Talk:Primordial Germ Cell Development
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Cite this page: Hill, M.A. (2021, January 23) Embryology Primordial Germ Cell Development. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Talk:Primordial_Germ_Cell_Development
Nicholls PK, Schorle H, Naqvi S, Hu YC, Fan Y, Carmell MA, Dobrinski I, Watson AL, Carlson DF, Fahrenkrug SC & Page DC. (2019). Mammalian germ cells are determined after PGC colonization of the nascent gonad. Proc. Natl. Acad. Sci. U.S.A. , 116, 25677-25687. PMID: 31754036 DOI.
Mammalian germ cells are determined after PGC colonization of the nascent gonad
Mammalian primordial germ cells (PGCs) are induced in the embryonic epiblast, before migrating to the nascent gonads. In fish, frogs, and birds, the germline segregates even earlier, through the action of maternally inherited germ plasm. Across vertebrates, migrating PGCs retain a broad developmental potential, regardless of whether they were induced or maternally segregated. In mammals, this potential is indicated by expression of pluripotency factors, and the ability to generate teratomas and pluripotent cell lines. How the germline loses this developmental potential remains unknown. Our genome-wide analyses of embryonic human and mouse germlines reveal a conserved transcriptional program, initiated in PGCs after gonadal colonization, that differentiates germ cells from their germline precursors and from somatic lineages. Through genetic studies in mice and pigs, we demonstrate that one such gonad-induced factor, the RNA-binding protein DAZL, is necessary in vivo to restrict the developmental potential of the germline; DAZL's absence prolongs expression of a Nanog pluripotency reporter, facilitates derivation of pluripotent cell lines, and causes spontaneous gonadal teratomas. Based on these observations in humans, mice, and pigs, we propose that germ cells are determined after gonadal colonization in mammals. We suggest that germ cell determination was induced late in embryogenesis-after organogenesis has begun-in the common ancestor of all vertebrates, as in modern mammals, where this transition is induced by somatic cells of the gonad. We suggest that failure of this process of germ cell determination likely accounts for the origin of human testis cancer. KEYWORDS: Dazl; commitment; germ cell; pluripotency; teratoma Comment in Quelling germ cell pluripotency on the genital ridge. [Proc Natl Acad Sci U S A. 2019] PMID: 31754036 PMCID: PMC6925976 [Available on 2020-05-21] DOI: 10.1073/pnas.1910733116
Differentiation of primordial germ cells from premature ovarian insufficiency-derived induced pluripotent stem cells
Stem Cell Res Ther. 2019 May 31;10(1):156. doi: 10.1186/s13287-019-1261-6.
Yang S1,2, Ding S3, He S4, He L5, Gao K5, Peng S6, Shuai C7,8.
BACKGROUND: Premature ovarian insufficiency (POI) is a common disease in reproductive women. The pathogenesis of POI is not clear, although it is known that it involves the disorder of oocyte differentiation and development. The introduction of reprogramming human somatic cells into induced pluripotent stem cells (iPSCs) offers a unique opportunity to study many aspects of POI from cell differentiation in vitro that could ultimately lead to novel drug development and testing to help treat the disorder.
METHODS: The fibroblasts from POI patients, including fragile X syndrome, abnormal karyotype (45, X; 45, X/46, XX; 45, XO and 47, XXX), and the gene mutation (FIGLA and GDF9) were reprogrammed to pluripotency status by retroviral transduction using defined factors. The morphology, growth characteristics, gene expression profiles, epigenetic status, and in vitro and in vivo differentiation potential of the POI-1-iPSCs (from fragile X syndrome) were analyzed. Then, POI-1-iPSCs were induced to differentiation into primordial germ cells (PGCs) with DNA methyltransferase inhibitors.
RESULTS: The iPSCs were successfully generated from POI patients' fibroblasts. The formed iPS clones have the same characteristics of human ESCs. POI-1-iPSCs were successfully generated with germline competence. The POI-1-iPSCs, with genotypes of fragile X syndrome, can be induced to differentiation into PGCs with high efficiency under our culture system by DNA demethylation. This study proved that disease-specific iPSC lines derived from POI patients could be generated and successfully differentiated into PGCs.
