The molecular evolution of spermatogenesis across mammals.

The testis produces gametes through spermatogenesis and evolves rapidly at both the morphological and molecular level in mammals1-6, probably owing to the evolutionary pressure on males to be reproductively successful7. However, the molecular evolution of individual spermatogenic cell types across mammals remains largely uncharacterized. Here we report evolutionary analyses of single-nucleus transcriptome data for testes from 11 species that cover the three main mammalian lineages (eutherians, marsupials and monotremes) and birds (the evolutionary outgroup), and include seven primates. We find that the rapid evolution of the testis was driven by accelerated fixation rates of gene expression changes, amino acid substitutions and new genes in late spermatogenic stages, probably facilitated by reduced pleiotropic constraints, haploid selection and transcriptionally permissive chromatin. We identify temporal expression changes of individual genes across species and conserved expression programs controlling ancestral spermatogenic processes. Genes predominantly expressed in spermatogonia (germ cells fuelling spermatogenesis) and Sertoli (somatic support) cells accumulated on X chromosomes during evolution, presumably owing to male-beneficial selective forces. Further work identified transcriptomal differences between X- and Y-bearing spermatids and uncovered that meiotic sex-chromosome inactivation (MSCI) also occurs in monotremes and hence is common to mammalian sex-chromosome systems. Thus, the mechanism of meiotic silencing of unsynapsed chromatin, which underlies MSCI, is an ancestral mammalian feature. Our study illuminates the molecular evolution of spermatogenesis and associated selective forces, and provides a resource for investigating the biology of the testis across mammals.

Spatial profiling of early primate gastrulation in utero.

Gastrulation controls the emergence of cellular diversity and axis patterning in the early embryo. In mammals, this transformation is orchestrated by dynamic signalling centres at the interface of embryonic and extraembryonic tissues1-3. Elucidating the molecular framework of axis formation in vivo is fundamental for our understanding of human development4-6 and to advance stem-cell-based regenerative approaches7. Here we illuminate early gastrulation of marmoset embryos in utero using spatial transcriptomics and stem-cell-based embryo models. Gaussian process regression-based 3D transcriptomes delineate the emergence of the anterior visceral endoderm, which is hallmarked by conserved (HHEX, LEFTY2, LHX1) and primate-specific (POSTN, SDC4, FZD5) factors. WNT signalling spatially coordinates the formation of the primitive streak in the embryonic disc and is counteracted by SFRP1 and SFRP2 to sustain pluripotency in the anterior domain. Amnion specification occurs at the boundaries of the embryonic disc through ID1, ID2 and ID3 in response to BMP signalling, providing a developmental rationale for amnion differentiation of primate pluripotent stem cells (PSCs). Spatial identity mapping demonstrates that primed marmoset PSCs exhibit the highest similarity to the anterior embryonic disc, whereas naive PSCs resemble the preimplantation epiblast. Our 3D transcriptome models reveal the molecular code of lineage specification in the primate embryo and provide an in vivo reference to decipher human development.

Gene expression across mammalian organ development.

The evolution of gene expression in mammalian organ development remains largely uncharacterized. Here we report the transcriptomes of seven organs (cerebrum, cerebellum, heart, kidney, liver, ovary and testis) across developmental time points from early organogenesis to adulthood for human, rhesus macaque, mouse, rat, rabbit, opossum and chicken. Comparisons of gene expression patterns identified correspondences of developmental stages across species, and differences in the timing of key events during the development of the gonads. We found that the breadth of gene expression and the extent of purifying selection gradually decrease during development, whereas the amount of positive selection and expression of new genes increase. We identified differences in the temporal trajectories of expression of individual genes across species, with brain tissues showing the smallest percentage of trajectory changes, and the liver and testis showing the largest. Our work provides a resource of developmental transcriptomes of seven organs across seven species, and comparative analyses that characterize the development and evolution of mammalian organs.

