MicroRNAs (miRNAs) are small (~21nucleotides), evolutionarily conserved, noncoding RNA molecules that regulate gene expression. In mammalian genomes, conservative predictions suggest that between 500-1500 miRNAs exist. There miRNAs appear to be capable of regulating the expression of multiple genes, with many genes appearing to be regulated by multiple, different, miRNAs. Less conservative estimates suggest their may be tens of thousands of miRNAs in mammalian genomes, that between 20-30% of all human genes may be subject to regulation by miRNAs, and that each miRNA may contribute to the regulation of 200 or more mRNA targets. Therefore it is easy to see why miRNA and their potential targets have received a lot of interest in recent times, as they offer a previously unknown mechanism of fundamental molecular biology that can subtly attenuate mRNA / protein expression.

Gene silencing by RNA interference (RNAi) uses double-stranded RNA to shut down gene expression in cells. This provides the possibility that this new methodology could be used in the treatment of disease symptoms and disease processes. A particular attraction of RNAi (as well as other gene knockdown methods of treatment, including antisense) is that, at present, no one class of protein appears to be refractive to silencing using this method and, therefore, it has the potential to make any gene product a target for pharmaceutical intervention. As will be discussed later though, delivery of these large polyanionic molecules to their site of action may pose a significant challenge.

MicroRNAs (miRNAs) are a class of small non-coding RNA molecules, which are potent post-transcriptional gene expression regulators. They have been shown to participate in the regulation of numerous cellular processes, the list of which is still growing. miRNAs affect numerous targets that can be determined by direct experiments or predicted by bioinformatics approaches, and are presented in several online databases. Feasibility of miRNA for high-throughput experimentation is becoming possible due to the availability of commercially produced molecules, which are able to alter the levels of endogenous miRNAs. miRNA functional analysis will help to validate predicted targets and reveal the role of these small molecules in biological pathways. miRNAs have a high potential to be used as a new gene expression regulating reagent for microscopy based assays.

The last few years have seen a rush of discoveries within a new field of post-transcriptional gene regulation. microRNAs, or miRNAs for short, are small regulating RNAs akin to small interfering RNAs (siRNA), but which are naturally expressed in vivo. Originally discovered in C. elegans 14 years ago, these small 20-22 nucleotide non-coding RNA molecules bind specifically to target messenger RNAs (mRNA) blocking their translation into protein or causing their degradation.

One of the most profound advances in biology and medicine has been the sequencing of entire genomes, including the human genome. The end product was the availability of the complete genetic blue print of organisms of importance to medicine and biotechnology. This changed how we conducted science. Cloning individual genes was no longer a limiting factor. Instead, entire scientific communities set upon understanding how genes interact with each other in pathways and across pathways so as to explain complex biological and physiological processes. For the biotechnology and pharmaceutical industries, the identification, cloning, and engineering of a single gene to produce a key biological product such as erythropoietin, was no longer an attractive investment prospect. Instead, companies that produced either a clinically tested end-product, or provided entire platforms for high throughput screening, were the only ones being funded. The new benchmark for success is now speed and comprehensiveness, which are orders of magnitude greater than just ten years ago.

There has been much interest in the promise of proteomics to deliver biomarkers with utility for disease diagnosis and classification, and for assessing therapeutic efficacy and monitoring disease progression. However recently, particularly in the past year, expressions of concern have started to emerge regarding the paucity of protein biomarkers that have reached the stage of FDA approval or at least that have been sufficiently validated in independent studies. Therefore, a clear understanding of the current situation with respect to biomarkers and proteomics would be useful in assessing whether the field does hold promise and is ready to ‘deliver’ or whether effort should be focused elsewhere. The observations and derived conclusions presented here are intended to assess the current status of the field.

The early 21st century has seen a revolution in RNA biology, bringing with it the prospect of a new class of medicines based on RNA. What are the prospects for developing these RNA-based medicines for the growing medical problem of neurodegenerative disease and what are the challenges to making these new medicines work successfully within the complex environment of the nervous system? Recent progress on RNA silencing of neurodegenerative disease targets and RNAi delivery to the nervous system is encouraging and suggests that clinical evaluation of these therapeutic agents is realistic within the next few years.

The availability of the human and the mouse sequence has allowed genome-wide analysis of transcription to produce 'transcriptomes' that list all RNA transcripts in specific cell types or tissues...

Non-coding RNAs (ncRNAs) consist of a growing heterogeneous class of transcripts defined as RNA molecules that lack any extensive “Open Reading Frame” (ORF) and function as structural, catalytic or regulatory entities rather than serving as templates for protein synthesis. While non-coding sequences make up only a small fraction of the DNA of prokaryotes, among eukaryotes, the proportion of DNA that does not code for protein increases with their complexity, underscoring the likelihood of a “hidden layer” of gene regulation in animal genomes1.

Over the last ten years a small RNA revolution has swept biology. In 1998 RNA interference (RNAi) was discovered as an experimental tool by Andy Fire and Craig Mello, a finding that was awarded with the 2006 Nobel Prize for Physiology or Medicine. Although the biology of RNAi is still not understood, it has become a powerful experimental tool and is currently being developed for human gene therapy. During a similar time-frame and linked in some aspects to RNAi, microRNAs (miRNAs) were discovered as a new class of regulatory RNAs in animals, plants and viruses.

