Improving Cell Survival in Injected Embryos Allows Primed Pluripotent Stem Cells to Generate Chimeric Cynomolgus Monkeys

Long-term in vivo chimeric cells tracking in non-human primate

Non-human primates (NHPs) are increasingly used in preclinical trials to test the safety and efficacy of biotechnology therapies. Nonetheless, given the ethical issues and costs associated with this model, it would be highly advantageous to use NHP cellular models in clinical studies. However, developing and maintaining the naïve state of primate pluripotent stem cells (PSCs) remains difficult as does in vivo detection of PSCs, thus limiting biotechnology application in the cynomolgus monkey. Here, we report a chemically defined, xeno-free culture system for culturing and deriving monkey PSCs in vitro. The cells display global gene expression and genome-wide hypomethylation patterns distinct from monkey-primed cells. We also found expression of signaling pathways components that may increase the potential for chimera formation. Crucially for biomedical applications, we were also able to integrate bioluminescent reporter genes into monkey PSCs and track them in chimeric embryos in vivo and in vitro. The engineered cells retained embryonic and extra-embryonic developmental potential. Meanwhile, we generated a chimeric monkey carrying bioluminescent cells, which were able to track chimeric cells for more than 2 years in living animals. Our study could have broad utility in primate stem cell engineering and in utilizing chimeric monkey models for clinical studies.

Dissecting embryonic and extraembryonic lineage crosstalk with stem cell co-culture

Embryogenesis necessitates harmonious coordination between embryonic and extraembryonic tissues. Although stem cells of both embryonic and extraembryonic origins have been generated, they are grown in different culture conditions. In this study, utilizing a unified culture condition that activates the FGF, TGF-β, and WNT pathways, we have successfully derived embryonic stem cells (FTW-ESCs), extraembryonic endoderm stem cells (FTW-XENs), and trophoblast stem cells (FTW-TSCs) from the three foundational tissues of mouse and cynomolgus monkey (Macaca fascicularis) blastocysts. This approach facilitates the co-culture of embryonic and extraembryonic stem cells, revealing a growth inhibition effect exerted by extraembryonic endoderm cells on pluripotent cells, partially through extracellular matrix signaling. Additionally, our cross-species analysis identified both shared and unique transcription factors and pathways regulating FTW-XENs. The embryonic and extraembryonic stem cell co-culture strategy offers promising avenues for developing more faithful embryo models and devising more developmentally pertinent differentiation protocols.

Live birth of chimeric monkey with high contribution from embryonic stem cells

A formal demonstration that mammalian pluripotent stem cells possess preimplantation embryonic cell-like (naive) pluripotency is the generation of chimeric animals through early embryo complementation with homologous cells. Whereas such naive pluripotency has been well demonstrated in rodents, poor chimerism has been achieved in other species including non-human primates due to the inability of the donor cells to match the developmental state of the host embryos. Here, we have systematically tested various culture conditions for establishing monkey naive embryonic stem cells and optimized the procedures for chimeric embryo culture. This approach generated an aborted fetus and a live chimeric monkey with high donor cell contribution. A stringent characterization pipeline demonstrated that donor cells efficiently (up to 90%) incorporated into various tissues (including the gonads and placenta) of the chimeric monkeys. Our results have major implications for the study of primate naive pluripotency and genetic engineering of non-human primates.

Dissecting embryonic and extra-embryonic lineage crosstalk with stem cell co-culture

Faithful embryogenesis requires precise coordination between embryonic and extraembryonic tissues. Although stem cells from embryonic and extraembryonic origins have been generated for several mammalian species(Bogliotti et al., 2018; Choi et al., 2019; Cui et al., 2019; Evans and Kaufman, 1981; Kunath et al., 2005; Li et al., 2008; Martin, 1981; Okae et al., 2018; Tanaka et al., 1998; Thomson et al., 1998; Vandevoort et al., 2007; Vilarino et al., 2020; Yu et al., 2021b; Zhong et al., 2018), they are grown in different culture conditions with diverse media composition, which makes it difficult to study cross-lineage communication. Here, by using the same culture condition that activates FGF, TGF-β and WNT signaling pathways, we derived stable embryonic stem cells (ESCs), extraembryonic endoderm stem cells (XENs) and trophoblast stem cells (TSCs) from all three founding tissues of mouse and cynomolgus monkey blastocysts. This allowed us to establish embryonic and extraembryonic stem cell co-cultures to dissect lineage crosstalk during early mammalian development. Co-cultures of ESCs and XENs uncovered a conserved and previously unrecognized growth inhibition of pluripotent cells by extraembryonic endoderm cells, which is in part mediated through extracellular matrix signaling. Our study unveils a more universal state of stem cell self-renewal stabilized by activation, as opposed to inhibition, of developmental signaling pathways. The embryonic and extraembryonic stem cell co-culture strategy developed here will open new avenues for creating more faithful embryo models and developing more developmentally relevant differentiation protocols.

