Generation of AQP2-Cre transgenic mini-pigs specifically expressing Cre recombinase in kidney collecting duct cells

The Missing Link: Cre Pigs for Cancer Research

The Cre/loxP system is a powerful tool for the generation of animal models with precise spatial and temporal gene expression. It has proven indispensable in the generation of cancer models with tissue specific expression of oncogenes or the inactivation of tumor suppressor genes. Consequently, Cre-transgenic mice have become an essential prerequisite in basic cancer research. While it is unlikely that pigs will ever replace mice in basic research they are already providing powerful complementary resources for translational studies. But, although conditionally targeted onco-pigs have been generated, no Cre-driver lines exist for any of the major human cancers. To model human pancreatic cancer in pigs, Cre-driver lines were generated by CRISPR/Cas9-mediated insertion of codon-improved Cre (iCre) into the porcine PTF1A gene, thus guaranteeing tissue and cell type specific function which was proven using dual fluorescent reporter pigs. The method used can easily be adapted for the generation of other porcine Cre-driver lines, providing a missing tool for modeling human cancers in large animals.

CRISPR/Cas9-Mediated Hitchhike Expression of Functional shRNAs at the Porcine miR-17-92 Cluster

Successful RNAi applications depend on strategies allowing stable and persistent expression of minimal gene silencing triggers without perturbing endogenous gene expression. In this study, we proposed an endogenous microRNA (miRNA) cluster as a novel integration site for small hairpin RNAs (shRNAs). We successfully integrated exogenous shRNAs at the porcine miRNA-17-92 (pmiR-17-92) cluster via a CRISPR/Cas9-mediated knock-in strategy. The anti-EGFP or anti-CSFV shRNAs could be stably and effectively expressed at the control of the endogenous promoter of the pmiR-17-92 cluster. Importantly, we confirmed that hitchhike expression of anti- classical swine fever (CSFV) shRNA had no effect on cell growth, blastocyst development and endogenous pmiR-17-92 expression in selected transgene (TG) porcine fetal fibroblasts (PFFs) clones. Moreover, these TG PFFs could inhibit the replication of CSFV by half and could be further used for generation of transgenic pigs. Taken together, these results show that our RNA interference (RNAi) expression strategy benefits numerous applications, from miRNA, genome and transgenic research, to gene therapy.

Genetically engineered pigs as models for human disease

Genetically modified animals are vital for gaining a proper understanding of disease mechanisms. Mice have long been the mainstay of basic research into a wide variety of diseases but are not always the most suitable means of translating basic knowledge into clinical application. The shortcomings of rodent preclinical studies are widely recognised, and regulatory agencies around the world now require preclinical trial data from nonrodent species. Pigs are well suited to biomedical research, sharing many similarities with humans, including body size, anatomical features, physiology and pathophysiology, and they already play an important role in translational studies. This role is set to increase as advanced genetic techniques simplify the generation of pigs with precisely tailored modifications designed to replicate lesions responsible for human disease. This article provides an overview of the most promising and clinically relevant genetically modified porcine models of human disease for translational biomedical research, including cardiovascular diseases, cancers, diabetes mellitus, Alzheimer's disease, cystic fibrosis and Duchenne muscular dystrophy. We briefly summarise the technologies involved and consider the future impact of recent technical advances.

Summary: An overview of porcine models of human disease, including cardiovascular diseases, cancers, diabetes mellitus, Alzheimer's disease, cystic fibrosis and Duchenne muscular dystrophy. We summarise the technologies involved and potential future impact of recent technical advances.

Genetic characteristics of polycistronic system‑mediated randomly‑inserted multi‑transgenes in miniature pigs and mice

Multi-transgenic technology is superior to single transgenic technology in biological and medical research. Multi-transgene insertion mediated by a polycistronic system is more effective for the integration of polygenes. The multi-transgene insertion patterns and manners of inheritance are not completely understood. Copy number quantification is one available approach for addressing this issue. The present study determined copy numbers in two multi-transgenic mice (K3 and L3) and two multi-transgenic miniature pigs (Z2 and Z3) using absolute quantitative polymerase chain reaction analysis. For the F0 generation, a given transgene was able to exhibit different copy number integration capacities in different individuals. For the F1 generation, the most notable characteristic was that the copy number proportions were different among pedigrees (P<0.05). The results of the present study demonstrated that transgenes within the same vector exhibited the same integration trend between the F0 and F1 generations. In conclusion, intraspecific consistency and intergenerational copy numbers were compared and the integration capacity of each specific transgene differed in multi-transgenic animals. In particular, the copy number of one transgene may not be used to represent other transgenes in polycistronic vector-mediated multi-transgenic organisms. Consequently, in multi-transgenic experimental animal disease model research or breeding, copy numbers provide an important reference. Therefore, each transgene in multi-transgenic animals must be separately screened to prevent large copy number differences, and inconsistent expression between transgenes and miscellaneous data, in subsequent research.

