Membrane-bound steel factor maintains a high local concentration for mouse primordial germ cell motility, and defines the region of their migration

Diaph1 knockout inhibits mouse primordial germ cell proliferation and affects gonadal development

BACKGROUND

Exploring the molecular mechanisms of primordial germ cell (PGC) migration and the involvement of gonadal somatic cells in gonad development is valuable for comprehending the origins and potential treatments of reproductive-related diseases.

METHODS

Diaphanous related formin 1 (Diaph1, also known as mDia1) was screened by analyzing publicly available datasets (ATAC-seq, DNase-seq, and RNA-seq). Subsequently, the CRISPR-Cas9 technology was used to construct Diaph1 knockout mice to investigate the role of Diaph1 in gonad development.

RESULTS

Based on data from public databases, a differentially expressed gene Diaph1, was identified in the migration of mouse PGC. Additionally, the number of PGCs was significantly reduced in Diaph1 knockout mice compared to wild type mice, and the expression levels of genes related to proliferation (Dicer1, Mcm9), adhesion (E-cadherin, Cdh1), and migration (Cxcr4, Hmgcr, Dazl) were significantly decreased. Diaph1 knockout also inhibited Leydig cell proliferation and induced apoptosis in the testis, as well as granulosa cell apoptosis in the ovary. Moreover, the sperm count in the epididymal region and the count of ovarian follicles were significantly reduced in Diaph1 knockout mice, resulting in decreased fertility, concomitant with lowered levels of serum testosterone and estradiol. Further research found that in Diaph1 knockout mice, the key enzymes involved in testosterone synthesis (CYP11A1, 3β-HSD) were decreased in Leydig cells, and the estradiol-associated factor (FSH receptor, AMH) in granulosa cells were also downregulated.

CONCLUSIONS

Overall, our findings indicate that the knockout of Diaph1 can disrupt the expression of factors that regulate sex hormone production, leading to impaired secretion of sex hormones, ultimately resulting in damage to reproductive function. These results provide a new perspective on the molecular mechanisms underlying PGC migration and gonadal development, and offer valuable insights for further research on the causes, diagnosis, and treatment of related diseases.

A novel HMGA2::KITLG fusion in a dedifferentiated liposarcoma with amplification of MDM2 and HMGA2

High-mobility group AT-hook 2 (HMGA2) is rearranged in various types of mesenchymal tumors, particularly lipomas. HMGA2 is also co-amplified with mouse double minute 2 (MDM2) in well-differentiated liposarcoma/dedifferentiated liposarcoma (WDLPS/DDLPS). We report a case of relapsed DDLPS with a novel in-frame fusion between HMGA2 and KITLG, which encodes the ligand for KIT kinase, a critical protein involved in gametogenesis, hematopoiesis, and melanogenesis. The HMGA2 breakpoint is in intron 3, a commonly observed location for HMGA2 rearrangements, while the KITLG breakpoint is in intron 2, leading to a fusion protein that contains almost the entire coding sequence of KITLG. By immunohistochemical staining, tumor cells expressed KIT and showed phosphorylated MAPK, a major KIT downstream target. We suggest an oncogenic mechanism that involves the overexpression of KITLG caused by its rearrangement with HMGA2, leading to the constitutive activation of KIT kinase. While MDM2 amplification was observed in both the primary tumor and the relapsed tumor, the HMGA2::KITLG was only present in the relapsed tumor, indicating the role of HMGA2::KITLG in disease progression.

Factors within the Developing Embryo and Ovarian Microenvironment That Influence Primordial Germ Cell Fate

BACKGROUND

Primordial germ cell (PGC) fate is dictated by the designation, taxis, and influence of the surrounding embryonic somatic cells. Whereas gonadal sex determination results from a balance of factors within the tissue microenvironment.

