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.

The common marmoset as suitable nonhuman alternative for the analysis of primate cochlear development.

Cochlear development is a complex process with precise spatiotemporal patterns. A detailed understanding of this process is important for studies of congenital hearing loss and regenerative medicine. However, much of our understanding of cochlear development is based on rodent models. Animal models that bridge the gap between humans and rodents are needed. In this study, we investigated the development of hearing organs in a small New World monkey species, the common marmoset (Callithrix jacchus). We describe the general stages of cochlear development in comparison with those of humans and mice. Moreover, we examined more than 25 proteins involved in cochlear development and found that expression patterns were generally conserved between rodents and primates. However, several proteins involved in supporting cell processes and neuronal development exhibited interspecific expression differences. Human fetal samples for studies of primate-specific cochlear development are extremely rare, especially for late developmental stages. Our results support the use of the common marmoset as an effective alternative for analyses of primate cochlear development.

Primordial germ cells do not migrate along nerve fibres in marmoset monkey and mouse embryos.

Primordial germ cells (PGCs) are the embryonic precursors of spermatozoa and eggs. In mammals, PGCs arise early in embryonic development and migrate from their tissue of specification over a significant distance to reach their destinations, the genital ridges. However, the exact mechanism of translocation is still debated. A study on human embryos demonstrated a very close spatial association between migrating PGCs and developing peripheral nerves. Thus, it was proposed that peripheral nerves act as guiding structures for migrating PGCs. The goal of the present study is to test whether the association between nerves and PGCs may be a human-specific finding or whether this represents a general strategy to guide PGCs in mammals. Therefore, we investigated embryos of different developmental stages from the mouse and a non-human primate, the marmoset monkey (Callithrix jacchus), covering the phase from PGC emergence to their arrival in the gonadal ridge. Embryo sections were immunohistochemically co-stained for tubulin beta-3 chain (TUBB3) to visualise neurons and Octamer-binding protein 4 (OCT4 (POU5F1)) as marker for PGCs. The distance between PGCs and the nearest detectable neuron was measured. We discovered that in all embryos analysed of both species, the majority of PGCs (>94%) was found at a minimum distance of 50 µm to the closest neuron and, more importantly, that the PGCs had reached the gonads before any TUBB3 signal could be detected in the vicinity of the gonads. In conclusion, our data indicate that PGC migration along peripheral nerves is not a general mechanism in mammals.

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.

Complex and dynamic expression of cadherins in the embryonic marmoset cerebral cortex.

Cadherin is a cell adhesion molecule widely expressed in the nervous system. Previously, we analyzed the expression of nine classic cadherins (Cdh4, Cdh6, Cdh7, Cdh8, Cdh9, Cdh10, Cdh11, Cdh12, and Cdh20) and T-cadherin (Cdh13) in the developing postnatal common marmoset (Callithrix jacchus) brain, and found differential expressions between mice and marmosets. In this study, to explore primate-specific cadherin expression at the embryonic stage, we extensively analyzed the expression of these cadherins in the developing embryonic marmoset brain. Each cadherin showed differential spatial and temporal expression and exhibited temporally complicated expression. Furthermore, the expression of some cadherins differed from that in rodent brains, even at the embryonic stage. These results suggest the possibility that the differential expressions of diverse cadherins are involved in primate specific cortical development, from the prenatal to postnatal period.

Reprogramming non-human primate somatic cells into functional neuronal cells by defined factors.

BACKGROUND: The common marmoset (Callithrix jacchus) is a New World primate sharing many similarities with humans. Recently developed technology for generating transgenic marmosets has opened new avenues for faithful recapitulation of human diseases, which could not be achieved in rodent models. However, the longer lifespan of common marmosets compared with rodents may result in an extended period for in vivo analysis of common marmoset disease models. Therefore, establishing rapid and efficient techniques for obtaining neuronal cells from transgenic individuals that enable in vitro analysis of molecular mechanisms underlying diseases are required. Recently, several groups have reported on methods, termed direct reprogramming, to generate neuronal cells by defined factors from somatic cells of various kinds of species, including mouse and human. The aim of the present study was to determine whether direct reprogramming technology was applicable to common marmosets. RESULTS: Common marmoset induced neuronal (cjiN) cells with neuronal morphology were generated from common marmoset embryonic skin fibroblasts (cjF) by overexpressing the neuronal transcription factors: ASCL1, BRN2, MYT1L and NEUROD1. Reverse transcription-polymerase chain reaction of cjiN cells showed upregulation of neuronal genes highly related to neuronal differentiation and function. The presence of neuronal marker proteins was also confirmed by immunocytochemistry. Electrical field stimulation to cjiN cells increased the intracellular calcium level, which was reversibly blocked by the voltage-gated sodium channel blocker, tetrodotoxin, indicating that these cells were functional. The neuronal function of these cells was further confirmed by electrophysiological analyses showing that action potentials could be elicited by membrane depolarization in current-clamp mode while both fast-activating and inactivating sodium currents and outward currents were observed in voltage-clamp mode. The 5-bromodeoxyuridine (BrdU) incorporation assay showed that cjiN cells were directly converted from cjFs without passing a proliferative state. CONCLUSIONS: Functional common marmoset neuronal cells can be obtained directly from embryonic fibroblasts by overexpressing four neuronal transcription factors under in vitro conditions. Overall, direct conversion technology on marmoset somatic cells provides the opportunity to analyze and screen phenotypes of genetically-modified common marmosets.

