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

Marmosets as models of infectious diseases

Animal models of infectious disease often serve a crucial purpose in obtaining licensure of therapeutics and medical countermeasures, particularly in situations where human trials are not feasible, i.e., for those diseases that occur infrequently in the human population. The common marmoset (Callithrix jacchus), a Neotropical new-world (platyrrhines) non-human primate, has gained increasing attention as an animal model for a number of diseases given its small size, availability and evolutionary proximity to humans. This review aims to (i) discuss the pros and cons of the common marmoset as an animal model by providing a brief snapshot of how marmosets are currently utilized in biomedical research, (ii) summarize and evaluate relevant aspects of the marmoset immune system to the study of infectious diseases, (iii) provide a historical backdrop, outlining the significance of infectious diseases and the importance of developing reliable animal models to test novel therapeutics, and (iv) provide a summary of infectious diseases for which a marmoset model exists, followed by an in-depth discussion of the marmoset models of two studied bacterial infectious diseases (tularemia and melioidosis) and one viral infectious disease (viral hepatitis C).

Importance of nuclear localization signal-fused Cas9 in the production of genome-edited mice via embryo electroporation

Previously, to generate genome-edited animals by introducing CRISPR-associated protein 9 (Cas9) into embryos, we developed the Technique for Animal Knockout system by Electroporation (TAKE). Additionally, by fluorescently labeling Cas9, we successfully visualized the Cas9 introduced into the pronuclei of embryos; however, whether Cas9 was introduced directly into the pronuclei by electric pulse or transferred from the cytoplasm by nuclear localization signal (NLS) remained unknown. Herein, we evaluated the localization of Cas9 with (Cas9-NLS) or without NLS (Cas9-noNLS) in mice embryos following electroporation by fusing them with GFP. Furthermore, we visually studied their effects on genome-editing rates in offspring by targeting tyrosinase gene. Fluorescence intensity in pronuclei of Cas9-NLS-electroporated embryos and genome-editing rates of offspring were significantly higher than those of Cas9-noNLS-electroporated embryos. Furthermore, fluorescence in Cas9-NLS-electroporated embryos in which pronuclei had not yet appeared 2.5 h after insemination was observed in the pronuclei of embryos appearing 3.5 h after electroporation. We demonstrated the effective transportation of Cas9 from the cytoplasm to pronuclei by the NLS following TAKE, which resulted in increased genome-editing rates in offspring. The TAKE along with fluorescently labeled nucleases can be used to verify nuclease delivery into individual embryos prior to embryo transfer for efficiently producing genome-edited animals.

An expedition in the jungle of pluripotent stem cells of non-human primates

For nearly three decades, more than 80 embryonic stem cell lines and more than 100 induced pluripotent stem cell lines have been derived from New World monkeys, Old World monkeys, and great apes. In this comprehensive review, we examine these cell lines originating from marmoset, cynomolgus macaque, rhesus macaque, pig-tailed macaque, Japanese macaque, African green monkey, baboon, chimpanzee, bonobo, gorilla, and orangutan. We outline the methodologies implemented for their establishment, the culture protocols for their long-term maintenance, and their basic molecular characterization. Further, we spotlight any cell lines that express fluorescent reporters. Additionally, we compare these cell lines with human pluripotent stem cell lines, and we discuss cell lines reprogrammed into a pluripotent naive state, detailing the processes used to attain this. Last, we present the findings from the application of these cell lines in two emerging fields: intra- and interspecies embryonic chimeras and blastoids.

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.

Common Marmoset Cell Lines and Their Applications in Biomedical Research

Common marmosets (Callithrix jacchus; CMs) are small New World primates widely used in biomedical research. Early stages of such research often include in vitro experiments which require standardized and well-characterized CM cell cultures derived from different tissues. Despite the long history of laboratory work with CMs and high translational potential of such studies, the number of available standardized, well-defined, stable, and validated CM cell lines is still small. While primary cells and immortalized cell lines are mostly used for the studies of infectious diseases, biochemical research, and targeted gene therapy, the main current applications of CM embryonic stem cells and induced pluripotent stem cells are regenerative medicine, stem cell research, generation of transgenic CMs, transplantology, cell therapy, reproductive physiology, oncology, and neurodegenerative diseases. In this review we summarize the data on the main advantages, drawbacks and research applications of CM cell lines published to date including primary cells, immortalized cell lines, lymphoblastoid cell lines, embryonic stem cells, and induced pluripotent stem cells.