SUMMARY

Our understanding of mammalian ovary development is formed in large part from developmental time courses established using murine models. Genomic tools where genes implicated in the PGC designation or gonadal sex determination have been modulated through complete or conditional knockouts in vivo, and studies in in situ models with inhibitors or cultures that alter the native gonadal environment have pieced together the interplay of pioneering transcription factors, co-regulators and chromosomes critical for the progression of PGCs to oocytes. Tools such as pluripotent stem cell derivation, genomic modifications, and aggregate differentiation cultures have yielded some insight into the human condition. Additional understanding of sex determination, both gonadal and anatomical, may be inferred from phenotypes that arise from de novo or inherited gene variants in humans who have differences in sex development.

KEY MESSAGES

This review highlights major factors critical for PGC specification and migration, and in ovarian gonad specification by reviewing seminal murine models. These pathways are compared to what is known about the human condition from expression profiles of fetal gonadal tissue, use of human pluripotent stem cells, or disorders resulting from disease variants. Many of these pathways are challenging to decipher in human tissues. However, the impact of new single-cell technologies and whole-genome sequencing to reveal disease variants of idiopathic reproductive tract phenotypes will help elucidate the mechanisms involved in human ovary development.

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’.

Germline stem cells in human

The germline cells are essential for the propagation of human beings, thus essential for the survival of mankind. The germline stem cells, as a unique cell type, generate various states of germ stem cells and then differentiate into specialized cells, spermatozoa and ova, for producing offspring, while self-renew to generate more stem cells. Abnormal development of germline stem cells often causes severe diseases in humans, including infertility and cancer. Primordial germ cells (PGCs) first emerge during early embryonic development, migrate into the gentile ridge, and then join in the formation of gonads. In males, they differentiate into spermatogonial stem cells, which give rise to spermatozoa via meiosis from the onset of puberty, while in females, the female germline stem cells (FGSCs) retain stemness in the ovary and initiate meiosis to generate oocytes. Primordial germ cell-like cells (PGCLCs) can be induced in vitro from embryonic stem cells or induced pluripotent stem cells. In this review, we focus on current advances in these embryonic and adult germline stem cells, and the induced PGCLCs in humans, provide an overview of molecular mechanisms underlying the development and differentiation of the germline stem cells and outline their physiological functions, pathological implications, and clinical applications.

Molecular regulation of polycystic ovary syndrome: altered gene expression levels in mouse models pretreatment and post-treatment

Polycystic ovary syndrome (PCOS) is a complex disorder and genetic factors are believed to play a role. The main aim was to investigate expression levels of genes involved in PI3K/AKT signalling pathway pretreatment and post-treatment. Mouse models of PCOS were generated. Group one included control mice with no polycystic ovaries (n = 4), Group 2 included a PCOS mouse model (n = 8), Group 3 included PCOS mice treated with clomiphene citrate (n = 7) and Group 4 included PCOS mice treated with clomiphene citrate, metformin and pioglitazone (n = 8). Histochemical analyses were performed. Total RNA was extracted and cDNA was synthesized. Irs, Akt1 and Akt2, mTor and Pdpk1 gene expression levels were evaluated by RT-PCR amplification. In Group 1, cortex and medulla were evaluated as normal; in Group 2, ovarian cortex was composed of immature oocytes and cystic follicles with atretic follicles. In Groups 3 and 4, follicles were in the process of normal follicle differentiation. The expression levels of Akt1 and Pi3k were significantly different (P < 0.0001) between Groups 1 and 2. The significant differences in expression levels of Pi3k and Akt1 were also observed between the Group 1 and both Groups 3 and 4 (P < 0.0001). Furthermore, significant variations of the expression levels of mTor between Groups 1 and 4 were observed. The extrapolation of results of this study may imply that follicular development may be regulated by molecular pathways involving Pi3k, Akt1 and mTor expression. Therefore, genes in the PI3K/AKT pathway may have a direct regulatory role in the development of PCOS.

