Generation and characterization of a Tet-On (rtTA-M2) transgenic rat

The evidence-based multifaceted roles of hepatic stellate cells in liver diseases: A concise review

Hepatic stellate cells (HSCs) play central roles in liver disease pathogenesis, spanning steatosis to cirrhosis and hepatocellular carcinoma. These cells, located in the liver's sinusoidal space of Disse, transition from a quiescent, vitamin A-rich state to an activated, myofibroblast-like phenotype in response to liver injury. This activation results from a complex interplay of cytokines, growth factors, and oxidative stress, leading to excessive collagen deposition and liver fibrosis, a hallmark of chronic liver diseases. Recently, HSCs have gained recognition for their dynamic, multifaceted roles in liver health and disease. Attention has shifted toward their involvement in various liver conditions, including acute liver injury, alcoholic and non-alcoholic fatty liver disease, and liver regeneration. This review aims to explore diverse functions of HSCs in these acute or chronic liver pathologies, with a focus on their roles beyond fibrogenesis. HSCs exhibit a wide range of actions, including lipid storage, immunomodulation, and interactions with other hepatic and extrahepatic cells, making them pivotal in the hepatic microenvironment. Understanding HSC involvement in the progression of liver diseases can offer novel insights into pathogenic mechanisms and guide targeted therapeutic strategies for various liver conditions.

The Lentiviral System Construction for Highly Expressed Porcine Stearoyl-CoA Desaturase-1 and Functional Characterization in Stably Transduced Porcine Swine Kidney Cells

The most highly regulated and abundant fatty acid in animal tissue is oleic acid (18:1n9). Oleic acid is synthesized by the Δ9 desaturase, stearoyl-CoA desaturase-1 (SCD1), which is responsible for the synthesis of the putative cytokine palmitoleic acid (16:1n7) and 18:2 cis-9, trans-11 conjugated linoleic acid. Owing to the importance of SCD1 in lipid metabolism, we generated porcine swine kidney (SK6) transgenic cell lines for sustained overexpression or knockdown of porcine stearoyl-CoA desaturase-1 (pSCD1) in an inducible manner by utilizing a lentiviral expression system. We successfully validated these cell culture models for expression and functionality of pSCD1 by documenting that the pSCD-transduced cells overexpressed pSCD1 protein and mRNA. Additionally, the pSCD1-transduced cells increased the conversion of palmitate (16:0) to palmitoleic acid nearly fourfold. The lentiviral vectors utilized in this study can be further used to generate transgenic animals to document the effects of the overexpression of SCD1 on obesity and steatosis.

Utilization of a Strongly Inducible DDI2 Promoter to Control Gene Expression in Saccharomyces cerevisiae

Regulating target gene expression is a common method in yeast research. In Saccharomyces cerevisiae, there are several widely used regulated expression systems, such as the GAL and Tet-off systems. However, all current expression systems possess some intrinsic deficiencies. We have previously reported that the DDI2 gene can be induced to very high levels upon cyanamide or methyl methanesulfonate treatment. Here we report the construction of gene expression systems based on the DDI2 promoter in both single- and multi-copy plasmids. Using GFP as a reporter gene, it was demonstrated that the target gene expression could be increased by up to 2,000-fold at the transcriptional level by utilizing the above systems. In addition, a DDI2-based construct was created for promoter shuffling in the budding yeast genome to control endogenous gene expression. Overall, this study offers a set of convenient and highly efficient experimental tools to control target gene expression in budding yeast.

Experimental methods to preserve male fertility and treat male factor infertility

Infertility is a prevalent condition that has insidious impacts on the infertile individuals, their families, and society, which extend far beyond the inability to have a biological child. Lifestyle changes, fertility treatments, and assisted reproductive technology (ART) are available to help many infertile couples achieve their reproductive goals. All of these technologies require that the infertile individual is able to produce at least a small number of functional gametes (eggs or sperm). It is not possible for a person who does not produce gametes to have a biological child. This review focuses on the infertile man and describes several stem cell-based methods and gene therapy approaches that are in the research pipeline and may lead to new fertility treatment options for men with azoospermia.

A novel TetR-regulating peptide turns off rtTA-mediated activation of gene expression

Conditional regulation of gene expression is a powerful and indispensable method for analyzing gene function. The “Tet-On” system is a tool widely used for that purpose. Here, the transregulator rtTA mediates expression of a gene of interest after addition of the small molecule effector doxycycline. Although very effective in rapidly turning on gene expression, the system is hampered by the long half-life of doxycycline which makes shutting down gene expression rapidly very difficult to achieve. We isolated an rtTA-binding peptide by in vivo selection that acts as a doxycycline antagonist and leads to rapid and efficient shut down of rtTA-mediated reporter gene expression in a human cell line. This peptide represents the basis for novel effector molecules which complement the “Tet-system” by enabling the investigator to rapidly turn gene expression not just on at will, but now also off.

