Preformation and epigenesis converge to specify primordial germ cell fate in the early Drosophila embryo

A critical step in animal development is the specification of primordial germ cells (PGCs), the precursors of the germline. Two seemingly mutually exclusive mechanisms are implemented across the animal kingdom: epigenesis and preformation. In epigenesis, PGC specification is non-autonomous and depends on extrinsic signaling pathways. The BMP pathway provides the key PGC specification signals in mammals. Preformation is autonomous and mediated by determinants localized within PGCs. In Drosophila, a classic example of preformation, constituents of the germ plasm localized at the embryonic posterior are thought to be both necessary and sufficient for proper determination of PGCs. Contrary to this longstanding model, here we show that these localized determinants are insufficient by themselves to direct PGC specification in blastoderm stage embryos. Instead, we find that the BMP signaling pathway is required at multiple steps during the specification process and functions in conjunction with components of the germ plasm to orchestrate PGC fate.

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Quantitative analysis of signaling responses during mouse primordial germ cell specification

Biology Open ◽

10.1242/bio.058741 ◽

2021 ◽

Vol 10 (5) ◽

Author(s):

Sophie M. Morgani ◽

Anna-Katerina Hadjantonakis

Keyword(s):

Cell Fate ◽

Primordial Germ Cells ◽

Primordial Germ Cell ◽

Small Population ◽

Bmp Signaling ◽

Pluripotent Cells ◽

Cell Fate Decisions ◽

Germ Cell Specification

ABSTRACT During early mammalian development, the pluripotent cells of the embryo are exposed to a combination of signals that drive exit from pluripotency and germ layer differentiation. At the same time, a small population of pluripotent cells give rise to the primordial germ cells (PGCs), the precursors of the sperm and egg, which pass on heritable genetic information to the next generation. Despite the importance of PGCs, it remains unclear how they are first segregated from the soma, and if this involves distinct responses to their signaling environment. To investigate this question, we mapped BMP, MAPK and WNT signaling responses over time in PGCs and their surrounding niche in vitro and in vivo at single-cell resolution. We showed that, in the mouse embryo, early PGCs exhibit lower BMP and MAPK responses compared to neighboring extraembryonic mesoderm cells, suggesting the emergence of distinct signaling regulatory mechanisms in the germline versus soma. In contrast, PGCs and somatic cells responded comparably to WNT, indicating that this signal alone is not sufficient to promote somatic differentiation. Finally, we investigated the requirement of a BMP response for these cell fate decisions. We found that cell lines with a mutation in the BMP receptor (Bmpr1a−/−), which exhibit an impaired BMP signaling response, can efficiently generate PGC-like cells revealing that canonical BMP signaling is not cell autonomously required to direct PGC-like differentiation.

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Quantitative analysis of signaling responses during mouse primordial germ cell specification

10.1101/2021.01.11.426293 ◽

2021 ◽

Author(s):

Sophie M. Morgani ◽

Anna-Katerina Hadjantonakis

Keyword(s):

Cell Fate ◽

Primordial Germ Cells ◽

Primordial Germ Cell ◽

Small Population ◽

Bmp Signaling ◽

Pluripotent Cells ◽

Cell Fate Decisions ◽

Germ Cell Specification

AbstractDuring early mammalian development, the pluripotent cells of the embryo are exposed to a combination of signals that drive exit from pluripotency and germ layer differentiation. At the same time, a small population of pluripotent cells give rise to the primordial germ cells (PGCs), the precursors of the sperm and egg, which pass on heritable genetic information to the next generation. Despite the importance of PGCs, it remains unclear how they are first segregated from the soma, and if this involves distinct responses to their signaling environment. To investigate this question, we mapped BMP, MAPK and WNT signaling responses over time in PGCs and their surrounding niche in vitro and in vivo at single-cell resolution. We showed that, in the mouse embryo, early PGCs exhibit lower BMP and MAPK responses compared to neighboring extraembryonic mesoderm cells, suggesting the emergence of distinct signaling regulatory mechanisms in the germline versus soma. In contrast, PGCs and somatic cells responded comparably to WNT, indicating that this signal alone is not sufficient to promote somatic differentiation. Finally, we investigated the requirement of a BMP response for these cell fate decisions. We found that cell lines with a mutation in the BMP receptor (Bmpr1a−/−), which exhibit an impaired BMP signaling response, can efficiently generate PGC-like cells revealing that canonical BMP signaling is not cell autonomously required to direct PGC-like differentiation.

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Germ plasm localisation dynamics mark distinct phases of transcriptional and post-transcriptional regulation control in primordial germ cells

10.1101/2020.01.12.903336 ◽

2020 ◽

Author(s):

Fabio M. D’Orazio ◽

Piotr Balwierz ◽

Yixuan Guo ◽

Benjamín Hernández-Rodríguez ◽

Aleksandra Jasiulewicz ◽

...

