Induction of primordial germ cells from murine epiblasts by synergistic action of BMP4 and BMP8B signaling pathways

Dzip1 is dynamically expressed in the vertebrate germline and regulates the development of Xenopus primordial germ cells

Primordial germ cells (PGCs) are the precursors of sperms and oocytes. Proper development of PGCs is crucial for the survival of the species. In many organisms, factors responsible for PGC development are synthesized during early oogenesis and assembled into the germ plasm. During early embryonic development, germ plasm is inherited by a few cells, leading to the formation of PGCs. While germline development has been extensively studied, how components of the germ plasm regulate PGC development is not fully understood. Here, we report that Dzip1 is dynamically expressed in vertebrate germline and is a novel component of the germ plasm in Xenopus and zebrafish. Knockdown of Dzip1 impairs PGC development in Xenopus embryos. At the molecular level, Dzip1 physically interacts with Dazl, an evolutionarily conserved RNA-binding protein that plays a multifaced role during germline development. We further showed that the sequence between amino acid residues 282 and 550 of Dzip1 is responsible for binding to Dazl. Disruption of the binding between Dzip1 and Dazl leads to defective PGC development. Taken together, our results presented here demonstrate that Dzip1 is dynamically expressed in the vertebrate germline and plays a novel function during Xenopus PGC development.

Dzip1 is dynamically expressed in the vertebrate germline and regulates the development of Xenopus primordial germ cells

Primordial germ cells (PGCs) are the precursors of sperms and oocytes. Proper development of PGCs is crucial for the survival of the species. In many organisms, factors responsible for PGC development are synthesized during early oogenesis and assembled into the germ plasm. During early embryonic development, germ plasm is inherited by a few cells, leading to the formation of PGCs. While germline development has been extensively studied, how components of the germ plasm regulate PGC development is not fully understood. Here, we report that Dzip1 is dynamically expressed in vertebrate germline and is a novel component of the germ plasm in Xenopus and zebrafish. Knockdown of Dzip1 impairs PGC development in Xenopus embryos. At the molecular level, Dzip1 physically interacts with Dazl, an evolutionarily conserved RNA-binding protein that plays a multifaced role during germline development. We further showed that the sequence between amino acid residues 282 and 550 of Dzip1 is responsible for binding to Dazl. Disruption of the binding between Dzip1 and Dazl leads to defective PGC development. Taken together, our results presented here demonstrate that Dzip1 is dynamically expressed in the vertebrate germline and plays a novel function during Xenopus PGC development.

lncCPSET1 acts as a scaffold for MLL2/COMPASS to regulate Bmp4 and promote the formation of chicken primordial germ cells

Primordial germ cells (PGCs) are the ancestors of female and male germ cells. Recent studies have shown that long non-coding RNA (lncRNA) and histone methylation are key epigenetic factors affecting PGC formation; however, their joint regulatory mechanisms have rarely been studied. Here, we explored the mechanism by which lncCPSET1 and H3K4me2 synergistically regulate the formation of chicken PGCs for the first time. Combined with chromatin immunoprecipitation (CHIP) sequencing and RNA-seq of PGCs transfected with the lncCPSET1 overexpression vector, GO annotation and KEGG enrichment analysis revealed that Wnt and TGF-β signaling pathways were significantly enriched, and Fzd2, Id1, Id4, and Bmp4 were identified as candidate genes. Quantitative reverse transcription polymerase chain reaction (qRT-PCR) showed that ASH2L, DPY30, WDR5, and RBBP5 overexpression significantly increased the expression of Bmp4, which was up-regulated after lncCPSET1 overexpression as well. It indicated that Bmp4 is a target gene co-regulated by lncCPSET1 and MLL2/COMPASS. Interestingly, co-immunoprecipitation results showed that ASH2L, DPY30 and WDR5 combined and RBBP5 weakly combined with DPY30 and WDR5. lncCPSET1 overexpression significantly increased Dpy30 expression and co-immunoprecipitation showed that interference/overexpression of lncCPSET1 did not affect the binding between the proteins in the complexes, but interference with lncCPSET1 inhibited DPY30 expression, which was confirmed by RNA immunoprecipitation that lncCPSET1 binds to DPY30. Additionally, CHIP-qPCR results showed that DPY30 enriched in the Bmp4 promoter region promoted its transcription, thus promoting the formation of PGCs. This study demonstrated that lncCPSET1 and H3K4me2 synergistically promote PGC formation, providing a reference for the study of the regulatory mechanisms between lncRNA and histone methylation, as well as a molecular basis for elucidating the formation mechanism of PGCs in chickens.

Gastruloid-derived primordial germ cell-like cells develop dynamically within integrated tissues

Primordial germ cells (PGCs) are the early embryonic precursors of gametes - sperm and egg cells. PGC-like cells (PGCLCs) can currently be derived in vitro from pluripotent cells exposed to signalling cocktails and aggregated into large embryonic bodies, but these do not recapitulate the native embryonic environment during PGC formation. Here, we show that mouse gastruloids, a three-dimensional in vitro model of gastrulation, contain a population of gastruloid-derived PGCLCs (Gld-PGCLCs) that resemble early PGCs in vivo. Importantly, the conserved organisation of mouse gastruloids leads to coordinated spatial and temporal localisation of Gld-PGCLCs relative to surrounding somatic cells, even in the absence of specific exogenous PGC-specific signalling or extra-embryonic tissues. In gastruloids, self-organised interactions between cells and tissues, including the endodermal epithelium, enables the specification and subsequent maturation of a pool of Gld-PGCLCs. As such, mouse gastruloids represent a new source of PGCLCs in vitro and, owing to their inherent co-development, serve as a novel model to study the dynamics of PGC development within integrated tissue environments.

Current progress on in vitro differentiation of ovarian follicles from pluripotent stem cells

Mammalian female reproduction requires a functional ovary. Competence of the ovary is determined by the quality of its basic unit-ovarian follicles. A normal follicle consists of an oocyte enclosed within ovarian follicular cells. In humans and mice, the ovarian follicles are formed at the foetal and the early neonatal stage respectively, and their renewal at the adult stage is controversial. Extensive research emerges recently to produce ovarian follicles in-vitro from different species. Previous reports demonstrated the differentiation of mouse and human pluripotent stem cells into germline cells, termed primordial germ cell-like cells (PGCLCs). The germ cell-specific gene expressions and epigenetic features including global DNA demethylation and histone modifications of the pluripotent stem cells-derived PGCLCs were extensively characterized. The PGCLCs hold potential for forming ovarian follicles or organoids upon cocultured with ovarian somatic cells. Intriguingly, the oocytes isolated from the organoids could be fertilized in-vitro. Based on the knowledge of in-vivo derived pre-granulosa cells, the generation of these cells from pluripotent stem cells termed foetal ovarian somatic cell-like cells was also reported recently. Despite successful in-vitro folliculogenesis from pluripotent stem cells, the efficiency remains low, mainly due to the lack of information on the interaction between PGCLCs and pre-granulosa cells. The establishment of in-vitro pluripotent stem cell-based models paves the way for understanding the critical signalling pathways and molecules during folliculogenesis. This article aims to review the developmental events during in-vivo follicular development and discuss the current progress of generation of PGCLCs, pre-granulosa and theca cells in-vitro.