Testis Development

Production of sperm and androgens is the main function of the testis. This depends on normal development of both testicular somatic cells and germ cells. A genetic program initiated from the Y chromosome gene sex-determining region Y (SRY) directs somatic cell specification to Sertoli cells that orchestrate further development. They first guide fetal germ cell differentiation toward spermatogenic destiny and then take care of the full service to spermatogenic cells during spermatogenesis. The number of Sertoli cells sets the limits of sperm production. Leydig cells secrete androgens that determine masculine development. Testis development does not depend on germ cells; that is, testicular somatic cells also develop in the absence of germ cells, and the testis can produce testosterone normally to induce full masculinization in these men. In contrast, spermatogenic cell development is totally dependent on somatic cells. We herein review germ cell differentiation from primordial germ cells to spermatogonia and development of the supporting somatic cells. Testicular descent to scrota is necessary for normal spermatogenesis, and cryptorchidism is the most common male birth defect. This is a mild form of a disorder of sex differentiation. Multiple genetic reasons for more severe forms of disorders of sex differentiation have been revealed during the last decades, and these are described along with the description of molecular regulation of testis development.

Mammalian germ cell migration during development, growth, and homeostasis

BACKGROUND

Germ cells represent one of the typical cell types that moves over a long period of time and large distance within the animal body. To continue its life cycle, germ cells must migrate to spatially distinct locations for proper development. Defects in such migration processes can result in infertility. Thus, for more than a century, the principles of germ cell migration have been a focus of interest in the field of reproductive biology.

METHODS

Based on published reports (mainly from rodents), investigations of germ cell migration before releasing from the body, including primordial germ cells (PGCs), gonocytes, spermatogonia, and immature spermatozoon, were summarized.

MAIN FINDINGS

Germ cells migrate with various patterns, with each migration step regulated by distinct mechanisms. During development, PGCs actively and passively migrate from the extraembryonic region toward genital ridges through the hindgut epithelium. After sex determination, male germline cells migrate heterogeneously in a developmental stage-dependent manner within the testis.

CONCLUSION

During migration, there are multiple gates that disallow germ cells from re-entering the proper developmental pathway after wandering off the original migration path. The presence of gates may ensure the robustness of germ cell development during development, growth, and homeostasis.

Efficient CRISPR-Cas9 editing of major evolutionary loci in sticklebacks

BACKGROUND

Stickleback fish are widely used to study the genetic and ecological basis of phenotypic evolution. Although several major loci have now been identified that contribute to evolutionary differences between wild populations, further study of the phenotypes associated with particular genes and mutations has been limited by the difficulty of generating targeted mutations at precise locations in the stickleback genome.

APPROACH AND AIMS

We compared different methods of expressing single-guide RNAs (sgRNAs) and Cas9 activity in fertilized stickleback eggs. We used an easily scored pigmentation gene (SLC24A5) to screen for molecular lesions, phenotypic effects, and possible germline transmission of newly induced alleles. We then used the optimized CRISPR methods to target two major evolutionary loci in sticklebacks, KITLG and EDA. We hypothesized that coding region mutations in the KITLG gene would alter body pigmentation and possibly sex determination, and that mutations in the EDA gene would disrupt the formation of most armor plates, fin rays, spines, teeth, and gill rakers.

RESULTS

Targeted deletions were successfully induced at each target locus by co-injecting one-cell stage stickleback embryos with either Cas9 mRNA or Cas9 protein, together with sgRNAs designed to protein-coding exons. Founder animals were typically mosaic for multiple mutations, which they transmitted through the germline at overall rates of 21 to 100%. We found that the copy of KITLG on the X chromosome (KITLGX) has diverged from the KITLG on the Y chromosome (KITLGY). Predicted loss-of-function mutations in the KITLGX gene dramatically altered pigmentation in both external skin and internal organ, but the same was not true for KITLGY mutations. Predicted loss-of-function mutations in either the KITLGX or KITLGY genes did not lead to sex reversal or prevent fertility. Homozygous loss-of-function mutations in the EDA gene led to complete loss of armor plates, severe reduction or loss of most soft rays in the dorsal, anal, and caudal fins, and severe reductions in tooth and gill raker number. In contrast, long dorsal and pelvic spines remained intact in EDA mutant animals, suggesting that common co-segregation of plate loss and spine reduction in wild populations is unlikely to be due to pleiotropic effects of EDA mutations.