Keyword(s):

Germ Cell ◽

Cell Fate ◽

Germ Plasm ◽

Primordial Germ Cells ◽

Primordial Germ Cell ◽

Somatic Cells ◽

Chromatin Accessibility ◽

Post Transcriptional Regulation ◽

Genome Activation ◽

Chromatin Opening

SUMMARYIn many animal models, primordial germ cell (PGC) development depends on maternally-deposited germ plasm to avoid somatic cell fate. Here, we show that PGCs respond to regulatory information from the germ plasm in two distinct phases and mechanisms in zebrafish. We show that PGCs commence zygotic genome activation together with the rest of the embryo with no demonstrable differences in transcriptional and chromatin accessibility levels. Thus, cytoplasmic germ plasm determinants only affect post-transcriptional stabilisation of RNAs to diverge transcriptome from somatic cells, which, unexpectedly, also activate germ cell-specific genes. Perinuclear relocalisation of germ plasm is coupled to dramatic divergence in chromatin opening and transcriptome from somatic cells characterised by PGC-specific chromatin topology. Furthermore, we reveal Tdrd7, regulator of germ plasm localisation, as crucial determinant of germ fate acquisition.

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Partial characterization of ‘primordial germ cell-forming activity’ localized in vegetal pole cytoplasm in anuran eggs

Development ◽

10.1242/dev.39.1.221 ◽

1977 ◽

Vol 39 (1) ◽

pp. 221-233

Author(s):

Masami Wakahara

Keyword(s):

Germ Cells ◽

Germ Plasm ◽

Primordial Germ Cells ◽

Primordial Germ Cell ◽

Differential Centrifugation ◽

Rana Chensinensis ◽

Crude Homogenate ◽

Germinal Granules ◽

Vegetal Pole

Larvae of Rana chensinensis developed from fertilized eggs which had been subjected to ultraviolet (u.v.) irradiation on their vegetal hemisphere at a dose of 20000 ergs/mm2 within 60 min of fertilization contained no primordial germ cells (PGCs) when examined histologically at the stage when the operculum was complete (8 days after fertilization at 18 °C, stage 25 according to Shumway, 1940). The morphogenetic ability of vegetal pole cytoplasm from non-irradiated eggs to establish the PGCs was tested by injecting some fractions of this cytoplasm into the vegetal hemisphere of u.v.-irradiated eggs. Crude homogenate of the vegetal pole cytoplasm without large yolk platelets was able to restore the PGCs when injected into u.v.-irradiated eggs, but a similar fraction from animal half cytoplasm had no ability to form PGCs. The ‘PGC-forming activity’ demonstrated in the crude homogenate of the vegetal pole cytoplasm was not abolished by dialysis, lyophilization and heating to 90 °C for 10 min. When the homogenate was fractionated by differential centrifugation in 0·25 M sucrose, the ‘PGC-forming activity’ was recovered mainly in the precipitate of 15000g for 30 min. The precipitate of 7000 g for 10 min had also a little ‘activity’. The possibility was discussed that the ‘PGC-forming activity’ demonstrated in the vegetal pole cytoplasm was associated with the germinal granules in the germ plasm rather than the mitochondria.

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Signaling Dynamics Control Cell Fate in the Early Drosophila Embryo

Developmental Cell ◽

10.1016/j.devcel.2019.01.009 ◽

2019 ◽

Vol 48 (3) ◽

pp. 361-370.e3 ◽

Cited By ~ 38

Author(s):

Heath E. Johnson ◽

Jared E. Toettcher

Keyword(s):

Cell Fate ◽

Control Cell ◽

Drosophila Embryo ◽

Signaling Dynamics ◽

Early Drosophila Embryo

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TCam-2 Cells Deficient for SOX2 and FOXA2 Are Blocked in Differentiation and Maintain a Seminoma-Like Cell Fate In Vivo

Cancers ◽

10.3390/cancers11050728 ◽

2019 ◽

Vol 11 (5) ◽

pp. 728 ◽

Cited By ~ 1

Author(s):

Daniel Nettersheim ◽

Saskia Vadder ◽

Sina Jostes ◽

Alena Heimsoeth ◽

Hubert Schorle

Keyword(s):

