Generation of a tyrosine hydroxylase-2A-Cre knockin non-human primate model by homology-directed-repair-biased CRISPR genome editing.

Non-human primates (NHPs) are the closest animal model to humans; thus, gene engineering technology in these species holds great promise for the elucidation of higher brain functions and human disease models. Knockin (KI) gene targeting is a versatile approach to modify gene(s) of interest; however, it generally suffers from the low efficiency of homology-directed repair (HDR) in mammalian cells, especially in non-expressed gene loci. In the current study, we generated a tyrosine hydroxylase (TH)-2A-Cre KI model of the common marmoset monkey (marmoset; Callithrix jacchus) using an HDR-biased CRISPR-Cas9 genome editing approach using Cas9-DN1S and RAD51. This model should enable labeling and modification of a specific neuronal lineage using the Cre-loxP system. Collectively, the current study paves the way for versatile gene engineering in NHPs, which may be a significant step toward further biomedical and preclinical applications.

Multimodal analyses of a non-human primate model harboring mutant amyloid precursor protein transgenes driven by the human EF1α promoter.

Alzheimer's disease (AD) is the leading cause of dementia which afflicts tens of millions of people worldwide. Despite many scientific progresses to dissect the AD's molecular basis from studies on various mouse models, it has been suffered from evolutionary species differences. Here, we report generation of a non-human primate (NHP), common marmoset model ubiquitously expressing Amyloid-beta precursor protein (APP) transgenes with the Swedish (KM670/671NL) and Indiana (V717F) mutations. The transgene integration of generated two transgenic marmosets (TG1&TG2) was thoroughly investigated by genomic PCR, whole-genome sequencing, and fluorescence in situ hybridization. By reprogramming, we confirmed the validity of transgene expression in induced neurons in vitro. Moreover, we discovered structural changes in specific brain regions of transgenic marmosets by magnetic resonance imaging analysis, including in the entorhinal cortex and hippocampus. In immunohistochemistry, we detected increased Aß plaque-like structures in TG1 brain at 7 years old, although evident neuronal loss or glial inflammation was not observed. Thus, this study summarizes our attempt to establish an NHP AD model. Although the transgenesis approach alone seemed not sufficient to fully recapitulate AD in NHPs, it may be beneficial for drug development and further disease modeling by combination with other genetically engineered models and disease-inducing approaches.

Step-by-step protocols for non-viral derivation of transgene-free induced pluripotent stem cells from somatic fibroblasts of multiple mammalian species.

Potentials of immortal proliferation and unlimited differentiation into all the three germ layers and germ cells in induced pluripotent stem cells (iPSCs) render them important bioresources for in vitro reconstitution and modeling of intravital tissues and organs in various animal models, thus contributing to the elucidation of pathomechanisms, drug discovery and stem cell-based regenerative medicine. We previously reported promising approaches for deriving transgene-free iPSCs from somatic fibroblasts of multiple mammalian species by episomal vector or RNA transfection, although the respective step-by-step protocols and the combinatorial usage of these methods, which achieved high induction efficiency, have not been described in the literature so far. Here, we provide a detailed step-by-step description of these methods with critical tips and slight modifications (improvements) to previously reported methods. We also report a novel method for the establishment of iPSCs from the Syrian hamster (also known as golden hamster; Mesocricetus auratus), a unique animal model of hibernation. We anticipate this methodology will contribute to stem cell biology and regenerative medicine research.

Early development of the cochlea of the common marmoset, a non-human primate model.