Stay on the road: from germ cell specification to gonadal colonization in mammals

The founder cells of the gametes are primordial germ cells (PGCs). In mammals, PGCs are specified early during embryonic development, at the boundary between embryonic and extraembryonic tissue, long before their later residences, the gonads, have developed. Despite the differences in form and behaviour when differentiated into oocytes or sperm cells, in the period between specification and gonadal colonization, male and female PGCs are morphologically indistinct and largely regulated by similar mechanisms. Here, we compare different modes and mechanisms that lead to the formation of PGCs, putting in context protocols that are in place to differentiate both human and mouse pluripotent stem cells into PGC-like cells. In addition, we review important aspects of the migration of PGCs to the gonadal ridges, where they undergo further sex-specific differentiation. Defects in migration need to be effectively corrected, as misplaced PGCs can become tumorigenic. Concluding, a combination of in vivo studies and the development of adequate innovative in vitro models, ensuring both robustness and standardization, are providing us with the tools for a greater understanding of the first steps of gametogenesis and to develop disease models to study the origin of germ cell tumours.

This article is part of the theme issue ‘Extraembryonic tissues: exploring concepts, definitions and functions across the animal kingdom’.

Early Gonadal Development and Sex Determination in Mammal

Sex determination is crucial for the transmission of genetic information through generations. In mammal, this process is primarily regulated by an antagonistic network of sex-related genes beginning in embryonic development and continuing throughout life. Nonetheless, abnormal expression of these sex-related genes will lead to reproductive organ and germline abnormalities, resulting in disorders of sex development (DSD) and infertility. On the other hand, it is possible to predetermine the sex of animal offspring by artificially regulating sex-related gene expression, a recent research hotspot. In this paper, we reviewed recent research that has improved our understanding of the mechanisms underlying the development of the gonad and primordial germ cells (PGCs), progenitors of the germline, to provide new directions for the treatment of DSD and infertility, both of which involve manipulating the sex ratio of livestock offspring.

The context-dependent, combinatorial logic of BMP signaling

Cell-cell communication systems typically comprise families of ligand and receptor variants that function together in combinations. Pathway activation depends on the complex way in which ligands are presented extracellularly and receptors are expressed by the signal-receiving cell. To understand the combinatorial logic of such a system, we systematically measured pairwise bone morphogenetic protein (BMP) ligand interactions in cells with varying receptor expression. Ligands could be classified into equivalence groups based on their profile of positive and negative synergies with other ligands. These groups varied with receptor expression, explaining how ligands can functionally replace each other in one context but not another. Context-dependent combinatorial interactions could be explained by a biochemical model based on the competitive formation of alternative signaling complexes with distinct activities. Together, these results provide insights into the roles of BMP combinations in developmental and therapeutic contexts and establish a framework for analyzing other combinatorial, context-dependent signaling systems.

Tissue and cell interactions in mammalian PGC development

Primordial germ cells (PGCs) form early in embryo development and are crucial precursors to functioning gamete cells. Considerable research has focussed on identifying the transcriptional characteristics and signalling pathway requirements that confer PGC specification and development, enabling the derivation of PGC-like cells (PGCLCs) in vitro using specific signalling cocktails. However, full maturation to germ cells still relies on co-culture with supporting cell types, implicating an additional requirement for cellular- and tissue-level regulation. Here, we discuss the experimental evidence that highlights the nature of intercellular interactions between PGCs and neighbouring cell populations during mouse PGC development. We posit that the role that tissue interactions play on PGCs is not limited solely to signalling-based induction but extends to coordination of development by robust regulation of the proportions and position of the cells and tissues within the embryo, which is crucial for functional germ cell maturation. Such tissue co-development provides a dynamic, contextual niche for PGC development. We argue that there is evidence for a clear role for inter-tissue dependence of mouse PGCs, with potential implications for generating mammalian PGCLCs in vitro.

Conserved germ plasm characteristics across the Danio and Devario lineages

In many animal species, germ cell specification requires the inheritance of germ plasm, a biomolecular condensate containing maternally derived RNAs and proteins. Most studies of germ plasm composition and function have been performed in widely evolutionarily divergent model organisms, such as Caenorhabditis elegans, Drosophila, Xenopus laevis, and Danio rerio (zebrafish). In zebrafish, 12 RNAs localize to germ plasm at the furrows of the early embryo. Here, we tested for the presence of these RNAs in three additional species within the Danionin clade: Danio kyathit, Danio albolineatus, and Devario aequipinnatus. By visualizing nanos RNA, we find that germ plasm segregation patterns during early embryogenesis are conserved across these species. Ten additional germ plasm RNAs exhibit localization at the furrows of early embryos in all three non-zebrafish Danionin species, consistent with germ plasm localization. One component of zebrafish germ plasm, ca15b, lacked specific localization in embryos of the more distantly related D. aequipinnatus. Our findings show that within a subset of closely related Danionin species, the vast majority of germ plasm RNA components are conserved. At the same time, the lack of ca15b localization in D. aequipinnatus germ plasm highlights the potential for the divergence of germ plasm composition across a restricted phylogenetic space.

Biology of primordial germ cells in vertebrates with emphasis in urodeles amphibians

Primordial germ cells (PGCs) are highly specialized cells that play a relevant role in the maintenance and evolution of the species, since they create new combinations of genetic information between the organisms. Amphibians are a class of amniote vertebrates that are divided into three subclasses, the anurans (frogs and toads), the urodeles (salamanders and newts), and the gymnophiones (caecilians). The study of PGCs in amphibians has been addressed in more detail in anurans while little is known about the biology of this cell lineage in urodeles. Studies in some urodeles species have suggested that PGCs are of mesodermal origin, specifying in the lateral plate mesoderm at the late gastrula stage. With classical experiments it shown that, there is an induction of mesoderm, therefore most likely urodeles PGCs develop from unspecialized mesodermal tissue that responds to extracellular signals. However, some fundamental biological processes of PGCs such as the analysis of their specification, arrival, and colonization to the gonads, and their maintenance and differentiation into mature and fertile gametes remain to be elucidated. Therefore, knowledge about the biology of PGCs is of great importance to ensure the perpetuation of urodeles amphibians, as some species are in danger of becoming extinct.