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

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

Effect of the size of zona pellucida opening on hatching in the common marmoset monkey (Callithrix jacchus) embryo.

The use of the common marmoset monkey in biomedical research has increased recently, and further attention has been devoted to this model after the successful production of transgenic marmosets. To extend genetic engineering approaches to widespread biomedical research fields, efficient prolonged in vitro culturing of embryo development is necessary. We aimed to evaluate the effects of the size of the zona pellucida opening on promoting the hatching process in the marmoset embryo. Piezo-microdrilling of a 6-µm opening in eight embryos resulted in four partially hatched embryos and one hatched embryo after 5 days of culture. Piezo-microdrilling a 20-µm opening in 11 embryos resulted in nine partial hatchings and no hatched embryos. Piezo-scraping an 80-µm opening in six embryos resulted in no partially hatched embryos and five hatched embryos. These results suggest that an 80-µm opening, rather than 6-µm or 20-µm openings, is suitable to complete the hatching process in the marmoset embryo.

Ultrasound-guided non-surgical embryo collection in the common marmoset.

Experimental primate embryology has been hampered by limited access to embryos. In addition to surgical techniques, the less stressful non-surgical technique of uterine flushing has been developed but has had only limitedly used in recovering pre-implantation embryos from marmoset monkeys. In this study, we introduce the use of ultrasonography during marmoset non-surgical uterine flushing to make the cannulation easier, to further reduce stress, and to ensure thorough uterine flushing. We were able to cannulate in 99% of the transcervical cannulation attempts, repeat the flushing up to 17 times with the same animal, and recover up to 90% of the ovulation products. We also found that 8-cell or earlier stage embryos could be frequently obtained by non-surgical uterine flushing at 4 or 5 days after ovulation. The easiness and effectiveness of this novel ultrasound-guided technique will enable more research groups to study marmoset embryology and facilitate progress in this field.

Efficient embryo transfer in the common marmoset monkey (Callithrix jacchus) with a reduced transfer volume: a non-surgical approach with cryopreserved late-stage embryos.

Among primates, the common marmoset is suitable for primate embryology research. Its small body size, however, has delayed the technical development of efficient embryo transfer. Furthermore, three factors have been determined to adversely affect the performance of marmoset embryo transfer: nonsurgical approaches, the use of cryopreserved embryos, and the use of late-stage embryos. Here we performed embryo transfer under conditions that included the above three factors and using either a small (1 µl or less) or a large volume (2-3 µl) of medium. The pregnancy and birth rates were 50% (5/10) and 27% (3/11), respectively, when using the large volume, and 80% (8/10) and 75% (9/12), respectively, when using the small volume. The latter scores exceed those of previous reports using comparable conditions. Thus, it appears that these three previously considered factors could be overcome, and we propose that reducing the transfer volume to 1 µl or less is essential for successful marmoset embryo transfer.

The enhanced pre- and postnatal development study for monoclonal antibodies.

The enhanced pre- and postnatal (ePPND) study design has been developed in response to new scientific knowledge and subsequent guideline changes [ICH M3(R2) and ICH S6(R1)]. The changes in study design were basically driven by the experiences obtained during preclinical development of biopharmaceuticals. The standard ePPND concept does not apply to conventional small molecule pharmaceuticals. In essence, the ePPND design is a pre- and postnatal development (PPND) study in which key elements of an embryo-fetal development study are investigated in newborns and infants rather than in the fetus. The cynomolgus monkey is the current relevant nonhuman primate model. The ICH S6(R1) guideline reached step 5 in June 2011 and provides detailed recommendations on various parameters and the conduct of an ePPND study. This chapter provides working guidance for monitoring menstrual cycles to generate pregnant animals, ultrasound monitoring of pregnancy, morphometric measurements of fetuses and newborns, in vivo skeletal examination, various protocols for evaluation of infants (e.g., neurobehavioral assessment, learning and memory test, grip strength, immune system evaluation) and a comprehensive list of additional infant evaluation parameters for the cynomolgus monkey.