BACKGROUND: Fine-tuned cochlear development is essential for hearing. Owing to the difficulty in using early human fetal samples, most of our knowledge regarding cochlear development has been obtained from rodents. However, several inter-species differences in cochlear development between rodents and humans have been reported. To bridge these differences, we investigated early otic development of a non-human primate model animal, the common marmoset (Callithrix jacchus). METHODS: We examined 20 genes involved in early cochlear development and described the critical developmental steps for morphogenesis, which have been reported to vary between rodents and marmosets. RESULTS: The results revealed that several critical genes involved in prosensory epithelium specifications showed higher inter-species differences, suggesting that the molecular process for hair cell lineage acquisition in primates differs considerably from that of rodents. We also observed that the tempo of cochlear development was three times slower in the primate than in rodents. CONCLUSIONS: Our data provide new insights into early cochlear development in primates and humans and imply that the procedures used for manipulating rodent cochlear sensory cells cannot be directly used for the research of primate cells due to the intrinsic inter-species differences in the cell fate determination program.

Non-viral Induction of Transgene-free iPSCs from Somatic Fibroblasts of Multiple Mammalian Species.

Induced pluripotent stem cells (iPSCs) are capable of providing an unlimited source of cells from all three germ layers and germ cells. The derivation and usage of iPSCs from various animal models may facilitate stem cell-based therapy, gene-modified animal production, and evolutionary studies assessing interspecies differences. However, there is a lack of species-wide methods for deriving iPSCs, in particular by means of non-viral and non-transgene-integrating (NTI) approaches. Here, we demonstrate the iPSC derivation from somatic fibroblasts of multiple mammalian species from three different taxonomic orders, including the common marmoset (Callithrix jacchus) in Primates, the dog (Canis lupus familiaris) in Carnivora, and the pig (Sus scrofa) in Cetartiodactyla, by combinatorial usage of chemical compounds and NTI episomal vectors. Interestingly, the fibroblasts temporarily acquired a neural stem cell-like state during the reprogramming. Collectively, our method, robustly applicable to various species, holds a great potential for facilitating stem cell-based research using various animals in Mammalia.

No Tumorigenicity of Allogeneic Induced Pluripotent Stem Cells in Major Histocompatibility Complex-matched Cynomolgus Macaques.

Tumorigenicity of induced pluripotent stem cells (iPSCs) is anticipated when cells derived from iPSCs are transplanted. It has been reported that iPSCs formed a teratoma in vivo in autologous transplantation in a nonhuman primate model without immunosuppression. However, there has been no study on tumorigenicity in major histocompatibility complex (MHC)-matched allogeneic iPSC transplantation with immune-competent hosts. To examine the tumorigenicity of allogeneic iPSCs, we generated four iPSC clones carrying a homozygous haplotype of the MHC. Two clones were derived from female fibroblasts by using a retrovirus and the other two clones were derived from male peripheral blood mononuclear cells by using Sendai virus (episomal approach). The iPSC clones were transplanted into allogenic MHC-matched immune-competent cynomolgus macaques. After transplantation of the iPSCs into subcutaneous tissue of an MHC-matched female macaque and into four testes of two MHC-matched male macaques, histological analysis showed no tumor, inflammation, or regenerative change in the excised tissues 3 months after transplantation, despite the results that iPSCs formed teratomas in immune-deficient mice and in autologous transplantation as previously reported. The results in the present study suggest that there is no tumorigenicity of iPSCs in MHC-matched allogeneic transplantation in clinical application.

The polymicrogyria-associated GPR56 promoter preferentially drives gene expression in developing GABAergic neurons in common marmosets.

GPR56, a member of the adhesion G protein-coupled receptor family, is abundantly expressed in cells of the developing cerebral cortex, including neural progenitor cells and developing neurons. The human GPR56 gene has multiple presumptive promoters that drive the expression of the GPR56 protein in distinct patterns. Similar to coding mutations of the human GPR56 gene that may cause GPR56 dysfunction, a 15-bp homozygous deletion in the cis-regulatory element upstream of the noncoding exon 1 of GPR56 (e1m) leads to the cerebral cortex malformation and epilepsy. To clarify the expression profile of the e1m promoter-driven GPR56 in primate brain, we generated a transgenic marmoset line in which EGFP is expressed under the control of the human minimal e1m promoter. In contrast to the endogenous GPR56 protein, which is highly enriched in the ventricular zone of the cerebral cortex, EGFP is mostly expressed in developing neurons in the transgenic fetal brain. Furthermore, EGFP is predominantly expressed in GABAergic neurons, whereas the total GPR56 protein is evenly expressed in both GABAergic and glutamatergic neurons, suggesting the GABAergic neuron-preferential activity of the minimal e1m promoter. These results indicate a possible pathogenic role for GABAergic neuron in the cerebral cortex of patients with GPR56 mutations.

