Conditional gene silencing in mammalian cells mediated by a stress-inducible promoter

Sustained overexpression of spliced X-box-binding protein-1 in neurons leads to spontaneous seizures and sudden death in mice

The underlying etiologies of seizures are highly heterogeneous and remain incompletely understood. While studying the unfolded protein response (UPR) pathways in the brain, we unexpectedly discovered that transgenic mice (XBP1s-TG) expressing spliced X-box-binding protein-1 (Xbp1s), a key effector of UPR signaling, in forebrain excitatory neurons, rapidly develop neurologic deficits, most notably recurrent spontaneous seizures. This seizure phenotype begins around 8 days after Xbp1s transgene expression is induced in XBP1s-TG mice, and by approximately 14 days post induction, the seizures evolve into status epilepticus with nearly continuous seizure activity followed by sudden death. Animal death is likely due to severe seizures because the anticonvulsant valproic acid could significantly prolong the lives of XBP1s-TG mice. Mechanistically, our gene profiling analysis indicates that compared to control mice, XBP1s-TG mice exhibit 591 differentially regulated genes (mostly upregulated) in the brain, including several GABAA receptor genes that are notably downregulated. Finally, whole-cell patch clamp analysis reveals a significant reduction in both spontaneous and tonic GABAergic inhibitory responses in Xbp1s-expressing neurons. Taken together, our findings unravel a link between XBP1s signaling and seizure occurrence.

Imaging of conditional gene silencing in vivo using a bioluminescence-based method with thermo-inducible microRNAs

RNA interference (RNAi)-based gene therapy has great potential in cancer and infectious disease treatment to correct abnormal up-regulation of gene expression. We show a new original method uses synthetic microRNAs combined with a thermo-inducible promoter to reduce specific gene expression. The targeted gene is the luciferase firefly reporter gene overexpressed in a subcutaneous tumor which allows the RNAi monitoring by bioluminescence imaging (BLI). The inducible inhibition was first demonstrated in vitro using genetically modified cells lines and then in vivo using the corresponding xenograft model in mice. Achieving spatio-temporal control, we demonstrate the feasibility to induce, in vivo, a specific gene inhibition on demand. Future applications of this RNAi-based gene therapy, which can be restricted to pathological tissue, would offer wide-ranging potential for disease treatment.

A novel inducible lentiviral system for multi-gene expression with human HSP70 promoter and tetracycline-induced promoter

Despite lentiviral system's predominance, its ultimate potential for gene therapy has not been fully exploited. Currently, most lentivirus vectors are non-inducible expression system or single-gene-induced system, which limits the extensive application in gene therapy. In this study, we designed a novel lentiviral vector containing HSP70 promoter and TRE promoter. Compared to traditional lentiviral vectors and inducible vectors, our controllable system has many advantages. Firstly, it contains multiple gene or shRNA targets. Secondly, genes expression is on/off in response to heat shock and DOX induction in time of need respectively with high effectivity and sensitivity. Thirdly, TRE promoter and HSP70 promoter can work with no interference from each other in the same inducible lentiviral vector. In addition, our study also shows that our novel vector has a higher downstream gene expression efficiency than co-transfection method and can co-position multi-genes in single cell effectively. Finally, we propose four derived models based on our vector at the end, which may be useful in biological research and clinical research in the future. Therefore, we believe that this novel lentiviral system could be promising in gene therapy for tumor.

A novel conditional gene silencing method using a tumor-specific and heat-inducible siRNA system

RNAi technology is an invaluable tool for investigating gene function. However, the non-temporal and non-spatial control is the primary limitation, which leads to siRNA leakiness and off-target effects. In this study, we inserted three kinds of HSE into tumor specific promoter hTERT, which aims to construct a temperature-inducible and tumor-specific RNAi plasmid vector. In our system, the expression of mature siRNA is tightly controlled by the heat shock-inducible and tumor-specific promoters. From the expression level of RNA and protein, we determined the efficiency of the inducible siRNA system by targeting SNCG gene in HepG2 and MCF-7 cells. Results showed that the controllable siRNA system could be induced to initiate siRNA expression by heat-induce. The silencing effect of SNCG is on a relative low level (10 %) at 37 °C, while it is significantly increased to 50 or 60 % after heat inducing at 43 °C. This new conditional siRNA system provides a novel approach to drive the siRNA expression by heat-inducible and tumor-specific promoter.

