO?

Claudius Vincenz
Already a couple of years ago there was a Nature Cell Biology paper showing knockout phenotypes with RNAi very early in embryogenesis (Wianny and Zernicka-Goetz, 2000).

Dave Teplow
Do these KO phenotypes last?

Victor Miller
Has anyone tried blood-brain barrier permeabilization to deliver duplexes directly?

Ramesh Tennore
Actually, I was wondering if anyone has created systems to allow these molecules to penetrate BBB.

Zuoshang Xu
Shall we discuss what are the possible targets for treatment of Alzheimer's disease?

Gabrielle Strobel
Thanks, Claudius, and yes, let's move to targets in Alzheimer's disease. Let me put out BACE as the obvious candidate. I am sure people are trying. Does anyone know how far that has come?

Dave Teplow
There are two obvious choices: the structural gene for Ab and the genes encoding the enzymes responsible for its metabolism.

Victor Miller
BACE, tau, AbPP, the familial presenilin mutations are all possibilities.

Dave Teplow
I think that g-secretase may be an even more important target than BACE.

Gabrielle Strobel
Why, Dave?

Amita
I am of that opinion, too.

Dave Teplow
Because the initial cleavage of AbPP does not lead to the production of the p3 and Ab peptides that appear to be linked to the formation of soluble and insoluble neurotoxic assemblies. Of course, you could argue that BACE is a prerequisite for the production of these peptides, and you would be right.

Zuoshang Xu
But is g-secretase inhibition safe?

Claudius Vincenz
So little is known about the function of AbPP. Presenilins seem to control maturation and cleavage of a whole bunch of proteins. Am I just a pessimist?

Claudius Vincenz
Conditional knockout of presenilin in adults would indicate that it is fairly safe.

Gabrielle Strobel
Even with "antitargets," i.e., presenilin-like enzymes such as signal peptide peptidases and other substrates for presenilins, my sense is that the pharmaceutical industry still views g-secretase inhibition as an opportunity. What advantage would a siRNA have over small molecule compounds?

Victor Miller
I think some apprehension about the safety of reducing expression of incompletely characterized proteins such as AbPP is a rational concern for RNAi therapeutics in general, and simultaneously, a question it can help us answer. Do animals tolerate manipulations of levels of potentially important proteins that we may wish to target to treat disease?

Amita
Maybe RNAi can be used to block AbPP expression in mice in order to assess AbPP's function.

Gabrielle Strobel
Regarding BACE, the structure of its active site makes it tough to find inhibitors for. Screens turn up g inhibitors easily, but never BACE inhibitors. Perhaps this is a reason to turn to RNAi in this case?

Claudius Vincenz
Knocking out AbPP alone conventionally yields no phenotype.

Amita
No abnormalities in vasculature, considering its role on platelets?

Gabrielle Strobel
Claudius, I seem to recall that knockouts of AbPP and APLPs did have a phenotype, but were not fully analyzed? Correct me.

Claudius Vincenz
RNAi targets genes; small molecules target activities. They are not necessarily the same. Presenilins are a good example.

Gabrielle Strobel
What do you mean by that, Claudius?

Claudius Vincenz
It is still disputed if presenilins are directly involved in the proteolytic process. So, by knocking out presenilin, you may affect protein maturation of multiple ER resident proteins. On the other hand, a small molecule will inhibit the cleavage of multiple presenilin substrates.

Dave Teplow
Claudius, I believe your comment is "semantic" in nature. There is no controversy as to whether PS is involved in a catalytic complex, only whether it itself performs the proteolysis. Therefore, controlling its expression is tantamount to controlling the enzyme.

Claudius Vincenz
But controlling its expression and inhibiting its proteolytic activity are not necessarily the same.

Dave Teplow
Yes, but it doesn't have to be, from a therapeutic perspective.