CONCLUSION

CRISPR-Cas9 approaches can be used to induce germline mutations in key evolutionary loci in sticklebacks. Targeted coding region mutations confirm an important role for KITLG and EDA in skin pigmentation and armor plate reduction, respectively. They also provide new information about the functions of these genes in other body structures.

Stem cell factor in the serum of patients with esophageal cancer in relation to its histological types

INTRODUCTION

Hematopoietic growth factors (HGFs), such as stem cell factor (SCF), may stimulate proliferation and differentiation of hematopoietic progenitor cells. Stem cell factor is also able to affect the growth of malignant tumors, including esophageal cancer (EC). The prognosis of EC patients' survival is still unfavorable. Thus, novel biomarkers are necessary to improve the diagnosis and prognosis of EC patients. The aim of this study was to determine the serum SCF concentrations in EC patients in relation to its histological types and compare these levels with the classical tumor marker - carcinoembryonic antigen (CEA).

MATERIAL AND METHODS

The study included 56 EC patients and 65 healthy controls. Serum SCF and CEA concentrations were measured using immunoenzyme assays. Moreover, diagnostic criteria of both proteins tested and the survival of EC patients were assessed.

RESULTS

The serum SCF concentrations were lower in EC patients compared to healthy controls, but the difference was not significant, whereas CEA levels were higher in EC patients than in healthy subjects. The serum SCF concentrations were significantly higher in patients with adenocarcinoma of the esophagus (AC) than in patients with esophageal squamous cell carcinoma (ESCC). Moreover, the diagnostic sensitivity of SCF (88%) was higher than for CEA (29%) and increased for combined analysis of SCF with CEA.

CONCLUSIONS

Our findings suggest the potential role of serum SCF in the diagnosis of EC patients, especially in combination with the classical tumor marker. However, due to the non-specific nature of SCF, this issue requires further investigations performed on a larger population of EC patients.

A pilgrim's progress: Seeking meaning in primordial germ cell migration

Comparative studies of primordial germ cell (PGC) development across organisms in many phyla reveal surprising diversity in the route of migration, timing and underlying molecular mechanisms, suggesting that the process of migration itself is conserved. However, beyond the perfunctory transport of cellular precursors to their later arising home of the gonads, does PGC migration serve a function? Here we propose that the process of migration plays an additional role in quality control, by eliminating PGCs incapable of completing migration as well as through mechanisms that favor PGCs capable of responding appropriately to migration cues. Focusing on PGCs in mice, we explore evidence for a selective capacity of migration, considering the tandem regulation of proliferation and migration, cell-intrinsic and extrinsic control, the potential for tumors derived from failed PGC migrants, the potential mechanisms by which migratory PGCs vary in their cellular behaviors, and corresponding effects on development. We discuss the implications of a selective role of PGC migration for in vitro gametogenesis.

Alterations of oncogenes expression in NK cells in patients with cancer

INTRODUCTION

C-kit/SCF signaling plays a key role in regulating NK cell homeostasis, maturation, proliferation, and cytotoxicity. C-kit-deficiency in NK cells results in significant reduction of their number, suggesting an imperative role for c-kit signaling in NK cell biology. We have recently showed that human NK cells express not only c-kit-receptor, but also both membrane-bound and soluble forms of c-kit ligand-Stem cell factor. The goal of this study was to characterize the c-kit/SCF autocrine loop in peripheral blood NK cells obtained from patients with cancer.