The Efficiency of In Vitro Differentiation of Primate iPSCs into Cardiomyocytes Depending on Their Cell Seeding Density and Cell Line Specificity.

A thorough characterization of induced pluripotent stem cells (iPSCs) used with in vitro models or therapeutics is essential. Even iPSCs derived from a single donor can exhibit variability within and between cell lines, which can lead to heterogeneity in results and hinder the promising future of cell replacement therapies. In this study, the cell seeding density of human and rhesus monkey iPSCs was tested to maximize the cell line-specific yield of the generated cardiomyocytes. We found that, despite using the same iPSC generation and differentiation protocols, the cell seeding density for the cell line-specific best differentiation efficiency could differ by a factor of four for the four cell lines used here. In addition, the cell lines showed differences in the range of cell seeding densities that they could tolerate without the severe loss of differentiation efficiency. Overall, our data show that the cell seeding density is a critical parameter for the differentiation inefficiency of primate iPSCs to cardiomyocytes and that iPSCs generated with the same episomal approach still exhibit considerable heterogeneity. Therefore, individual characterization of iPSC lines is required, and functional comparability with in vivo processes must be ensured to warrant the translatability of in vitro research with iPSCs.

The endothelial-enriched lncRNA LINC00607 mediates angiogenic function.

Long non-coding RNAs (lncRNAs) can act as regulatory RNAs which, by altering the expression of target genes, impact on the cellular phenotype and cardiovascular disease development. Endothelial lncRNAs and their vascular functions are largely undefined. Deep RNA-Seq and FANTOM5 CAGE analysis revealed the lncRNA LINC00607 to be highly enriched in human endothelial cells. LINC00607 was induced in response to hypoxia, arteriosclerosis regression in non-human primates, post-atherosclerotic cultured endothelial cells from patients and also in response to propranolol used to induce regression of human arteriovenous malformations. siRNA knockdown or CRISPR/Cas9 knockout of LINC00607 attenuated VEGF-A-induced angiogenic sprouting. LINC00607 knockout in endothelial cells also integrated less into newly formed vascular networks in an in vivo assay in SCID mice. Overexpression of LINC00607 in CRISPR knockout cells restored normal endothelial function. RNA- and ATAC-Seq after LINC00607 knockout revealed changes in the transcription of endothelial gene sets linked to the endothelial phenotype and in chromatin accessibility around ERG-binding sites. Mechanistically, LINC00607 interacted with the SWI/SNF chromatin remodeling protein BRG1. CRISPR/Cas9-mediated knockout of BRG1 in HUVEC followed by CUT&RUN revealed that BRG1 is required to secure a stable chromatin state, mainly on ERG-binding sites. In conclusion, LINC00607 is an endothelial-enriched lncRNA that maintains ERG target gene transcription by interacting with the chromatin remodeler BRG1 to ultimately mediate angiogenesis.

SIRT1 Expression and Regulation in the Primate Testis.

The epigenetic mechanisms controlling germ cell development and differentiation are still not well understood. Sirtuin-1 (SIRT1) is a nicotinamide adenosine dinucleotide (NAD)-dependent histone deacetylase and belongs to the sirtuin family of deacetylases. It catalyzes the removal of acetyl groups from a number of protein substrates. Some studies reported a role of SIRT1 in the central and peripheral regulation of reproduction in various non-primate species. However, testicular SIRT1 expression and its possible role in the testis have not been analyzed in primates. Here, we document expression of SIRT1 in testes of different primates and some non-primate species. SIRT1 is expressed mainly in the cells of seminiferous tubules, particularly in germ cells. The majority of SIRT1-positive germ cells were in the meiotic and postmeiotic phase of differentiation. However, SIRT1 expression was also observed in selected premeiotic germ cells, i.e., spermatogonia. SIRT1 co-localized in spermatogonia with irisin, an endocrine factor specifically expressed in primate spermatogonia. In marmoset testicular explant cultures, SIRT1 transcript levels are upregulated by the addition of irisin as compared to untreated controls explants. Rhesus macaques are seasonal breeders with high testicular activity in winter and low testicular activity in summer. Of note, SIRT1 mRNA and SIRT1 protein expression are changed between nonbreeding (low spermatogenesis) and breeding (high spermatogenesis) season. Our data suggest that SIRT1 is a relevant factor for the regulation of spermatogenesis in primates. Further mechanistic studies are required to better understand the role of SIRT1 during spermatogenesis.

