Lobotomy of genes: use of RNA interference in Neuroscience

Characterisation of the RNA interference response against the long-wavelength receptor of the honeybee

Targeted knock-down is the method of choice to advance the study of sensory and brain functions in the honeybee by using molecular techniques. Here we report the results of a first attempt to interfere with the function of a visual receptor, the long-wavelength-sensitive (L-) photoreceptor. RNA interference to inhibit this receptor led to a reduction of the respective mRNA and protein. The interference effect was limited in time and space, and its induction depended on the time of the day most probably because of natural daily variations in opsin levels. The inhibition did not effectively change the physiological properties of the retina. Possible constraints and implications of this method for the study of the bee's visual system are discussed. Overall this study underpins the usefulness and feasibility of RNA interference as manipulation tool in insect brain research.

Regulation of conditional gene expression by coupled transcription repression and RNA degradation

Gene expression is determined by a combination of transcriptional and post-transcriptional regulatory events that were thought to occur independently. This report demonstrates that the genes associated with the Snf3p–Rgt2p glucose-sensing pathway are regulated by interconnected transcription repression and RNA degradation. Deletion of the dsRNA-specific ribonuclease III Rnt1p increased the expression of Snf3p–Rgt2p-associated transcription factors in vivo and the recombinant enzyme degraded their messenger RNA in vitro. Surprisingly, Rnt1ps effect on gene expression in vivo was both RNA and promoter dependent, thus linking RNA degradation to transcription. Strikingly, deletion of RNT1-induced promoter-specific transcription of the glucose sensing genes even in the absence of RNA cleavage signals. Together, the results presented here support a model in which co-transcriptional RNA degradation increases the efficiency of gene repression, thereby allowing an effective cellular response to the continuous changes in nutrient concentrations.

Acute disruption of the NMDA receptor subunit NR1 in the honeybee brain selectively impairs memory formation

Memory formation is a continuous process composed of multiple phases that can develop independently from each other. These phases depend on signaling pathways initiated after the activation of receptors in different brain regions. The NMDA receptor acts as a sensor of coincident activity between neural inputs, and, as such, its activation during learning is thought to be crucial for various forms of memory. In this study, we inhibited the expression of the NR1 subunit of the NMDA receptor in the honeybee brain using RNA interference. We show that the disruption of the subunit expression in the mushroom body region of the honeybee brain during and shortly after appetitive learning selectively impaired memory. Although the formation of mid-term memory and early long-term memory was impaired, late long-term memory was left intact. This indicates that late long-term memory formation differs in its dependence on NMDA receptor activity from earlier memory phases.

Differential neurotrophic regulation of sodium and calcium channels in an adult sympathetic neuron

Adult neuronal phenotype is maintained, at least in part, by the sensitivity of individual neurons to a specific selection of neurotrophic factors and the availability of such factors in the neurons' environment. Nerve growth factor (NGF) increases the functional expression of Na(+) channel currents (I(Na)) and both N- and L-type Ca(2+) currents (I(Ca,N) and I(Ca,L)) in adult bullfrog sympathetic ganglion (BFSG) B-neurons. The effects of NGF on I(Ca) involve the mitogen-activated protein kinase (MAPK) pathway. Prolonged exposure to the ganglionic neurotransmitter luteinizing hormone releasing hormone (LHRH) also increases I(Ca,N) but the transduction mechanism remains to be elucidated as does the transduction mechanism for NGF regulation of Na(+) channels. We therefore exposed cultured BFSG B-neurons to chicken II LHRH (0.45 microM; 6-9 days) or to NGF (200 ng/ml; 9-10 days) and used whole cell recording, immunoblot analysis, and ras or rap-1 pulldown assays to study effects of various inhibitors and activators of transduction pathways. We found that 1) LHRH signals via ras-MAPK to increase I(Ca,N), 2) this effect is mediated via protein kinase C-beta (PKC-beta-IotaIota), 3) protein kinase A (PKA) is necessary but not sufficient to effect transduction, 4) NGF signals via phosphatidylinositol 3-kinase (PI3K) to increase I(Na), and 5) long-term exposure to LHRH fails to affect I(Na). Thus downstream signaling from LHRH has access to the ras-MAPK pathway but not to the PI3K pathway. This allows for differential retrograde and anterograde neurotrophic regulation of sodium and calcium channels in an adult sympathetic neuron.

