Production of transgenic pigs using a pGFAP-CreERT2/EGFP LoxP inducible system for central nervous system disease models

Generation of a genetically engineered porcine melanoma model featuring oncogenic control through conditional Cre recombination

Melanoma is a serious type of skin cancer that originates from melanocytes. Rodent melanoma models have provided valuable insights into melanoma pathology; however, they often lack applicability to humans owing to genetic, anatomical, physiological, and metabolic differences. Herein, we developed a transgenic porcine melanoma model that closely resembles humans via somatic cell nuclear transfer (SCNT). Our model features the conditional oncogenes cassettes, TP53R167H and human BRAFV600E, controlled by melanocyte-specific CreER recombinase. After SCNT, transgenic embryos developed normally, with the capacity to develop porcine embryonic stem cells. Seven transgenic piglets with oncogene cassettes were born through embryo transfer. We demonstrated that Cre recombination-mediated oncogene activation remarkably triggered the mitogen-activated protein kinase pathway in vitro. Notably, intradermal injection of 4-hydroxytamoxifen activated oncogene cassettes in vivo, resulting in melanocytic lesions resembling hyperpigmented nevi with increased proliferative properties similar to early human melanomas. This melanoma-inducing system, heritably transmitted to offspring, supports large-scale studies. The novel porcine model provides a valuable tool for elucidating melanoma development and metastasis mechanism, advancing translational medicine, and facilitating preclinical evaluation of new anticancer drugs.

Physiological and Functional Roles of Neurotrophin-4 During In Vitro Maturation of Porcine Cumulus–Oocyte Complexes

Neurotrophin-4 (NT-4), a granulosa cell-derived factor and a member of the neurotrophin family, is known to promote follicular development and oocyte maturation in mammals. However, the physiological and functional roles of NT-4 in porcine ovarian development are not yet known. The aim of this study was to investigate the physiological role of NT-4-related signaling in the in vitro maturation (IVM) of porcine cumulus–oocyte complexes (COCs). The NT-4 protein and its receptors were detected in matured porcine COCs via immunofluorescence analysis. NT-4 was shown to promote the maturation of COCs by upregulating NFKB1 transcription via the neurotrophin/p75NTR signaling pathway. Notably, the mRNA expression levels of the oocyte-secreted factors GDF9 and BMP15, sperm–oocyte interaction regulator CD9, and DNA methylase DNMT3A were significantly upregulated in NT-4-treated than in untreated porcine oocytes. Concurrently, there were no significant differences in the levels of total and phosphorylated epidermal growth factor receptor and p38 mitogen-activated protein kinase between NT-4-treated and untreated cumulus cells (CCs); however, the level of phosphorylated ERK1/2 was significantly higher in NT-4-treated CCs. Both total and phosphorylated ERK1/2 levels were significantly higher in NT-4-treated than in untreated oocytes. In addition, NT-4 improved subsequent embryonic development after in vitro fertilization and somatic cell nuclear transfer. Therefore, the physiological and functional roles of NT-4 in porcine ovarian development include the promotion of oocyte maturation, CC expansion, and ERK1/2 phosphorylation in porcine COCs during IVM.

Generation of reproductive transgenic pigs of a CRISPR-Cas9-based oncogene-inducible system by somatic cell nuclear transfer

Alternative cancer models that are close to humans are required to create more valuable preclinical results during oncology studies. Here, we developed a new onco-pig model via developing a CRISPR-Cas9-based Conditional Polycistronic gene expression Cassette (CRI-CPC) system to control the tumor inducing simian virus 40 large T antigen (SV40LT) and oncogenic HRASG12V. After conducting somatic cell nuclear transfer (SCNT), transgenic embryos were transplanted into surrogate mothers and five male piglets were born. Umbilical cord analysis confirmed that all piglets were transgenic. Two of them survived, and they expressed a detectable green fluorescence. We tested whether our CRI-CPC models were naturally fertile and whether the CRI-CPC system was stably transferred to the offspring. By mating with a normal female pig, four offspring piglets were successfully produced. Among them, only three male piglets were transgenic. Finally, we tested their applicability as cancer models after transduction of Cas9 into fibroblasts from each CRI-CPC pig in vitro, resulting in cell acquisition of cancerous characteristics via the induction of oncogene expression. These results showed that our new CRISPR-Cas9-based onco-pig model was successfully developed. This article is protected by copyright. All rights reserved.

Lentiviral Vector Induced Modeling of High-Grade Spinal Cord Glioma in Minipigs

BACKGROUND

Prior studies have applied driver mutations targeting the RTK/RAS/PI3K and p53 pathways to induce the formation of high-grade gliomas in rodent models. In the present study, we report the production of a high-grade spinal cord glioma model in pigs using lentiviral gene transfer.

METHODS

Six Gottingen Minipigs received thoracolumbar (T14-L1) lateral white matter injections of a combination of lentiviral vectors, expressing platelet-derived growth factor beta (PDGF-B), constitutive HRAS, and shRNA-p53 respectively. All animals received injection of control vectors into the contralateral cord. Animals underwent baseline and endpoint magnetic resonance imaging (MRI) and were evaluated daily for clinical deficits. Hematoxylin and eosin (H&E) and immunohistochemical analysis was conducted. Data are presented using descriptive statistics including relative frequencies, mean, standard deviation, and range.

RESULTS

100% of animals (n = 6/6) developed clinical motor deficits ipsilateral to the oncogenic lentiviral injections by a three-week endpoint. MRI scans at endpoint demonstrated contrast enhancing mass lesions at the site of oncogenic lentiviral injection and not at the site of control injections. Immunohistochemistry demonstrated positive staining for GFAP, Olig2, and a high Ki-67 proliferative index. Histopathologic features demonstrate consistent and reproducible growth of a high-grade glioma in all animals.

CONCLUSIONS

Lentiviral gene transfer represents a feasible pathway to glioma modeling in higher order species. The present model is the first lentiviral vector induced pig model of high-grade spinal cord glioma and may potentially be used in preclinical therapeutic development programs.

Isolation and characterization of GFAP-positive porcine neural stem/progenitor cells derived from a GFAP-CreERT2 transgenic piglet

Background

The porcine brain is gyrencephalic with similar gray and white matter composition and size more comparable to the human rather than the rodent brain; however, there is lack of information about neural progenitor cells derived from this model.

Results

Here, we isolated GFAP-positive porcine neural stem cells (NSCs) from the brain explant of a transgenic piglet, with expression of CreER^T2 under the control of the GFAP promoter (pGFAP-CreER^T2). The isolated pGFAP-CreER^T2 NSCs showed self-renewal and expression of representative NSC markers such as Nestin and Sox2. Pharmacological inhibition studies revealed that Notch1 signaling is necessary to maintain NSC identity, whereas serum treatment induced cell differentiation into reactive astrocytes and neurons.

Conclusions

Collectively, these results indicate that GFAP promoter-driven porcine CreER^T2 NSCs would be a useful tool to study neurogenesis of the porcine adult central nervous system and furthers our understanding of its potential clinical application in the future.

Graphical abstract

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Electronic supplementary material

The online version of this article (10.1186/s12917-018-1660-4) contains supplementary material, which is available to authorized users.