Cell Fate ◽

Primordial Germ Cells ◽

Germ Cell Tumors ◽

Embryonic Stem ◽

Bmp Signaling ◽

Stem Cell Population ◽

Testicular Germ Cell ◽

Key Factor ◽

Pioneer Factor

Testicular germ cell tumors (GCTs) are very common in young men and can be stratified into seminomas and non-seminomas. While seminomas share a similar gene expression and epigenetic profile with primordial germ cells, the stem cell population of the non-seminomas, the embryonal carcinoma (EC), resembles malignant embryonic stem cells. Thus, ECs are able to differentiate into cells of all three germ layers (teratomas) and even extra-embryonic-tissue-like cells (yolk-sac tumor, choriocarcinoma). In the last years, we demonstrated that the cellular microenvironment considerably influences the plasticity of seminomas (TCam-2 cells). Upon a microenvironment-triggered inhibition of the BMP signaling pathway in vivo (murine flank or brain), seminomatous TCam-2 cells reprogram to an EC-like cell fate. We identified SOX2 as a key factor activated upon BMP inhibition mediating the reprogramming process by regulating pluripotency, reprogramming and epigenetic factors. Indeed, CRISPR/Cas9 SOX2-deleted TCam-2 cells were able to maintain a seminoma-cell fate in vivo for about six weeks, but after six weeks in vivo still small sub-populations initiated differentiation. Closer analyses of these differentiated clusters suggested that the pioneer factor FOXA2 might be the driving force behind this induction of differentiation, since many FOXA2 interacting genes and differentiation factors like AFP, EOMES, CDX1, ALB, HAND1, DKK, DLK1, MSX1 and PITX2 were upregulated. In this study, we generated TCam-2 cells double-deficient for SOX2 and FOXA2 using the CRISPR/Cas9 technique and xenografted those cells into the flank of nude mice. Upon loss of SOX2 and FOXA2, TCam-2 maintained a seminoma cell fate for at least twelve weeks, demonstrating that both factors are key players in the reprogramming to an EC-like cell fate. Therefore, our study adds an important piece to the puzzle of GCT development and plasticity, providing interesting insights in what can be expected in a patient, when GCT cells are confronted with different microenvironments.

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Signaling dynamics control cell fate in the early Drosophila embryo

10.1242/prelights.5188 ◽

2018 ◽

Author(s):

Yara E. Sánchez Corrales

Keyword(s):

Cell Fate ◽

Control Cell ◽

Drosophila Embryo ◽

Signaling Dynamics ◽

Early Drosophila Embryo

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A translational block to HSPG synthesis permits BMP signaling in the early Drosophila embryo

Development ◽

10.1242/dev.017061 ◽

2008 ◽

Vol 135 (6) ◽

pp. 1039-1047 ◽

Cited By ~ 31

Author(s):

D. J. Bornemann ◽

S. Park ◽

S. Phin ◽

R. Warrior

Keyword(s):

Bmp Signaling ◽

Drosophila Embryo ◽

Early Drosophila Embryo ◽

Translational Block

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Decoding temporal interpretation of the morphogen Bicoid in the early Drosophila embryo

10.1101/110841 ◽

2017 ◽

Cited By ~ 1

Author(s):

Anqi Huang ◽

Christopher Amourda ◽

Shaobo Zhang ◽

Nicholas S. Tolwinski ◽

Timothy E. Saunders

Keyword(s):

Cell Fate ◽

Spatial Information ◽

Drosophila Embryo ◽

High Temporal Resolution ◽

Local Concentration ◽

Cell Fates ◽

Cell Fate Decisions ◽

Gap Gene ◽

Early Drosophila Embryo ◽

Time Specific

SUMMARYMorphogen gradients provide essential spatial information during development. Not only the local concentration but also duration of morphogen exposure is critical for correct cell fate decisions. Yet, how and when cells temporally integrate signals from a morphogen remains unclear. Here, we use optogenetic manipulation to switch off Bicoid-dependent transcription in the early Drosophila embryo with high temporal resolution, allowing time-specific and reversible manipulation of morphogen signalling. We find that Bicoid transcriptional activity is dispensable for embryonic viability in the first hour after fertilization, but persistently required throughout the rest of the blastoderm stage. Short interruptions of Bicoid activity alter the most anterior cell fate decisions, while prolonged inactivation expands patterning defects from anterior to posterior. Such anterior susceptibility correlates with high reliance of anterior gap gene expression on Bicoid. Therefore, cell fates exposed to higher Bicoid concentration require input for longer duration, demonstrating a previously unknown aspect of morphogen decoding.

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Shuttling of Dorsal by Cactus: mechanism and implications

10.1101/739284 ◽

2019 ◽

Author(s):

Allison E. Schloop ◽

Sophia Carrell-Noel ◽

Gregory T. Reeves

Keyword(s):

Cell Types ◽

Bmp Signaling ◽

Previous Literature ◽

Drosophila Embryo ◽

Morphogen Gradient ◽

Facilitated Diffusion ◽

Morphogen Gradients ◽

Binding Partner ◽

Early Drosophila Embryo ◽

Gradient Formation

AbstractIn a developing animal, morphogen gradients act to pattern tissues into distinct domains of cell types. However, despite their prevalence in development, morphogen gradient formation is a matter of debate. In our recent publication, we showed that the Dorsal/NF-κB morphogen gradient, which patterns the DV axis of the early Drosophila embryo, is partially established by a mechanism of facilitated diffusion. This mechanism, also known as “shuttling,” occurs when a binding partner of the morphogen facilitates the diffusion of the morphogen, allowing it to accumulate at a given site. In this case, the inhibitor Cactus/IκB facilitates the diffusion of Dorsal/NF-κB. In the fly embryo, we used computation and experiment to not only show that shuttling occurs in the embryo, but also that it enables the viability of embryos that inherit only one copy of dorsal maternally. Here we further discuss our evidence behind the shuttling mechanism, the previous literature data explained by the mechanism, and how it may also be critical for robustness of development. Finally, we describe an interaction between Dorsal and BMP signaling that is likely affected by shuttling.

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