Niche Laminin and IGF-1 Additively Coordinate the Maintenance of Oct-4 Through CD49f/IGF-1R-Hif-2α Feedforward Loop in Mouse Germline Stem Cells

The mechanism on how extracellular matrix (ECM) cooperates with niche growth factors and oxygen tension to regulate the self-renewal of embryonic germline stem cells (GSCs) still remains unclear. Lacking of an appropriate in vitro cell model dramatically hinders the progress. Herein, using a serum-free culture system, we demonstrated that ECM laminin cooperated with hypoxia and insulin-like growth factor 1 receptor (IGF-1R) to additively maintain AP activity and Oct-4 expression of AP⁺GSCs. We found the laminin receptor CD49f expression in d2 testicular GSCs that were surrounded by laminin. Laminin and hypoxia significantly increased the GSC stemness-related genes, including Hif-2α, Oct-4, IGF-1R, and CD49f. Cotreatment of IGF-1 and laminin additively increased the expression of IGF-IR, CD49f, Hif-2α, and Oct-4. Conversely, silencing IGF-1R and/or CD49f decreased the expression of Hif-2α and Oct-4. The underlying mechanism involved CD49f/IGF1R-(PI3K/AKT)-Hif-2α signaling loop, which in turn maintains Oct-4 expression, symmetric self-renewal, and cell migration. These findings reveal the additive niche laminin/IGF-IR network during early GSC development.

Evolution of master sex determiners: TGF-β signalling pathways at regulatory crossroads

To date, more than 20 different vertebrate master sex-determining genes have been identified on different sex chromosomes of mammals, birds, frogs and fish. Interestingly, six of these genes are transcription factors (Dmrt1- or Sox3- related) and 13 others belong to the TGF-β signalling pathway (Amh, Amhr2, Bmpr1b, Gsdf and Gdf6). This pattern suggests that only a limited group of factors/signalling pathways are prone to become top regulators again and again. Although being clearly a subordinate member of the sex-regulatory network in mammals, the TGF-β signalling pathway made it to the top recurrently and independently. Facing this rolling wave of TGF-β signalling pathways, this review will decipher how the TGF-β signalling pathways cope with the canonical sex gene regulatory network and challenge the current evolutionary concepts accounting for the diversity of sex-determining mechanisms. This article is part of the theme issue 'Challenging the paradigm in sex chromosome evolution: empirical and theoretical insights with a focus on vertebrates (Part I)'.

Bmp8a is an essential positive regulator of antiviral immunity in zebrafish

Bone morphogenetic protein (BMP) is a kind of classical multi-functional growth factor that plays a vital role in the formation and maintenance of bone, cartilage, muscle, blood vessels, and the regulation of adipogenesis and thermogenesis. However, understanding of the role of BMPs in antiviral immunity is still limited. Here we demonstrate that Bmp8a is a newly-identified positive regulator for antiviral immune responses. The bmp8a^−/− zebrafish, when infected with viruses, show reduced antiviral immunity and increased viral load and mortality. We also show for the first time that Bmp8a interacts with Alk6a, which promotes the phosphorylation of Tbk1 and Irf3 through p38 MAPK pathway, and induces the production of type I interferons (IFNs) in response to viral infection. Our study uncovers a previously unrecognized role of Bmp8a in regulation of antiviral immune responses and provides a target for controlling viral infection.

Zhang, Liu and colleagues identify the role of Bmp8a in antiviral immunity in zebrafish and provide mechanistic insight into its function. Bmp8a could serve as a future target for investigative studies of antiviral immune responses.

Germ cell differentiation requires Tdrd7-dependent chromatin and transcriptome reprogramming marked by germ plasm relocalization

In many animal models, primordial germ cell (PGC) development depends on maternally deposited germ plasm, which prevents somatic cell fate. Here, we show that PGCs respond to regulatory information from the germ plasm in two distinct phases using two distinct mechanisms in zebrafish. We demonstrate that PGCs commence zygotic genome activation together with the somatic blastocysts with no demonstrable differences in transcriptional and chromatin opening. Unexpectedly, both PGC and somatic blastocysts activate germ-cell-specific genes, which are only stabilized in PGCs by cytoplasmic germ plasm determinants. Disaggregated perinuclear relocalization of germ plasm during PGC migration is regulated by the germ plasm determinant Tdrd7 and is coupled to dramatic divergence between PGC and somatic transcriptomes. This transcriptional divergence relies on PGC-specific cis-regulatory elements characterized by promoter-proximal distribution. We show that Tdrd7-dependent reconfiguration of chromatin accessibility is required for elaboration of PGC fate but not for PGC migration.

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No evidence for transcriptional activation delay in zebrafish PGCs

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Germ-plasm-associated post-transcriptional divergence during ZGA

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Epigenetic reprogramming marks onset of PGC migration

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Epigenetic reprogramming in PGCs relies on Tdrd7, coupled to germ plasm relocalization

Female Germ Cell Development, Functioning and Associated Adversities under Unfavorable Circumstances

In the present era, infertility is one of the major issues which restricts many couples to have their own children. Infertility is the inability to achieve a clinical pregnancy after regular unprotected sexual intercourse for the period of one year or more. Various factors including defective male or female germ cell development, unhealthy and improper lifestyles, diseases like cancer and associated chemo-or-radiation therapies, congenital disorders, etc., may be responsible for infertility. Therefore, it is highly important to understand the basic concepts of germ cell development including primordial germ cell (PGC) formation, specification, migration, entry to genital ridges and their molecular mechanisms, activated pathways, paracrine and autocrine signaling, along with possible alteration which can hamper germ cell development and can cause adversities like cancer progression and infertility. Knowing all these aspects in a proper way can be very much helpful in improving our understanding about gametogenesis and finding possible ways to cure related disorders. Here in this review, various aspects of gametogenesis especially female gametes and relevant factors causing functional impairment have been thoroughly discussed.

BMP4 activates the Wnt-Lin28A-Blimp1-Wnt pathway to promote primordial germ cell formation via altering H3K4me2

The unique developmental characteristics of chicken primordial germ cells (PGCs) enable them to be used in recovery of endangered bird species, gene editing and the generation of transgenic birds, but the limited number of PGCs greatly limits their application. Studies have shown that the formation of mammalian PGCs is induced by BMP4 signal, but the mechanism underlying chicken PGC formation has not been determined. Here, we confirmed that Wnt signaling activated via BMP4 activates transcription of Lin28A by inducing β-catenin to compete with LSD1 for binding to TCF7L2, causing LSD1 to dissociate from the Lin28A promoter and enhancing H3K4me2 methylation in this region. Lin28A promotes PGC formation by inhibiting gga-let7a-3p maturation to initiate Blimp1 expression. Interestingly, expression of Blimp1 helped sustain Wnt5A expression by preventing LSD1 binding to the Wnt5A promoter. We thus elucidated a positive feedback pathway involving Wnt-Lin28A-Blimp1-Wnt that ensures PGC formation. In summary, our data provide new insight into the development of PGCs in chickens.