Zuoshang Xu
Enzymes are usually better targets for small chemicals. You could argue that RNAi can inhibit any molecules that you wish. The problem is still in delivery. It seems to me difficult to achieve inhibition in wide areas of CNS in order to inhibit production of AbPP.

Natasha Caplen
There is no spread of the gene-silencing effect mediated by siRNAs, so you will only induce downregulation in those cells directly transfected in the tissue of interest.

Victor Miller
RNAi may also allow us to titrate the degree of KO that we achieve rather than dealing with an all-or-none scenario, where complete absence of a given protein (or total inhibition of function by a drug) may be deleterious, whereas a partial knockdown is both therapeutic and tolerated.

Dave Teplow
Zuoshang's comment and Victor's response are very relevant. Because the protein assembly issues in Alzheimer's disease are concentration-dependent, one might not need an "all-or-none" effect to see a therapeutic benefit.

Gabrielle Strobel
Dave, that argument about a small inhibition/therapeutic index is what is said about g-secretase inhibitors, too, is it not? Knocking down the AbPP gene would abrogate the a cleavage, too, right? Do we want that?

Dave Teplow
Gabrielle, I think the only way to answer your question is to do the experiment.

Zuoshang Xu
RNAi may be used to selectively inhibit expression of mutant presenilins.

Gabrielle Strobel
How difficult would it be to test this in animal models?

Zuoshang Xu
It can be tested in transgenic presenilin mice by viral vectors or transgenic RNAi mice.

Gabrielle Strobel
I should have invited the creators of various AD mouse models.... Short of therapy, are there important functional questions that RNAi is particularly well-suited to address? Just as a guess, perhaps knock down gene modifiers to tease out pathways of degeneration?

Zuoshang Xu
To my knowledge, many new members of g-secretase have not been knocked out in mice. RNAi may be a fast way to accomplish this.

Gabrielle Strobel
Zuoshang, can you elaborate a bit?

Zuoshang Xu
If you make a transgenic mouse that expresses a specific shRNA, it may knock down or knock out these proteins.

Victor Miller
At least over short windows of time (three to seven days), reporter genes can be suppressed in mouse brain via viral delivery of shRNA.

Gabrielle Strobel
Victor, interesting. Can you target that to a specific brain region?

Dave Teplow
This could be a nice corollary to the work of Dave Holtzman and the effects he sees with acute passive administration of Ab-specific antibodies in transgenic mice.

Zuoshang Xu
Victor, what kind of virus? I thought adenoviruses or lentiviruses could mediate longer-term expression.

Victor Miller
We have used adenoviruses most extensively but are also going to use lentiviruses for further studies.

Victor Miller
The injection site can be controlled, of course, as well as the tropism of the virus and the promoter used to drive the shRNA. All have shortcomings for human therapy, but it is a start.

Gabrielle Strobel
We have reached the end of the hour. This is most interesting, and I encourage everyone to chat on as long as you like. Before people start dropping out, let me just thank you for coming and making this a fascinating discussion. I hope a lot of people will pick up all these questions we brought up and sort them out.

Dave, do you think a small reduction of Ab would have a clinically relevant impact on aggregation? Yes? How about a temporary reduction. No?

Dave Teplow
I think the answer to the first question is, yes, depending on how you define "small." The answer to the second question is probably, not much effect.

Background

Background Text
By Zuoshang Xu

Diseases caused by dominant, gain-of-function mutations develop in people bearing one mutant and one wild-type copy of the gene. Some of the best-known examples of this class are neurodegenerative diseases, including Huntington's, some forms of amyotrophic lateral sclerosis (ALS) and rare, familial forms of the otherwise common Alzheimer's and Parkinson's diseases (Taylor et al., 2002). In all these diseases, the exact pathways whereby the mutant proteins cause cell degeneration are not clear, but the origin of the cellular toxicity is known to be the mutant protein. Thus, selectively lowering or eliminating the mutant protein is a key step in developing effective therapies. Until recently, it was not clear how specific down-regulation of a wide variety of mutant proteins could be achieved. But now, new advances in RNA interference (RNAi) raise the possibility that RNAi can be developed and eventually applied as a therapeutic means for these neurodegenerative diseases.