Modeling the marmoset brain using embryonic stem cell-derived cerebral assembloids

Studying the non-human primate (NHP) brain is required for the translation of rodent research to humans, but remains a challenge for molecular, cellular, and circuit-level analyses in the NHP brain due to the lack of in vitro NHP brain system. Here, we report an in vitro NHP cerebral model using marmoset (Callithrix jacchus) embryonic stem cell-derived cerebral assembloids (CAs) that recapitulate inhibitory neuron migration and cortical network activity. Cortical organoids (COs) and ganglionic eminence organoids (GEOs) were induced from cjESCs and fused to generate CAs. GEO cells expressing the inhibitory neuron marker LHX6 migrated toward the cortical side of CAs. COs developed their spontaneous neural activity from a synchronized pattern to an unsynchronized pattern as COs matured. CAs containing excitatory and inhibitory neurons showed mature neural activity with an unsynchronized pattern. The CAs represent a powerful in vitro model for studying excitatory and inhibitory neuron interactions, cortical dynamics, and their dysfunction. The marmoset assembloid system will provide an in vitro platform for the NHP neurobiology and facilitate translation into humans in neuroscience research, regenerative medicine, and drug discovery.

Attempts for deriving extended pluripotent stem cells from common marmoset embryonic stem cells

Extended pluripotent stem cells (EPSCs) derived from mice and humans showed an enhanced potential for chimeric formation. By exploiting transcriptomic approaches, we assessed the differences in gene expression profile between extended EPSCs derived from mice and humans, and those newly derived from the common marmoset (marmoset; Callithrix jacchus). Although the marmoset EPSC-like cells displayed a unique colony morphology distinct from murine and human EPSCs, they displayed a pluripotent state akin to embryonic stem cells (ESCs), as confirmed by gene expression and immunocytochemical analyses of pluripotency markers and three-germ-layer differentiation assay. Importantly, the marmoset EPSC-like cells showed interspecies chimeric contribution to mouse embryos, such as E6.5 blastocysts in vitro and E6.5 epiblasts in vivo in mouse development. Also, we discovered that the perturbation of gene expression of the marmoset EPSC-like cells from the original ESCs resembled that of human EPSCs. Taken together, our multiple analyses evaluated the efficacy of the method for the derivation of marmoset EPSCs.

CRISPR/Cas9 system: a reliable and facile genome editing tool in modern biology

Genome engineering has always been a versatile technique in biological research and medicine, with several applications. In the last several years, the discovery of Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)-Cas9 technology has swept the scientific community and revolutionised the speed of modern biology, heralding a new era of disease detection and rapid biotechnology discoveries. It enables successful gene editing by producing targeted double-strand breaks in virtually any organism or cell type. So, this review presents a comprehensive knowledge about the mechanism and structure of Cas9-mediated RNA-guided DNA targeting and cleavage. In addition, genome editing via CRISPR-Cas9 technology in various animals which are being used as models in scientific research including Non-Human Primates Pigs, Dogs, Zebra, fish and Drosophila has been discussed in this review. This review also aims to understand the applications, serious concerns and future perspective of CRISPR/Cas9-mediated genome editing.

CRISPR/Cas9 genome editing to create nonhuman primate models for studying stem cell therapies for HIV infection

Nonhuman primates (NHPs) are well-established basic and translational research models for human immunodeficiency virus (HIV) infections and pathophysiology, hematopoietic stem cell (HSC) transplantation, and assisted reproductive technologies. Recent advances in CRISPR/Cas9 gene editing technologies present opportunities to refine NHP HIV models for investigating genetic factors that affect HIV replication and designing cellular therapies that exploit genetic barriers to HIV infections, including engineering mutations into CCR5 and conferring resistance to HIV/simian immunodeficiency virus (SIV) infections. In this report, we provide an overview of recent advances and challenges in gene editing NHP embryos and discuss the value of genetically engineered animal models for developing novel stem cell-based therapies for curing HIV.