A translational cellular model for the study of peritubular cells of the testis.

Testicular peritubular cells (TPCs) are smooth muscle-like cells, which form a compartment surrounding the seminiferous tubules. Previous studies employing isolated human testicular peritubular cells (HTPCs) indicated that their roles in the testis go beyond sperm transport and include paracrine and immunological contributions. Peritubular cells from a non-human primate (MKTPCs), the common marmoset monkey, Callithrix jacchus, share a high degree of homology with HTPCs. However, like their human counterparts these cells age in vitro and replicative senescence limits in-depth functional or mechanistic studies. Therefore, a stable cellular model was established. MKTPCs of a young adult animal were immortalized by piggyBac transposition of human telomerase (hTERT), that is, without the expression of viral oncogenes. Immortalized MKTPCs (iMKTPCs) grew without discernable changes for more than 50 passages. An initial characterization revealed typical genes expressed by peritubular cells (androgen receptor (AR), smooth-muscle actin (ACTA2), calponin (CNN1)). A proteome analysis of the primary MKTPCs and the derived immortalized cell line confirmed that the cells almost completely retained their phenotype. To test whether they respond in a similar way as HTPCs, iMKTPCs were challenged with forskolin (FSK) and ATP. As HTPCs, they showed increased expression level of the StAR protein (StAR) after FSK stimulation, indicating steroidogenic capacity. ATP increased the expression of pro-inflammatory factors (e.g. IL1B; CCL7), as it is the case in HTPCs. Finally, we confirmed that iMKTPCs can efficiently be transfected. Therefore, they represent a highly relevant translational model, which allows mechanistic studies for further exploration of the roles of testicular peritubular cells.

Hydroxysteroid (17ß) dehydrogenase 1 expressed by Sertoli cells contributes to steroid synthesis and is required for male fertility.

The pituitary gonadotrophins and testosterone are the main hormonal regulators of spermatogenesis, but estradiol is also known to play a role in the process. The hormonal responses in the testis are partially mediated by somatic Sertoli cells that provide nutritional and physical support for differentiating male germ cells. Hydroxysteroid (17ß) dehydrogenase 1 (HSD17B1) is a steroidogenic enzyme that especially catalyzes the conversion of low potent 17keto-steroids to highly potent 17ß-hydroxysteroids. In this study, we show that Hsd17b1 is highly expressed in Sertoli cells of fetal and newborn mice, and HSD17B1 knockout males present with disrupted spermatogenesis with major defects, particularly in the head shape of elongating spermatids. The cell-cell junctions between Sertoli cells and germ cells were disrupted in the HSD17B1 knockout mice. This resulted in complications in the orientation of elongating spermatids in the seminiferous epithelium, reduced sperm production, and morphologically abnormal spermatozoa. We also showed that the Sertoli cell-expressed HSD17B1 participates in testicular steroid synthesis, evidenced by a compensatory up-regulation of HSD17B3 in Leydig cells. These results revealed a novel role for HSD17B1 in the control of spermatogenesis and male fertility, and that Sertoli cells significantly contribute to steroid synthesis in the testis.-Hakkarainen, J., Zhang, F.-P., Jokela, H., Mayerhofer, A., Behr, R., Cisneros-Montalvo, S., Nurmio, M., Toppari, J., Ohlsson, C., Kotaja, N., Sipilä, P., Poutanen, M. Hydroxysteroid (17ß) dehydrogenase 1 expressed by Sertoli cells contributes to steroid synthesis and is required for male fertility.