Long Noncoding RNA LncPGCR Mediated by TCF7L2 Regulates Primordial Germ Cell Formation in Chickens

Simple Summary

The potential of primordial germ cells (PGCs) for multidirectional differentiation, together with their unique regeneration ability, makes them one of the most promising seed cells in clinical medicine and tissue engineering research. However, not enough PGCs can be obtained to meet the demand, which limits their application. We defined a novel long noncoding RNA (lncRNA) mediated by epigenetics, which could activate the miR-6577-5p/Btrc pathway to promote the formation of PGCs. The technical system we have established is a useful tool to obtain sufficient PGCs for scientific research. Our study offers great theoretical and practical value in the production of transgenic animals or genomic imprinting in poultry. We believe that our study will help researchers in the fields of agricultural production, developmental biology, and cell biology.

Abstract

Although lncRNAs have been identified as playing critical roles in the development of germ cells, their potential involvement in the development of PGCs in chickens remains poorly understood. Differentially expressed lncRNAs (DELs) from previous RNA-seq of embryonic stem cells (ESCs), PGCs, and spermatogonial stem cells (SSCs) were analyzed by K-means clustering, from which a key candidate, lncRNA (lncRNA PGC regulator, LncPGCR) was obtained. We confirmed that LncPGCR plays a positive role in the development of PGCs by increasing the expression of the PGC marker gene (Cvh and C-kit), while downregulating the pluripotency-associated gene (Nanog) in vitro and in vivo. The activation and expression of LncPGCR are regulated by histone acetylation, and transcription factor TCF7L2. Mechanistically, a rescue assay was performed to further confirm that LncPGCR contributed to the development of PGCs by regulating the gga-miR-6577-5p/Btrc signaling pathway. Adsorption of gga-miR-6577-5p activated the WNT signaling cascade by relieving the gga-miR-6577-5p-dependent inhibition of Btrc expression. Taken together, our study discovered the growth-expedited role of LncPGCR in PGCs development, showing the potential LncPGCR/miR-6577-5p/Btrc pathway. The results and findings provide a novel insight into the development of PGCs.

Bovine oocyte maturation: acquisition of developmental competence

Although millions of oocytes are formed during embryo and fetal development in the cow, only a small fraction of these will form a developmentally competent oocyte and be fertilised. Development to competence relies on an intimate contact between the oocyte and the surrounding somatic cells in ovarian follicles, via both direct cell-cell contact and paracrine signalling. An important aspect of oocyte maturation is the segregation of homologous chromosomes and subsequently sister chromatids to form a haploid oocyte. Furthermore, the cytoplasm needs to be prepared for the formation of pronuclei and nuclear reprogramming to form a totipotent zygote. Conditions such as high levels of fatty acids or oxidative stress constrain the developmental competence of oocytes, and a better insight into these processes may help improve in vitro and in vivo oocyte maturation success. In addition, identification of the developmentally competent oocyte is useful for the efficiency of (artificial) reproduction.

Derivation of oocyte-like cells from putative embryonic stem cells and parthenogenetically activated into blastocysts in goat

Germ cells are responsible for the propagation of live animals from generation to generation, but to surprise, a steep increase in infertile problems among livestock poses great threat for economic development of human race. An alternative and robust approach is essential to combat these ailments. Here, we demonstrate that goat putative embryonic stem cells (ESCs) were successfully in vitro differentiated into primordial germ cells and oocyte-like cells using bone morphogenetic protein-4 (BMP-4) and trans-retinoic acid (RA). Oocyte-like cells having distinct zonapellucida recruited adjacent somatic cells in differentiating culture to form cumulus-oocyte complexes (COCs). The putative COCs were found to express the zonapellucida specific (ZP1 and ZP2) and oocyte-specific markers. Primordial germ cell-specific markers VASA, DAZL, STELLA, and PUM1 were detected at protein and mRNA level. In addition to that, the surface architecture of these putative COCs was thoroughly visualized by the scanning electron microscope. The putative COCs were further parthenogenetically activated to develop into healthy morula, blastocysts and hatched blastocyst stage like embryos. Our findings may contribute to the fundamental understanding of mammalian germ cell biology and may provide clinical insights regarding infertility ailments.

Human Ovarian Cortex biobanking: A Fascinating Resource for Fertility Preservation in Cancer

Novel anti-cancer treatments have improved the survival rates of female young patients, reopening pregnancy issues for female cancer survivors affected by the tumor treatment-related infertility. This condition occurs in approximately one third of women of fertile age and is mainly dependent on gonadotoxic protocols, including radiation treatments. Besides routine procedures such as the hormonal induction of follicular growth and subsequent cryopreservation of oocytes or embryos, the ovarian protection by gonadotropin-releasing hormone (GnRH) agonists during chemotherapy as well as even gonadal shielding during radiotherapy, other innovative techniques are available today and need to be optimized to support their introduction into the clinical practice. These novel methods are hormone stimulation-free and include the ovarian cortex cryopreservation before anti-cancer treatments and its subsequent autologous reimplantation and a regenerative medicine approach using oocytes derived in vitro from ovarian stem cells (OSCs). For both procedures, the major benefit is related to the prompt recruitment and processing of the ovarian cortex fragments before gonadotoxic treatments. However, while the functional competence of oocytes within the cryopreserved cortex is not assessable, the in vitro maturation of OSCs to oocytes, allows to select the most competent eggs to be cryopreserved for fertility restoration.

Esrrb function is required for proper primordial germ cell development in presomite stage mouse embryos

Estrogen related receptor beta (Esrrb) is an orphan nuclear receptor that is required for self-renewal and pluripotency in mouse embryonic stem (ES) cells. However, in the early post-implantation mouse embryo, Esrrb is specifically expressed in the extraembryonic ectoderm (ExE) and plays a crucial role in trophoblast development. Previous studies showed that Esrrb is also required to maintain trophoblast stem (TS) cells, the in vitro stem cell model of the early trophoblast lineage. In order to identify regulatory targets of Esrrb in vivo, we performed microarray analysis of Esrrb-null versus wild-type post-implantation ExE, and identified 30 genes down-regulated in Esrrb-mutants. Among them is Bmp4, which is produced by the ExE and known to be critical for primordial germ cell (PGC) specification in vivo. We further identified an enhancer region bound by Esrrb at the Bmp4 locus by performing Esrrb ChIP-seq and luciferase reporter assay using TS cells. Finally, we established a knockout mouse line in which the enhancer region was deleted using CRISPR/Cas9 technology. Both Esrrb-null embryos and enhancer knockout embryos expressed lower levels of Bmp4 in the ExE, and had reduced numbers of PGCs. These results suggested that Esrrb functions as an upstream factor of Bmp4 in the ExE, regulating proper PGC development in mice.