Delamination of trophoblast-like syncytia from the amniotic ectodermal analogue in human primed embryonic stem cell-based differentiation model

Human primed embryonic stem cells (ESCs) are known to be converted to cells with several trophoblast properties, but it has remained controversial whether this phenomenon represents the inherent differentiation competence of human primed ESCs to trophoblast lineages. In this study, we report that chemical blockage of ACTIVIN/NODAL and FGF signals is sufficient to steer human primed ESCs into GATA3-expressing cells that give rise to placental hormone-producing syncytia analogous to syncytiotrophoblasts of the post-implantation stage of the human embryo. Despite their cytological similarity to syncytiotrophoblasts, these syncytia arise from the non-trophoblastic differentiation trajectory that recapitulates amniogenesis. These results provide insights into the possible extraembryonic differentiation pathway that is unique in primate embryogenesis.

New Animal Models for Understanding FMRP Functions and FXS Pathology

Fragile X encompasses a range of genetic conditions, all of which result as a function of changes within the FMR1 gene and abnormal production and/or expression of the FMR1 gene products. Individuals with Fragile X syndrome (FXS), the most common heritable form of intellectual disability, have a full-mutation sequence (>200 CGG repeats) which brings about transcriptional silencing of FMR1 and loss of FMR protein (FMRP). Despite considerable progress in our understanding of FXS, safe, effective, and reliable treatments that either prevent or reduce the severity of the FXS phenotype have not been approved. While current FXS animal models contribute their own unique understanding to the molecular, cellular, physiological, and behavioral deficits associated with FXS, no single animal model is able to fully recreate the FXS phenotype. This review will describe the status and rationale in the development, validation, and utility of three emerging animal model systems for FXS, namely the nonhuman primate (NHP), Mongolian gerbil, and chicken. These developing animal models will provide a sophisticated resource in which the deficits in complex functions of perception, action, and cognition in the human disorder are accurately reflected and aid in the successful translation of novel therapeutics and interventions to the clinic setting.

High and fluctuating levels of ovarian hormones induce an anxiogenic effect, which can be modulated under stress conditions: Evidence from an assisted reproductive rodent model

Elevated levels of endogenous ovarian hormones are conditions commonly experienced by women undergoing assisted reproductive technologies (ART). Additionally, infertility-associated stress and treatment routines are factors that together may have a highly negative impact on female emotionality, which can be aggravated when several cycles of ART are needed to attempt pregnancy. This study aimed to investigate the effect of high and fluctuating levels of gonadal hormones induced by repeated ovarian stimulation on the stress response in rodents. To mimic the context of ART, female rats were exposed to an unpredictable chronic mild stress (UCMS) paradigm for four weeks. During this time, three cycles of ovarian stimulation (superovulation) (150 IU/Kg of PMSG and 75 IU/Kg of hCG) were applied, with intervals of two estrous cycles between them. The rats were distributed into four groups: Repeated Superovulation/UCMS; Repeated Superovulation/No Stress; Saline/UCMS; and Saline/No Stress. Anxiety-like and depressive-like behaviors were evaluated in a light-dark transition box and by splash test, respectively. Corticosterone, estradiol, progesterone, and biometric parameters were assessed. Data were analyzed using a two-way Generalized Linear Model (GzLM). Our results showed that repeated ovarian stimulation exerts by itself an expressive anxiogenic effect. Surprisingly, when high and fluctuating levels of ovarian hormones were combined with chronic stress, anxiety-like behavior was no longer observed, and a depressive-like state was not detected. Our findings suggest that females subjected to emotional overload induced by repeated ovarian stimulation and chronic stress seem to trigger the elaboration of adaptive coping strategies.