NLRP3 in somatic non-immune cells of rodent and primate testes.

NLRP3 is part of the NLRP3 inflammasome and a global sensor of cellular damage. It was recently discovered in rodent Sertoli cells. We investigated NLRP3 in mouse, human and non-human primate (marmoset and rhesus macaque) testes, employing immunohistochemistry. Sertoli cells of all species expressed NLRP3, and the expression preceded puberty. In addition, peritubular cells of the adult human testes expressed NLRP3. NLRP3 and associated genes (PYCARD, CASP1, IL1B) were also found in isolated human testicular peritubular cells and the mouse Sertoli cell line TM4. Male infertility due to impairments of spermatogenesis may be related to sterile inflammatory events. We observed that the expression of NLRP3 was altered in the testes of patients suffering from mixed atrophy syndrome, in which tubules with impairments of spermatogenesis showed prominent NLRP3 staining. In order to explore a possible role of NLRP3 in male infertility, associated with sterile testicular inflammation, we studied a mouse model of male infertility. These human aromatase-expressing transgenic mice (AROM+) develop testicular inflammation and impaired spermatogenesis during aging, and the present data show that this is associated with strikingly elevated Nlrp3 expression in the testes compared to WT controls. Interference by aromatase inhibitor treatment significantly reduced increased Nlrp3 levels. Thus, throughout species NLRP3 is expressed by somatic cells of the testis, which are involved in testicular immune surveillance. We conclude that NLRP3 may be a novel player in testicular immune regulation.

On the Enigma of the Human Neurenteric Canal.

Existence and biomedical relevance of the neurenteric canal, a transient midline structure during early neurulation in the human embryo, have been controversially discussed for more than a century by embryologists and clinicians alike. In this study, the authors address the long-standing enigma by high-resolution histology and three-dimensional reconstruction using new and historic histological sections of 5 human 17- to 21-day-old embryos and of 2 marmoset monkey embryos of the species Callithrix jacchus at corresponding stages. The neurenteric canal presents itself as the classical vertical connection between the amniotic cavity and the yolk sac cavity and is lined (a) craniolaterally by a horseshoe-shaped "hinge of involuting notochordal cells" within Hensen's node and (b) caudally by the receding primitive streak epiblast dorsally and by notochordal plate epithelium ventrally, the latter of which covered the (longitudinal) notochordal canal on its ventral side at the preceding stage. Furthermore, asymmetric parachordal nodal expression in Callithrix and morphological asymmetries within the nodes of the other specimens suggest an early non-cilium-dependent left-right symmetry breaking mode previously postulated for other mammals. We conclude that structure and position of the mammalian neurenteric canal support the notion of its homology with the reptilian blastopore as a whole and with a dorsal segment of the blastopore in amphibia. These new features of the neurenteric canal may further clarify the aetiology of foetal malformations such as junctional neurulation defects, neuroendodermal cysts, and the split notochord syndrome.

Importance of the pluripotency factor LIN28 in the mammalian nucleolus during early embryonic development.

The maternal nucleolus is required for proper activation of the embryonic genome (EGA) and early embryonic development. Nucleologenesis is characterized by the transformation of a nucleolar precursor body (NPB) to a mature nucleolus during preimplantation development. However, the function of NPBs and the involved molecular factors are unknown. We uncover a novel role for the pluripotency factor LIN28, the biological significance of which was previously demonstrated in the reprogramming of human somatic cells to induced pluripotent stem (iPS) cells. Here, we show that LIN28 accumulates at the NPB and the mature nucleolus in mouse preimplantation embryos and embryonic stem cells (ESCs), where it colocalizes with the nucleolar marker B23 (nucleophosmin 1). LIN28 has nucleolar localization in non-human primate (NHP) preimplantation embryos, but is cytoplasmic in NHP ESCs. Lin28 transcripts show a striking decline before mouse EGA, whereas LIN28 protein localizes to NPBs at the time of EGA. Following knockdown with a Lin28 morpholino, the majority of embryos arrest between the 2- and 4-cell stages and never develop to morula or blastocyst. Lin28 morpholino-injected embryos arrested at the 2-cell stage were not enriched with nucleophosmin at presumptive NPB sites, indicating that functional NPBs were not assembled. Based on these results, we propose that LIN28 is an essential factor of nucleologenesis during early embryonic development.