CONCLUSIONS: We established some novel, systemic cell models for the studying of the pathogenesis of POI patients. Second, DNA demethylation may accelerate the induction of human PGCs from iPSCs in vitro and the conclusion needs further exploration. This represents an important step in the novel approach for the study of the pathophysiology and potential egg resource for POI patients.
KEYWORDS: Differentiation; Induced pluripotent stem cells; Premature ovarian insufficient; Primordial germ cells; Reprogramming PMID: 31151408 DOI: 10.1186/s13287-019-1261-6
On the origin of the human germline
Development. 2018 Jul 23;145(16). pii: dev150433. doi: 10.1242/dev.150433.
Kobayashi T1,2, Surani MA3,4.
In mice, primordial germ cells (PGCs), the precursors of eggs and sperm, originate from pregastrulation postimplantation embryos. By contrast, the origin of human PGCs (hPGCs) has been less clear and has been difficult to study because of the technical and ethical constraints that limit direct studies on human embryos. In recent years, however, in vitro simulation models using human pluripotent stem cells, together with surrogate non-rodent mammalian embryos, have provided insights and experimental approaches to address this issue. Here, we review these studies, which suggest that the posterior epiblast and/or the nascent amnion in pregastrulation human embryos is a likely source of hPGCs, and that a different gene regulatory network controls PGCs in humans compared with in the mouse. Such studies on the origins and mechanisms of hPGC specification prompt further consideration of the somatic cell fate decisions that occur during early human development. KEYWORDS: Amnion; Epiblast; Epigenetic resetting; Gastrulation; Human development; Primordial germ cells; Signalling; Transcription factors PMID: 30037844 DOI: 10.1242/dev.150433
Rapid progression through the cell cycle ensures efficient migration of primordial germ cells - The role of Hsp90
Dev Biol. 2018 Apr 15;436(2):84-93. doi: 10.1016/j.ydbio.2018.02.014. Epub 2018 Feb 22.
Pfeiffer J1, Tarbashevich K1, Bandemer J1, Palm T1, Raz E2.
Zebrafish primordial germ cells (PGCs) constitute a useful in vivo model to study cell migration and to elucidate the role of specific proteins in this process. Here we report on the role of the heat shock protein Hsp90aa1.2, a protein whose RNA level is elevated in the PGCs during their migration. Reducing Hsp90aa1.2 activity slows down the progression through the cell cycle and leads to defects in the control over the MTOC number in the migrating cells. These defects result in a slower migration rate and compromise the arrival of PGCs at their target, the region where the gonad develops. Our results emphasize the importance of ensuring rapid progression through the cell cycle during single-cell migration and highlight the role of heat shock proteins in the process. KEYWORDS: Cancer; Cell cycle; Hsp90; Migration; Motility; Stress response; Zebrafish; in vivo PMID: 29477339 DOI: 10.1016/j.ydbio.2018.02.014
Dynamics of male canine germ cell development
PLoS One. 2018 Feb 28;13(2):e0193026. doi: 10.1371/journal.pone.0193026. eCollection 2018.
de Souza AF1,2, Pieri NCG3, Roballo KCS2, Bressan FF1,2, Casals JB1, Ambrósio CE1,2, Perecin F1,2, Martins DS1,2.