Transgenesis for pig models

Animal models, particularly pigs, have come to play an important role in translational biomedical research. There have been many pig models with genetically modifications via somatic cell nuclear transfer (SCNT). However, because most transgenic pigs have been produced by random integration to date, the necessity for more exact gene-mutated models using recombinase based conditional gene expression like mice has been raised. Currently, advanced genome-editing technologies enable us to generate specific gene-deleted and -inserted pig models. In the future, the development of pig models with gene editing technologies could be a valuable resource for biomedical research.

Efficient Generation of Orthologous Point Mutations in Pigs via CRISPR-assisted ssODN-mediated Homology-directed Repair

Precise genome editing in livestock is of great value for the fundamental investigation of disease modeling. However, genetically modified pigs carrying subtle point mutations were still seldom reported despite the rapid development of programmable endonucleases. Here, we attempt to investigate single-stranded oligonucleotides (ssODN) mediated knockin by introducing two orthologous pathogenic mutations, p.E693G for Alzheimer's disease and p.G2019S for Parkinson's disease, into porcine APP and LRRK2 loci, respectively. Desirable homology-directed repair (HDR) efficiency was achieved in porcine fetal fibroblasts (PFFs) by optimizing the dosage and length of ssODN templates. Interestingly, incomplete HDR alleles harboring partial point mutations were observed in single-cell colonies, which indicate the complex mechanism of ssODN-mediated HDR. The effect of mutation-to-cut distance on incorporation rate was further analyzed by deep sequencing. We demonstrated that a mutation-to-cut distance of 11 bp resulted in a remarkable difference in HDR efficiency between two point mutations. Finally, we successfully obtained one cloned piglet harboring the orthologous p.C313Y mutation at the MSTN locus via somatic cell nuclear transfer (SCNT). Our proof-of-concept study demonstrated efficient ssODN-mediated incorporation of pathogenic point mutations in porcine somatic cells, thus facilitating further development of disease modeling and genetic breeding in pigs.

Identification of TRPM6 and TRPM7 expression changes in response to a diet supplemented with inulin in porcine kidney

Abstract. Magnesium is the fourth most abundant mineral element in vertebrates and the second most common intracellular cation. Recently identified Mg2+-specific channels – TRPM6 and TRPM7 – have been shown to be essential for whole-body and cellular Mg2+ homeostasis. The aim of the study was to determine the effect of inulin on the expression of TRPM6 and TRPM7 in the renal cortex and medulla of growing pigs. The study was carried out on 16 Danbred  ×  Duroc castrated male piglets fed a cereal-based diet without inulin or with 2 % addition of inulin from chicory root from the 10th day of life. In pigs fed a diet with inulin, TRPM6 expression was greater in both the renal cortex and medulla compared to the control group. The expression of TRPM7 in both the renal cortex and medulla in the control group and in piglets fed a diet enriched with inulin was relatively stable. To our knowledge, this is the first study aimed at the identification of TRPM6 and TRPM7 in the kidneys of pig. It is proposed that inulin addition to fodder resulted not only in a magnesium absorption increase, but also, due to prolonged low plasma Mg concentration of examined piglets, renal magnesium retention. Therefore, higher magnesium reabsorption via increased TRPM6 expression in the kidney was probably observed in order to supplement deficiencies of this element. Diet-unresponsive expression of TRPM7 supports the concept that this channel is not involved in the extracellular magnesium homeostasis.

N-3 polyunsaturated fatty acids attenuates triglyceride and inflammatory factors level in hfat-1 transgenic pigs

BACKGROUND

The consumption of n-3 polyunsaturated fatty acids (PUFAs) is important to human health, especially in cases of cardiovascular disease. Although beneficial effects of n-3 PUFAs have been observed in a number of studies, the mechanisms involved in these effects have yet to be discovered.

METHODS

We generated hfat-1 transgenic pigs with traditional somatic cell nuclear transfer (SCNT) technology. The fatty acid composition in ear tissue of pigs were detected with gas chromatography. The cholesterol, triglycerides (TAG) and inflammation mediators in circulation were investigated.

RESULTS

The hfat-1 transgenic pigs were developed which accumulate high levels of n-3 PUFAs than wild-types pigs. Gas chromatography results demonstrated that the total n-3 PUFAs in the ear tissues of the transgenic founders were 2-fold higher than the wild-type pigs. A lipid analysis demonstrated that the levels of TAG in the transgenic pigs were decreased significantly. The basal levels of the inflammation mediators tumor necrosis factor-α (TNF-α), monocyte chemoattractant protein-1 (MCP-1) and interleukin-6 (IL-6) in transgenic pigs were inhibited markedly compared with the wild-type pigs.