Among the genetic model organisms, the laboratory mouse (Mus musculus) has a predominant role in the study of human disease and in pre-clinical drug development. Apart from the high degree of sequence homology of mouse and human genomes, and similarities in many physiological aspects, advanced targeting technologies make the crucial difference; providing unique tools for elucidating gene function in vivo.

The archetypal microRNAs, lin-4 and let-7, were discovered in the nematode worm Caenorhabditis elegans over a decade ago and, at that time, no one would have predicted that they would be anything other than an interesting feature of worm developmental biology. However, in recent years there has been an explosion of research activity in the field of microRNAs (miRNAs), so much so that the number of publications has almost doubled every year over the last five years

RNA interference (RNAi) is a regulatory mechanism of most eukaryotic cells that uses small double stranded RNA (dsRNA) molecules as triggers to direct homology-dependent control of gene activity (Almeida and Allshire 2005).

ntroduction of double-stranded RNA (dsRNA) can elicit a gene-specific RNA interference response in a variety of organisms and cell types. In many cases, this response has a systemic character in that silencing of gene expression is observed in cells distal from the site of dsRNA delivery. The molecular mechanisms underlying the mobile nature of RNA silencing are unknown. For example, although cellular entry of dsRNA is possible, cellular exit of dsRNA from normal animal cells has not been directly observed.

Immunotherapy has recently emerged as an attractive form of treatment for cancer due to the potential of the immune system to eradicate tumours without inflicting damage on normal tissue. However, natural immune responses are usually inadequate to control cancer progression and require enhancement by vaccines.

Huge progress has been made, both in RNA interference technology applied to mammalian cells and in automated microscopy to analyse gene functions upon silencing in the cellular context. Large-scale siRNA screens have been published recently, mainly applying assays that gain multi-parametric information on biological processes. It is a long way to establish an infrastructure that allows high-content siRNA screening, and in this article the major challenges are summarised.

The RIGHT (RNA Interference Technology as Human Therapeutic Tool) consortium consists of 18 research institutions and four companies from nine European countries. The project has been funded as an integrated project by the European Commission’s Sixth Framework Programme for Research and Development (FP6) since January 2005. Thomas F. Meyer from the Max Planck Institute for Infection Biology in Berlin is coordinating this European research project that aims at exploiting the vast potential of RNA interference (RNAi) for human therapy.

MitoCheck is a multi-national, multi-disciplinary research project on cell cycle control. It is funded by the European Union within its 6th framework program (FP6). Leading scientists from 11 research institutes, universities and industry in Austria, Germany, UK, Italy and France with a wide range of expertise in molecular and cell biology, biochemistry, modern microscopy techniques, proteomics, bio-informatics and clinical pathology have joined forces to take on the challenge of unraveling the mystery of cell division using RNAi.

MicroRNAs (miRNAs) are an abundant class of short endogenous RNAs that act as important post-transcriptional regulators of gene expression.

Select Biosciences’ RNAi Europe has become a must attend meeting during the last few years. And here’s why…
The event gathers prominent specialists from the field as well as leading representatives from this focussed industry. This strong mix of people ensures there are participants from academia and industry on the podium as well as in the audience. Confirmed speakers include Professor René Bernards, The Netherlands Cancer Institute, Dr. Eberhard Krausz, Max Planck Institute of Molecular Cell Biology and Genetics (MPI-CBG) and Dr. Mark Behlke, Integrated DNA Technologies Inc. speaking on subjects related to RNAi technologies – from biology to therapeutics.

Large DNA-sequencing projects such as the Human Genome Project have provided the scientific community with a new challenge: to try to understand the information encoded in the primary sequence of the genome. Studies investigating the role and function of the components of the genome are often called functional genomics.

Large and small drug development companies have used RNAi intensively for several years now. The adoption of RNAi technologies by drug companies followed fairly closely with their adoption by academic research labs, and as such many of the challenges and problems that were a natural consequence of the rapid expansion of RNAi needed to be worked out by the industrial sector along with academia.

Although synthetic siRNA libraries are becoming more available, most high throughput siRNA library-based screening was carried out with siRNA libraries encoded by different vectors. In this article, siRNA library construction methods and HTS applications are summarised.

RNAi technology provides the ‘loss of function’ approach, which has been widely used in the last couple of years for analysis of gene function, and in drug discovery for identification and validation of potential drug target candidates. This technology is now widely applied for functional screens in order to identify disease associated signals and targets whose specific inhibition could potentially result in a curative effect for treatment of complex human diseases. The focus of such screens is evolving more towards druggable gene families rather than genome wide approaches – the latter being expensive, complex and sometimes confusing.

Perhaps the most significant technological advancement in the study of gene function in the post-genome era has been the discovery that RNA interference (RNAi) can be exploited for depletion of endogenous mRNA in mammalian cells. As the pharmaceutical industry has fallen under intense pressure to both identify and validate high-quality drug targets, the lure of bona fide genome-wide functional analysis and target identification using small interfering RNA (siRNA) has fueled the interest in what can now be truly called ‘functional’ genomics.

All diseases have a genetic component, whether inherited or resulting from the body's response to environmental stresses such as viruses, toxins or trauma. The successes of the human genome project have enabled researchers to pinpoint errors in genes that cause or contribute to disease.

Small interfering RNAs are irreplaceable tools for the functional analysis of pathological gene products. Therapeutic siRNA development leads to new treatment strategies for gene products, where conventional small molecule approaches have failed.