Primordial germ cells (PGCs) are precursors of gametes that can generate new individuals throughout life in both males and females. Additionally, PGCs have been shown to differentiate into embryonic germ cells (EGCs) after in vitro culture. Most studies investigating germinative cells have been performed in rodents and humans but not dogs (Canis lupus familiaris). Here, we elucidated the dynamics of the expression of pluripotent (POU5F1 and NANOG), germline (DDX4, DAZL and DPPA3), and epigenetic (5mC, 5hmC, H3K27me3 and H3K9me2) markers that are important for the development of male canine germ cells during the early (22-30 days post-fertilization (dpf)), middle (35-40 dpf) and late (45-50 dpf) gestational periods. We performed sex genotype characterization, immunofluorescence, immunohistochemistry, and quantitative reverse transcriptase polymerase chain reaction (RT-qPCR) analyses. Furthermore, in a preliminary study, we evaluated the capacity of canine embryo PGCs (30 dpf) to differentiate into EGCs. To confirm the canine EGCs phenotype, we performed alkaline phosphatase detection, immunohistochemistry, electron and transmission scanning microscopy and RT-qPCR analyses. The PGCs were positive for POU5F1 and H3K27me3 during all assessed developmental periods, including all periods between the gonadal tissue stage and foetal testes development. The number of NANOG, DDX4, DAZL, DPPA3 and 5mC-positive cells increased along with the developing cords from 35-50 dpf. Moreover, our results demonstrate the feasibility of inducing canine PGCs into putative EGCs that present pluripotent markers, such as POU5F1 and the NANOG gene, and exhibit reduced expression of germinative genes and increased expression of H3K27me3. This study provides new insight into male germ cell development mechanisms in dogs. PMID: 29489867 DOI: 10.1371/journal.pone.0193026
A pilgrim's progress: Seeking meaning in primordial germ cell migration
Stem Cell Res. 2017 Oct;24:181-187. doi: 10.1016/j.scr.2017.07.017. Epub 2017 Jul 18.
Cantú AV1, Laird DJ2.
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. KEYWORDS: Cell competition; Germ cell selection; Germ cell tumor; Migration; Primordial germ cell PMID: 28754603 PMCID: PMC5634928 [Available on 2018-10-01] DOI: 10.1016/j.scr.2017.07.017
Primate Primordial Germ Cells Acquire Transplantation Potential by Carnegie Stage 23
Stem Cell Reports. 2017 Jul 11;9(1):329-341. doi: 10.1016/j.stemcr.2017.05.002. Epub 2017 Jun 1.
Clark AT1, Gkountela S2, Chen D3, Liu W4, Sosa E3, Sukhwani M5, Hennebold JD6, Orwig KE5. Author information Abstract Primordial germ cells (PGCs) are the earliest embryonic progenitors in the germline. Correct formation of PGCs is critical to reproductive health as an adult. Recent work has shown that primate PGCs can be differentiated from pluripotent stem cells; however, a bioassay that supports their identity as transplantable germ cells has not been reported. Here, we adopted a xenotransplantation assay by transplanting single-cell suspensions of human and nonhuman primate embryonic Macaca mulatta (rhesus macaque) testes containing PGCs into the seminiferous tubules of adult busulfan-treated nude mice. We discovered that both human and nonhuman primate embryonic testis are xenotransplantable, generating colonies while not generating tumors. Taken together, this work provides two critical references (molecular and functional) for defining transplantable primate PGCs. These results provide a blueprint for differentiating pluripotent stem cells to transplantable PGC-like cells in a species that is amenable to transplantation and fertility studies. KEYWORDS: PGC; primordial-germ-cell; transplant; xenotransplant PMID: 28579394 PMCID: PMC5511048 DOI: 10.1016/j.stemcr.2017.05.002
MicroRNA dynamics at the onset of primordial germ and somatic cells sex differentiation during mouse embryonic gonad development
RNA. 2017 Nov 29. pii: rna.062869.117. doi: 10.1261/rna.062869.117. [Epub ahead of print]
Fernandez-Perez D1, Brieño-Enriquez MA2, Isoler-Alcaraz J1, Larriba E1, Del Mazo J3.