When exposed to double-stranded RNA (dsRNA), eukaryotic cells respond by destroying their own mRNA that shares sequence with the dsRNA. This phenomenon is called RNA interference (RNAi). A similar cellular process was first discovered in plants, where it is called co-suppression (Napoli et al., 1990; Smith et al., 1990; van der Krol et al., 1990), and in the fungus Neurospora crassa, where it is known as quelling (Romano and Macino, 1992; Cogoni et al., 1996). Since its first description in animal cells (Fire et al., 1998), a growing number of investigators have been using RNAi for reverse genetics to investigate gene functions in cells and animals (Kennerdell and Carthew, 1998; Ngo et al., 1998; Lohmann et al., 1999; Sanchez Alvarado and Newmark, 1999; Gonczy et al., 2000; Svoboda et al., 2000; Wianny and Zernicka-Goetz, 2000; Yang et al., 2001). Expression of virtually any gene can be disrupted by delivering dsRNA corresponding to that gene's sequence. Capping this broad-based application are several new reports where RNAi has been used for genome-wide scans of gene function (Dillin et al., 2002; Ashrafi et al., 2003; Kamath et al., 2003; Lee et al., 2003).

The exact mechanism of RNAi has not been worked out completely, but current biochemical evidence suggests a four-step process. First, Dicer, an enzyme in the RNase III family (Bernstein et al., 2001), initiates ATP-dependent fragmentation of long dsRNA into 21-25 nucleotide double-stranded fragments, termed small interfering RNAs (siRNAs) (Zamore et al., 2000; Bernstein et al., 2001; Nykanen et al., 2001). Second, ATP-dependent unwinding of the siRNA duplex remodels the complex to generate an active RNA-induced silencing complex (RISC) (Hammond et al., 2000; Nykanen et al., 2001). Third, the RISC recognizes and cleaves a target RNA complementary to the guide strand (the antisense strand) of the siRNA (Hammond et al., 2000; Nykanen et al., 2001). Finally, the RISC releases its products and goes on to catalyze a new cycle of target recognition and cleavage (Hutvágner and Zamore, 2002).

It was clear from the beginning that RNAi would be a powerful tool for probing gene function, however, its uses in differentiated mammalian cells had been limited because long dsRNA elicits an interferon reaction that leads to apoptosis (McManus and Sharp, 2002). But then in 2001, two groups showed that synthetic siRNAs can mediate efficient RNAi without eliciting the interferon response in mammalian cells (Caplen et al., 2001; Elbashir et al., 2001c ). This opened the floodgates for applying RNAi to test the functions of a great number of genes in mammalian cells, as attested by the wealth of recent publications on this topic.

In the less than two years since the original report on gene silencing using siRNA in differentiated mammalian cells, the technology for delivering siRNA into cells in culture and in vivo has improved rapidly. Most notable is the method of synthesizing small hairpin RNA (shRNA) from plasmid constructs directly in cells. A popular approach uses type III RNA polymerase III (Pol III) promoters (Paule et al., 2000), which offer several advantages. First, this class of RNA polymerases naturally produces small, non-coding transcripts such as U6 small nuclear RNA (snRNA) and H1 RNA. Second, their natural transcripts are neither capped at the 5' nor polyadenylated at the 3' ends, and therefore resemble siRNA. Third, all of their promoter elements are located 5' to the transcription initiation site, therefore allowing convenient design of transcript sequences. Fourth, transcription directed by these promoters initiates at defined nucleotides (e.g., a G for the U6 promoter or an A for the H1 promoter) and terminates when the transcription encounters four or more Ts in succession (Bogenhagen et al., 1980). Incidentally, the transcripts also carry 3' overhangs of one to four Us (the termination sequence), a structural feature similar to what has been defined in vitro for effective siRNAs (Elbashir et al., 2001a ).