Embryo fetal development studies in nonhuman primates.

Embryo fetal development (EFD) studies in nonhuman primates are frequently conducted in macaques with Macaca fascicularis (cynomolgus monkey, long-tailed macaque, crab-eating macaque) being the most accepted model. EFD studies are also feasible in the marmoset. Due to recent guideline changes (ICH M3(R2) and S6(R1)), EFD studies are largely confined to conventional pharmaceutical compounds rather than biopharmaceuticals. This chapter describes basic study designs and provides working protocols for collecting, processing, and staining fetuses, including collection of amniotic fluid and umbilical cord blood. The chapter also covers the examination and terminology for external, visceral, and skeletal examinations of fetuses. The species covered in this chapter are cynomolgus monkey (long-tailed macaque) and marmoset monkey.

Birth of common marmoset (Callithrix jacchus) offspring derived from in vitro-matured oocytes in chemically defined medium.

Optimization of oocyte culture conditions is a crucial aspect of reproductive biology and technology. In the present study, maturation of germinal vesicle-stage marmoset oocytes were evaluated in the following media: Waymouth medium, Waymouth medium containing porcine follicular fluid (pFF) (Waymouth-pFF medium), and porcine oocyte medium (POM). Oocytes cultured in Waymouth-pFF medium had higher maturation rates to the metaphase II stage than those cultured in Waymouth medium (36.1% vs. 24.8%, respectively, P < 0.05), indicating the suitability of this medium for culturing marmoset oocytes. Hence, maturation of marmoset oocytes cultured in POM was subsequently evaluated. The rate of maturation to the metaphase I stage was significantly higher and degradation rates were significantly lower in oocytes cultured in POM than those cultured in Waymouth medium. In addition, three offspring were successfully obtained after transfer of embryos matured in chemically defined medium. Therefore, we concluded that POM was suitable for marmoset oocyte culture. Furthermore, this was apparently the first report of marmoset offspring derived from oocytes cultured in chemically defined medium.

Prenatal stress programs lipid metabolism enhancing cardiovascular risk in the female F1, F2, and F3 generation in the primate model common marmoset (Callithrix jacchus).

BACKGROUND: Many human diseases are modulated by intrauterine environment, which is called prenatal programming. This study investigated effects of prenatal glucocorticoids on the lipid metabolism of three filial generations of common marmosets. METHODS: Pregnant primates were treated with dexamethasone during pregnancy. Body weight and blood lipid parameters of adult female offspring (F1: n = 5, F2: n = 6, F3: n = 3) were compared with age-related female controls (n = 12). RESULTS: F1, F2, and F3 offspring showed significantly lower percentage of plasma n3 fatty acids than controls. F2 and F3 presented higher cholesterol levels, with significantly more LDL cholesterol, significantly less HDL triglycerides and an enhanced cholesterol/HDL cholesterol ratio. Body weight was not significantly affected. CONCLUSIONS: Prenatal dexamethasone led to higher amounts of cardiovascular risk factors and less protective parameters in female F1-F3 offspring. The intergenerational consequences suggest prenatal programming through epigenetic effects.

Minimally invasive transabdominal collection of preimplantation embryos from the common marmoset monkey (Callithrix jacchus).

A novel, minimally invasive, transabdominal embryo collection method (transabdominal method) was developed as an alternative to a standard abdominal incision for embryo collection in the common marmoset. The abdominal incision method was used for 304 flushes using 36 female animals, whereas the transabdominal method was used for 488 flushes using 48 females; successful embryo collection rates were 48.0% and 48.4% (P > 0.05), respectively. These techniques were successfully duplicated at another institute (German Primate Center, DPZ). At that institution, successful embryo collection rates were 88.9% and 77.8% for the abdominal incision and transabdominal methods, respectively (P > 0.05), whereas the average numbers of preimplantation embryos obtained per flush were (mean ± SD) 1.91 ± 0.35 and 1.71 ± 0.14 (P > 0.05). The transabdominal method reduced animal stress, did not require incisional wound healing, and enabled successive embryo recoveries to be done much sooner. More embryos in early developmental stages (zygotes/morulae) were recovered using the transabdominal method (76.1%) than the abdominal incision method (52.6%, P < 0.01). In contrast, recovery of arrested or abnormal embryos was not significantly different between these two methods (9.8% and 8.3%). To verify developmental ability of embryos recovered by the transabdominal method, transfer of 28 normal embryos to 14 surrogate mothers yielded a nidation rate of 57%. Five females sustained term pregnancies and eight neonates were born. This novel transabdominal method will facilitate progress in marmoset developmental biology and embryology.