In mammals, commitment and specification of germ cell lines implies involves complex programs that include sex differentiation, control of proliferation and meiotic initiation. Regulation of these processes is genetically controlled by fine-tuned mechanisms of gene regulation in which microRNAs (miRNAs) are involved. We have characterized, by small-RNAseq and bioinformatics analyses, the miRNA expression patterns of male and female mouse Primordial Germ Cells (PGCs) and gonadal somatic cells at embryonic stages: E11.5, E12.5 and E13.5. Differential expression analyses revealed differences in the regulation of key miRNA clusters such as miR-199-214, miR-182-183-96 and miR-34c-5p whose targets have defined roles during gonadal sexual determination in both germ and somatic cells. Extensive analyses of miRNA sequences revealed an increase in non-canonical isoforms on PGCs at E12.5 and dramatic changes of 3' isomiR expres-sion and 3' non-template nucleotide additions in female PGCs at E13.5. Additionally, RT-qPCR analyses of genes encoding proteins involved in miRNA biogenesis and 3' nucleotide addition uncovered sexually and developmentally specific expression, char-acterized by the decay of Drosha, Dgcr8 and Xpo5 expression along gonadal develop-ment. These results demonstrate that miRNAs, their isomiRs and miRNA machinery are differentially regulated and participate actively in gonadal sexual differentiation in both PGCs and gonadal somatic cells. KEYWORDS: Next Generation Sequencing (NGS); germ cell differentiation; meiosis; miRNAs; primordial germ cells (PGCs)
PMID: 29187591 DOI: 10.1261/rna.062869.117
Key Signaling Events for Committing Mouse Pluripotent Stem Cells to the Germline Fate
Biol Reprod. 2016 Dec;94(1):24. doi: 10.1095/biolreprod.115.135095. Epub 2015 Dec 16.
Wang JQ1, Cao WG2.
The process of germline development carries genetic information and preparatory totipotency across generations. The last decade has witnessed remarkable successes in the generation of germline cells from mouse pluripotent stem cells, especially induced germline cells with the capacity for producing viable offspring, suggesting clinical applications of induced germline cells in humans. However, to date, the culture systems for germline induction with accurate sex-specific meiosis and epigenetic reprogramming have not been well-established. In this study, we primarily focus on the mouse model to discuss key signaling events for germline induction. We review mechanisms of competent regulators on primordial germ cell induction and discuss current achievements and difficulties in inducing sex-specific germline development. Furthermore, we review the developmental identities of mouse embryonic stem cells and epiblast stem cells under certain defined culture conditions as it relates to the differentiation process of becoming germline cells. © 2016 by the Society for the Study of Reproduction, Inc. KEYWORDS: epiblastlike cells; genomic imprinting; germline induction; pluripotent stem cells; sex determination
© 2016 by the Society for the Study of Reproduction, Inc. This article is available under a Creative Commons License 4.0 (Attribution-Non-Commercial), as described at http://creativecommons.org/licenses/by/4.0/
Generation of mouse functional oocytes in rat by xeno-ectopic transplantation of primordial germ cells
Biol Reprod. 2014 Oct;91(4):89. doi: 10.1095/biolreprod.114.121640. Epub 2014 Aug 27.
Hayama T1, Yamaguchi T2, Kato-Itoh M1, Hamanaka S1, Kawarai M1, Sanbo M3, Tamura C3, Lee YS1, Yanagida A1, Murayama H1, Mizuno N1, Umino A1, Sato H1, Yamazaki S1, Masaki H1, Kobayashi T1, Hirabayashi M3, Nakauchi H4.
Primordial germ cells (PGCs) are germ cell progenitors in the fetal genital ridge; female PGCs give rise to definitive oocytes that contribute to the next generation. Artificial PGCs have been induced in vitro from pluripotent stem cells and gonad-like tissue has been induced in vivo by cotransplantation of PGCs with PGC-free gonadal cells. To apply these technologies to human infertility treatment or conservation of rare species, PGC transplantation must be established in xenogenic animals. Here, we established a xenogeneic transplantation model by inducing ovary-like tissue from PGCs in xenogenic animals. We transplanted enzymatically dispersed PGCs with PGC-free gonadal cells under the kidney capsule of xenogenic immunodeficient animals. The transplanted cells formed ovary-like tissues under the kidney capsule. These tissues were histologically similar to the normal gonad and expressed the oocyte markers Vasa and Stella. In addition, mouse germinal vesicle-stage oocyte-like cells collected from ovary-like tissue in rats matured to metaphase II via in vitro maturation and gave rise to offspring by intracytoplasmic sperm injection. Our studies show that rat/mouse female PGCs and PGC-free gonadal cells can develop and reconstruct ovary-like tissue containing functional oocytes in an ectopic xenogenic microenvironment. © 2014 by the Society for the Study of Reproduction, Inc. KEYWORDS: PGC; oocyte; ovary-like tissue; xeno-ectopic transplantation
Sall4 is Essential for Mouse Primordial Germ Cell Specification by Suppressing Somatic Cell Program Genes
Stem Cells. 2014 Sep 29. doi: 10.1002/stem.1853. [Epub ahead of print]
Yamaguchi YL1, Tanaka SS, Kumagai M, Fujimoto Y, Terabayashi T, Matsui Y, Nishinakamura R.