METHODS

Using Smart Flare and qRT-PCR, we have characterized expression of c-kit and two forms of SCF in patients' NK cells and correlated these results with the expression of c-myc and STAT3.

RESULTS

Our results demonstrated that the expression of proto-oncogenes c-myc and c-kit was significantly decreased in NK cells from all cancer patients. Expression of membrane-bound SCF in NK cells correlated with the presence of remote metastases.

CONCLUSIONS

We suggest that the abnormal signaling and expression of c-kit/SCF, c-myc, and STAT3 in NK cells is responsible for the defect in their cytolytic activity in cancer and these defects at the gene expression level may be the cause rather than the result of tumor progression.

A dynamic niche provides Kit ligand in a stage-specific manner to the earliest thymocyte progenitors

Thymic T cell development is initiated from bone-marrow-derived multi potent thymus-seeding progenitors. During the early stages of thymocyte differentiation, progenitors become T cell restricted. However, the cellular environments supporting these critical initial stages of T cell development within the thymic cortex are not known. Here we use the dependence of early, c-Kit-expressing thymic progenitors on Kit ligand (KitL) to show that CD4(-)CD8(-)c-Kit(+)CD25(-) DN1-stage progenitors associate with, and depend on, the membrane-bound form of KitL (mKitL) provided by a cortex-specific KitL-expressing vascular endothelial cell (VEC) population. In contrast, the subsequent CD4(-)CD8(-)c-Kit(+)CD25(+) DN2-stage progenitors associate selectively with cortical thymic epithelial cells (cTECs) and depend on cTEC-presented mKitL. These results show that the dynamic process of early thymic progenitor differentiation is paralleled by migration-dependent change to the supporting niche, and identify VECs as a thymic niche cell, with mKitL as a critical ligand.

SCF, regulated by HIF-1α, promotes pancreatic ductal adenocarcinoma cell progression

Stem cell factor (SCF) and hypoxia-inducible factor-1α (HIF-1α) both have important functions in pancreatic ductal adenocarcinoma (PDAC). This study aims to analyze the expression and clinicopathological significance of SCF and HIF-1α in PDAC specimens and explore the molecular mechanism at PDAC cells in vitro and in vivo. We showed that the expression of SCF was significantly correlated with HIF-1α expression via Western blot, PCR, chromatin immunoprecipitation (ChIP) assay, and luciferase assay analysis. The SCF level was also correlated with lymph node metastasis and the pathological tumor node metastasis (pTNM) stage in PDAC samples. The SCF higher-expression group had significantly lower survival rates than the SCF lower-expression group (p<0.05). Hypoxia up-regulated the expression of SCF through the hypoxia-inducible factor (HIF)-1α in PDAC cells at the protein and RNA levels. When HIF-1α was knocked down by RNA interference, the SCF level decreased significantly. Additionally, ChIP and luciferase results demonstrated that HIF-1α can directly bind to the hypoxia response element (HRE) region of the SCF promoter and activate the SCF transcription under hypoxia. The results of colony formation, cell scratch, and transwell migration assay showed that SCF promoted the proliferation and invasion of PANC-1 cells under hypoxia. Furthermore, the down-regulated ability of cell proliferation and invasion following HIF-1α knockdown was rescued by adding exogenous SCF under hypoxia in vitro. Finally, when the HIF-1α expression was inhibited by digoxin, the tumor volume and the SCF level decreased, thereby proving the relationship between HIF-1α and SCF in vivo. In conclusion, SCF is an important factor for the growth of PDAC. In our experiments, we proved that SCF, a downstream gene of HIF-1α, can promote the development of PDAC under hypoxia. Thus, SCF might be a potential therapeutic target for PDAC.

