Generation of the regulatory protein rtTA transgenic mice

Characterization of changes in global gene expression in the hearts and kidneys of transgenic mice overexpressing human angiotensin-converting enzyme 2

Human angiotensin-converting enzyme 2 (hACE2) has recently received a great attention due to it play a critical role as SARS-CoV receptor in the infection of human body. However, no further analysis for gene regulation has been performed in target tissues of model mice during hACE2 overproduction. To characterize changes in global gene expression in the hearts and kidneys of rtTA/hACE2 double transgenic (dTg) mice in response to hACE2 overexpression, total RNA extracted from these tissues from dTg mice after doxycycline (Dox) treatment was hybridized to oligonucleotide microarrays. Briefly, dTg mice were generated by cross-mating pα-MHC/rtTA Tg mice with pTRE/hACE2 Tg mice. The expression level of hACE2 protein was determined to be high in hearts, kidneys, and brains of dTg mice, whereas lung, liver, and testis tissues expressed low levels. The level of hACE2 was significantly enhanced in hearts and kidneys of the Dox+dTg group compared to that in Vehicle+dTg mice although consistent levels of mouse ACE2 (mACE2) remained in the same tissues. Based on the microarray analysis of heart tissue, 385 genes were differentially expressed, including 168 upregulated and 217 downregulated, when comparing non-Tg and Vehicle+dTg mice, whereas 216 genes were differentially expressed, including 136 upregulated and 80 downregulated, between Vehicle+dTg and Dox+dTg mice. In the kidneys, 402 genes were differentially expressed, including 159 upregulated and 243 downregulated, between non-Tg and Vehicle+dTg mice. Dox-treated dTg mice exhibited the differential expression of 4735 genes including 1636 upregulated and 3109 downregulated. Taken together, these findings suggested that several functional groups and individual genes can be considered biomarkers that respond to hACE2 overexpression in dTg mice. Moreover, our results provided a lot of useful information to predict physiological responses when these dTg mice are applied as a susceptible model for novel coronavirus (SARS-CoV, COVID-19) in both vaccine and drug development.

Establishment of A Reversibly Inducible Porcine Granulosa Cell Line

Granulosa cells (GCs) are the key components of ovarian follicles for regulating oocyte maturation. Previous established GC lines have allowed prolonged proliferation, but lost some physiological features owing to long-term immortalization. This study was to establish an induced immortal porcine GC line with reversible proliferation status by the tetracycline inducible (Tet-on) 3G system. Our conditional immortal porcine GCs (CIPGCs) line steadily propagated for at least six months and displayed primary GC morphology when cultured in the presence of 50 ng/mL doxycycline [Dox (+)]. Upon Dox withdrawal [Dox (–)], Large T-antigen expression, reflected by mCherry fluorescence, gradually became undetectable within 48 h, accompanied by less proliferation and size increase. The levels of estradiol and progesterone, and the expression of genes associated with steroid production, such as CYP11A1 (cytochrome P450 family 11), 3β-HSD (3β-hydroxysteroid dehydrogenase), StAR (steroidogenic acute regulatory protein), and CYP19A1 (cytochrome P450 family 19 subfamily a member 1), were all significantly higher in the Dox (–) group than Dox (+) group. The CIPGCs could switch into a proliferative state upon Dox induction. Interestingly, the expression of StAR and CYP19A1 in the CIPGCs (–Dox) was significantly increased by adding porcine follicular fluid (PFF) to mimic an ovary follicle environment. Moreover, PFF priming the CIPGCs in Dox (–) group resulted in similar estradiol production as that of primary GC, and enabled this cell line to respond to gonadotrophins in estradiol production. Collectively, we have established an inducible immortal porcine GC line, which offers a unique and valuable model for future research on the regulation of ovarian functions.

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.

Use of the 2A peptide for generation of multi-transgenic pigs through a single round of nuclear transfer

Multiple genetic modifications in pigs can essentially benefit research on agriculture, human disease and xenotransplantation. Most multi-transgenic pigs have been produced by complex and time-consuming breeding programs using multiple single-transgenic pigs. This study explored the feasibility of producing multi-transgenic pigs using the viral 2A peptide in the light of previous research indicating that it can be utilized for multi-gene transfer in gene therapy and somatic cell reprogramming. A 2A peptide-based double-promoter expression vector that mediated the expression of four fluorescent proteins was constructed and transfected into primary porcine fetal fibroblasts. Cell colonies (54.3%) formed under G418 selection co-expressed the four fluorescent proteins at uniformly high levels. The reconstructed embryos, which were obtained by somatic cell nuclear transfer and confirmed to express the four fluorescent proteins evenly, were transplanted into seven recipient gilts. Eleven piglets were delivered by two gilts, and seven of them co-expressed the four fluorescent proteins at equivalently high levels in various tissues. The fluorescence intensities were directly observed at the nose, hoof and tongue using goggles. The results suggest that the strategy of combining the 2A peptide and double promoters efficiently mediates the co-expression of the four fluorescent proteins in pigs and is hence a promising methodology to generate multi-transgenic pigs by a single nuclear transfer.

Development of hepatitis C virus vaccine using hepatitis B core antigen as immuno-carrier

AIM: To develop hepatitis C virus (HCV) vaccine using HBcAg as the immuno-carrier to express HCV T epitope and to investigate its immunogenicity in mice.

METHODS: We constructed the plasmid pTrc-core^NheI using gene engineering technique, constructed the pcDNA3.1-core^NheI-GFP plasmid with GFP as the reporter gene, and transfected them into Hela cells. The expression of GFP was observed under confocal microscopy and the feasibility of using HBcAg as an immuno-carrier vaccine was studied. pTrc-core gene with a synthetic T epitope antigen gene of HCV (35-44aa) was fused and expressed in the plasmid pTrc-core-HCV (T). For the fusion of the HBcAg-T protein, sucrose, density gradient centrifugation was used, and its molecular weight and purity were analyzed by SDS-PAGE. Then balb/c mice were immunized by the plasmid with the HBcAg (expressed by pTrc-core) protein as control. The tumor regression potential was investigated in mice and evaluated at appropriate time. After three times of immunization, the peripheral blood and spleen of vaccinated mice were collected. HBcAb was detected by ELISA, and nonspecific T lymphocyte proliferation and response of splenocytes were respectively examined by MTT assay. T cell subset of blood and spleen were detected by FACS.

RESULTS: GFP was successfully expressed. Tumor regression trial showed that no tumor formation was found in the group receiving immunization, while tumor xenograft progression was not changed in the control group. Strong nonspecific lymphocyte proliferation response was induced. FACS also showed that the ratio of CD8⁺ T cells in the experimental group was higher than the controls, but the serum HBcAb in experimental group was similar to the control.

CONCLUSION: HBcAg can be used as an immuno-carrier of vaccine, the fusion of HBcAg-T protein could induce stronger cellular immune responses and it might be a candidate for therapeutic vaccines specific for HCV.