The Sall4 zinc finger protein is a critical transcription factor for pluripotency in embryonic stem cells (ESCs). It is also involved in the formation of a variety of organs, in mice and humans. We report the essential roles of Sall4 in mouse primordial germ cell (PGC) specification. PGC specification is accompanied by the activation of the stem cell program and repression of the somatic cell program in progenitor cells. Conditional inactivation of Sall4 during PGC specification led to a reduction in the number of PGCs in embryonic gonads. Sall4del/del PGCs failed to translocate from the mesoderm to the endoderm and underwent apoptosis. In Sall4del/del PGC progenitors, somatic cell program genes (Hoxa1 and Hoxb1) were de-repressed, while activation of the stem cell program was not impaired. We demonstrated that in differentiated ESCs, Sall4 bound to these somatic cell program gene loci, which are reportedly occupied by Prdm1 in embryonic carcinoma cells. Given that Sall4 and Prdm1 are known to associate with the histone deacetylase repressor complex, our findings suggest that Sall4 suppresses the somatic cell program possibly by recruiting the repressor complex in conjunction with Prdm1; therefore, it is essential for PGC specification. Stem Cells 2014. Copyright © 2014 AlphaMed Press. KEYWORDS: HDAC; Ifitm1; mouse; primordial germ cells (PGCs); spalt-like 4 (Sall4) PMID 25263278
Germ cell specification and pluripotency in mammals: a perspective from early embryogenesis
Reprod Med Biol. 2014;13(4):203-215. Epub 2014 Jun 10.
Irie N, Tang WW, Azim Surani M.
Abstract Germ cells are unique cell types that generate a totipotent zygote upon fertilization, giving rise to the next generation in mammals and many other multicellular organisms. How germ cells acquire this ability has been of considerable interest. In mammals, primordial germ cells (PGCs), the precursors of sperm and oocytes, are specified around the time of gastrulation. PGCs are induced by signals from the surrounding extra-embryonic tissues to the equipotent epiblast cells that give rise to all cell types. Currently, the mechanism of PGC specification in mammals is best understood from studies in mice. Following implantation, the epiblast cells develop as an egg cylinder while the extra-embryonic ectoderm cells which are the source of important signals for PGC specification are located over the egg cylinder. However, in most cases, including humans, the epiblast cells develop as a planar disc, which alters the organization and the source of the signaling for cell fates. This, in turn, might have an effect on the precise mechanism of PGC specification in vivo as well as in vitro using pluripotent embryonic stem cells. Here, we discuss how the key early embryonic differences between rodents and other mammals may affect the establishment of the pluripotency network in vivo and in vitro, and consequently the basis for PGC specification, particularly from pluripotent embryonic stem cells in vitro. KEYWORDS: Epiblast; Human; Mouse; Pluripotent stem cells; Primordial germ cells PMID 25298745
Licensing of gametogenesis, dependent on RNA binding protein DAZL, as a gateway to sexual differentiation of fetal germ cells
Proc Natl Acad Sci U S A. 2011 Apr 19. [Epub ahead of print]
Gill ME, Hu YC, Lin Y, Page DC. Source Howard Hughes Medical Institute, Whitehead Institute, and Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02142.