Using this strategy, numerous groups have demonstrated that shRNAs transcribed in cells can trigger degradation of corresponding mRNAs, probably because shRNA is processed into siRNAs (Brummelkamp et al., 2002b; Jacque et al., 2002; Lee et al., 2002; McManus et al., 2002; Miyagishi and Taira, 2002;Paddison et al., 2002; Paul et al., 2002; Sui et al., 2002; Yu et al., 2002). Recent work suggests that tRNA promoters, which are also transcribed by Pol III, may facilitate export of shRNA to the cytoplasm, where Dicer resides (Kawasaki and Taira, 2003). An alternative to the PolIII promoter is a strategy developed by Cullen and colleagues, in which a PolII CMV promoter was used to direct synthesis of shRNA (Zeng et al., 2002). This is more complex because one must incorporate the shRNA coding sequence into the stem of a microRNA precursor (pre-miRNA), but provides for more exquisite developmental or tissue-specific regulation.

These technical advances raise the possibility that specific constructs can be designed to express shRNA in vivo to silence target genes. For example, constructs may be inserted into a virus for transducing cells in vivo. Such a strategy may become a therapeutic intervention for diseases caused by dominant, gain-of-function gene mutations. In addition, these constructs may be used to inhibit expression of genes to investigate gene function by transfection in cultured cells or by transgenic approach in vivo. The initial experiments demonstrating the feasibility of these strategies have already been carried out. Both viral vector- and transgene-directed synthesis of shRNA have been shown to mediate inhibition of endogenous genes in cultured cells and in vivo (Brummelkamp et al., 2002a ; Hasuwa et al., 2002; Xia et al., 2002; Rubinson, 2003; Tiscornia et al., 2003). The therapeutic potential of RNAi has already been tested in several cellular models of diseases. Efficacy of RNAi has been demonstrated against viral infection (Gitlin et al., 2002; Jacque et al., 2002), cancer cell proliferation (Brummelkamp et al., 2002a ; Wilda et al., 2002; Cioca et al., 2003) and polyglutamine diseases (Caplen et al., 2002; Xia et al., 2002). Most recently, Judy Lieberman's group reports in the February 10 online Nature Medicine that intravenous injection of siRNA duplexes that target the gene encoding the Fas receptor inhibited apoptosis, protected against liver fibrosis, and prolonged survival in a mouse model of autoimmune hepatitis (Song, 2003). The list will surely increase rapidly in the near future.

To treat dominant genetic disorders of the gain-of-function type, ideally one should seek to silence expression of the mutant protein selectively, thereby allowing the wild-type allele to continue functioning. Given that the vast majority of gene mutations that cause dominant diseases are single nucleotide changes, one wonders whether RNAi mediated by siRNA can discriminate mutant from the wild-type mRNA with single nucleotide specificity. Current literature presents conflicting answers to this question. siRNAs that differ from the sequence of their target RNA at one or more nucleotides retain efficacy in some cases (Boutla et al., 2001; Holen et al., 2002) and lose activity in others (Boutla et al., 2001; Elbashir et al., 2001b ; Brummelkamp et al., 2002a ; Brummelkamp et al., 2002b; Yu et al., 2002). One recent report concludes that siRNAs cannot differentiate RNAs with single nucleotide difference (Zeng and Cullen, 2003). In collaboration with Phillip Zamore's and Yang Shi's groups, we have investigated the potential of siRNA to selectively silence the expression of mutant Cu, Zn superoxide dismutase (SOD1), which causes motor neuron degeneration and ALS by gaining a toxic property (Cleveland and Rothstein, 2001). Our data suggest that siRNA sequences that selectively silence the mutant can be found by screens using in vitro RNAi reactions and transfected cells (unpublished observation). The rules in designing the siRNA that can silence genes with single nucleotide specificity are currently unclear and remain to be further investigated.