The (not necessarily) convoluted role of basal radial glia in cortical neurogenesis.

Recent advances in cell labeling and imaging techniques have dramatically expanded our knowledge of the neural precursor cells responsible for corticogenesis. In particular, radial glial cells are now known to generate several classes of restricted progenitors and neurons. While radial glial cells in the ventricular zone have received the most attention, it has become increasingly clear that a distinct subclass of radial glial cells situated in the subventricular zone (SVZ) and intermediate zone also play an important role in corticogenesis. These delaminated radial glial cells, which lack an apical process attached to the ventricular surface but maintain a basal process, were discovered over 3 decades ago. Recently, they have been further characterized as cortical progenitors and renamed outer, intermediate, or basal radial glia (bRG). Some of these studies indicated that bRG abundance in the outer SVZ (oSVZ) is correlated with enhanced gyrencephaly, particularly in primates and especially human, and therefore suggested that bRG may be responsible for the emergence and evolution of cerebral convolutions. In this issue of Cerebral Cortex, 2 papers provide new information about bRG in common marmosets, a near-lissencephalic primate, and in agouti, a near-gyrencephalic rodent (Garcia-Moreno et al. 2011; Kelava et al. 2011). They demonstrate that bRG are abundant and proliferate in inner as well as oSVZ, in both species. Together, these findings indicate that bRG and the oSVZ might not be correlated with gyrification or phylogeny. Rather, differential regulation of bRG and other progenitor types may enhance the adaptability and diversity of cortical morphogenesis.

Abundant occurrence of basal radial glia in the subventricular zone of embryonic neocortex of a lissencephalic primate, the common marmoset Callithrix jacchus.

Subventricular zone (SVZ) progenitors are a hallmark of the developing neocortex. Recent studies described a novel type of SVZ progenitor that retains a basal process at mitosis, sustains expression of radial glial markers, and is capable of self-renewal. These progenitors, referred to here as basal radial glia (bRG), occur at high relative abundance in the SVZ of gyrencephalic primates (human) and nonprimates (ferret) but not lissencephalic rodents (mouse). Here, we analyzed the occurrence of bRG cells in the embryonic neocortex of the common marmoset Callithrix jacchus, a near-lissencephalic primate. bRG cells, expressing Pax6, Sox2 (but not Tbr2), glutamate aspartate transporter, and glial fibrillary acidic protein and retaining a basal process at mitosis, occur at similar relative abundance in the marmoset SVZ as in human and ferret. The proportion of progenitors in M-phase was lower in embryonic marmoset than developing ferret neocortex, raising the possibility of a longer cell cycle. Fitting the gyrification indices of 26 anthropoid species to an evolutionary model suggested that the marmoset evolved from a gyrencephalic ancestor. Our results suggest that a high relative abundance of bRG cells may be necessary, but is not sufficient, for gyrencephaly and that the marmoset's lissencephaly evolved secondarily by changing progenitor parameters other than progenitor type.

Changes in cortical interneuron migration contribute to the evolution of the neocortex.

The establishment of the mammalian neocortex is often explained phylogenetically by an evolutionary change in the pallial neuronal progenitors of excitatory projection neurons. It remains unclear, however, whether and how the evolutionary change in inhibitory interneurons, which originate outside the neocortex, has been involved in the establishment of the neocortex. In this study, we transplanted chicken, turtle, mouse, and marmoset medial ganglionic eminence (MGE) cells into the embryonic mouse MGE in utero and compared their migratory behaviors. We found that the MGE cells from all of the species were able to migrate through the mouse neocortical subventricular zone and that both the mouse and marmoset cells subsequently invaded the neocortical cortical plate (CP). However, regardless of their birthdates and interneuron subtypes, most of the chicken and turtle cells ignored the neocortical CP and passed beneath it, although they were able to invade the archicortex and paleocortex, suggesting that the proper responsiveness of MGE cells to guidance cues to enter the neocortical CP is unique to mammals. When chicken MGE cells were transplanted directly into the neocortical CP, they were able to survive and mature, suggesting that the neocortical CP itself is essentially permissive for postmigratory development of chicken MGE cells. These results suggest that an evolutionary change in the migratory ability of inhibitory interneurons, which originate outside the neocortex, was involved in the establishment of the neocortex by supplying inhibitory components to the network.