A siRNA system based on HSP70 promoter results in controllable and powerful gene silencing by heat-induction

RNAi is a powerful tool for gene-specific knockdown and gene therapy. However, the imprecise expression of siRNA limits the extensive application of RNAi in gene therapy. Here we report the development of a novel controllable siRNA expression vector pMHSP70psil that is initiated by HSP70 promoter. We determined the efficiency of the controllable siRNA system by targeting the gama-synuclein (SNCG) gene in breast cancer cells MCF-7. The results show that the controllable siRNA system can be induced to initiate siRNA expression by heat-induction. The silencing effect of SNCG occurs at a relatively low level (10.1%) at 37°C, while it is significantly increased to 69.4% after heat induction at 43°C. The results also show that the controllable siRNA system inhibits proliferation of cancer cells by heat-shock. Therefore, this RNAi strategy holds the promise of the high efficiency in gene knockdown at targeted times and locations, avoiding systemic side effects. It provides, for the first time, an approach to control siRNA expression by heat-shock.

Model systems of genetically modified platelets

Although platelets are the smallest cells in the blood, they are implied in various processes ranging from immunology and oncology to thrombosis and hemostasis. Many large-scale screening programs, genome-wide association, and "omics" studies have generated lists of genes and loci that are probably involved in the formation or physiology of platelets under normal and pathologic conditions. This creates an increasing demand for new and improved model systems that allow functional assessment of the corresponding gene products in vivo. Such animal models not only render invaluable insight in the platelet biology, but in addition, provide improved test systems for the validation of newly developed anti-thrombotics. This review summarizes the most important models to generate transgenic platelets and to study their influence on platelet physiology in vivo. Here we focus on the zebrafish morpholino oligonucleotide technology, the (platelet-specific) knockout mouse, and the transplantation of genetically modified human or murine platelet progenitor cells in myelo-conditioned mice. The various strengths and pitfalls of these animal models are illustrated by recent examples from the platelet field. Finally, we highlight the latest developments in genetic engineering techniques and their possible application in platelet research.

Reversible suppression of an essential gene in adult mice using transgenic RNA interference

RNAi has revolutionized loss-of-function genetics by enabling sequence-specific suppression of virtually any gene. Furthermore, tetracycline response elements (TRE) can drive expression of short hairpin RNAs (shRNAs) for inducible and reversible target gene suppression. Here, we demonstrate the feasibility of transgenic inducible RNAi for suppression of essential genes. We set out to directly target cell proliferation by screening an RNAi library against DNA replication factors and identified multiple shRNAs against Replication Protein A, subunit 3 (RPA3). We generated transgenic mice with TRE-driven Rpa3 shRNAs whose expression enforced a reversible cell cycle arrest. In adult mice, the block in cell proliferation caused rapid atrophy of the intestinal epithelium which led to weight loss and lethality within 8-11 d of shRNA induction. Upon shRNA withdrawal, villus atrophy and weight loss were fully reversible. Thus, shRpa3 transgenic mice provide an interesting tool to study tissue maintenance and regeneration. Overall, we have established a robust system that serves the purpose of temperature-sensitive alleles in other model organisms, enabling inducible and reversible suppression of essential genes in a mammalian system.

Cell- and region-specific miR30-based gene knock-down with temporal control in the rat brain

Background

RNA interference (RNAi) emerges as a powerful tool to induce loss-of-function phenotypes. In the context of the brain, gene manipulation is best targeted to specific subsets of cells in order to achieve a physiologically relevant outcome. Polymerase II-based viral expression systems can be used to cell-specifically express constructs incorporating flanking and loop sequences from endogenous microRNA (miRNA), which directs the designed hairpins into the endogenous gene silencing machinery. While many studies have documented non-cell-selective gene knock-down in the brain, it has not been tested whether different cell types or different areas of the central nervous system (CNS) are equally amenable to this approach. We have evaluated this issue using a tetracycline (Tet)-controllable and cell-specific miRNA 30 (miR30)-based short hairpin (shRNA) interference system.

Results

To achieve targeted expression two cell type-specific promoters were used; the enhanced compact glial fibrillary acidic protein (GfaABC₁D) promoter and the enhanced human synapsin-1 (SYN) promoter. Powerful luciferase (Luc) and the neuronal isoform of nitric oxide synthase (nNOS) gene knock-down were achieved both in vitro and in vivo. Administration of doxycycline (Dox) abrogated gene silencing. However, the efficacy of gene knock-down in both neurones and astrocytes in the hippocampus (HIP) was lower than that in the dorsal vagal complex of the brainstem (DVC). This was not due to regional differences in the expression of the the key enzymes involved in miRNA processing.

Conclusions

The results from the presented experiments demonstrated that selective gene knock-down in subsets of brain cells is achievable. However, there are some presently unknown regional factors which affect either the processing of miRNA-based cassettes or their potency for gene silencing.