A New Horizon in Reproductive Research with Pluripotent Stem Cells: Successful In Vitro Gametogenesis in Rodents, Its Application to Large Animals, and Future In Vitro Reconstitution of Reproductive Organs Such as “Uteroid” and “Oviductoid”

Simple Summary

Functional gametes, such as oocytes and spermatozoa, have been derived from rodent pluripotent stem cells, which can be applied to large animals and ultimately, to humans. In addition to summarizing these topics, we also review additional approaches for in vitro reconstitution of reproductive organs. This review illustrates intensive past efforts and future challenges on stem cell research for in vitro biogenesis in various mammalian models.

Abstract

Recent success in derivation of functional gametes (oocytes and spermatozoa) from pluripotent stem cells (PSCs) of rodents has made it feasible for future application to large animals including endangered species and to ultimately humans. Here, we summarize backgrounds and recent studies on in vitro gametogenesis from rodent PSCs, and similar approaches using PSCs from large animals, including livestock, nonhuman primates (NHPs), and humans. We also describe additional developing approaches for in vitro reconstitution of reproductive organs, such as the ovary (ovarioid), testis (testisoid), and future challenges in the uterus (uteroid) and oviduct (oviductoid), all of which may be derived from PSCs. Once established, these in vitro systems may serve as a robust platform for elucidating the pathology of infertility-related disorders and ectopic pregnancy, principle of reproduction, and artificial biogenesis. Therefore, these possibilities, especially when using human cells, require consideration of ethical issues, and international agreements and guidelines need to be raised before opening “Pandora’s Box”.

Modeling genetic diseases in nonhuman primates through embryonic and germline modification: Considerations and challenges

Genetic modification of the embryo or germ line of nonhuman primates is envisioned as a method to develop improved models of human disease, yet the promise of such animal models remains unfulfilled. Here, we discuss current methods and their limitations for producing nonhuman primate genetic models that faithfully genocopy and phenocopy human disease. We reflect on how to ethically maximize the translational relevance of such models in the search for new therapeutic strategies to treat human disease.

Homologous Recombination-Enhancing Factors Identified by Comparative Transcriptomic Analyses of Pluripotent Stem Cell of Human and Common Marmoset

A previous study assessing the efficiency of the genome editing technology CRISPR-Cas9 for knock-in gene targeting in common marmoset (marmoset; Callithrix jacchus) embryonic stem cells (ESCs) unexpectedly identified innately enhanced homologous recombination activity in marmoset ESCs. Here, we compared gene expression in marmoset and human pluripotent stem cells using transcriptomic and quantitative PCR analyses and found that five HR-related genes (BRCA1, BRCA2, RAD51C, RAD51D, and RAD51) were upregulated in marmoset cells. A total of four of these upregulated genes enhanced HR efficiency with CRISPR-Cas9 in human pluripotent stem cells. Thus, the present study provides a novel insight into species-specific mechanisms for the choice of DNA repair pathways.

Strengths and challenges of longitudinal non-human primate neuroimaging

Longitudinal non-human primate neuroimaging has the potential to greatly enhance our understanding of primate brain structure and function. Here we describe its specific strengths, compared to both cross-sectional non-human primate neuroimaging and longitudinal human neuroimaging, but also its associated challenges. We elaborate on factors guiding the use of different analytical tools, subject-specific versus age-specific templates for analyses, and issues related to statistical power.