The potential of using RNAi for therapy is not limited to directly silencing pathogenic genes or disease-causing mutant genes. As disease mechanisms become increasingly clear, its application can be expanded to silence genes involved in known pathogenic pathways. For example, an obvious target for treatment of Alzheimer's disease is the b-site APP-cleaving enzyme BACE, which is required for the production of Ab peptide (Cai et al., 2001; Luo et al., 2001; Roberds et al., 2001) and is present at elevated levels in the cortex of people with AD than controls (see related ARF news story). If such a strategy is successful, one can envision that RNAi could be applied not only to familial disease with identified dominant gene mutations, but also to sporadic disease.

While the therapeutic potential of RNAi is real and will undoubtedly grow, urgent problems must be resolved to prepare this technology for eventual human trials. First, how can siRNA be delivered in vivo? One way is to administer siRNA directly. This will require its modification or formulation with other agents to increase its stability and enable it to enter cells. While this method might work in treating diseases of peripheral organs, its uses for CNS diseases have not been well supported. A gene therapy approach using viral vectors offers an alternative. The concept has not yet been proven for CNS diseases in humans, but animal experiments indicate that long-term transgene expression in the CNS cells is achievable using AAV or lentiviral vectors (Kordower et al., 2000; Azzouz et al., 2002; Fu et al., 2002; Muramatsu et al., 2002; Wang et al., 2002). Human trials in peripheral disease have had limited success but serious problems remain (Verma, 2002). To overcome the threshold of clinical application, answers to other important questions are also eagerly awaited: Is inhibiting expression of mutant proteins, or proteins involved in pathogenesis, sufficient to prevent, slow, stop, or even reverse the disease? What is the maximal therapeutic effect achievable by RNAi? What's the right cell type for inhibition? Are there long-term adverse effects from expressing high levels of shRNA?

I suggest we address these questions during the discussion:

1. What are the key technical obstacles to overcome in moving RNAi therapy forward in ALS, Huntington's, Parkinson's and Alzheimer's?

2. What is the optimal delivery method for RNAi, direct administration of siRNA or gene therapy?

3. What questions about RNAi in the CNS do we need answers for before therapeutic trials?

4. What are the potential targets in neurodegenerative diseases for RNAi therapy?

5. Short of therapy, what are the most fruitful research questions to address with current RNAi technology?

Acknowledgement
I thank Gabrielle Strobel and Phillip Zamore for editing and suggestions.

For a news summary of two experimental therapeutic approaches, see ARF related news story

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Kordower JH, Emborg ME, Bloch J, Ma SY, Chu Y, Leventhal L, McBride J, Chen EY, Palfi S, Roitberg BZ, Brown WD, Holden JE, Pyzalski R, Taylor MD, Carvey P, Ling Z, Trono D, Hantraye P, Deglon N, Aebischer P. Neurodegeneration prevented by lentiviral vector delivery of GDNF in primate models of Parkinson's disease. Science. 2000 Oct 27;290(5492):767-73. Abstract

Lee NS, Dohjima T, Bauer G, Li H, Li MJ, Ehsani A, Salvaterra P, Rossi J. Expression of small interfering RNAs targeted against HIV-1 rev transcripts in human cells. Nat Biotechnol. 2002 May;20(5):500-5. Abstract

Lee SS, Lee RY, Fraser AG, Kamath RS, Ahringer J, Ruvkun G. A systematic RNAi screen identifies a critical role for mitochondria in C. elegans longevity. Nat Genet. 2003 Jan;33(1):40-8. Abstract

Lohmann JU, Endl I, Bosch TC. Silencing of developmental genes in Hydra. Dev Biol. 1999 Oct 1;214(1):211-4. Abstract