Black carbon exposures, blood pressure, and interactions with single nucleotide polymorphisms in MicroRNA processing genes

BACKGROUND

Black carbon (BC) is a marker of traffic pollution that has been associated with blood pressure (BP), but findings have been inconsistent. MicroRNAs (miRNAs) are emerging as key regulators of gene expression, but whether polymorphisms in genes involved in processing of miRNAs to maturity influence susceptibility to BC has not been elucidated.

OBJECTIVES

We investigated the association between BC and BP, as well as potential effect modification by single nucleotide polymorphisms (SNPs) in miRNA processing genes.

METHODS

Repeated measures analyses were performed using data from the VA Normative Aging Study. Complete covariate data were available for 789 participants with one to six study visits between 1995 and 2008. In models of systolic and diastolic BP, we examined SNP-by-BC interactions with 19 miRNA-related variants under recessive models of inheritance. Mixed-effects models were adjusted for potential confounders including clinical characteristics, lifestyle, and meteorologic factors.

RESULTS

A 1-SD increase in BC (0.415 microg/m(3)) was associated with 3.04 mmHg higher systolic (95% confidence interval (CI), 2.29-3.79) and 2.28 mmHg higher diastolic BP (95% CI, 1.88-2.67). Interactions modifying BC associations were observed with SNPs in the DICER, GEMIN4, and DiGeorge critical region-8 (DGCR8) genes, and in GEMIN3 and GEMIN4, predicting diastolic and systolic BP, respectively.

CONCLUSIONS

We observed evidence of effect modification of the association between BP and 7-day BC moving averages by SNPs associated with miRNA processing. Although the mechanisms underlying these associations are not well understood, they suggest a role for miRNA genesis and processing in influencing BC effects.

Pathogenic mechanisms of congenital heart disease

Congenital heart disease (CHD) is the most common type of birth defect. Despite the many advances in the understanding of cardiac development and the identification of many genes related to cardiac development, the fundamental etiology for the majority of cases of congenital heart disease remains unknown. This review summarizes normal cardiac development, and outlines the recent discoveries of the genetic causes of congenital heart disease and provides possible strategies for exploring genetic causes.

The second wave of synthetic biology: from modules to systems

Synthetic biology is a research field that combines the investigative nature of biology with the constructive nature of engineering. Efforts in synthetic biology have largely focused on the creation and perfection of genetic devices and small modules that are constructed from these devices. But to view cells as true 'programmable' entities, it is now essential to develop effective strategies for assembling devices and modules into intricate, customizable larger scale systems. The ability to create such systems will result in innovative approaches to a wide range of applications, such as bioremediation, sustainable energy production and biomedical therapies.

Conditional RNAi: towards a silent gene therapy

RNA interference (RNAi) has the potential to permit the downregulation of virtually any gene. While transgenic RNAi enables stable propagation of the resulting phenotype to progeny, the dominant nature of RNAi limits its use to applications where the continued suppression of gene expression does not disturb normal cell functioning. This is of particular importance when the target gene product is essential for cell survival, development or differentiation. It is therefore desirable that knockdown be externally regulatable. This review is aimed at providing an overview of the approaches for conditional RNAi in mammalian systems, with a special mention of studies employing these approaches to target therapeutically/biologically relevant molecules, their advantages and disadvantages, and a pointer towards approaches best suited for RNAi-based gene therapy.

MicroRNA: An emerging therapeutic target and intervention tool

MicroRNAs (miRNAs) are a class of short non-coding RNAs with posttranscriptional regulatory functions. To date, more than 600 human miRNAs have been experimentally identified, and estimated to regulate more than one third of cellular messenger RNAs. Accumulating evidence has linked the dysregulated expression patterns of miRNAs to a variety of diseases, such as cancer, neurodegenerative diseases, cardiovascular diseases and viral infections. MiRNAs provide its particular layer of network for gene regulation, thus possessing the great potential both as a novel class of therapeutic targets and as a powerful intervention tool. In this regard, synthetic RNAs that contain the binding sites of miRNA have been shown to work as a “decoy” or “miRNA sponge” to inhibit the function of specific miRNAs. On the other hand, miRNA expression vectors have been used to restore or overexpress specific miRNAs to achieve a long-term effect. Further, double-stranded miRNA mimetics for transient replacement have been experimentally validated. Endogenous precursor miRNAs have also been used as scaffolds for the induction of RNA interference. This article reviews the recent progress on this emerging technology as a powerful tool for gene regulation studies and particularly as a rationale strategy for design of therapeutics.