Expression of sperm-specific protamines impairs bacterial and eukaryotic cell proliferation.

Protamines are the predominant nuclear proteins in testicular spermatids and ejaculated spermatozoa. During spermiogenesis, protamine-DNA interaction induces a higher-order chromatin packaging which finally results in a complete transcriptional stop in elongating spermatids. Although numerous studies investigated the role of protamines in male fertility, to date, no study is available that investigates protamine function, particularly transcriptional silencing, in non-germ cells. Transcriptional stop due to the high binding affinity of arginine-rich protamines to the negatively charged DNA backbone, however, may be induced in somatic cells and may result in suppressing cell division in tumor cells. In the present study, we therefore analyzed whether a protamine-mediated chromatin condensation in somatic cancer cell lines can stop gene expression and arrest cancer cell proliferation. In contrast to terminally differentiated sperm, cancer cells represent immortalized cells that have modulated natural mechanisms for the regulation of apoptosis and cell proliferation. We expressed human protamines in two fast-growing cell systems, E. coli and HeLa cells. In both cases, protamine expression significantly attenuated cell proliferation when compared with control cells. To our knowledge, this is the first study that demonstrates a stop of cell proliferation in both E. coli and HeLa cells by protamine expression. Follow-up studies on the molecular effect of protamines on proliferative cells may, in the future, open new avenues to investigate effective and specific treatments of cancer cells.

Non-viral reprogramming of fibroblasts into induced pluripotent stem cells by Sleeping Beauty and piggyBac transposons.

The generation of induced pluripotent stem (iPS) cells represents a promising approach for innovative cell therapies. The original method requires viral transduction of several reprogramming factors, which may be associated with an increased risk of tumorigenicity. Transposition of reprogramming cassettes represents a recent alternative to viral approaches. Since binary transposons can be produced as common plasmids they provide a safe and cost-efficient alternative to viral delivery methods. Here, we compared the efficiency of two different transposon systems, Sleeping Beauty (SB) and piggyBac (PB), for the generation of murine iPS. Murine fibroblasts derived from an inbred BL/6 mouse line carrying a pluripotency reporter, Oct4-EGFP, and fibroblasts derived from outbred NMRI mice were employed for reprogramming. Both transposon systems resulted in the successful isolation of murine iPS cell lines. The reduction of the core reprogramming factors to omit the proto-oncogene c-Myc was compatible with iPS cell line derivation, albeit with reduced reprogramming efficiencies. The transposon-derived iPS cells featured typical hallmarks of pluripotency, including teratoma growth in immunodeficient mice. Thus SB and PB transposons represent a promising non-viral approach for iPS cell derivation.

Separation of somatic and germ cells is required to establish primate spermatogonial cultures.