PI3K/PTEN/Akt and TSC/mTOR signaling pathways, ovarian dysfunction, and infertility: an update

Abnormalities in ovarian function, including defective oogenesis and folliculogenesis, represent a key female reproductive deficiency. Accumulating evidence in the literature has shown that the PI3K/PTEN/Akt and TSC/mTOR signaling pathways are critical regulators of ovarian function including quiescence, activation, and survival of primordial follicles, granulosa cell proliferation and differentiation, and meiotic maturation of oocytes. Dysregulation of these signaling pathways may contribute to infertility caused by impaired follicular development, intrafollicular oocyte development, and ovulation. This article reviews the current state of knowledge of the functional role of the PI3K/PTEN/Akt and TSC/mTOR pathways during mammalian oogenesis and folliculogenesis and their association with female infertility.

A novel piggyBac transposon inducible expression system identifies a role for AKT signalling in primordial germ cell migration

In this work, we describe a single piggyBac transposon system containing both a tet-activator and a doxycycline-inducible expression cassette. We demonstrate that a gene product can be conditionally expressed from the integrated transposon and a second gene can be simultaneously targeted by a short hairpin RNA contained within the transposon, both in vivo and in mammalian and avian cell lines. We applied this system to stably modify chicken primordial germ cell (PGC) lines in vitro and induce a reporter gene at specific developmental stages after injection of the transposon-modified germ cells into chicken embryos. We used this vector to express a constitutively-active AKT molecule during PGC migration to the forming gonad. We found that PGC migration was retarded and cells could not colonise the forming gonad. Correct levels of AKT activation are thus essential for germ cell migration during early embryonic development.

A role for hedgehog signaling in the differentiation of the insertion site of the patellar tendon in the mouse

Tendons are typically composed of two histologically different regions: the midsubstance and insertion site. We previously showed that Gli1, a downstream effector of the hedgehog (Hh) signaling pathway, is expressed only in the insertion site of the mouse patellar tendon during its differentiation. To test for a functional role of Hh signaling, we targeted the Smoothened (Smo) gene in vivo using a Cre/Lox system. Constitutive activation of the Hh pathway in the mid-substance caused molecular markers of the insertion site, e.g. type II collagen, to be ectopically expressed or up-regulated in the midsubstance. This was confirmed using a novel organ culture method in vitro. Conversely, when Smo was excised in the scleraxis-positive cell population, the development of the fibrocartilaginous insertion site was affected. Whole transcriptome analysis revealed that the expression of genes involved in chondrogenesis and mineralization was down-regulated in the insertion site, and expression of insertion site markers was decreased. Biomechanical testing of murine adult patellar tendon, which developed in the absence of Hh signaling, showed impairment of tendon structural properties (lower linear stiffness and greater displacement) and material properties (greater strain), although the linear modulus of the mutant group was not significantly lower than controls. These studies provide new insights into the role of Hh signaling during tendon development.

On the embryonic origin of adult melanophores: the role of ErbB and Kit signalling in establishing melanophore stem cells in zebrafish

Pigment cells in vertebrates are derived from the neural crest (NC), a pluripotent and migratory embryonic cell population. In fishes, larval melanophores develop during embryogenesis directly from NC cells migrating along dorsolateral and ventromedial paths. The embryonic origin of the melanophores that emerge during juvenile development in the skin to contribute to the striking colour patterns of adult fishes remains elusive. We have identified a small set of melanophore progenitor cells (MPs) in the zebrafish (Danio rerio, Cyprinidae) that is established within the first 2 days of embryonic development in close association with the segmentally reiterated dorsal root ganglia (DRGs). Lineage analysis and 4D in vivo imaging indicate that progeny of these embryonic MPs spread segmentally, giving rise to the melanophores that create the adult melanophore stripes. Upon depletion of larval melanophores by morpholino knockdown of Mitfa, the embryonic MPs are prematurely activated; their progeny migrate along the spinal nerves restoring the larval pattern and giving rise to postembryonic MPs associated with the spinal nerves. Mutational or chemical inhibition of ErbB receptors blocks all early NC migration along the ventromedial path, causing a loss of DRGs and embryonic MPs. We show that the sparse like (slk) mutant lacks larval and metamorphic melanophores and identify kit ligand a (kitlga) as the underlying gene. Our data suggest that kitlga is required for the establishment or survival of embryonic MPs. We propose a model in which DRGs provide a niche for the stem cells of adult melanophores.