Germ cell differentiation of mouse embryonic stem cells can be influenced by the culture medium

Although embryonic stem (ES) cells can differentiate into germ cells, little is known about the influence of culture media on this process. We investigated the effect of two culture media on the capacity of ES cells to differentiate into germ cells using embryoid body (EB) and monolayer culture protocols. Germ cell differentiation was induced in mouse ES cells under four experimental conditions: EB/Dulbecco's modified Eagle's medium (EB/DMEM), EB/knockout Dulbecco's modified Eagle's medium (EB/KO-DMEM), monolayer/Dulbecco's modified Eagle's medium (monolayer/DMEM), and monolayer/knockout Dulbecco's modified Eagle's medium (monolayer/KO-DMEM). After incubation for 6 days, quantitative real-time polymerase chain reaction (qRT-PCR) was used to assess expression of the germ cell markers, Mvh, Oct4, Rec8, Scp1, Scp3 and Stra8. Also, Oct4 and Mvh expressions at the protein level were assessed using immunocytochemistry; we evaluated alkaline phosphatase activity in addition to cell number and viability. Germ cell-specific marker expression was increased significantly in cells differentiated in KO-DMEM for both EB and monolayer protocols; the highest level was in cultures using the EB protocol. The highest cell proliferation rate was observed using the monolayer/KO-DMEM protocol and the lowest using the EB/DMEM protocol. Generally, KO-DMEM exhibited the greatest impact on germ cell differentiation and cell proliferation. Optimization of germ cell differentiation of ES cells requires careful selection of culture medium.

Genetic basis for primordial germ cells specification in mouse and human: Conserved and divergent roles of PRDM and SOX transcription factors

Primordial germ cells (PGCs) are embryonic precursors of sperm and egg that pass on genetic and epigenetic information from one generation to the next. In mammals, they are induced from a subset of cells in peri-implantation epiblast by BMP signaling from the surrounding tissues. PGCs then initiate a unique developmental program that involves comprehensive epigenetic resetting and repression of somatic genes. This is orchestrated by a set of signaling molecules and transcription factors that promote germ cell identity. Here we review significant findings on mammalian PGC biology, in particular, the genetic basis for PGC specification in mice and human, which has revealed an evolutionary divergence between the two species. We discuss the importance and potential basis for these differences and focus on several examples to illustrate the conserved and divergent roles of critical transcription factors in mouse and human germline.

MRG-1 is required for both chromatin-based transcriptional silencing and genomic integrity of primordial germ cells in Caenorhabditis elegans

In Caenorhabditis elegans, germline cells remain transcriptionally silenced during embryogenesis. The transcriptional silencing is achieved by two different mechanisms: One is the inhibition of RNA polymerase II in P2-P4 cells at the establishment stage, and another is chromatin-based silencing in two primordial germ cells (PGCs) at the maintenance stage; however, the molecular mechanism underlying chromatin-based silencing is less understood. We investigated the role of the chromodomain protein MRG-1, which is an essential maternal factor for germline development, in transcriptional silencing in PGCs. PGCs lacking maternal MRG-1 showed increased levels of two histone modifications (H3K4me2 and H4K16ac), which are epigenetic markers for active transcription, and precocious activation of germline promoters. Loss of MES-4, a H3K36 methyltransferase, also caused similar derepression of the germline genes in PGCs, suggesting that both MRG-1 and MES-4 function in chromatin-based silencing in PGCs. In addition, the mrg-1 null mutant showed abnormal chromosome structures and a decrease in homologous recombinase RAD-51 foci in PGCs, but the mes-4 null mutant did not show such phenotypes. Taken together, we propose that MRG-1 has two distinct functions: chromatin-based transcriptional silencing and preserving genomic integrity at the maintenance stage of PGCs.

Novel functions of the ubiquitin-independent proteasome system in regulating Xenopus germline development

In most species, early germline development occurs in the absence of transcription with germline determinants subject to complex translational and post-translational regulations. Here, we report for the first time that early germline development is influenced by dynamic regulation of the proteasome system, previously thought to be ubiquitously expressed and to serve 'housekeeping' roles in controlling protein homeostasis. We show that proteasomes are present in a gradient with the highest levels in the animal hemisphere and extending into the vegetal hemisphere of Xenopus oocytes. This distribution changes dramatically during the oocyte-to-embryo transition, with proteasomes becoming enriched in and restricted to the animal hemisphere and therefore separated from vegetally localized germline determinants. We identify Dead-end1 (Dnd1), a master regulator of vertebrate germline development, as a novel substrate of the ubiquitin-independent proteasomes. In the oocyte, ubiquitin-independent proteasomal degradation acts together with translational repression to prevent premature accumulation of Dnd1 protein. In the embryo, artificially increasing ubiquitin-independent proteasomal degradation in the vegetal pole interferes with germline development. Our work thus reveals novel inhibitory functions and spatial regulation of the ubiquitin-independent proteasome during vertebrate germline development.

Out of sight, out of mind? Germ cells and the potential impacts of epigenomic drugs

Epigenetic modifications, including DNA methylation and histone modifications, determine the way DNA is packaged within the nucleus and regulate cell-specific gene expression. The heritability of these modifications provides a memory of cell identity and function. Common dysregulation of epigenetic modifications in cancer has driven substantial interest in the development of epigenetic modifying drugs. Although these drugs have the potential to be highly beneficial for patients, they act systemically and may have “off-target” effects in other cells such as the patients’ sperm or eggs. This review discusses the potential for epigenomic drugs to impact on the germline epigenome and subsequent offspring and aims to foster further examination into the possible effects of these drugs on gametes. Ultimately, the information gained by further research may improve the clinical guidelines for the use of such drugs in patients of reproductive age.

Evaluation of specific germ cell genes expression in mouse embryonic stem cell-derived germ cell like cells treated with bone morphogenetic protein 4 in vitro

BACKGROUND

Bone morphogenetic protein 4 (BMP4) is a significant signaling molecule that involves in initiating of differentiation and performs multifunctional effects on embryonic stem cells (ESCs) and embryos.

OBJECTIVE

The goal of the present study was to evaluate an in vitro differentiation model of mouse embryonic stem cells into germ cells, using BMP4.

MATERIALS AND METHODS

in this experimental study, we used Oct4-GFP mouse ESCs to form embryoid body (EB) aggregations for two days. Then, single cells from EB were cultured for four days with BMP4. Using MTT assay and gene expression levels for evaluation of Mvh and Riken by real-time RT-PCR of six concentrations, 12.5 ng/ ml BMP4 was determined as an optimized dose. Then, the expression level of Fkbp6, Mov10l1, 4930432K21Rik, Tex13, Mvh, Scp3, Stra8, Oct4 were evaluated. Flow cytometry and immunostaning were used to confirm the findings of the real-time RT-PCR.