Luo Y, Bolon B, Kahn S, Bennett BD, Babu-Khan S, Denis P, Fan W, Kha H, Zhang J, Gong Y, Martin L, Louis JC, Yan Q, Richards WG, Citron M, Vassar R. Mice deficient in BACE1, the Alzheimer's b-secretase, have normal phenotype and abolished b-amyloid generation. Nat Neurosci. 2001 Mar;4(3):231-2. No abstract available. Abstract

McManus MT, Sharp PA. Gene silencing in mammals by small interfering RNAs. Nat Rev Genet. 2002 Oct;3(10):737-47. Review. Abstract

McManus MT, Petersen CP, Haines BB, Chen J, Sharp PA. Gene silencing using micro-RNA designed hairpins. RNA. 2002 Jun;8(6):842-50. Abstract

Miyagishi M, Taira K. U6 promoter-driven siRNAs with four uridine 3' overhangs efficiently suppress targeted gene expression in mammalian cells. Nat Biotechnol. 2002 May;20(5):497-500. Abstract

Muramatsu S, Fujimoto K, Ikeguchi K, Shizuma N, Kawasaki K, Ono F, Shen Y, Wang L, Mizukami H, Kume A, Matsumura M, Nagatsu I, Urano F, Ichinose H, Nagatsu T, Terao K, Nakano I, Ozawa K. Behavioral recovery in a primate model of Parkinson's disease by triple transduction of striatal cells with adeno-associated viral vectors expressing dopamine-synthesizing enzymes. Hum Gene Ther. 2002 Feb 10;13(3):345-54. Abstract

Napoli C, Lemieux C, Jorgensen R. Introduction of a Chimeric Chalcone Synthase Gene into Petunia Results in Reversible Co-Suppression of Homologous Genes in trans. Plant Cell. 1990 Apr;2(4):279-289. Abstract

Ngo H, Tschudi C, Gull K, Ullu E. Double-stranded RNA induces mRNA degradation in Trypanosoma brucei. Proc Natl Acad Sci U S A. 1998 Dec 8;95(25):14687-92. Abstract

Nykanen A, Haley B, Zamore PD. ATP requirements and small interfering RNA structure in the RNA interference pathway. Cell. 2001 Nov 2;107(3):309-21. Abstract

Paddison PJ, Caudy AA, Bernstein E, Hannon GJ, Conklin DS. Short hairpin RNAs (shRNAs) induce sequence-specific silencing in mammalian cells. Genes Dev. 2002 Apr 15;16(8):948-58. Abstract

Paul CP, Good PD, Winer I, Engelke DR. Effective expression of small interfering RNA in human cells. Nat Biotechnol. 2002 May;20(5):505-8. Abstract

Paule MG, Rowland AS, Ferguson SA, Chelonis JJ, Tannock R, Swanson JM, Castellanos FX. Attention deficit/hyperactivity disorder: characteristics, interventions and models. Neurotoxicol Teratol. 2000 Sep-Oct;22(5):631-51. Review. Abstract

Roberds SL, Anderson J, Basi G, Bienkowski MJ, Branstetter DG, Chen KS, Freedman SB, Frigon NL, Games D, Hu K, Johnson-Wood K, Kappenman KE, Kawabe TT, Kola I, Kuehn R, Lee M, Liu W, Motter R, Nichols NF, Power M, Robertson DW, Schenk D, Schoor M, Shopp GM, Shuck ME, Sinha S, Svensson KA, Tatsuno G, Tintrup H, Wijsman J, Wright S, McConlogue L. BACE knockout mice are healthy despite lacking the primary b-secretase activity in brain: implications for Alzheimer's disease therapeutics. Hum Mol Genet. 2001 Jun 1;10(12):1317-24. Abstract

Romano N, Macino G. Quelling: transient inactivation of gene expression in Neurospora crassa by transformation with homologous sequences. Mol Microbiol. 1992 Nov;6(22):3343-53. Abstract

Rubinson EA. A lentivirus-based system to functionally silence genes in primary mammalian cells, stem cells and transgenic mice by RNA interference. Nat Genet. 2003. (In press)