STUDY QUESTION: Can primate spermatogonial cultures be optimized by application of separation steps and well defined culture conditions? SUMMARY ANSWER: We identified the cell fraction which provides the best source for primate spermatogonia when prolonged culture is desired. WHAT IS KNOWN ALREADY: Man and marmoset show similar characteristics in regard to germ cell development and function. Several protocols for isolation and culture of human testis-derived germline stem cells have been described. Subsequent analysis revealed doubts on the germline origin of these cells and characterized them as mesenchymal stem cells or fibroblasts. Studies using marmosets as preclinical model confirmed that the published isolation protocols did not lead to propagation of germline cells. STUDY DESIGN, SIZE, DURATION: Testicular cells derived from nine adult marmoset monkeys (Callithrix jacchus) were cultured for 1, 3, 6 and 11 days and consecutively analyzed for the presence of spermatogonia, differentiating germ cells and testicular somatic cells. PARTICIPANTS/MATERIALS, SETTING, METHODS: Testicular tissue of nine adult marmoset monkeys was enzymatically dissociated and subjected to two different cell culture approaches. In the first approach all cells were kept in the same dish (non-separate culture, n = 5). In the second approach the supernatant cells were transferred into a new dish 24 h after seeding and subsequently supernatant and attached cells were cultured separately (separate culture, n = 4). Real-time quantitative PCR and immunofluorescence were used to analyze the expression of reliable germ cell and somatic markers throughout the culture period. Germ cell transplantation assays and subsequent wholemount analyses were performed to functionally evaluate the colonization of spermatogonial cells. MAIN RESULTS AND THE ROLE OF CHANCE: This is the first report revealing an efficient isolation and culture of putative marmoset spermatogonial stem cells with colonization ability. Our results indicate that a separation of spermatogonia from testicular somatic cells is a crucial step during cell preparation. We identified the overgrowth of more rapidly expanding somatic cells to be a major problem when establishing spermatogonial cultures. Initiating germ cell cultures from the supernatant and maintaining germ cells in suspension cultures minimized the somatic cell contamination and provided enriched germ cell fractions which displayed after 11 days of culture a significantly higher expression of germ cell markers genes (DDX-4, MAGE A-4; P < 0.05) compared with separately cultured attached cells. Additionally, germ cell transplantation experiments demonstrated a significantly higher absolute number of cells with colonization ability (P < 0.001) in supernatant cells after 11 days of separate culture. LIMITATIONS, REASONS FOR CAUTION: This study presents a relevant aspect for the successful setup of spermatogonial cultures but provides limited data regarding the question of whether the long-term maintenance of spermatogonia can be achieved. Transfer of these preclinical data to man may require modifications of the protocol. WIDER IMPLICATIONS OF THE FINDINGS: Spermatogonial cultures from rodents have become important and innovative tools for basic and applied research in reproductive biology and veterinary medicine. It is expected that spermatogonia-based strategies will be transformed into clinical applications for the treatment of male infertility. Our data in the marmoset monkey may be highly relevant to establish spermatogonial cultures of human testes. STUDY FUNDING/COMPETING INTERESTS: Funding was provided by the DFG-Research Unit FOR 1041 Germ Cell Potential (SCHL394/11-2) and by the Graduate Program Cell Dynamics and Disease (CEDAD) together with the International Max Planck Research School - Molecular Biomedicine (IMPRS-MBM). The authors declare that there is no conflict of interest. TRIAL REGISTRATION NUMBER: Not applicable.

In vitro matured oocytes have a higher developmental potential than in vivo matured oocytes after hormonal ovarian stimulation in Callithrix jacchus.