RESULTS

In the +BMP4 group, the genes encoding Riken (p≤0.001) and Mvh (p≤0.001) were found to be increased with significant differences compared with the control group. Mov10l1 (p=0.22), Tex13 (p=0.10), Fkbp6 (p=0.90), Scp3 (p=0.61) and Stra8 (p=0.08) were up-regulated without significance differences compared with control group. Flow cytometry analysis showed that the mean number of Mvh-positive cells in the +BMP4 group was greater when compared with ESCs, -BMP4 and EB groups (p=0.03, p≤0.001, p=0.02, respectively).

CONCLUSION

Down-regulation of Oct4, expression of germ cells genes and meiosis markers expression raise this hypothesis that ESCs were differentiated by BMP4, and may be introduced into the first meiosis as germ cell-like cells.

NICD-mediated notch transduction regulates the different fate of chicken primordial germ cells and spermatogonial stem cells

Background

Notch signaling is mainly regulated by Notch1 during development of chicken germ stem cells; however, the molecular mechanisms that contribute to generation of these germ stem cells have not been thoroughly investigated.

Results

In our studies, Overexpression of the Notch1 NICD promoted development of the reproductive ridge, but inhibited the formation of seminiferous tubules. The formation efficiency of PGCs in the reproductive ridge following overexpression of NICD (7.5% ± 0.11) was significantly higher than that (4.9% ± 0.17, p < 0.05) following inhibition of NICD, While the formation efficiency of spermatogonial stem cells (SSCs) in the testes (12.7% ± 0.08) was significantly lower after NICD overexpression than that after inhibition of NICD (16.3% ± 0.16, p < 0.05). Using co-immunoprecipitation, we found that this anomaly stemmed from the reversal of dissociation of the Notch-regulated transcription factor CBF-1/RBP co-suppression complex during the differentiation of PGCs into SSCs. This dissociation of the CBF-1/RBP co-suppressing complex during the differentiation of ESCs into PGCs resulted in the release of HDAC1 and HDAC2 and the recruitment of mastermind-like 1 to form a coactive complex to promote the expression of the downstream transcription suppressor hairy/enhancer of split-1. Dynamic expression of transducin-like enhancer of split 3, TLE4, and C-terminal binding protein 2 during further differentiation of PGCs inhibited the dissociation of the CBF-1/RBP co-suppression complex and inhibited the expression of the downstream genes.

Conclusions

In summary, Notch signaling plays diametrically opposing roles during normal development of chicken PGCs and SSCs, and these functions was determined by the expression of NICD, changes in the CBF-1/RBP complex composition, and histone modification.

Application of induced pluripotent stem cell and embryonic stem cell technology to the study of male infertility

Stem cells (SCs) are classes of undifferentiated biological cells existing only at the embryonic, fetal, and adult stages that can divide to produce specialized cell types during fetal development and remain in our bodies throughout life. The progression of regenerative and reproductive medicine owes the advancement of respective in vitro and in vivo biological science on the stem cell nature under appropriate conditions. The SCs are promising therapeutic tools to treat currently of infertility because of wide sources and high potency to differentiate. Nevertheless, no effective remedies are available to deal with severe infertility due to congenital or gonadotoxic stem cell deficiency in prepubertal childhood. Some recent solutions have been developed to address the severe fertility problems, including in vitro formation of germ cells from stem cells, induction of pluripotency from somatic cells, and production of patient-specific pluripotent stem cells. There is a possibility of fertility restoration using the in vitro formation of germ cells from somatic cells. Accordingly, the present review aimed at studying the literature published on the medical application of stem cells in reproductive concerns.

TGF-β Family Signaling in Early Vertebrate Development

TGF-β family ligands function in inducing and patterning many tissues of the early vertebrate embryonic body plan. Nodal signaling is essential for the specification of mesendodermal tissues and the concurrent cellular movements of gastrulation. Bone morphogenetic protein (BMP) signaling patterns tissues along the dorsal-ventral axis and simultaneously directs the cell movements of convergence and extension. After gastrulation, a second wave of Nodal signaling breaks the symmetry between the left and right sides of the embryo. During these processes, elaborate regulatory feedback between TGF-β ligands and their antagonists direct the proper specification and patterning of embryonic tissues. In this review, we summarize the current knowledge of the function and regulation of TGF-β family signaling in these processes. Although we cover principles that are involved in the development of all vertebrate embryos, we focus specifically on three popular model organisms: the mouse Mus musculus, the African clawed frog of the genus Xenopus, and the zebrafish Danio rerio, highlighting the similarities and differences between these species.

Causes and evolutionary consequences of primordial germ-cell specification mode in metazoans

In animals, primordial germ cells (PGCs) give rise to the germ lines, the cell lineages that produce sperm and eggs. PGCs form in embryogenesis, typically by one of two modes: a likely ancestral mode wherein germ cells are induced during embryogenesis by cell-cell signaling (induction) or a derived mechanism whereby germ cells are specified by using germ plasm-that is, maternally specified germ-line determinants (inheritance). The causes of the shift to germ plasm for PGC specification in some animal clades remain largely unknown, but its repeated convergent evolution raises the question of whether it may result from or confer an innate selective advantage. It has been hypothesized that the acquisition of germ plasm confers enhanced evolvability, resulting from the release of selective constraint on somatic gene networks in embryogenesis, thus leading to acceleration of an organism's protein-sequence evolution, particularly for genes expressed at early developmental stages, and resulting in high speciation rates in germ plasm-containing lineages (denoted herein as the "PGC-specification hypothesis"). Although that hypothesis, if supported, could have major implications for animal evolution, our recent large-scale coding-sequence analyses from vertebrates and invertebrates provided important examples of genera that do not support the hypothesis of liberated constraint under germ plasm. Here, we consider reasons why germ plasm might be neither a direct target of selection nor causally linked to accelerated animal evolution. We explore alternate scenarios that could explain the repeated evolution of germ plasm and propose potential consequences of the inheritance and induction modes to animal evolutionary biology.

Contextual determinants of TGFβ action in development, immunity and cancer

Few cell signals match the impact of the transforming growth factor-β (TGFβ) family in metazoan biology. TGFβ cytokines regulate cell fate decisions during development, tissue homeostasis and regeneration, and are major players in tumorigenesis, fibrotic disorders, immune malfunctions and various congenital diseases. The effects of the TGFβ family are mediated by a combinatorial set of ligands and receptors and by a common set of receptor-activated mothers against decapentaplegic homologue (SMAD) transcription factors, yet the effects can differ dramatically depending on the cell type and the conditions. Recent progress has illuminated a model of TGFβ action in which SMADs bind genome-wide in partnership with lineage-determining transcription factors and additionally integrate inputs from other pathways and the chromatin to trigger specific cellular responses. These new insights clarify the operating logic of the TGFβ pathway in physiology and disease.