Abstract Mammalian oocytes and spermatozoa derive from fetal cells shared by the sexes. These primordial germ cells (PGCs) migrate to the developing somatic gonad, giving rise to oocytes or spermatozoa. These opposing sexual fates are determined not by the PGCs' own sex chromosome constitution (XX or XY), but by the sexual identity of the fetal gonad that they enter. We asked whether PGCs undergo a developmental transition that enables them to respond to feminizing or masculinizing cues from fetal ovary or testis. We conducted in vivo genetic studies of DAZL, an RNA-binding protein expressed in both ovarian and testicular germ cells. We found that germ cells in C57BL/6 Dazl-deficient fetuses-whether XX or XY-migrate to the gonad but do not develop either male or female features. Instead, they remain in a sexually undifferentiated state similar to that of migrating PGCs. Thus, germ cells in C57BL/6 Dazl-deficient fetuses do not respond to sexual cues from ovary or testis, whereas the earlier processes of germ cell specification and migration are unaffected. We propose that PGCs of both XX and XY fetuses undergo licensing, an active developmental transition that enables the resultant gametogenesis-competent cells to respond to feminizing or masculinizing cues produced by the fetal ovary or testis and hence to embark on oogenesis or spermatogenesis. In C57BL/6 mice, Dazl is required for licensing. Licensing serves as a gateway from the embryonic processes shared between the sexes-germ cell specification and migration-to the sex-specific pathways of oogenesis and spermatogenesis.
PMID: 21504946 http://www.ncbi.nlm.nih.gov/pubmed/21504946
Dazl functions in maintenance of pluripotency and genetic and epigenetic programs of differentiation in mouse primordial germ cells in vivo and in vitro
Haston KM, Tung JY, Reijo Pera RA. PLoS One. 2009 May 21;4(5):e5654.
BACKGROUND: Mammalian germ cells progress through a unique developmental program that encompasses proliferation and migration of the nascent primordial germ cell (PGC) population, reprogramming of nuclear DNA to reset imprinted gene expression, and differentiation of mature gametes. Little is known of the genes that regulate quantitative and qualitative aspects of early mammalian germ cell development both in vivo, and during differentiation of germ cells from mouse embryonic stem cells (mESCs) in vitro.
METHODOLOGY AND PRINCIPAL FINDINGS: We used a transgenic mouse system that enabled isolation of small numbers of Oct4DeltaPE:GFP-positive germ cells in vivo, and following differentiation from mESCs in vitro, to uncover quantitate and qualitative phenotypes associated with the disruption of a single translational regulator, Dazl. We demonstrate that disruption of Dazl results in a post-migratory, pre-meiotic reduction in PGC number accompanied by aberrant expression of pluripotency genes and failure to erase and re-establish genomic imprints in isolated male and female PGCs, as well as subsequent defect in progression through meiosis. Moreover, the phenotypes observed in vivo were mirrored by those in vitro, with inability of isolated mutant PGCs to establish pluripotent EG (embryonic germ) cell lines and few residual Oct-4-expressing cells remaining after somatic differentiation of mESCs carrying a Dazl null mutation. Finally, we observed that even within undifferentiated mESCs, a nascent germ cell subpopulation exists that was effectively eliminated with ablation of Dazl.
CONCLUSIONS AND SIGNIFICANCE: This report establishes the translational regulator Dazl as a component of pluripotency, genetic, and epigenetic programs at multiple time points of germ cell development in vivo and in vitro, and validates use of the ESC system to model and explore germ cell biology.
Steel factor controls primordial germ cell survival and motility from the time of their specification in the allantois, and provides a continuous niche throughout their migration
Development. 2009 Apr;136(8):1295-303. Epub 2009 Mar 11.
Gu Y, Runyan C, Shoemaker A, Surani A, Wylie C.