Airway-specific inducible transgene expression using aerosolized doxycycline

Tissue-specific transgene expression using tetracycline (tet)-regulated promoter/operator elements has been used to revolutionize our understanding of cellular and molecular processes. However, because most tet-regulated mouse strains use promoters of genes expressed in multiple tissues, to achieve exclusive expression in an organ of interest is often impossible. Indeed, in the extreme case, unwanted transgene expression in other organ systems causes lethality and precludes the study of the transgene in the actual organ of interest. Here, we describe a novel approach to activating tet-inducible transgene expression solely in the airway by administering aerosolized doxycycline. By optimizing the dose and duration of aerosolized doxycycline exposure in mice possessing a ubiquitously expressed Rosa26 promoter-driven reverse tet-controlled transcriptional activator (rtTA) element, we induce transgene expression exclusively in the airways. We detect no changes in the cellular composition or proliferative behavior of airway cells. We used this newly developed method to achieve airway basal stem cell-specific transgene expression using a cytokeratin 5 (also known as keratin 5)-driven rtTA driver line to induce Notch pathway activation. We observed a more robust mucous metaplasia phenotype than in mice receiving doxycycline systemically. In addition, unwanted phenotypes outside of the lung that were evident when doxycycline was received systemically were now absent. Thus, our approach allows for rapid and efficient airway-specific transgene expression. After the careful strain by strain titration of the dose and timing of doxycycline inhalation, a suite of preexisting transgenic mice can now be used to study airway biology specifically in cases where transient transgene expression is sufficient to induce a phenotype.

Inducible, tightly regulated and non-leaky neuronal gene expression in mice

The Tetracycline (Tet)-controlled inducible system is the most widely used reversible system for transgene expression in mice with over 500 lines created to date. Although this system has been optimized over the years, it still has limitations such as residual transgene expression when turned off, referred to as leakiness. Here, we present a series of new Tet-OFF transgenic mice based on the second generation tetracycline-responsive transactivator system. The tTA-Advanced (tTA2(S)) is expressed under control of the neuron-specific Thy1.2 promoter (Thy-OFF), to regulate expression in the mouse brain. In addition, we generated a lacZ reporter line, utilizing the P tight Tet-responsive promoter (P(tight)-lacZ), to test our system. Two Thy-OFF transgenic lines displaying two distinct patterns of expression were selected. Oral doxycycline treatment of Thy-OFF/P tight-lacZ mice demonstrated tight transgene regulation with no leak expression. These new Thy-OFF mice are valuable for studies in a broad range of neurodegenerative diseases such as Alzheimer's disease and related forms of dementia, where control of transgene expression is critical to understanding mechanisms underlying the disease. Furthermore, P tight-lacZ reporter mice may be widely applicable.

Inducible gene expression in fetal thymic epithelium: a new BAC transgenic model

The thymus is the site of T cell development. Several stromal and hematopoietic cell types are necessary for the proper function of thymic selection and eventually peripheral immunity. Thymic epithelial cells (TECs) are essential for T cell lineage commitment, expansion, and maturation in the thymus. We were interested in developing an in vivo model in which exogenous gene expression could be transiently induced in embryonic TEC (Tet-On system). To this end, we have generated a bacterial artificial chromosome (BAC) transgenic mouse line in which the reverse tetracycline-dependent transactivator (rtTA) is expressed under the control of the Foxn1 promoter, a transcriptional factor indispensable for TEC development. To analyze the expression pattern and efficiency of this novel mouse model, we crossed the Foxn1-rtTA founder with a Tet-Responsive Element (TRE)-LacZ GFP mouse reporter to obtain a double transgenic mouse. In the presence of doxycycline, rtTA can interact with TRE and induce the expression of GFP and LacZ. In this double transgenic mouse, we observed that GFP expression was high, inducible and limited to TEC in fetal thymus. In contrast, in adult thymus, when TEC development and maturation is completed, GFP was barely detectable. Therefore, Foxn1-rtTA represents a new and efficient transgenic mouse model to induce genes of interest specifically in fetal thymic epithelium.

Effects of doxycycline on mesenchymal stem cell chondrogenesis and cartilage repair

OBJECTIVE

Strategies to improve cartilage repair tissue quality after bone marrow cell-based procedures may reduce later development of osteoarthritis. Doxycycline is inexpensive, well-tolerated, and has been shown to reduce matrix-metalloproteinases (MMPs) and osteoarthritis progression. This study tests the hypotheses that doxycycline reduces MMP, enhances chondrogenesis of human bone marrow-derived mesenchymal stem cells (hMSC), and improves in vivo cartilage repair.

DESIGN

Ninety hMSC pellets were cultured in chondrogenic media with either 0-, 1- or 2-μg/mL doxycycline. Pellets were evaluated with stereomicroscopy, proteoglycan assay, qRT-PCR, and histology. Osteochondral defects (OCDs) were created in the trochlear grooves of 24-Sprague-Dawley rats treated with/without oral doxycycline. Rats were sacrificed at 12-weeks and repair tissues were examined grossly and histologically.