Morphometric analysis of astrocytes in vocal production circuits of common marmoset (Callithrix jacchus)

Astrocytes, the star-shaped glial cells, are the most abundant non-neuronal cell population in the central nervous system. They play a key role in modulating activities of neural networks, including those involved in complex motor behaviors. Common marmosets (Callithrix jacchus), the most vocal non-human primate (NHP), have been used to study the physiology of vocalization and social vocal production. However, the neural circuitry involved in vocal production is not fully understood. In addition, even less is known about the involvement of astrocytes in this circuit. To understand the role, that astrocytes may play in the complex behavior of vocalization, the initial step may be to study their structural properties in the cortical and subcortical regions that are known to be involved in vocalization. Here, in the common marmoset, we identify all astrocytic subtypes seen in other primate's brains, including intralaminar astrocytes. In addition, we reveal detailed structural characteristics of astrocytes and perform morphometric analysis of astrocytes residing in the cortex and midbrain regions that are associated with vocal production. We found that cortical astrocytes in these regions illustrate a higher level of complexity when compared to those in the midbrain. We hypothesize that this complexity that is expressed in cortical astrocytes may reflect their functions to meet the metabolic/structural needs of these regions.

Transcriptional dynamics of transposable elements when converting fibroblast cells of Macaca mulatta to neuroepithelial stem cells

BACKGROUND

Transposable elements (TE) account for more than 50% of human genome. It has been reported that some types of TEs are dynamically regulated in the reprogramming of human cell lines. However, it is largely unknown whether some TEs in Macaca mulatta are also regulated during the reprogramming of cell lines of monkey.

RESULTS

Here, we systematically examined the transcriptional activities of TEs during the conversion of Macaca mulatta fibroblast cells to neuroepithelial stem cells (NESCs). Hundreds of TEs were dynamically regulated during the reprogramming of Macaca mulatta fibroblast cells. Furthermore, 48 Long Terminal Repeats (LTRs), as well as some integrase elements, of Macaca endogenous retrovirus 3 (MacERV3) were transiently activated during the early stages of the conversion process, some of which were further confirmed with PCR experiments. These LTRs were potentially bound by critical transcription factors for reprogramming, such as KLF4 and ETV5.

CONCLUSION

These results suggest that the transcription of TEs are delicately regulated during the reprogramming of Macaca mulatta fibroblast cells. Although the family of ERVs activated during the reprogramming of fibroblast cells in Macaca mulatta is different from those in the reprogramming of human fibroblast cells, our results suggest that the activation of some ERVs is a conserved mechanism in primates for converting fibroblast cells to stem cells.

Apoptosis, G1 Phase Stall, and Premature Differentiation Account for Low Chimeric Competence of Human and Rhesus Monkey Naive Pluripotent Stem Cells

After reprogramming to naive pluripotency, human pluripotent stem cells (PSCs) still exhibit very low ability to make interspecies chimeras. Whether this is because they are inherently devoid of the attributes of chimeric competency or because naive PSCs cannot colonize embryos from distant species remains to be elucidated. Here, we have used different types of mouse, human, and rhesus monkey naive PSCs and analyzed their ability to colonize rabbit and cynomolgus monkey embryos. Mouse embryonic stem cells (ESCs) remained mitotically active and efficiently colonized host embryos. In contrast, primate naive PSCs colonized host embryos with much lower efficiency. Unlike mouse ESCs, they slowed DNA replication after dissociation and, after injection into host embryos, they stalled in the G1 phase and differentiated prematurely, regardless of host species. We conclude that human and non-human primate naive PSCs do not efficiently make chimeras because they are inherently unfit to remain mitotically active during colonization.

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Mouse ESCs are highly effective in colonizing rabbit and non-human primate embryos

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Rhesus monkey and human naive PSCs ineffectively colonize rabbit and monkey embryos

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Most rhesus/human naive PSCs differentiate prematurely upon injection into embryos

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Rhesus monkey PSCs stall in the G1 phase after transfer into rabbit embryos

Chicken Interspecies Chimerism Unveils Human Pluripotency

Human pluripotent stem cells (hPSCs) are commonly kept in a primed state but also able to acquire a more immature naive state under specific conditions in vitro. Acquisition of naive state changes several properties of hPSCs and might affect their contribution to embryonic development in vivo. However, the lack of an appropriate animal test system has made it difficult to assess potential differences for chimera formation between naive and primed hPSCs. Here, we report that the developing chicken embryo is a permissive host for hPSCs, allowing analysis of the pluripotency potential of hPSCs. Transplantation of naive-like and primed hPSCs at matched developmental stages resulted in robust chimerism. Importantly, the ability of naive-like but not of primed hPSCs to form chimera was substantially reduced when injected at non-matched developmental stages. We propose that contribution to chick embryogenesis is an informative and versatile test to identify different pluripotent states of hPSCs.