Derivation of male germ cells from induced pluripotent stem cells by inducers: A review

Induced pluripotent stem cells (iPSCs) refer to stem cells that are artificially produced using a new technology known as cellular reprogramming, which can use gene transduction in somatic cells. There are numerous potential applications for iPSCs in the field of stem cell biology becauase they are able to give rise to several different cell features of lineages such as three-germ layers. Primordial germ cells, generated via in vitro differentiation of iPSCs, have been demonstrated to produce functional gametes. Therefore, in this review we discussed past and recent advances in the in vitro differentiation of germ cells using pluripotent stem cells with an emphasis on iPSCs. Although this domain of research is still in its infancy, exploring development mechanisms of germ cells is promising, especially in humans, to promote future reproductive and developmental engineering technologies. While few studies have evaluated the ability and efficiency of iPSCs to differentiate toward male germ cells in vitro by different inducers, the given effect was investigated in this review.

IGF-1R Promotes Symmetric Self-Renewal and Migration of Alkaline Phosphatase+ Germ Stem Cells through HIF-2α-OCT4/CXCR4 Loop under Hypoxia

Hypoxia cooperates with endocrine signaling to maintain the symmetric self-renewal proliferation and migration of embryonic germline stem cells (GSCs). However, the lack of an appropriate in vitro cell model has dramatically hindered the understanding of the mechanism underlying this cooperation. Here, using a serum-free system, we demonstrated that hypoxia significantly induced the GSC mesenchymal transition, increased the expression levels of the pluripotent transcription factor OCT4 and migration-associated proteins (SDF-1, CXCR4, IGF-1, and IGF-1R), and activated the cellular expression and translocalization of the CXCR4-downstream proteins ARP3/pFAK. The underlying mechanism involved significant IGF-1/IGF-1R activation of OCT4/CXCR4 expression through HIF-2α regulation. Picropodophyllin-induced inhibition of IGF-1R phosphorylation significantly suppressed hypoxia-induced SDF-1/CXCR4 expression and cell migration. Furthermore, transactivation between IGF-1R and CXCR4 was involved. In summary, we demonstrated that niche hypoxia synergistically cooperates with its associated IGF-1R signaling to regulate the symmetric division (self-renewal proliferation) and cell migration of alkaline phosphatase-positive GSCs through HIF-2α-OCT4/CXCR4 during embryogenesis.

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Hypoxia regulated AP⁺GSC self-renewal and cell migration via IGF-1R and CXCR4

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Hypoxia increased IGF1/IGF-1R and SDF-1/CXCR4 to promote AP⁺GSC migration

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Crosstalk of IGF-1/IGF-1R and SDF-1/CXCR4 signaling in AP⁺GSCs under hypoxia

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Inhibition of IGF-1R phosphorylation suppressed hypoxia-induced cell migration

What Can Stem Cell Models Tell Us About Human Germ Cell Biology?

Fusion of sperm and egg generates a totipotent zygote that develops into a whole organism. Accordingly, the "immortal" germline transmits genetic and epigenetic information to subsequent generations with consequences for human health and disease. In mammals, primordial germ cells (PGCs) originate from peri-gastrulation embryos. While early human embryos are inaccessible for research, in vitro model systems using pluripotent stem cells have provided critical insights into human PGC specification, which differs from that in mice. This might stem from significant differences in early embryogenesis at the morphological and molecular levels, including pluripotency networks. Here, we discuss recent advances and experimental systems used to study mammalian germ cell development. We also highlight key aspects of germ cell disorders, as well as mitochondrial and potentially epigenetic inheritance in humans.

Effect of bone morphogenetic proteins 2 and 4 on survival and development of bovine secondary follicles cultured in vitro

This study evaluated the effect of bone morphogenetic proteins 2 (BMP2) and 4 (BMP2) on follicle development and mRNA expression for GDF9, Cyclin B1, BMPR1A, BMPR1B, BMPRII, FSHR and SMAD1 in bovine secondary follicles cultured in vitro. Isolated secondary follicles were cultured for 18 days in TCM199⁺ medium alone or supplemented with BMP2 (10 ng/mL), BMP4 (100 ng/mL) or combination of both BMP2 and 4. Real-time PCR was used to analyze mRNA levels in fresh and cultured follicles. After 18 days of culture, follicles cultured with BMP2 alone or with BMP4 alone had larger diameters when compared to control (P < .05). In addition, all treatments promoted antrum formation and maintained a high viability rate through the growing period. The presence of BMP2, BMP4 or both together did not influence mRNA expression for the tested genes. However, the in vitro culture induces down-regulation for mRNA expression of BMPR1A. In conclusion, the addition of BMP2 or BMP4 alone in cultured medium promotes follicular growth and antrum formation in bovine follicles after 18 days of in vitro culture.

[In vitro oogenesis: How far have we come?]

Oogenesis is a complex cellular and molecular process whose fundamental mechanisms are still poorly described or not yet elucidated, especially in human species. The development of an in vitro model of oogenesis, particularly during fetal development in humans, is a critical step that would allow: (i) a better understand of the biological mechanisms of oogenesis; (ii) a refinement of medical diagnosis for women suffering from infertility; and (iii) providing new therapeutics for reproductive pathologies. The genesis of this model could be considered from ES/iPS cells. In this article, we will trace the physiological mechanisms of oogenesis in vivo and discuss the studies carried out in the field of in vitro oogenesis from ES/iPS cells, as well as the challenges to be met in the future.

Neuronal signaling repertoire in the mammalian sperm functionality

The common embryonic origin has been a recurrent explanation to understand the presence of "neural receptors" in sperm. However, this designation has conditioned a bias marked by the classical neurotransmission model, dismissing the possibility that neurotransmitters can play specific roles in the sperm function by themselves. For instance, the launching of acrosome reaction, a fundamental sperm function, includes several steps that recall the process of presynaptic secretion. Unlike of postsynaptic neuron, whose activation is mediated by molecular interaction between neurotransmitter and postsynaptic receptors, the oocyte activation is not mediated by receptors, but by cytosolic translocation of sperm phospholipase (PLCζ). Thus, the sperm has a cellular design to access and activate the oocyte and restore the ploidy of the species by an "allogenic pronuclear fusion." At subcellular level, the events controlling sperm function, particularly the capacitation process, are activated by chemical signals that trigger ion fluxes, sterol oxidation, synthesis of cyclic adenosine monophosphate, protein kinase A activation, tyrosine phosphorylations and calcium signaling, which correspond to second messengers similar to those associated with exocytosis and growth cone guidance in neurons. Classically, the sperm function associated with neural signals has been analyzed as a unidimensional approach (single ligand-receptor effect). However, the in vivo sperm are exposed to multidimensional signaling context, for example, the GABAergic, monoaminergic, purinergic, cholinergic, and melatoninergic, to name a few. The aim of this review is to present an overview of sperm functionality associated with "neuronal signaling" and possible cellular and molecular mechanisms involved in their regulation.