Primed to Naive-Like Conversion of the Common Marmoset Embryonic Stem Cells.

Mammalian pluripotent stem cells are thought to exist in two states: naive and primed. Generally, unlike those in rodents, pluripotent stem cells in primates, including humans, are regarded as being in the primed pluripotent state. Recently, several groups reported the existence of naive pluripotent stem cells in humans. In this study, we report the conversion of primed state embryonic stem cells from common marmoset, a New World monkey, to the naive state using transgenes. The cells showed typical naive state features, including dome-like colony morphology, growth factor requirement, gene expression profile, X chromosome activation state, and energy metabolic status. Moreover, interspecies chimeric embryo formation ability with mouse embryos was increased in the naive state. This technique can be applied in basic medical research using nonhuman primates, such as preclinical use of naive pluripotent stem cells and generating genetically modified primates.

Establishment of induced pluripotent stem cells from common marmoset fibroblasts by RNA-based reprogramming.

The common marmoset (marmoset; Callithrix jacchus) shows anatomical and physiological features that are in common with humans. Establishing induced pluripotent stem cells (iPSCs) from marmosets holds promise for enhancing the utility of the animal model for biomedical and preclinical studies. However, in spite of the presence of some previous reports on marmoset iPSCs, the reprogramming technology in marmosets is still under development. In particular, the efficacy of RNA-based reprogramming has not been thoroughly investigated. In this study, we attempted RNA-based reprogramming for deriving iPSCs from marmoset fibroblasts. Although we failed to derive iPSC colonies from marmoset fibroblasts by using a conventional RNA-based reprogramming method previously validated in human fibroblasts, we succeeded in deriving colony-forming cells with a modified induction medium supplemented with a novel set of small molecules. Importantly, following one-week culture of the colony-forming cells in conventional embryonic stem cell (ESC) medium, we obtained iPSCs which express endogenous pluripotent markers and show a differentiation potential into all three germ layers. Taken together, our results indicate that RNA-based reprogramming, which is valuable for deriving transgene-free iPSCs, is applicable to marmosets.

Robust and efficient knock-in in embryonic stem cells and early-stage embryos of the common marmoset using the CRISPR-Cas9 system.

Genome editing technology greatly facilitates the genetic modification of various cells and animals. The common marmoset (Callithrix jacchus), a small non-human primate which exhibits high reproductive efficiency, is a widely used animal model in biomedical research. Developing genome editing techniques in the common marmoset will further enhance its utility. Here, we report the successful establishment of a knock-in (KI) method for marmoset embryonic stem cells (ESCs), which is based on the CRISPR-Cas9 system. The use of CRISPR-Cas9, mediated by homologous recombination (HR), enhanced the KI efficiency in marmoset ESCs. Furthermore, we succeeded in performing KI in early-stage marmoset embryos. In the course of the experiments, we found that HR in the marmoset ESCs is innately highly efficient. This suggested that the marmoset possesses a repair mechanism for DNA double-strand breaks. The current study will facilitate the generation of genetically modified marmosets and gene function analysis in the marmoset.

Transplantation of iPS-Derived Tumor Cells with a Homozygous MHC Haplotype Induces GRP94 Antibody Production in MHC-Matched Macaques.

