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Proceedings of the National Academy of... Jul 2020The polar trophoblast overlays the epiblast in eutherian mammals and, depending on the species, has one of two different fates. It either remains a single-layered,...
The polar trophoblast overlays the epiblast in eutherian mammals and, depending on the species, has one of two different fates. It either remains a single-layered, thinning epithelium called "Rauber's layer," which soon disintegrates, or, alternatively, it keeps proliferating, contributing heavily to the population of differentiating, invasive trophoblast cells and, at least in mice, to the induction of gastrulation. While loss of the persistent polar trophoblast in mice leads to reduced induction of gastrulation, we show here that prevention of the loss of the polar trophoblast in cattle results in ectopic domains of the gastrulation marker, This phenotype, and increased epiblast proliferation, arose when Rauber's layer was maintained for a day longer by countering apoptosis through BCL2 overexpression. This suggests that the disappearance of Rauber's layer is a necessity, presumably to avoid excessive signaling interactions between this layer and the subjacent epiblast. We note that, in all species in which the polar trophoblast persists, including humans and mice, ectopic polar trophoblast signaling is prevented via epiblast cavitation which leads to the (pro)amniotic cavity, whose function is to distance the central epiblast from such signaling interactions.
Topics: Animals; Apoptosis; Cattle; Cell Differentiation; Cell Proliferation; Female; Fetal Proteins; Gastrulation; Germ Layers; Mice; Proto-Oncogene Proteins c-bcl-2; T-Box Domain Proteins; Trophoblasts
PubMed: 32601185
DOI: 10.1073/pnas.2002008117 -
Cell Reports Nov 2021As pluripotent human embryonic stem cells progress toward one germ layer fate, they lose the ability to adopt alternative fates. Using a low-dimensional reaction...
As pluripotent human embryonic stem cells progress toward one germ layer fate, they lose the ability to adopt alternative fates. Using a low-dimensional reaction coordinate to monitor progression toward ectoderm, we show that a differentiating stem cell's probability of adopting a mesendodermal fate given appropriate signals falls sharply at a point along the ectoderm trajectory. We use this reaction coordinate to prospectively isolate and profile differentiating cells based on their mesendoderm competence and analyze their RNA sequencing (RNA-seq) and assay for transposase-accessible chromatin using sequencing (ATAC-seq) profiles to identify transcription factors that control the cell's mesendoderm competence. By modulating these key transcription factors, we can expand or contract the window of competence to adopt the mesendodermal fate along the ectodermal differentiation trajectory. The ability of the underlying gene regulatory network to modulate competence is essential for understanding human development and controlling the fate choices of stem cells in vitro.
Topics: Cell Differentiation; Cell Lineage; Gene Expression Profiling; Gene Expression Regulation, Developmental; Gene Regulatory Networks; Germ Layers; Human Embryonic Stem Cells; Humans; Mesoderm; Octamer Transcription Factor-3; RNA-Seq; SOXB1 Transcription Factors
PubMed: 34758327
DOI: 10.1016/j.celrep.2021.109990 -
Mechanisms of Development Sep 2020Gastrulation is generally understood as the morphogenetic processes that result in the spatial organization of the blastomere into the three germ layers, ectoderm,... (Review)
Review
Gastrulation is generally understood as the morphogenetic processes that result in the spatial organization of the blastomere into the three germ layers, ectoderm, mesoderm and endoderm. This review summarizes our current knowledge of the morphogenetic mechanisms in Drosophila gastrulation. In addition to the events that drive mesoderm invagination and germband elongation, we pay particular attention to other, less well-known mechanisms including midgut invagination, cephalic furrow formation, dorsal fold formation, and mesoderm layer formation. This review covers topics ranging from the identification and functional characterization of developmental and morphogenetic control genes to the analysis of the physical properties of cells and tissues and the control of cell and tissue mechanics of the morphogenetic movements in the gastrula.
Topics: Animals; Biomechanical Phenomena; Drosophila melanogaster; Ectoderm; Embryo, Nonmammalian; Endoderm; Gastrula; Gastrulation; Gene Expression Regulation, Developmental; Mesoderm; Morphogenesis
PubMed: 32615151
DOI: 10.1016/j.mod.2020.103629 -
Seminars in Cell & Developmental Biology Nov 2022Gastrulation is a fundamental process during embryonic development, conserved across all multicellular animals [1]. In the majority of metazoans, gastrulation is... (Review)
Review
Gastrulation is a fundamental process during embryonic development, conserved across all multicellular animals [1]. In the majority of metazoans, gastrulation is characterised by large scale morphogenetic remodeling, leading to the conversion of an early pluripotent embryonic cell layer into the three primary 'germ layers': an outer ectoderm, inner endoderm and intervening mesoderm layer. The morphogenesis of these three layers of cells is closely coordinated with cellular diversification, laying the foundation for the generation of the hundreds of distinct specialized cell types in the animal body. The process of gastrulation has for a long time attracted tremendous attention in a broad range of experimental systems ranging from sponges to mice. In humans the process of gastrulation starts approximately 14 days after fertilization and continues for slightly over a week. However our understanding of this important process, as it pertains to human, is limited. Donations of human fetal material at these early stages are exceptionally rare, making it nearly impossible to study human gastrulation directly. Therefore, our understanding of human gastrulation is predominantly derived from animal models such as the mouse [2,3] and from studies of limited collections of fixed whole samples and histological sections of human gastrulae [4-7], some of which date back to over a century ago. More recently we have been gaining valuable molecular insights into human gastrulation using in vitro models of hESCs [8-12] and increasingly, in vitro cultured human and non-human primate embryos [13-16]. However, while methods have been developed to culture human embryos into this stage (and probably beyond), current ethical standards prohibit the culture of human embryos past 14 days again limiting our ability to experimentally probe human gastrulation. This review discusses recent molecular insights from the study of a rare CS 7 human gastrula obtained as a live sample and raises several questions arising from this recent study that it will be interesting to address in the future using emerging models of human gastrulation.