CONCLUSIONS

These results suggest that n-3 PUFAs accumulation in vivo may have beneficial effects on vascular and hfat-1 transgenic pigs may be a useful tool for investigating the involved mechanisms.

Germ cell-specific expression of Cre recombinase using the VASA promoter in the pig

The Cre–loxP system is a powerful tool for genetic analysis of distinct cell lineages and tissue‐specific gene knockout in animal models. VASA is specifically expressed in reproductive tissues, and is known to play important roles in spermatogenesis and germ‐cell growth. In this study, Cre recombinase transgenic pigs under the control of the VASA promoter were generated by somatic cell nuclear transfer. Germ cell‐specific expression of Cre recombinase in VASA‐Cre transgenic pigs was shown by western blotting and immunohistochemistry. VASA‐Cre transgenic pigs will be a useful tool for germ cell‐specific gene knockout and a disease model for disorders of the reproductive system.

Multi‑transgenic minipig models exhibiting potential for hepatic insulin resistance and pancreatic apoptosis

There are currently no multi‑transgenic minipig models of diabetes for the regulation of multiple genes involved in its pathogenesis. The foot and mouth disease virus 2A (F2A)‑mediated polycistronic system possesses several advantages, and the present study developed a novel multi‑transgenic minipig model associated with diabetes using this system. The tissue‑specific polycistronic system used in the present study consisted of two expression cassettes, separated by an insulator: (i) 11‑β‑hydroxysteroid dehydrogenase 1 (11β‑HSD1), driven by the porcine liver‑specific apolipoprotein E promoter; (ii) human islet amyloid polypeptide (hIAPP) and C/EBP homologous protein (CHOP), linked to the furin digested site and F‑2A, driven by the porcine pancreas‑specific insulin promoter. In the present study, porcine fetal fibroblasts were transfected with this vector. Following somatic cell nuclear transfer using 10 cell clones and the transplantation of 1,459 embryos in total, three Landrace x Yorkshire surrogates became pregnant and delivered three Wuzhishan piglets. Genomic polymerase chain reaction (PCR) demonstrated that the piglets were multi‑transgenic. Reverse transcription‑quantitative PCR confirmed that 11β‑HSD1 transcription was upregulated in the targeted liver. Similarly, hIAPP and CHOP were expressed at high levels, compared with the control (P<0.05 and P<0.01) in the pancreas, consistent with the western blotting and immunohistochemistry results. The primary results also showed that overexpression of 11β‑HSD1 in the liver increased the liver fat lipid parameters; and the levels of hIAPP and CHOP in the pancreatic islet cells, leading to delayed β‑cell development and apoptosis. This novel tissue‑specific polycistronic system offers a promising starting point for efficiently mimicking multigenic metabolic disease.

Efficient Generation of Myostatin Mutations in Pigs Using the CRISPR/Cas9 System

Genetically modified pigs are increasingly used for biomedical and agricultural applications. The efficient CRISPR/Cas9 gene editing system holds great promise for the generation of gene-targeting pigs without selection marker genes. In this study, we aimed to disrupt the porcine myostatin (MSTN) gene, which functions as a negative regulator of muscle growth. The transfection efficiency of porcine fetal fibroblasts (PFFs) was improved to facilitate the targeting of Cas9/gRNA. We also demonstrated that Cas9/gRNA can induce non-homologous end-joining (NHEJ), long fragment deletions/inversions and homology-directed repair (HDR) at the MSTN locus of PFFs. Single-cell MSTN knockout colonies were used to generate cloned pigs via somatic cell nuclear transfer (SCNT), which resulted in 8 marker-gene-free cloned pigs with biallelic mutations. Some of the piglets showed obvious intermuscular grooves and enlarged tongues, which are characteristic of the double muscling (DM) phenotype. The protein level of MSTN was decreased in the mutant cloned pigs compared with the wild-type controls, and the mRNA levels of MSTN and related signaling pathway factors were also analyzed. Finally, we carefully assessed off-target mutations in the cloned pigs. The gene editing platform used in this study can efficiently generate genetically modified pigs with biological safety.

Efficacy of the porcine species in biomedical research

Since domestication, pigs have been used extensively in agriculture and kept as companion animals. More recently they have been used in biomedical research, given they share many physiological and anatomical similarities with humans. Recent technological advances in assisted reproduction, somatic cell cloning, stem cell culture, genome editing, and transgenesis now enable the creation of unique porcine models of human diseases. Here, we highlight the potential applications and advantages of using pigs, particularly minipigs, as indispensable large animal models in fundamental and clinical research, including the development of therapeutics for inherited and chronic disorders, and cancers.