Immune surveillance is a critical component of the antitumor response in vivo, yet the specific components of the immune system involved in this regulatory response remain unclear. In this study, we demonstrate that autoantibodies can mitigate tumor growth in vitro and in vivo We generated two cancer cell lines, embryonal carcinoma and glioblastoma cell lines, from monkey-induced pluripotent stem cells (iPSC) carrying a homozygous haplotype of major histocompatibility complex (MHC, Mafa in Macaca fascicularis). To establish a monkey cancer model, we transplanted these cells into monkeys carrying the matched Mafa haplotype in one of the chromosomes. Neither Mafa-homozygous cancer cell line grew in monkeys carrying the matched Mafa haplotype heterozygously. We detected in the plasma of these monkeys an IgG autoantibody against GRP94, a heat shock protein. Injection of the plasma prevented growth of the tumor cells in immunodeficient mice, whereas plasma IgG depleted of GRP94 IgG exhibited reduced killing activity against cancer cells in vitro These results indicate that humoral immunity, including autoantibodies against GRP94, plays a role in cancer immune surveillance. Cancer Res; 77(21); 6001-10. ©2017 AACR.

Elucidation of developmental patterns of marmoset corpus callosum through a comparative MRI in marmosets, chimpanzees, and humans.

The corpus callosum (CC) is present in all primate brains and is the major white matter tract connecting the cerebral hemispheres for integration of sensory, motor and higher-order cognitive information. The midsagittal area of the CC has frequently been used as a sensitive biomarker of brain development. Although the marmoset has been considered as an alternative non-human primate model for neuroscience research, the developmental patterns of the CC have not been explored. The present longitudinal study of magnetic resonance imaging demonstrated that marmosets show a rapid increase of CC during infancy, followed by a slow increase during the juvenile stage, as observed in chimpanzees and humans. Marmosets also show a tendency toward a greater increase in CC during late infancy and the juvenile stage, as observed in humans, but not in chimpanzees. However, several differences between marmosets and humans were identified. There was a tendency toward a greater maturation of the human CC during early infancy. Furthermore, there was a tendency toward a greater increase during late infancy and the juvenile stage in marmosets, compared to that observed in chimpanzees and humans. These differences in the developmental trajectories of the CC may be related to evolutional changes in social behavior.

Generation of transgenic marmosets expressing genetically encoded calcium indicators.

Chronic monitoring of neuronal activity in the living brain with optical imaging techniques became feasible owing to the continued development of genetically encoded calcium indicators (GECIs). Here we report for the first time the successful generation of transgenic marmosets (Callithrix jacchus), an important nonhuman primate model in neurophysiological research, which were engineered to express the green fluorescent protein (GFP)-based family of GECIs, GCaMP, under control of either the CMV or the hSyn promoter. High titer lentiviral vectors were produced, and injected into embryos collected from donor females. The infected embryos were then transferred to recipient females. Eight transgenic animals were born and shown to have stable and functional GCaMP expression in several different tissues. Germline transmission of the transgene was confirmed in embryos generated from two of the founder transgenic marmosets that reached sexual maturity. These embryos were implanted into six recipient females, three of which became pregnant and are in advanced stages of gestation. We believe these transgenic marmosets will be invaluable non-human primate models in neuroscience, allowing chronic in vivo monitoring of neural activity with functional confocal and multi-photon optical microscopy imaging of intracellular calcium dynamics.

Generation of a Nonhuman Primate Model of Severe Combined Immunodeficiency Using Highly Efficient Genome Editing.

Recent advances in genome editing have facilitated the generation of nonhuman primate (NHP) models, with potential to unmask the complex biology of human disease not revealed by rodent models. However, their broader use is hindered by the challenges associated with generation of adult NHP models as well as the cost of their production. Here, we describe the generation of a marmoset model of severe combined immunodeficiency (SCID). This study optimized zinc-finger nucleases (ZFNs) and transcription activator-like effector nucleases (TALENs) to target interleukin-2 receptor subunit gamma (IL2RG) in pronuclear stage marmoset embryos. Nine of 21 neonates exhibited mutations in the IL2RG gene, concomitant with immunodeficiency, and three neonates have currently survived from 240 days to 1.8 years. Our approach demonstrates highly efficient production of founder NHP with SCID phenotypes, with promises of multiple pre-clinical and translational applications.