A piggyBac-based platform for genome editing and clonal rhesus macaque iPSC line derivation

Non-human primates (NHPs) are, due to their close phylogenetic relationship to humans, excellent animal models to study clinically relevant mutations. However, the toolbox for the genetic modification of NHPs is less developed than those for other species like mice. Therefore, it is necessary to further develop and refine genome editing approaches in NHPs. NHP pluripotent stem cells (PSCs) share key molecular signatures with the early embryo, which is an important target for genomic modification. Therefore, PSCs are a valuable test system for the validation of embryonic genome editing approaches. In the present study, we made use of the versatility of the piggyBac transposon system for different purposes in the context of NHP stem cell technology and genome editing. These include (1) Robust reprogramming of rhesus macaque fibroblasts to induced pluripotent stem cells (iPSCs); (2) Culture of the iPSCs under feeder-free conditions even after removal of the transgene resulting in transgene-free iPSCs; (3) Development of a CRISPR/Cas-based work-flow to edit the genome of rhesus macaque PSCs with high efficiency; (4) Establishment of a novel protocol for the derivation of gene-edited monoclonal NHP-iPSC lines. These findings facilitate efficient testing of genome editing approaches in NHP-PSC before their in vivo application.

Species variations in tenocytes' response to inflammation require careful selection of animal models for tendon research

For research on tendon injury, many different animal models are utilized; however, the extent to which these species simulate the clinical condition and disease pathophysiology has not yet been critically evaluated. Considering the importance of inflammation in tendon disease, this study compared the cellular and molecular features of inflammation in tenocytes of humans and four common model species (mouse, rat, sheep, and horse). While mouse and rat tenocytes most closely equalled human tenocytes’ low proliferation capacity and the negligible effect of inflammation on proliferation, the wound closure speed of humans was best approximated by rats and horses. The overall gene expression of human tenocytes was most similar to mice under healthy, to horses under transient and to sheep under constant inflammatory conditions. Humans were best matched by mice and horses in their tendon marker and collagen expression, by horses in extracellular matrix remodelling genes, and by rats in inflammatory mediators. As no single animal model perfectly replicates the clinical condition and sufficiently emulates human tenocytes, fit-for-purpose selection of the model species for each specific research question and combination of data from multiple species will be essential to optimize translational predictive validity.

Primate Organoids and Gene-Editing Technologies toward Next-Generation Biomedical Research

The improved ability to organize pluripotent stem cells (PSCs) into 3D structures in vitro has shed light on organoid technology to recapitulate organs and tumors in vivo. Advances in gene-editing technologies, particularly CRISPR-mediated techniques, offer tremendous potential in facilitating organoid research, including the study of development, disease modeling, and personalized medicine. This review discusses how the combination of two novel technologies - organoids and gene editing - not only contributes to revealing molecular events taking place during development and tumorigenesis but also has implications for biobanking, precision medicine, and other diverse biomedical applications.

CRISPeering: Bioengineering the Host Cells through CRISPR-Cas9 Genome Editing System as the Next-Generation of Cell Factories

BACKGROUND

Nowadays, CRISPR-Cas9 genome editing system has become a popular bioengineering-based tool for various applications. Owing to its high-target specificity, efficiency, versatility and simplicity, it has gained attraction as a robust tool for molecular biology research, which unveils the biological functions of unstudied genes. As well as engineering the metabolic pathways. Chinese hamster ovary (CHO) cells, and Escherichia coli, are regarded as the most commonly used expression platforms for industrial-scale production of recombinant proteins. The immergence of CRISPR-Cas9 genome editing system, will promote the current status of expression hosts towards controllable and predictable strains.

OBJECTIVES

Here, I present the current status of expression hosts for biopharmaceuticals production. Some major accomplishments in utilization of CRISPR-Cas9 genome editing tool in different prokaryotic and eukaryotic system will be discussed and more importantly the future directions of this newly arrived technology to make the next-generation cell factories with improved or novel properties will be suggested. Besides, the challenges facing with recent patents on this field is discussed as well.

RESULTS AND CONCLUSION

The CRISPR-Cas9 genome-editing tool has been adopted to be utilized in some major expression platforms. CRISPeering has been successfully employed for genome editing in different prokaryotic and eukaryotic host cells. The immergence of systems metabolic engineering, systems biology and synthetic biology will fortify the current situation of CRISPR-Cas9 genome editing system.