Division of Developmental Biology, Cincinnati Children's Hospital Research Foundation, 3333 Burnet Avenue, Cincinnati, OH 45229, USA. Abstract Steel factor is an essential survival and proliferation factor for primordial germ cells (PGCs) during their migration in the early mouse embryo. PGCs arise during gastrulation, and migrate into the posterior endoderm that becomes the hindgut. Previous reports have suggested that PGCs become dependent on Steel factor when they colonize the hindgut. However, in the absence of a good marker for living PGCs, their behavior before hindgut colonization has not been previously studied. We report here the normal behavior of PGCs in live embryos before hindgut colonization, and the roles of Steel factor, using a reporter line in which GFP is driven by the promoter of the Stella gene, whose activation accompanies the initial specification of PGCs. We show first that PGCs are surrounded by Steel factor-expressing cells from their first appearance in the allantois to the time they enter the genital ridges. Second, fewer PGCs are found in the allantois in Steel-null embryos, but this is not due to a failure of PGC specification. Third, the analysis of cultured Steel-null early embryos shows that Steel factor is required for normal PGC motility, both in the allantois and in the hindgut. Germ cells migrate actively in the allantois, and move directionally from the allantois into the proximal epiblast. In the absence of Steel factor, caused by either null mutation or antibody blockade, PGC motility is dramatically decreased, but directionality is maintained, demonstrating a primary role for Steel factor in PGC motility. This was found both before and after colonization of the hindgut. These data, together with previously published data, show that PGCs are Steel factor dependent from their initial specification until they colonize the genital ridges, and suggest the existence of a ;spatio-temporal niche' that travels with this important pluripotential cell population in the embryo.
Analysis of chicken primordial germ cells
Motono M, Ohashi T, Nishijima K, Iijima S. Cytotechnology. 2008 Jun;57(2):199-205. Epub 2008 Jul 23. PMID: 19003166
Primordial germ cell specification from embryonic stem cells
Wei W, Qing T, Ye X, Liu H, Zhang D, Yang W, Deng H. PLoS One. 2008;3(12):e4013. Epub 2008 Dec 24.
BACKGROUND: Primordial germ cell (PGC) specification is the first crucial step in germ line development. However, owing to significant challenges regarding the in vivo system, such as the complex cellular environment and potential problems with embryo manipulation, it is desirable to generate embryonic stem (ES) cells that are capable of overcoming these aforementioned limitations in order to provide a potential in vitro model to recapitulate the developmental processes in vivo.
METHODOLOGY AND PRINCIPAL FINDINGS: Here, we studied the detailed process of PGC specification from stella-GFP ES cells. We first observed the heterogeneous expression of stella in ES cells. However, neither Stella-positive ES cells nor Stella-negative ES cells shared a similar gene expression pattern with either PGCs or PGC precursors. Second, we derived PGCs from ES cells using two differentiation methods, namely the attachment culture technique and the embryoid body (EB) method. Compared with PGCs derived via the attachment culture technique, PGCs derived via the EB method that had undergone the sequential erasure of Peg3 followed by Igf2r resulted in a cell line in which the expression dynamics of T, Fgf8 and Sox17, in addition to the expression of the epiblast markers, were more similar to the in vivo expression, thus demonstrating that the process of PGC derivation was more faithfully recapitulated using the EB method. Furthermore, we developed an in vitro model of PGC specification in a completely chemically defined medium (CDM) that indicated that BMP4 and Wnt3a promoted PGC derivation, whereas BMP8b and activinA had no observable effect on PGC derivation.
CONCLUSIONS AND SIGNIFICANCE: The in vitro model we have established can recapitulate the developmental processes in vivo and provides new insights into the mechanism of PGC specification.
A potential model of PGC specification. Some of the cells in the ICM (inner cell mass)/ES cells were Stella and/or Blimp1 positive cells. with the development of the embryo, the expression of Blimp1 was depressed in these cells with the help of signals from neighboring cells. Later, induced by WNT and/or BMP signaling, a subpopulation of these cells with the expression of mesoderm markers emerged, some of which acquired the expression of Blimp1. Then, Blimp1 functions to repress the expression of somatic markers that were normally down-regulated in PGCs . Subsequently, cells with the expression of both Blimp1 and Stella were fated to germ-line development.
The fragilis interferon-inducible gene family of transmembrane proteins is associated with germ cell specification in mice
BMC Dev Biol. 2003 Mar 19;3:1. Epub 2003 Mar 19. Lange UC, Saitou M, Western PS, Barton SC, Surani MA.