Sanchez Alvarado A, Newmark PA. Double-stranded RNA specifically disrupts gene expression during planarian regeneration. Proc Natl Acad Sci U S A. 1999 Apr 27;96(9):5049-54. Abstract

Smith CJ, Watson CF, Bird CR, Ray J, Schuch W, Grierson D. Expression of a truncated tomato polygalacturonase gene inhibits expression of the endogenous gene in transgenic plants. Mol Gen Genet. 1990 Dec;224(3):477-81. Abstract

Song EA (2003) RNA interference tergeting Fas protects mice from fulminant hepatitis. Nat Med. (In press)

Sui G, Soohoo C, Affar el B, Gay F, Shi Y, Forrester WC, Shi Y. A DNA vector-based RNAi technology to suppress gene expression in mammalian cells. Proc Natl Acad Sci U S A. 2002 Apr 16;99(8):5515-20. Abstract

Svoboda P, Stein P, Hayashi H, Schultz RM. Selective reduction of dormant maternal mRNAs in mouse oocytes by RNA interference. Development. 2000 Oct;127(19):4147-56. Abstract

Taylor JP, Hardy J, Fischbeck KH. Toxic proteins in neurodegenerative disease. Science. 2002 Jun 14;296(5575):1991-5. Review. Abstract

Tiscornia G, Singer O, Ikawa M, Verma IM. A general method for gene knockdown in mice by using lentiviral vectors expressing small interfering RNA. Proc Natl Acad Sci U S A. 2003 Jan 27 Abstract

van der Krol AR, Mur LA, Beld M, Mol JN, Stuitje AR. Flavonoid genes in petunia: addition of a limited number of gene copies may lead to a suppression of gene expression. Plant Cell. 1990 Apr;2(4):291-9. Abstract

Verma IM. Success and setback: another adverse event. Mol Ther. 2002 Nov;6(5):565-6. No abstract available.

Wang L, Muramatsu S, Lu Y, Ikeguchi K, Fujimoto K, Okada T, Mizukami H, Hanazono Y, Kume A, Urano F, Ichinose H, Nagatsu T, Nakano I, Ozawa K. Delayed delivery of AAV-GDNF prevents nigral neurodegeneration and promotes functional recovery in a rat model of Parkinson's disease. Gene Ther. 2002 Mar;9(6):381-9. Abstract

Wianny F, Zernicka-Goetz M. Specific interference with gene function by double-stranded RNA in early mouse development. Nat Cell Biol. 2000 Feb;2(2):70-5. Abstract

Wilda M, Fuchs U, Wossmann W, Borkhardt A. Killing of leukemic cells with a BCR/ABL fusion gene by RNA interference (RNAi). Oncogene. 2002 Aug 22;21(37):5716-24. Abstract

Xia H, Mao Q, Paulson HL, Davidson BL. siRNA-mediated gene silencing in vitro and in vivo. Nat Biotechnol. 2002 Oct;20(10):1006-10. Abstract

Yang S, Tutton S, Pierce E, Yoon K. Specific double-stranded RNA interference in undifferentiated mouse embryonic stem cells. Mol Cell Biol. 2001 Nov;21(22):7807-16. Abstract

Yu JY, DeRuiter SL, Turner DL. RNA interference by expression of short-interfering RNAs and hairpin RNAs in mammalian cells. Proc Natl Acad Sci U S A. 2002 Apr 30;99(9):6047-52. Abstract

Zamore PD, Tuschl T, Sharp PA, Bartel DP. RNAi: double-stranded RNA directs the ATP-dependent cleavage of mRNA at 21 to 23 nucleotide intervals. Cell. 2000 Mar 31;101(1):25-33. Abstract

Zeng Y, Cullen BR. Sequence requirements for micro RNA processing and function in human cells. RNA. 2003 Jan;9(1):112-123. Abstract