RESULTS

hMSC pellets with 1-μg/mL (P = 0.014) and 2-μg/mL (P = 0.002) doxycycline had larger areas than pellets without doxycycline. hMSC pellets with 2-μg/mL doxycycline showed reduced mmp-13 mRNA (P = 0.010) and protein at 21-days. Proteoglycan, DNA contents, and mRNA expressions of chondrogenic genes were similar (P > 0.05). For the in vivo study, while the histological scores were similar between the two groups (P = 0.116), the gross scores of the OCD repair tissues in doxycycline-treated rats were higher at 12-weeks (P = 0.017), reflective of improved repair quality. The doxycycline-treated repairs also showed lower MMP-13 protein (P = 0.029).

CONCLUSIONS

This study shows that doxycycline improves hMSC chondrogenesis and decreases MMP-13 in pellet cultures and within rat OCDs. Doxycycline exerted no negative effect on multiple measures of chondrogenesis and cartilage repair. These data support potential use of doxycycline to improve cartilage repair to delay the onset of osteoarthritis.

Transient, inducible, placenta-specific gene expression in mice

Molecular understanding of placental functions and pregnancy disorders is limited by the absence of methods for placenta-specific gene manipulation. Although persistent placenta-specific gene expression has been achieved by lentivirus-based gene delivery methods, developmentally and physiologically important placental genes have highly stage-specific functions, requiring controllable, transient expression systems for functional analysis. Here, we describe an inducible, placenta-specific gene expression system that enables high-level, transient transgene expression and monitoring of gene expression by live bioluminescence imaging in mouse placenta at different stages of pregnancy. We used the third generation tetracycline-responsive tranactivator protein Tet-On 3G, with 10- to 100-fold increased sensitivity to doxycycline (Dox) compared with previous versions, enabling unusually sensitive on-off control of gene expression in vivo. Transgenic mice expressing Tet-On 3G were created using a new integrase-based, site-specific approach, yielding high-level transgene expression driven by a ubiquitous promoter. Blastocysts from these mice were transduced with the Tet-On 3G-response element promoter-driving firefly luciferase using lentivirus-mediated placenta-specific gene delivery and transferred into wild-type pseudopregnant recipients for placenta-specific, Dox-inducible gene expression. Systemic Dox administration at various time points during pregnancy led to transient, placenta-specific firefly luciferase expression as early as d 5 of pregnancy in a Dox dose-dependent manner. This system enables, for the first time, reliable pregnancy stage-specific induction of gene expression in the placenta and live monitoring of gene expression during pregnancy. It will be widely applicable to studies of both placental development and pregnancy, and the site-specific Tet-On G3 mouse will be valuable for studies in a broad range of tissues.

Progress on RNAi-based molecular medicines

RNA interference (RNAi) is a promising strategy to suppress the expression of disease-relevant genes and induce post-transcriptional gene silencing. Their simplicity and stability endow RNAi with great advantages in molecular medicine. Several RNAi-based drugs are in various stages of clinical investigation. This review summarizes the ongoing research endeavors on RNAi in molecular medicine, delivery systems for RNAi-based drugs, and a compendium of RNAi drugs in different stages of clinical development. Of special interest are RNAi-based drug target discovery and validation, delivery systems for RNAi-based drugs, such as nanoparticles, rabies virus protein-based vehicles, and bacteriophages for RNA packaging.

Polyswitch lentivectors: "all-in-one" lentiviral vectors for drug-inducible gene expression, live selection, and recombination cloning

Lentiviral vectors are now widely considered one of the safest and most efficient tools for gene delivery and stable gene expression. Even though inducible gene expression cassettes are mandatory for many genetic engineering strategies, most current systems suffer from various issues, such as the requirement of two vectors, which decreases the overall efficiency of the transduction, leakiness and/or insufficient levels of activation of the inducible promoter, lack of selectable marker, low titers, or general issues associated with the cloning of large plasmids. In this article, we describe the design and functional characterization of a set of "all-in-one" multicistronic autoinducible lentivectors. They combine: (1) an optimized drug-inducible promoter; (2) a multicistronic strategy to express living color, selectable marker, and transactivator; and (3) acceptor sites for easy recombination cloning of genes of interest. These polyswitch lentivectors have good titers, very low basal activity, and reversible high induced activity, and can accept a growing number of genes already cloned in entry plasmids. These combined features make them a novel, powerful, and versatile tool for current and future genetic engineering approaches.

The power of reversibility regulating gene activities via tetracycline-controlled transcription

Tetracycline-controlled transcriptional activation systems are widely used to control gene expression in transgenic animals in a truly conditional manner. By this we refer to the capability of these expression systems to control gene activities not only in a tissue specific and temporal defined but also reversible manner. This versatility has made the Tet regulatory systems to a preeminent tool in reverse mouse genetics. The development of the technology in the past 15 years will be reviewed and guidelines will be given for its implementation in creating transgenic rodents. Finally, we highlight some recent exciting applications of the Tet technology as well as its foreseeable combination with other emerging technologies in mouse transgenesis.