RNA interference-mediated inhibition of brain-derived neurotrophic factor expression increases cocaine's cytotoxicity in cultured cells

Previous studies showed that cocaine exposure decreased brain-derived neurotrophic factor (BDNF) function and resulted in neuronal cell death. To investigate a role of BDNF in cocaine's cytotoxicity, an RNA interference (RNAi) approach was used. Transfection of neuroblastoma SK-N-AS cells or primary rat hippocampal neurons with the small double-stranded interfering RNA (siRNA) targeting BDNF mRNA, but not the scrambled siRNA, resulted in reductions in levels of BDNF mRNA and proteins by more than 70% in the transfected cells as compared with the control group, suggesting an RNAi-mediated, sequence-specific gene silencing. The results also showed that cocaine-induced cytotoxicity, assessed by the MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazodium bromide) assay, was more pronounced in the cells transfected with the siRNA than in the cells transfected with the scrambled siRNA or in the cells treated with Lipofectamine 2000 alone (the control group), suggesting that inhibition of BDNF expression enhances cocaine's cytotoxicity. Together with previous studies showing that cocaine suppresses BDNF expression, the present data suggest that the drug-induced reduction of BDNF productions may make neurons more vulnerable to cocaine's toxic effects and precipitate cocaine-induced central nervous system damages.

Unraveling in vivo functions of amyloid precursor protein: insights from knockout and knockdown studies

The amyloid precursor protein (APP) is a widely expressed transmembrane protein that is cleaved to generate Abeta peptides in the central nervous system and is a key player in the pathogenesis of Alzheimer's disease. The precise biological functions of APP still remain unclear although various roles have been proposed. While a commonly accepted model argues that Abeta peptides are the cause of onset and early pathogenesis of Alzheimer's disease, recent discussions challenge this 'Abeta hypothesis' and suggest a direct role for APP in this neurodegenerative disease. Loss-of-function studies are an efficient way to elucidate the role of proteins and concurrently a variety of in vitro and in vivo studies has been performed for APP where protein levels have been downregulated and functional consequences monitored. Complete disruption of APP gene expression has been achieved by the generation of APP knockout animal models. Further knockdown studies using antisense and RNA interference have allowed scientists to reduce APP expression levels and have opened new avenues to explore the physiological roles of APP. In the present review, we focus on knockout and knockdown approaches that have provided insights into the physiological functions of APP and discuss their advantages and drawbacks.

RNA interference in neuroscience: progress and challenges

1.RNA interference (RNAi) is a recently discovered biological pathway that mediates post-transcriptional gene silencing. The process of RNAi is orchestrated by an increasingly well-understood cellular machinery. 2. The common entry point for both natural and engineered RNAi are double stranded RNA molecules known as short interfering RNAs (siRNAs), that mediate the sequence-specific identification and degradation of the targeted messenger RNA (mRNA). The study and manipulation of these siRNAs has recently revolutionized biomedical research. 3. In this review, we first provide a brief overview of the process of RNAi, focusing on its potential role in brain function and involvement in neurological disease. We then describe the methods developed to manipulate RNAi in the laboratory and its applications to neuroscience. Finally, we focus on the potential therapeutic application of RNAi to neurological disease.

[Viral and nonviral gene therapy for treatment of retinal diseases]

The development of gene therapeutic approaches offers new perspectives for the treatment of retinal diseases. The use of both, nonviral methods employing oligonucleotides as well as viral expression vectors provide the possibility to treat neovascularization defects and retinal degeneration, respectively. The mechanism by which the therapeutic oligonucleotides (antisense oligonucleotides, aptamers and siRNA) work is based on degradation of specific transcripts. Consequently, a reduction of the corresponding protein, which is involved in the particular pathogenesis, follows. In contrast, viral vector transduction can substitute the disease-associated gene with an intact copy. So far, animal models have successfully contributed to the development of gene therapeutic medication and further treatments are at the recruiting phase of clinical trials.