BACKGROUND: The common marmoset, Callithrix jacchus, is an invaluable model in biomedical research. Its use includes genetic engineering applications, which require manipulations of oocytes and production of embryos in vitro. To maximize the recovery of oocytes suitable for embryo production and to fulfil the requirements of the 3R principles to the highest degree possible, optimization of ovarian stimulation protocols is crucial. Here, we compared the efficacy of two hormonal ovarian stimulation approaches: 1) stimulation of follicular growth with hFSH followed by triggering of oocyte maturation with hCG (FSH + hCG) and 2) stimulation with hFSH only (FSH-priming). METHODS: In total, 14 female marmosets were used as oocyte donors in this study. Each animal underwent up to four surgical interventions, with the first three performed as ovum pick-up (OPU) procedures and the last one being an ovariohysterectomy (OvH). In total, 20 experiments were carried out with FSH + hCG stimulation and 18 with FSH-priming. Efficacy of each stimulation protocol was assessed through in vitro maturation (IVM), in vitro fertilization (IVF) and embryo production rates. RESULTS: Each study group consisted of two subgroups: the in vivo matured oocytes and the oocytes that underwent IVM. Surprisingly, in the absence of hCG triggering some of the oocytes recovered were at the MII stage, moreover, their number was not significantly lower compared to FSH + hCG stimulation (2.8 vs. 3.9, respectively (ns)). While the IVM and IVF rates did not differ between the two stimulation groups, the IVF rates of in vivo matured oocytes were significantly lower compared to in vitro matured ones in both FSH-priming and FSH + hCG groups. In total, 1.7 eight-cell embryos/experiment (OPU) and 2.1 eight-cell embryos/experiment (OvH) were obtained after FSH + hCG stimulation vs. 1.8 eight-cell embryos/experiment (OPU) and 5.0 eight-cell embryos/experiment (OvH) following FSH-priming. These numbers include embryos obtained from both in vivo and in vitro matured oocytes. CONCLUSION: A significantly lower developmental competence of the in vivo matured oocytes renders triggering of the in vivo maturation with hCG as a part of the currently used FSH-stimulation protocol unnecessary. In actual numbers, between 1 and 7 blastocysts were obtained following each FSH-priming. In the absence of further studies, FSH-priming appears superior to FSH + hCG stimulation in the common marmoset under current experimental settings.

Generation of marmoset primordial germ cell-like cells under chemically defined conditions.

Primordial germ cells (PGCs) are the embryonic precursors of sperm and oocytes, which transmit genetic/epigenetic information across generations. Mouse PGC and subsequent gamete development can be fully reconstituted in vitro, opening up new avenues for germ cell studies in biomedical research. However, PGCs show molecular differences between rodents and humans. Therefore, to establish an in vitro system that is closely related to humans, we studied PGC development in vivo and in vitro in the common marmoset monkey Callithrix jacchus (cj). Gonadal cjPGCs at embryonic day 74 express SOX17, AP2Ɣ, BLIMP1, NANOG, and OCT4A, which is reminiscent of human PGCs. We established transgene-free induced pluripotent stem cell (cjiPSC) lines from foetal and postnatal fibroblasts. These cjiPSCs, cultured in defined and feeder-free conditions, can be differentiated into precursors of mesendoderm and subsequently into cjPGC-like cells (cjPGCLCs) with a transcriptome similar to human PGCs/PGCLCs. Our results not only pave the way for studying PGC development in a non-human primate in vitro under experimentally controlled conditions, but also provide the opportunity to derive functional marmoset gametes in future studies.

Transgene-Free Cynomolgus Monkey iPSCs Generated under Chemically Defined Conditions.

Non-human primates (NHPs) are pivotal animal models for translating novel cell replacement therapies into clinical applications, including validating the safety and efficacy of induced pluripotent stem cell (iPSC)-derived products. Preclinical development and the testing of cell-based therapies ideally comprise xenogeneic (human stem cells into NHPs) and allogenic (NHP stem cells into NHPs) transplantation studies. For the allogeneic approach, it is necessary to generate NHP-iPSCs with generally equivalent quality to the human counterparts that will be used later on in patients. Here, we report the generation and characterization of transgene- and feeder-free cynomolgus monkey (Macaca fascicularis) iPSCs (Cyno-iPSCs). These novel cell lines have been generated according to a previously developed protocol for the generation of rhesus macaque, baboon, and human iPSC lines. Beyond their generation, we demonstrate the potential of the novel Cyno-iPSCs to differentiate into two clinically relevant cell types, i.e., cardiomyocytes and neurons. Overall, we provide a resource of novel iPSCs from the most frequently used NHP species in the regulatory testing of biologics and classical pharmaceutics to expand our panel of iPSC lines from NHP species with high relevance in preclinical testing and translational research.

Age-related and species-specific methylation changes in the protein-coding marmoset sperm epigenome.