Generation of transgenic cynomolgus monkeys that express green fluorescent protein throughout the whole body.

Nonhuman primates are valuable for human disease modelling, because rodents poorly recapitulate some human diseases such as Parkinson's disease and Alzheimer's disease amongst others. Here, we report for the first time, the generation of green fluorescent protein (GFP) transgenic cynomolgus monkeys by lentivirus infection. Our data show that the use of a human cytomegalovirus immediate-early enhancer and chicken beta actin promoter (CAG) directed the ubiquitous expression of the transgene in cynomolgus monkeys. We also found that injection into mature oocytes before fertilization achieved homogenous expression of GFP in each tissue, including the amnion, and fibroblasts, whereas injection into fertilized oocytes generated a transgenic cynomolgus monkey with mosaic GFP expression. Thus, the injection timing was important to create transgenic cynomolgus monkeys that expressed GFP homogenously in each of the various tissues. The strategy established in this work will be useful for the generation of transgenic cynomolgus monkeys for transplantation studies as well as biomedical research.

Lineage-Specific Profiling Delineates the Emergence and Progression of Naive Pluripotency in Mammalian Embryogenesis.

Naive pluripotency is manifest in the preimplantation mammalian embryo. Here we determine transcriptome dynamics of mouse development from the eight-cell stage to postimplantation using lineage-specific RNA sequencing. This method combines high sensitivity and reporter-based fate assignment to acquire the full spectrum of gene expression from discrete embryonic cell types. We define expression modules indicative of developmental state and temporal regulatory patterns marking the establishment and dissolution of naive pluripotency in vivo. Analysis of embryonic stem cells and diapaused embryos reveals near-complete conservation of the core transcriptional circuitry operative in the preimplantation epiblast. Comparison to inner cell masses of marmoset primate blastocysts identifies a similar complement of pluripotency factors but use of alternative signaling pathways. Embryo culture experiments further indicate that marmoset embryos utilize WNT signaling during early lineage segregation, unlike rodents. These findings support a conserved transcription factor foundation for naive pluripotency while revealing species-specific regulatory features of lineage segregation.

Birth of healthy offspring following ICSI in in vitro-matured common marmoset (Callithrix jacchus) oocytes.

Intracytoplasmic sperm injection (ICSI), an important method used to treat male subfertility, is applied in the transgenic technology of sperm-mediated gene transfer. However, no study has described successful generation of offspring using ICSI in the common marmoset, a small non-human primate used as a model for biomedical translational research. In this study, we investigated blastocyst development and the subsequent live offspring stages of marmoset oocytes matured in vitro and fertilized by ICSI. To investigate the optimal timing of performing ICSI, corrected immature oocytes were matured in vitro and ICSI was performed at various time points (1-2 h, 2-4 h, 4-6 h, 6-8 h, and 8-10 h after extrusion of the first polar body (PB)). Matured oocytes were then divided randomly into two groups: one was used for in vitro fertilization (IVF) and the other for ICSI. To investigate in vivo development of embryos followed by ICSI, 6-cell- to 8-cell-stage embryos and blastocysts were nonsurgically transferred into recipient marmosets. Although no significant differences were observed in the fertilization rate of blastocysts among ICSI timing after the first PB extrusion, the blastocyst rate at 1-2 h was lowest among groups at 2-4 h, 4-6 h, 6-8 h, and 8-10 h. Comparing ICSI to IVF, the fertilization rates obtained in ICSI were higher than in IVF (p>0.05). No significant difference was noted in the cleaved blastocyst rate between ICSI and IVF. Following the transfer of 37 ICSI blastocysts, 4 of 20 recipients became pregnant, while with the transfer of 21 6-cell- to 8-cell-stage ICSI embryos, 3 of 8 recipients became pregnant. Four healthy offspring were produced and grew normally. These are the first marmoset offspring produced by ICSI, making it an effective fertilization method for marmosets.