A single ovarian stimulation, as performed in assisted reproductive technologies, can modulate the anxiety-like behavior and neuronal activation in stress-related brain areas in rats

Infertility affects about 8 to 12% of couples of childbearing age around the world, and is recognized as a global public health issue by the WHO. From a psychosocial perspective, infertile individuals experience intense psychological distress, related to emotional disorders, which have repercussions on marital and social relationships. The symptoms persist even after seeking specialized treatment, such as assisted reproductive technologies (ART). While the stress impact of ART outcome has been comprehensively studied, the role of supraphysiological concentrations of gonadal hormones on stress response, remains to be elucidated. This study aimed to evaluate the effect of a single ovarian stimulation on the stress response in rats. To mimic the context of ART in rodents, female rats were submitted to the superovulation (150 UI/kg of PMSG and 75 UI/kg of hCG) and then to psychogenic stress (restraint stress for 30 min/day, repeated for three days). Anxiety-like behavior was evaluated in the elevated plus-maze, and neuronal activation in the stress-related brain areas assessed by Fos protein immunoreactivity. Corticosterone, estradiol, progesterone and corpora lutea were quantified. Data were analyzed using Generalized Linear Model (GzLM). Our findings indicate anxiolytic-like and protective effects of supraphysiological concentrations of gonadal hormones induced by a single ovarian stimulation on stress response. An activation of hypothalamus-pituitary-adrenal response inhibitory pathways, with participation of the prefrontal cortex, basomedial amygdala, lateral septum, medial preoptic area, dorsomedial and paraventricular hypothalamus, was detected.

Combinatorial metabolism drives the naive to primed pluripotent chromatin landscape

Since epigenetic modifications are a key driver for cellular differentiation, the regulation of these modifications is tightly controlled. Interestingly, recent studies have revealed metabolic regulation for epigenetic modifications in pluripotent cells. As metabolic differences are prominent between naive (pre-implantation) and primed (post-implantation) pluripotent cells, the epigenetic changes regulated by metabolites has become an interesting topic of analysis. In this review we discuss how combinatorial metabolic activities drive the developmental progression through early pluripotent stages.

Chimeras for the twenty-first century

Recent advances in stem cell biology and molecular engineering have improved and simplified the methodology employed to create experimental chimeras, highlighting their value in basic research and broadening the spectrum of potential applications. Experimental chimeras have been used for decades during the generation of murine genetic models, this being especially relevant in developmental and regeneration studies. Indeed, their value for the research and modeling of human diseases was recognized by the 2007 Nobel Prize to Mario Capecchi, Martin Evans, and Oliver Smithies. More recently, their potential application in regenerative medicine has generated a lot of interest, particularly the enticing possibility to generate human organs for transplantation in livestock animals. In this review, we provide an update on interspecific chimeric organogenesis, its possibilities, current limitations, alternatives, and ethical issues.

Human-animal chimeras for autologous organ transplantation: technological advances and future perspectives

Organ transplantation is the most promising curation for end-stage organ disease. However, the donor organ shortage has become a global problem that has limited the development of organ transplantation. Human-animal chimeras provide the ability to produce human organs in other species using autologous stem cells [e.g., induced pluripotent stem cells (iPSCs) or adult stem cells], which would be patient-specific and immune-matched for transplantation. Due to the potential application prospect of interspecies chimeras in basic and translational research, this technology has attracted much interest. This review focuses primarily on technological advances, including options of donor stem cell types and gene editing in donor cells and host animals, in addition to perspectives on human-animal chimeras in clinical and basic research.

Domesticated cynomolgus monkey embryonic stem cells allow the generation of neonatal interspecies chimeric pigs

Blastocyst complementation by pluripotent stem cell (PSC) injection is believed to be the most promising method to generate xenogeneic organs. However, ethical issues prevent the study of human chimeras in the late embryonic stage of development. Primate embryonic stem cells (ESCs), which have similar pluripotency to human ESCs, are a good model for studying interspecies chimerism and organ generation. However, whether primate ESCs can be used in xenogenous grafts remains unclear. In this study, we evaluated the chimeric ability of cynomolgus monkey (Macaca fascicularis) ESCs (cmESCs) in pigs, which are excellent hosts because of their many similarities to humans. We report an optimized culture medium that enhanced the anti-apoptotic ability of cmESCs and improved the development of chimeric embryos, in which domesticated cmESCs (D-ESCs) injected into pig blastocysts differentiated into cells of all three germ layers. In addition, we obtained two neonatal interspecies chimeras, in which we observed tissue-specific D-ESC differentiation. Taken together, the results demonstrate the capability of D-ESCs to integrate and differentiate into functional cells in a porcine model, with a chimeric ratio of 0.001–0.0001 in different neonate tissues. We believe this work will facilitate future developments in xenogeneic organogenesis, bringing us one step closer to producing tissue-specific functional cells and organs in a large animal model through interspecies blastocyst complementation.