The use of small interfering RNA to elucidate the activity and function of ion channel genes in an intact tissue

Small interfering RNA (siRNA) directs the targeted destruction of mRNA encoding a specific protein, in a process known as RNA interference (RNAi). This stops translation of the targeted mRNA into protein, effectively silencing the gene. RNAi is a recent discovery, identified in mammalian cells in 2001, but it has rapidly advanced into a practical technique and is being used increasingly to investigate mammalian gene function. Tools are available to induce RNAi in cell lines, intact tissue preparations and even in vivo. Depending on the method used, loss of gene expression may be transient or sustained, enabling a wide range of functions to be investigated. RNAi therefore offers a powerful technique that can be used to produce targeted knockout of ion channel genes in mammalian cells. Its applications potentially include identification of ion channel function in health and disease, identification of novel channel genes and drug target validation. This paper outlines our current understanding of siRNA and the experimental requirements for producing efficient RNAi and gene silencing. Effective RNAi requires an appropriate siRNA sequence to be designed and an efficient method for delivering the siRNA to the cells of interest. Since not all potential siRNA sequences are effective, it is also important to verify the loss of gene expression by measuring the level of channel protein remaining. Limitations of the methods available for delivering siRNA are one of the main obstacles to producing efficient RNAi, especially in intact tissue preparations. Here we describe an in vitro method for targeted RNAi against the TASK-1 potassium channel gene in an isolated vascular preparation, using a DNA construct to direct the expression of siRNA, along with a non-viral method for transfecting cells within the vessel. Successful silencing of the TASK-1 gene is verified by immunostaining with an antibody directed against the TASK-1 protein.

Neurochemical and behavioral consequences of widespread gene knockdown in the adult mouse brain by using nonviral RNA interference

Gene expression analysis implicates an increasing number of novel genes in the brain as potential targets for the treatment of neurological and psychiatric disorders. Frequently, these genes are ubiquitously expressed in the brain and, thus, may contribute to a pathophysiological state through actions in several brain nuclei. Current strategies employing genetically modified animals for in vivo validation of such targets are time-consuming and often limited by developmental adaptations. Somatic gene manipulation using viral-mediated RNA interference (RNAi) has emerged recently, although restricting the target validation to specific brain nuclei. We investigated whether nonviral infusion of short interfering RNA (siRNA) into the ventricular system would enable a sequence-specific gene knockdown. The temporality and extent of siRNA-induced down-regulation were analyzed by targeting a transgene, EGFP, in mice overexpressing EGFP. Extensive knockdown of EGFP was observed, especially in regions adjacent or dorsoventrally and mediolaterally distant to the infusion site (dorsal third ventricle), with lesser knockdown in more distal regions. We challenged our RNAi approach to generate a specific knockdown of an endogenous gene, encoding the dopamine transporter (DAT) in regions (ventral midbrain) far distal to the infusion site. DAT-siRNA infusion in adult mice produced a significant down-regulation of DAT mRNA and protein in the brain and also elicited a temporal hyperlocomotor response similar to that (but delayed) obtained upon infusion of GBR-12909, a pharmacologically selective DAT inhibitor. Application of this nonviral RNAi approach may accelerate target validation for neuropsychiatric disorders that involve a complex interplay of gene(s) from various brain regions.

RNA interference: potential therapeutic targets

One of the most exciting findings in recent years has been the discovery of RNA interference (RNAi). RNAi methodologies hold the promise to selectively inhibit gene expression in mammals. RNAi is an innate cellular process activated when a double-stranded RNA (dsRNA) molecule of greater than 19 duplex nucleotides enters the cell, causing the degradation of not only the invading dsRNA molecule, but also single-stranded (ssRNAs) RNAs of identical sequences, including endogenous mRNAs. The use of RNAi for genetic-based therapies has been widely studied, especially in viral infections, cancers, and inherited genetic disorders. As such, RNAi technology is a potentially useful method to develop highly specific dsRNA-based gene-silencing therapeutics.