Zeng Y, Wagner EJ, Cullen BR. Both natural and designed micro RNAs can inhibit the expression of cognate mRNAs when expressed in human cells. Mol Cell. 2002 Jun;9(6):1327-33. Abstract

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References

News Citations

1. BACE Above Base in Alzheimer’s Patients 22 Nov 2002
2. Budding RNAi Therapies, APP Protein Interaction Map Impress at Meeting 3 Jan 2003

Webinar Citations

1. RNAi in Neurodegenerative Diseases—What's the Therapeutic Potential? 18 Mar 2003

Paper Citations

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3. Smith CJ, Watson CF, Bird CR, Ray J, Schuch W, Grierson D. Expression of a truncated tomato polygalacturonase gene inhibits expression of the endogenous gene in transgenic plants. Mol Gen Genet. 1990 Dec;224(3):477-81. PubMed.
4. van der Krol AR, Mur LA, Beld M, Mol JN, Stuitje AR. Flavonoid genes in petunia: addition of a limited number of gene copies may lead to a suppression of gene expression. Plant Cell. 1990 Apr;2(4):291-9. PubMed.
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30. McManus MT, Petersen CP, Haines BB, Chen J, Sharp PA. Gene silencing using micro-RNA designed hairpins. RNA. 2002 Jun;8(6):842-50. PubMed.
31. Miyagishi M, Taira K. U6 promoter-driven siRNAs with four uridine 3' overhangs efficiently suppress targeted gene expression in mammalian cells. Nat Biotechnol. 2002 May;20(5):497-500. PubMed.
32. Paddison PJ, Caudy AA, Bernstein E, Hannon GJ, Conklin DS. Short hairpin RNAs (shRNAs) induce sequence-specific silencing in mammalian cells. Genes Dev. 2002 Apr 15;16(8):948-58. PubMed.
33. Paul CP, Good PD, Winer I, Engelke DR. Effective expression of small interfering RNA in human cells. Nat Biotechnol. 2002 May;20(5):505-8. PubMed.
34. Sui G, Soohoo C, Affar el, Gay F, Shi Y, Forrester WC. A DNA vector-based RNAi technology to suppress gene expression in mammalian cells. Proc Natl Acad Sci U S A. 2002 Apr 16;99(8):5515-20. PubMed.
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36. Kawasaki H, Taira K. Short hairpin type of dsRNAs that are controlled by tRNA(Val) promoter significantly induce RNAi-mediated gene silencing in the cytoplasm of human cells. Nucleic Acids Res. 2003 Jan 15;31(2):700-7. PubMed.
37. Zeng Y, Wagner EJ, Cullen BR. Both natural and designed micro RNAs can inhibit the expression of cognate mRNAs when expressed in human cells. Mol Cell. 2002 Jun;9(6):1327-33. PubMed.
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43. Wilda M, Fuchs U, Wössmann W, Borkhardt A. Killing of leukemic cells with a BCR/ABL fusion gene by RNA interference (RNAi). Oncogene. 2002 Aug 22;21(37):5716-24. PubMed.
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55. Wang L, Muramatsu S, Lu Y, Ikeguchi K, Fujimoto K, Okada T, Mizukami H, Hanazono Y, Kume A, Urano F, Ichinose H, Nagatsu T, Nakano I, Ozawa K. Delayed delivery of AAV-GDNF prevents nigral neurodegeneration and promotes functional recovery in a rat model of Parkinson's disease. Gene Ther. 2002 Mar;9(6):381-9. PubMed.
56. Fire A, Xu S, Montgomery MK, Kostas SA, Driver SE, Mello CC. Potent and specific genetic interference by double-stranded RNA in Caenorhabditis elegans. Nature. 1998 Feb 19;391(6669):806-11. PubMed.
57. Taylor JP, Hardy J, Fischbeck KH. Toxic proteins in neurodegenerative disease. Science. 2002 Jun 14;296(5575):1991-5. PubMed.

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