Generation of a common marmoset embryonic stem cell line CMES40-OC harboring a POU5F1 (OCT4)-2A-mCerulean3 knock-in reporter allele

POU class 5 homeobox 1 (POU5F1, also known as OCT4) is critical for maintenance of pluripotency, germ cell fate, reprogramming into a pluripotent state, and early embryogenesis. We generated an embryonic stem cell (ESC) line of the common marmoset (Callithrix jacchus) harboring a heterozygous knock-in allele of OCT4-P2A-mCerulean-T2A-pac. The ESC line (CMES40-OC) will be valuable for investigation of primed/naïve pluripotency and germ cell fate. Homozygous OCT4 knock-in clones were generated but could not be sustained in an undifferentiated state in long-term culture. The OCT4 knock-in system facilitated simultaneous knock-in of a reporter construct at another locus, DDX4 (VASA).

Generation and validation of a common marmoset embryonic stem cell line ActiCre-B1 that ubiquitously expresses a tamoxifen-inducible Cre-driver

We previously reported the efficient targeted introduction of transgenes into the genomic DNA of the common marmoset (Callithrix jacchus) using CRISPR-Cas9. In this study, we generated a marmoset embryonic stem cell (ESC) line that ubiquitously expresses the tamoxifen-inducible Cre-driver ERT2CreERT2. We validated the pluripotency of the ESC line and also successfully demonstrated the temporal control of the Cre-driver in a tamoxifen-dependent manner in the ESCs. This ESC line, named ActiCre-B1, will be a valuable resource for in vitro investigation of phenotypes related to embryonic lethality by targeted knockout of functionally important genes.

Current Status of and Perspectives on the Application of Marmosets in Neurobiology

The common marmoset (Callithrix jacchus), a small New World primate, is receiving substantial attention in the neuroscience and biomedical science fields because its anatomical features, functional and behavioral characteristics, and reproductive features and its amenability to available genetic modification technologies make it an attractive experimental subject. In this review, I outline the progress of marmoset neuroscience research and summarize both the current status (opportunities and limitations) of and the future perspectives on the application of marmosets in neuroscience and disease modeling.

The dawn of non-human primate models for neurodevelopmental disorders

Non-human primates (NHPs) have been proposed as good models for neurodevelopmental disorders due to close similarities to humans in terms of brain structure and cognitive function. The recent development of genome editing technologies has opened new avenues to generate and investigate genetically modified NHPs as models for human disorders. Here, we review the early successes of genetic NHP models for neurodevelopmental disorders and further discuss the technological challenges and opportunities to create next generation NHP models with more sophisticated genetic manipulation and faithful representations of the human genetic mutations. Taken together, the field is now poised to usher in a new era of research using genetically modified NHP models to empower a more rapid translation of basic research and maximize the preclinical potential for biomarker discovery and therapeutic development.

Production of genome-edited mice by visualization of nucleases introduced into the embryos using electroporation

Genome editing technology contributes to the quick and highly efficient production of genetically engineered animals. These animals are helpful in clarifying the mechanism of human disease. Recently, a new electroporation technique (TAKE: Technique for animal knockout system by electroporation) was developed to produce genome-edited animals by introducing nucleases into intact embryos using electroporation instead of the microinjection method. The aim of this study was to increase the efficiency of production of genome-edited animals using the TAKE method. In the conventional protocol, it was difficult to confirm the introduction of nucleases into embryos and energization during operation. Using only embryos that introduced nucleases for embryo transfer, it will lead to increased efficiency in the production of genome-edited animals. This study examined the visualization in the introduction of nucleases into the embryos by using nucleases fluorescent labeled with ATTO-550. The embryos were transfected with Cas9 protein and fluorescent labeled dual guide RNA (mixture with crRNA and tracrRNA with ATTO-550) targeted tyrosinase gene by the TAKE method. All embryos that survived after electroporation showed fluorescence. Of these embryos with fluorescence, 43.7% developed to morphologically normal offspring. In addition, 91.7% of offspring were edited by the tyrosinase gene. This study is the first to demonstrate that the introduction of nucleases into embryos by the TAKE method could be visualized using fluorescent-labeled nucleases. This improved TAKE method can be used to produce genome-edited animals and confirm energization during operation.

