Design of an HIV-1 lentiviral-based gene-trap vector to detect developmentally regulated genes in mammalian cells

Determination of melatonin by a whole cell bioassay in fermented beverages

Melatonin is a bioactive compound that is present in fermented beverages, such as wine and beer, at concentrations ranging from picograms to nanograms per mL of product. The purpose of this study was to optimize a novel fluorescent bioassay for detecting melatonin based on a cell line that contains the human melatonin receptor 1B gene and to compare these results with LC-MS/MS as a reference method. Conditions that could affect cell growth and detection (cell number per well, stimulation time, presence or absence of fetal bovine serum and adhesion of cells) were tested in the TANGO^® cell line. Food matrices (wine and grape must) could not be directly used for the cell line due to low response. Therefore, for the determination of melatonin in food samples, an extraction procedure was required before conducting the assay. We demonstrated an improvement in melatonin determination by the cell-based bioassay due to increased sensitivity and specificity and improved quantification in complex matrices. Therefore, this method is a good alternative to determine melatonin content in some food samples, especially for those containing very low melatonin levels.

Strategies to achieve conditional gene mutation in mice

The laboratory mouse is an ideal model organism for studying disease because it is physiologically similar to human and also because its genome is readily manipulated. Genetic engineering allows researchers to introduce specific loss-of-function or gain-of-function mutations into genes and then to study the resulting phenotypes in an in vivo context. One drawback of using traditional transgenic and knockout mice to study human diseases is that many mutations passed through the germline can profoundly affect development, thus impeding the study of disease phenotypes in adults. New technology has made it possible to generate conditional mutations that can be introduced in a spatially and/or temporally restricted manner. Mouse strains carrying conditional mutations represent valuable experimental models for the study of human diseases and they can be used to develop strategies for prevention and treatment of these diseases. In this article, we will describe the most widely used DNA recombinase systems used to achieve conditional gene mutation in mouse models and discuss how these systems can be employed in vivo.

Effect of the regulation of retinoid X receptor-α gene expression on rat hepatic fibrosis

AIM

  To study the effect of retinoid X receptor-α (RXR-α) expression on rat hepatic fibrosis.

METHODS

  Rat hepatic fibrosis was induced by CCl(4) , and the rats were randomly divided into an early-phase hepatic fibrosis group (2 weeks) and a sustained hepatic fibrosis group (8 weeks). They were then divided into four groups (normal control, hepatic fibrosis, negative control and RXR-α groups). A recombinant lentiviral expression vector carrying the rat RXR-α gene was injected into the rats to induce RXR-α expression by intraportal infusion, hepatic tissue pathological examination was performed, and hydroxyproline content was detected. Hepatic stellate cells (HSC) were cultured in vitro, an RXR-α lentivirus vector was used to activate HSC, and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) activation was assayed to detect HSC proliferation.

RESULTS

  In vivo experiments indicated that in the sustained hepatic fibrosis group, there were significant differences in the hydroxyproline content, and expression of RXR-α, α-smooth muscle actin (α-SMA) and type I collagen (P < 0.01). However, in the early-phase hepatic fibrosis group, hydroxyproline content and the protein level of RXR-α showed no significant difference compared with the normal control group (P > 0.05). In vitro studies revealed that expression of RXR-α significantly inhibited expression of α-SMA and type I collagen in activated HSC (P < 0.01), as well as HSC proliferation (P < 0.01).

CONCLUSION

  The increased RXR-α gene expression inhibited HSC activation and proliferation and the degree of hepatic fibrosis.

β-Lactamase: an ideal reporter system for monitoring gene expression in live eukaryotic cells

To gain insightful information about the mechanisms through which genes are activated and repressed requires gene reporter systems that are sensitive, robust, and cost-effective. Although numerous reporter gene technologies are commercially available, none are as sophisticated and user-friendly as β-lactamase (BLA) when it comes to studying gene expression in live cells. This article presents an overview of the BLA technology and describes how it can be exploited for studying rare events such as homologous recombination in somatic cells and be used to deliver any DNA sequence of choice anywhere within the genome.

Mobilization and mechanism of transcription of integrated self-inactivating lentiviral vectors

Permanent genetic modification of replicating primitive hematopoietic cells by an integrated vector has many potential therapeutic applications. Both oncoretroviral and lentiviral vectors have a predilection for integration into transcriptionally active genes, creating the potential for promoter activation or gene disruption. The use of self-inactivating (SIN) vectors in which a deletion of the enhancer and promoter sequences from the 3' long terminal repeat (LTR) is copied over into the 5' LTR during vector integration is designed to improve safety by reducing the risk of mobilization of the vector genome and the influence of the LTR on nearby cellular promoters. Our results indicate that SIN vectors are mobilized in cells expressing lentiviral proteins, with the frequency of mobilization influenced by features of the vector design. The mechanism of transcription of integrated vector genomes was evaluated using a promoter trap design with a vector encoding tat but lacking an upstream promoter in a cell line in which drug resistance depended on tat expression. In six clones studied, all transcripts originated from cryptic promoters either upstream or within the vector genome. We estimate that approximately 1 in 3,000 integrated vector genomes is transcribed, leading to the inference that activation of cryptic promoters must depend on local features of chromatin structure and the constellation of nearby regulatory elements as well as the nature of the regulatory elements within the vector.