Cell-intrinsic reprogramming capability: gain or loss of pluripotency in germ cells

In multicellular organisms, germ cells are an extremely specialized cell type with the vital function of transmitting genetic information across generations. In this respect, they are responsible for the perpetuity of species, and are separated from somatic lineages at each generation. Interestingly, in the past two decades research has shown that germ cells have the potential to proceed along two distinct pathways: gametogenesis or pluripotency. Unequivocally, the primary role of germ cells is to produce gametes, the sperm or oocyte, to produce offspring. However, under specific conditions germ cells can become pluripotent, as shown by teratoma formation in vivo or cell culture-induced reprogramming in vitro. This phenomenon seems to be a general propensity of germ cells, irrespective of developmental phase. Recent attempts at cellular reprogramming have resulted in the generation of induced pluripotent stem cells (iPSCs). In iPSCs, the intracellular molecular networks instructing pluripotency have been activated and override the exclusively somatic cell programs that existed. Because the generation of iPSCs is highly artificial and depends on gene transduction, whether the resulting machinery reflects any physiological cell-intrinsic programs is open to question. In contrast, germ cells can spontaneously shift their fate to pluripotency during in-vitro culture. Here, we review the two fates of germ cells, i.e., differentiation and reprogramming. Understanding the molecular mechanisms regulating differentiation versus reprogramming would provide invaluable insight into understanding the mechanisms of cellular reprogramming that generate iPSCs.

Ror2 enhances polarity and directional migration of primordial germ cells

The trafficking of primordial germ cells (PGCs) across multiple embryonic structures to the nascent gonads ensures the transmission of genetic information to the next generation through the gametes, yet our understanding of the mechanisms underlying PGC migration remains incomplete. Here we identify a role for the receptor tyrosine kinase-like protein Ror2 in PGC development. In a Ror2 mouse mutant we isolated in a genetic screen, PGC migration and survival are dysregulated, resulting in a diminished number of PGCs in the embryonic gonad. A similar phenotype in Wnt5a mutants suggests that Wnt5a acts as a ligand to Ror2 in PGCs, although we do not find evidence that WNT5A functions as a PGC chemoattractant. We show that cultured PGCs undergo polarization, elongation, and reorientation in response to the chemotactic factor SCF (secreted KitL), whereas Ror2 PGCs are deficient in these SCF-induced responses. In the embryo, migratory PGCs exhibit a similar elongated geometry, whereas their counterparts in Ror2 mutants are round. The protein distribution of ROR2 within PGCs is asymmetric, both in vitro and in vivo; however, this asymmetry is lost in Ror2 mutants. Together these results indicate that Ror2 acts autonomously to permit the polarized response of PGCs to KitL. We propose a model by which Wnt5a potentiates PGC chemotaxis toward secreted KitL by redistribution of Ror2 within the cell.

Egg and sperm derive from precursors in the early embryo called primordial germ cells (PGCs). The mechanisms underlying the migration of PGCs through the embryo to the forming gonads remain unclear. In a genetic screen, we identified a role for the receptor Ror2 and its ligand Wnt5a in promoting PGC colonization of the embryonic gonads. By ex vivo culture, we show that Ror2 acts autonomously in PGCs to enhance their polarized response to the chemotactic factor SCF. Asymmetric distribution of ROR2 within PGCs in vitro and in vivo suggests that signaling via Ror2 locally amplifies cell polarity in response to other directional cues. These studies identify a novel relationship between Ror2 and cKit signaling in polarized migration.