Opportunities and limitations of genetically modified nonhuman primate models for neuroscience research

The recently developed new genome-editing technologies, such as the CRISPR/Cas system, have opened the door for generating genetically modified nonhuman primate (NHP) models for basic neuroscience and brain disorders research. The complex circuit formation and experience-dependent refinement of the human brain are very difficult to model in vitro, and thus require use of in vivo whole-animal models. For many neurodevelopmental and psychiatric disorders, abnormal circuit formation and refinement might be at the center of their pathophysiology. Importantly, many of the critical circuits and regional cell populations implicated in higher human cognitive function and in many psychiatric disorders are not present in lower mammalian brains, while these analogous areas are replicated in NHP brains. Indeed, neuropsychiatric disorders represent a tremendous health and economic burden globally. The emerging field of genetically modified NHP models has the potential to transform our study of higher brain function and dramatically facilitate the development of effective treatment for human brain disorders. In this paper, we discuss the importance of developing such models, the infrastructure and training needed to maximize the impact of such models, and ethical standards required for using these models.

Utility of Common Marmoset (Callithrix jacchus) Embryonic Stem Cells in Liver Disease Modeling, Tissue Engineering and Drug Metabolism

The incidence of liver disease is increasing significantly worldwide and, as a result, there is a pressing need to develop new technologies and applications for end-stage liver diseases. For many of them, orthotopic liver transplantation is the only viable therapeutic option. Stem cells that are capable of differentiating into all liver cell types and could closely mimic human liver disease are extremely valuable for disease modeling, tissue regeneration and repair, and for drug metabolism studies to develop novel therapeutic treatments. Despite the extensive research efforts, positive results from rodent models have not translated meaningfully into realistic preclinical models and therapies. The common marmoset Callithrix jacchus has emerged as a viable non-human primate model to study various human diseases because of its distinct features and close physiologic, genetic and metabolic similarities to humans. C. jacchus embryonic stem cells (cjESC) and recently generated cjESC-derived hepatocyte-like cells (cjESC-HLCs) could fill the gaps in disease modeling, liver regeneration and metabolic studies. They are extremely useful for cell therapy to regenerate and repair damaged liver tissues in vivo as they could efficiently engraft into the liver parenchyma. For in vitro studies, they would be advantageous for drug design and metabolism in developing novel drugs and cell-based therapies. Specifically, they express both phase I and II metabolic enzymes that share similar substrate specificities, inhibition and induction characteristics, and drug metabolism as their human counterparts. In addition, cjESCs and cjESC-HLCs are advantageous for investigations on emerging research areas, including blastocyst complementation to generate entire livers, and bioengineering of discarded livers to regenerate whole livers for transplantation.

In Vitro CRISPR/Cas9-Directed Gene Editing to Model LRRK2 G2019S Parkinson's Disease in Common Marmosets

Leucine-rich repeat kinase 2 (LRRK2) G2019S is a relatively common mutation, associated with 1-3% of Parkinson's disease (PD) cases worldwide. G2019S is hypothesized to increase LRRK2 kinase activity. Dopaminergic neurons derived from induced pluripotent stem cells of PD patients carrying LRRK2 G2019S are reported to have several phenotypes compared to wild type controls, including increased activated caspase-3 and reactive oxygen species (ROS), autophagy dysfunction, and simplification of neurites. The common marmoset is envisioned as a candidate nonhuman primate species for comprehensive modeling of genetic mutations. Here, we report our successful use of CRISPR/Cas9 with repair template-mediated homology directed repair to introduce the LRRK2 G2019S mutation, as well as a truncation of the LRRK2 kinase domain, into marmoset embryonic and induced pluripotent stem cells. We found that, similar to humans, marmoset LRRK2 G2019S resulted in elevated kinase activity. Phenotypic evaluation after dopaminergic differentiation demonstrated LRRK2 G2019S-mediated increased intracellular ROS, decreased neuronal viability, and reduced neurite complexity. Importantly, these phenotypes were not observed in clones with LRRK2 truncation. These results demonstrate the feasibility of inducing monogenic mutations in common marmosets and support the use of this species for generating a novel genetic-based model of PD that expresses physiological levels of LRRK2 G2019S.