Serotonergic-like progenitor cells propagated from neural stem cells in vitro: survival with SERT protein expression following implantation into brains of mice lacking SERT

Neural stem cells (NSCs) obtained from the midbrain region of embryonic (E14) mice were initially cultured with basic fibroblast growth factor (bFGF), Sonic hedgehog, and FGF-8 in a serum-free N-2 culture medium to foster differentiation into a serotonergic-like phenotype. During the initial differentiating phase, these progenitor cells expressed En1, Pax3, and Pax5 mRNA. Subsequently, a single serotonin [5-hydroxytryptamine (5-HT)] and tryptophan hydroxylase-positive clone was isolated, which gave rise to cells that developed serotonergic properties. Sixty percent of these progenitor cells expressed the serotonin transporter (SERT), as indicated by specific ligand binding of [125I]-RTI-55. To further evaluate SERT functionality, we showed that these progenitor cells possessed specific [3H]-5-HT uptake activity. Implantation of the serotonergic-like progenitors into the hippocampus of adult mice genetically lacking SERT was followed by migration of these cells into adjacent brain regions, and survival of the cells at 8 weeks was accompanied by a gradual increase in density of SERT protein expression, which was not found in vehicle-injected, control mice. These findings suggest that this serotonergic-like NSC model will be a useful contribution to the development of cell biotechnology in regard to the expression of missing genes such as SERT in the adult brain.

Lesion-dependent regulation of transgene expression in the rat brain using a human glial fibrillary acidic protein-lentiviral vector

The ability to regulate transgene expression will be crucial for development of gene therapy to the brain. The most commonly used systems are based on a transactivator in combination with a drug, e.g. the tetracycline-regulated system. Here we describe a different method of transgene regulation by the use of the human glial fibrillary acidic protein (GFAP) promoter. We constructed a lentiviral vector that directs transgene expression to astrocytes. Using toxin-induced lesions we investigated to what extent transgene expression could be regulated in accordance with the activation of the endogenous GFAP gene. In animals receiving excitotoxic lesions of the striatum we detected an eightfold increase of green fluorescent protein (GFP)-expressing cells. The vast majority of these cells did not divide, suggesting that the transgene was indeed regulated in a similar fashion as the endogenous GFAP gene. This finding will lead to the development of lentiviral vectors with autoregulatory capacities that may be very useful for gene therapy to the brain.

Protein-trap version 2.1: screening for expressed proteins in mammalian cells based on their localizations

Background

"Protein-trap" is a method that allows epitope-tagging of endogenous proteins. This method allows for the identification of endogenously expressed proteins that exhibit specific localization of interest. This method has been recently reported for its application in the study of Drosophila development by using a relatively large epitope, green-fluorescent-protein (GFP).

Result

Herein, we report a new "protein-trap" vector for mammalian cells. This new method utilizes a much smaller epitope-tag and also allows for drug-selection prior to the epitope-tagging. Pre-selection by drug resulted in the highly efficient protein-trapping frequency.

Conclusion

The "protein-trap" method based on this new vector is expected to serve as a complimentary approach to the previously reported GFP-based method.

Lentiviral vectors for gene delivery into cells

Human immunodeficiency virus type I (HIV) is the etiologic agent of acquired immunodeficiency syndrome or AIDS. Vectors based upon HIV have been in use for over a decade. Beginning in 1996, with the demonstration of improved pseudotyping using vesicular stomatitis virus (VSV) G protein along with transduction of resting mammalian cells, a series of improvements have been made in these vectors, making them both safer and more efficacious. Taking a cue from vector development of murine leukemia virus (MLV), split coding and self-inactivating HIV vectors now appear quite suitable for phase I clinical trials. In parallel, a number of pre-clinical efficacy studies in animals have demonstrated the utility of these vectors for various diseases processes, especially neurodegenerative and hematopoietic illnesses. These vectors are also appropriate for the study of other viruses (specifically of viral entry) and investigation of the HIV replicative cycle, along with straightforward transgene delivery to target cells of interest. Vectors based upon other lentiviruses have shown similar abilities and promise. Although concerns remain, particularly with regards to detection and propagation of replication-competent lentivirus, it is almost certain that these vectors will be introduced into the clinic within the next 3-5 years.

Production of transgenic rats by lentiviral transduction of male germ-line stem cells

Primary cultures of rat spermatogenic cells that did not bind to collagen matrices were able to colonize and form mature spermatozoa when transferred to testes of recipient males. Up to 73% of the progeny from matings with recipient males were derived from the transferred spermatogenic cells. Subsequently, two populations of germ cells were obtained by selection on laminin matrices. Both populations expressed the spermatogenic cell marker, DAZL, but not the somatic cell marker, vimentin. The cells that bound to laminin represented approximately 5% of the total population and were greatly enriched in ability to colonize a recipient testis, suggesting an enrichment in germ-line stem cells. The colonization potential was maintained for at least 7 days in culture. These cells were subsequently transduced with a lentiviral enhanced GFP reporter vector and then transferred to WT recipient males. After mating, 26 of 44 pups were derived from the cultured donor germ cells, and 13 pups carried the lentiviral transgene. Based on Southern analysis, the transgene was integrated at a different genetic locus in each animal and was transmitted to approximately 50% of pups in the F(2) generation. Thus, by using these procedures, approximately 30% of pups in the F(1) generation inherited and stably transmitted a lentiviral transgene that integrated at various genomic sites.