The sperm epigenome is thought to affect the developmental programming of the resulting embryo, influencing health and disease in later life. Age-related methylation changes in the sperm of old fathers may mediate the increased risks for reproductive and offspring medical problems. The impact of paternal age on sperm methylation has been extensively studied in humans and, to a lesser extent, in rodents and cattle. Here, we performed a comparative analysis of paternal age effects on protein-coding genes in the human and marmoset sperm methylomes. The marmoset has gained growing importance as a non-human primate model of aging and age-related diseases. Using reduced representation bisulfite sequencing, we identified age-related differentially methylated transcription start site (ageTSS) regions in 204 marmoset and 27 human genes. The direction of methylation changes was the opposite, increasing with age in marmosets and decreasing in humans. None of the identified ageTSS was differentially methylated in both species. Although the average methylation levels of all TSS regions were highly correlated between marmosets and humans, with the majority of TSS being hypomethylated in sperm, more than 300 protein-coding genes were endowed with species-specifically (hypo)methylated TSS. Several genes of the glycosphingolipid (GSL) biosynthesis pathway, which plays a role in embryonic stem cell differentiation and regulation of development, were hypomethylated (<5%) in human and fully methylated (>95%) in marmoset sperm. The expression levels and patterns of defined sets of GSL genes differed considerably between human and marmoset pre-implantation embryo stages and blastocyst tissues, respectively.

Marmoset and human trophoblast stem cells differ in signaling requirements and recapitulate divergent modes of trophoblast invasion.

Early human trophoblast development has remained elusive due to the inaccessibility of the early conceptus. Non-human primate models recapitulate many features of human development and allow access to early postimplantation stages. Here, we tracked the pre- to postimplantation transition of the trophoblast lineage in superficially implanting marmoset embryos in vivo. We differentiated marmoset naive pluripotent stem cells into trophoblast stem cells (TSCs), which exhibited trophoblast-specific transcriptome, methylome, differentiation potential, and long-term self-renewal. Notably, human TSC culture conditions failed to support marmoset TSC derivation, instead inducing an extraembryonic mesoderm-like fate in marmoset cells. We show that combined MEK, TGF-ß/NODAL, and histone deacetylase inhibition stabilizes a periimplantation trophoblast-like identity in marmoset TSCs. By contrast, these conditions differentiated human TSCs toward extravillous trophoblasts. Our work presents a paradigm to harness the evolutionary divergence in implantation strategies to elucidate human trophoblast development and invasion.

Grafting of Neonatal marmoset monkey testicular single-cell suspensions into immunodeficient mice leads to ex situ testicular cord neomorphogenesis.

Single-cell suspensions derived from immature rodent and ungulate testes can reconstitute testicular cords upon grafting into immunodeficient mice. In the present study, neonatal common marmoset monkey (Callithrix jacchus) testes were digested to a single-cell suspension, which was transplanted subcutaneously into immunodeficient mice. After 9 or 18 weeks of incubation, the derivatives of the grafted single-cell suspensions were retrieved and analyzed histologically and immunohistochemically. Three of 4 (75%) neonatal grafts exhibited reconstituted seminiferous cords strongly resembling seminiferous cords of the intact neonatal testis. The cords consisted of Sertoli cells, germ cells and peritubular myoid cells, which was confirmed by immunohistochemical marker analysis. Three-dimensional reconstruction models of the grafts revealed elongated tubules. Some of the tubules were branched, which occurs also in vivo, as we show here for the marmoset monkey. Importantly, no teratoma formation by immature pluripotency factor-expressing germ cells was observed. In summary, the reconstituted testicular cords were almost indistinguishable from the cords formed in situ, thereby impressively demonstrating a very high reconstructive potential of a single-cell suspension obtained from the neonatal marmoset monkey testis. To our knowledge, this is the first study demonstrating testicular cord neomorphogenesis for a primate species ex situ.