Generation of a male common marmoset embryonic stem cell line DSY127-BV8VT1 carrying double reporters specific for the germ cell linage using the CRISPR-Cas9 and PiggyBac transposase systems

BLIMP1 (PRDM1) and VASA (DDX4) play pivotal roles in the development of the germ cell linage. Importantly, these genes are specifically expressed in germ cells; BLIMP1 in primordial germ cells (PGCs) to early-stage gonocytes, and VASA in migration-stage PGCs to mature gametes. The high reproductive efficiency of common marmosets (marmosets; Callithrix jacchus) makes them advantageous for use in germ cell research. We herein report the generation of a male marmoset embryonic stem cell (ESC) line harboring BLIMP1 and DDX4 double reporters. This ESC line will be a useful tool for investigating male gametogenesis in non-human primates.

CRISPR/Cas9-mediated genome editing in nonhuman primates

Owing to their high similarity to humans, non-human primates (NHPs) provide an exceedingly suitable model for the study of human disease. In this Review, we summarize the history of transgenic NHP models and the progress of CRISPR/Cas9-mediated genome editing in NHPs, from the first proof-of-principle green fluorescent protein-expressing monkeys to sophisticated NHP models of human neurodegenerative disease that accurately phenocopy several complex disease features. We discuss not only the breakthroughs and advantages, but also the potential shortcomings of the application of the CRISPR/Cas9 system to NHPs that have emerged from the expanded understanding of this technology in recent years. Although off-target and mosaic mutations are the main concerns in CRISPR/Cas9-mediated NHP modeling, recent progress in genome editing techniques make it likely that these technical limitations will be overcome soon, bringing excellent prospects to human disease studies.

Evaluating the efficacy of small molecules for neural differentiation of common marmoset ESCs and iPSCs

The common marmoset (marmoset; Callithrix jacchus) harbors various desired features as a non-human primate (NHP) model for neuroscience research. Recently, efforts have been made to induce neural cells in vitro from marmoset pluripotent stem cells (PSCs), including embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs), which are characterized by their capacity to differentiate into all cell types from the three germ layers. Successful generation of marmoset neural cells is not only invaluable for understanding neural development and for modeling neurodegenerative and psychiatric disorders, but is also necessary for the phenotypic screening of genetically-modified marmosets. However, differences in the differentiation propensity among PSC lines hamper the applicability and the reproducibility of differentiation methods. To overcome this limitation, we evaluated the efficacy of small molecules for neural differentiation of marmoset ESCs (cjESCs) and iPSCs using multiple differentiation methods. By immunochemical and transcriptomic analyses, we confirmed that our methods using the small molecules are efficient for various differentiation protocols by either enhancing the yield of a mixture of neural cells including both neurons and glial cells, or a pure population of neurons. Collectively, our findings optimized in vitro neural differentiation methods for marmoset PSCs, which would ultimately help enhance the utility of the animal model in neuroscience.

A versatile toolbox for knock-in gene targeting based on the Multisite Gateway technology

Knock-in (KI) gene targeting can be employed for a wide range of applications in stem cell research. However, vectors for KI require multiple complicated processes for construction, including multiple times of digestion/ligation steps and extensive restriction mapping, which has imposed limitations for the robust applicability of KI gene targeting. To circumvent this issue, here we introduce versatile and systematic methods for generating KI vectors by molecular cloning. In this approach, we employed the Multisite Gateway technology, an efficient in vitro DNA recombination system using proprietary sequences and enzymes. KI vector construction exploiting these methods requires only efficient steps, such as PCR and recombination, enabling robust KI gene targeting. We show that combinatorial usage of the KI vectors generated using this method and site-specific nucleases enabled the precise integration of fluorescent protein genes in multiple loci of human and common marmoset (marmoset; Callithrix jacchus) pluripotent stem cells. The methods described here will facilitate the usage of KI technology and ultimately help to accelerate stem cell research.