Stimulation of primordial follicle assembly by estradiol-17β requires the action of bone morphogenetic protein-2 (BMP2)

Primordial follicle (PF) pool determines the availability of follicles for ovulation in all mammals. Premature depletion of the PF reserve leads to subfertility or infertility. Bone morphogenetic protein 2 (BMP2) promotes PF formation by facilitating oocyte and granulosa cell development. Estradiol-17β (E2) upregulates PF formation in developing hamster ovaries. However, if BMP2 mediates E2 effect is not known. We hypothesize that E2 facilitates the effect of BMP2 on somatic to granulosa cell transition. BMP2 and E2 together significantly upregulated the percentage of PFs in hamster fetal ovaries in vitro compared with either of the treatments alone. E2 also promoted BMP2 expression in vivo. Inhibition of BMP2 receptors suppressed E2-stimulation of PF formation while knockdown of BMP2 in vitro significantly suppressed the E2 effect. In contrast, estrogen receptor blocker did not affect BMP2 action. Inhibition of the activity of E2 or BMP2 receptors, either alone or combined during the last two days of the culture (C6-C8) resulted in a significant decrease in PF formation by C8, suggesting that both BMP2 and E2 action is essential for somatic cell differentiation for PF formation. Together, the results suggest that E2 activates BMP2-BMPR system leading to the formation of primordial follicles.

Mouse Germ Cell Development in-vivo and in-vitro

In mammalian development, primordial germ cells (PGCs) represent the initial population of cells that are committed to the germ cell lineage. PGCs segregate early in development, triggered by signals from the extra-embryonic ectoderm. They are distinguished from surrounding cells by their unique gene expression patterns. Some of the more common genes used to identify them are Blimp1, Oct3/4, Fragilis, Stella, c-Kit, Mvh, Dazl and Gcna1. These genes are involved in regulating their migration and differentiation, and in maintaining the pluripotency of these cells.

Recent research has demonstrated the possibility of obtaining PGCs, and subsequently, mature germ cells from a starting population of embryonic stem cells (ESCs) in culture. This phenomenon has been investigated using a variety of methods, and ESC lines of both mouse and human origin. Embryonic stem cells can differentiate into germ cells of both the male and female phenotype and in one case has resulted in the birth of live pups from the fertilization of oocytes with ESC derived sperm. This finding leads to the prospect of using ESC derived germ cells as a treatment for sterility. This review outlines the evolvement of germ cells from ESCs in vitro in relation to in vivo events.

Complete in vitro oogenesis: retrospects and prospects

Precise control of mammalian oogenesis has been a traditional focus of reproductive and developmental biology research. Recently, new reports have introduced the possibility of obtaining functional gametes derived in vitro from stem cells. The potential to produce functional gametes from stem cells has exciting applications for regenerative medicine though still remains challenging. In mammalian females ovulation and fertilization is a privilege reserved for a small number of oocytes. In reality the vast majority of oocytes formed from primordial germ cells (PGCs) will undergo apoptosis, or other forms of cell death. Removal occurs during germ cell cyst breakdown and the establishment of the primordial follicle (PF) pool, during the long dormancy at the PF stage, or through follicular atresia prior to reaching the ovulatory stage. A way to solve this limitation could be to produce large numbers of oocytes, in vitro, from stem cells. However, to recapitulate mammalian oogenesis and produce fertilizable oocytes in vitro is a complex process involving several different cell types, precise follicular cell-oocyte reciprocal interactions, a variety of nutrients and combinations of cytokines, and precise growth factors and hormones depending on the developmental stage. In 2016, two papers published by Morohaku et al. and Hikabe et al. reported in vitro procedures that appear to reproduce efficiently these conditions allowing for the production, completely in a dish, of a relatively large number of oocytes that are fertilizable and capable of giving rise to viable offspring in the mouse. The present article offers a critical overview of these results as well as other previous work performed mainly in mouse attempting to reproduce oogenesis completely in vitro and considers some perspectives for the potential to adapt the methods to produce functional human oocytes.

Combinatorial Signal Perception in the BMP Pathway

The bone morphogenetic protein (BMP) signaling pathway comprises multiple ligands and receptors that interact promiscuously with one another and typically appear in combinations. This feature is often explained in terms of redundancy and regulatory flexibility, but it has remained unclear what signal-processing capabilities it provides. Here, we show that the BMP pathway processes multi-ligand inputs using a specific repertoire of computations, including ratiometric sensing, balance detection, and imbalance detection. These computations operate on the relative levels of different ligands and can arise directly from competitive receptor-ligand interactions. Furthermore, cells can select different computations to perform on the same ligand combination through expression of alternative sets of receptor variants. These results provide a direct signal-processing role for promiscuous receptor-ligand interactions and establish operational principles for quantitatively controlling cells with BMP ligands. Similar principles could apply to other promiscuous signaling pathways.

Embryonic stem cell derived germ cells induce spermatogenesis after transplantation into the testes of an adult mouse azoospermia model

The present study aimed to: (i) identify the exogenous factors that allow in vitro differentiation of mouse spermatogonial stem cells (SSCs) from embryonic stem cells (ESCs); (ii) evaluate the effects of Sertoli cells in SSC enrichment; and (iii) assess the success of transplantation using in vitro differentiated SSCs in a mouse busulfan-treated azoospermia model. A 1-day-old embryoid body (EB) received 5 ng/ml of bone morphogenetic protein 4 (BMP4) for 4 days, 3 µM retinoic acid (RA) in a SIM mouse embryo-derived thioguanine and ouabain resistant (STO) co-culture system for 7 days, and was subsequently co-cultured for 2 days with Sertoli cells in the presence or absence of a leukaemia inhibitory factor (LIF), basic fibroblast growth factor (bFGF) and RA composition, and in the presence of these factors in simple culture medium. Higher viability, proliferation and germ cell gene expression were seen in the presence of the LIF, bFGF and RA composition, on top of Sertoli cells. Immunocytochemistry results showed higher CDH1 expression in this group. Sertoli co-culture had no effects on SSC proliferation. Eight weeks after transplantation, injected cells were observed at the base of the seminiferous tubules and in the recipient testes. The number of spermatogonia and the mass of the testes were higher in transplanted testes relative to the control group. It seems that transplantation of these cells can be useful in infertility treatment.