Wellcome Trust/Cancer Research UK Institute of Cancer and Developmental Biology, University of Cambridge, Tennis Court Road, Cambridge, CB2 1QR, UK. firstname.lastname@example.org Abstract BACKGROUND: Specification of primordial germ cells in mice depends on instructive signalling events, which act first to confer germ cell competence on epiblast cells, and second, to impose a germ cell fate upon competent precursors. fragilis, an interferon-inducible gene coding for a transmembrane protein, is the first gene to be implicated in the acquisition of germ cell competence.
RESULTS: Here, we describe four additional fragilis-related genes, fragilis2-5, which are clustered within a 68 kb region in the vicinity of the fragilis locus on Chr 7. These genes exist in a number of mammalian species, which in the human are also clustered on the syntenic region on Chr 11. In the mouse, fragilis2 and fragilis3, which are proximate to fragilis, exhibit expression that overlaps with the latter in the region of specification of primordial germ cells. Using single cell analysis, we confirm that all these three fragilis-related genes are predominant in nascent primordial germ cells, as well as in gonadal germ cells.
CONCLUSION: The Fragilis family of interferon-inducible genes is tightly associated with germ cell specification in mice. Furthermore, its evolutionary conservation suggests that it probably plays a critical role in all mammals. Detailed analysis of these genes may also elucidate the role of interferons as signalling molecules during development.
The origin, migration and fine morphology of human primordial germ cells
Anat Rec. 1977 Jul;188(3):315-30.
Fujimoto T, Miyayama Y, Fuyuta M.
Human primordial germ cells (PGCs) were observed ultrastructurally in stages from their endodermal to gonadal locations. Primitive PGCs in the hind-gut epithelium of the 4-week embryo, were recognized as well demarcated cells from the neighboring cells. At the time fo separation, the basal lamina of the epithelium was broken, then, through the gap so opened, the PGCs started to escape into the outer mesenchyme. In embryos at five weeks, PGCs were in the migration stage, and were found in the dorsal mesentery, at the coelomic angle and in the forming germinal ridge. In embryos at six weeks or later, almost all PGCS were accumulated in the gonad. The PGC was characterized by its large size and the large and round nucleus with conspicuous nucleolus, and by the presence of abundant glycogen particles and a considerable number of lipid droplets in the cytoplasm. Alkaline phosphatase activity was demonstrated selectively on the plasma membrane of the PGC. The shape of PGC was irregular, often had pseudopodia in PGCs in the separation and migration stages, suggesting their amoeboid movement in vivo, but was generally round or elliptic in PGCs in the settlement stage. The PGC was usually surrounded by and in close association with adjacent somatic cells. PMID: 900520 DOI: 10.1002/ar.1091880305
Fifty-Ninth Annual Session Western Reserve University Cleveland April 4-6, 1946 p507
45. Early history of the human germ cells
Department of Zoology, State University of Iowa.
About fifty well-preserved human embryos and fetuses from the Carnegie and the Iowa collections were studied to trace the prenatal history of human germ cells. A series of twenty four represent the period during which the primordial gonia migrate from the yolk sac epithelium to the sex gland primordia (12 somite to 8 mm stages). Progressing with ameboid movements, the cells apparently pass through membranes and other obstacles by lytic destruction. During the entire migratory period they continue to multiply, their number increasing from about 100 to near 2,000. This indicates an average of four to ﬁve mitotic sequences for this interval of approximately 12 days.
At the site of the gonad primordia, the germ cells become individually encapsulated with follicle cells which are probably derived from the coelomic epithelium of this region. With ovarian differentiation they become the granulosa cells; in the testicular direction they form sustentacular cells. In female fetuses of 11 weeks (60 min), some ovogonia have entered the synaptic phase, thus becoming ovocytes. Three weeks later (93 mm fetus) the ovocytes prevail and ovogonial multiplication seems near its end. An estimate based on germ cell counts in deﬁnite parts of the sectioned ovaries puts the number of germ cells for this fetus in the neighborhood of ﬁve million. Since follicular atresia starts early, this number decreases even before birth.