Topics: Animals; Ectoderm; Endoderm; Female; Gastrula; Gastrulation; Humans; Mesoderm; Mice; Pregnancy
PubMed: 35606274
DOI: 10.1016/j.semcdb.2022.05.004 -
Cell Reports Aug 2022During mammalian embryogenesis, spatial regulation of gene expression and cell signaling are functionally coupled with lineage specification, patterning of tissue...
During mammalian embryogenesis, spatial regulation of gene expression and cell signaling are functionally coupled with lineage specification, patterning of tissue progenitors, and germ layer morphogenesis. While the mouse model has been instrumental for understanding mammalian development, comparatively little is known about human and non-human primate gastrulation due to the restriction of both technical and ethical issues. Here, we present a spatial and temporal survey of the molecular dynamics of cell types populating the non-human primate embryos during gastrulation. We reconstructed three-dimensional digital models from serial sections of cynomolgus monkey (Macaca fascicularis) gastrulating embryos at 1-day temporal resolution from E17 to E21. Spatial transcriptomics identifies gene expression profiles unique to the germ layers. Cross-species comparison reveals a developmental coordinate of germ layer segregation between mouse and primates, and species-specific transcription programs during gastrulation. These findings offer insights into evolutionarily conserved and divergent processes during mammalian gastrulation.
Topics: Animals; Embryo, Mammalian; Gastrulation; Gene Expression Regulation, Developmental; Germ Layers; Macaca fascicularis; Mammals; Mice; Transcriptome
PubMed: 36044859
DOI: 10.1016/j.celrep.2022.111285 -
Developmental Cell Mar 2022Human pluripotent stem cells (hPSCs) can self-renew indefinitely or can be induced to differentiate. We previously showed that exogenous glutamine (Gln) withdrawal...
Human pluripotent stem cells (hPSCs) can self-renew indefinitely or can be induced to differentiate. We previously showed that exogenous glutamine (Gln) withdrawal biased hPSC differentiation toward ectoderm and away from mesoderm. We revealed that, although all three germ lineages are capable of de novo Gln synthesis, only ectoderm generates sufficient Gln to sustain cell viability and differentiation, and this finding clarifies lineage fate restrictions under Gln withdrawal. Furthermore, we found that Gln acts as a signaling molecule for ectoderm that supersedes lineage-specifying cytokine induction. In contrast, Gln in mesoderm and endoderm is the preferred precursor of α-ketoglutarate without a direct signaling role. Our work raises a question about whether the nutrient environment functions directly in cell differentiation during development. Interestingly, transcriptome analysis of a gastrulation-stage human embryo shows that unique Gln enzyme-encoding gene expression patterns may also distinguish germ lineages in vivo. Together, our study suggests that intracellular Gln may help coordinate differentiation of the three germ layers.
Topics: Cell Differentiation; Cell Lineage; Endoderm; Germ Layers; Glutamine; Humans; Mesoderm; Pluripotent Stem Cells
PubMed: 35216682
DOI: 10.1016/j.devcel.2022.02.003 -
Current Biology : CB Mar 2005Vertebrate embryogenesis entails an exquisitely coordinated combination of cell proliferation, fate specification and movement. After induction of the germ layers, the... (Review)
Review
Vertebrate embryogenesis entails an exquisitely coordinated combination of cell proliferation, fate specification and movement. After induction of the germ layers, the blastula is transformed by gastrulation movements into a multilayered embryo with head, trunk and tail rudiments. Gastrulation is heralded by formation of a blastopore, an opening in the blastula. The axial side of the blastopore is marked by the organizer, a signaling center that patterns the germ layers and regulates gastrulation movements. During internalization, endoderm and mesoderm cells move via the blastopore beneath the ectoderm. Epiboly movements expand and thin the nascent germ layers. Convergence movements narrow the germ layers from lateral to medial while extension movements elongate them from head to tail. Despite different morphology, parallels emerge with respect to the cellular and genetic mechanisms of gastrulation in different vertebrate groups. Patterns of gastrulation cell movements relative to the blastopore and the organizer are similar from fish to mammals, and conserved molecular pathways mediate gastrulation movements.
Topics: Animals; Cell Differentiation; Cell Movement; Embryonic Induction; Endoderm; Gastrula; Gene Expression Regulation, Developmental; Mesoderm; Models, Biological; Organizers, Embryonic; Signal Transduction; Vertebrates
PubMed: 15797016
DOI: 10.1016/j.cub.2005.03.016 -
Mechanisms of Development Dec 2018Pluripotent stem cells (PSCs) are capable of self-renewing and producing all cell types derived from the three germ layers in response to developmental cues,... (Review)
Review
Pluripotent stem cells (PSCs) are capable of self-renewing and producing all cell types derived from the three germ layers in response to developmental cues, constituting an important promise for regenerative medicine. Pluripotency depends on specific transcription factors (TFs) that induce genes required to preserve the undifferentiated state and repress other genes related to differentiation. The transcription machinery and regulatory components such as TFs are recruited dynamically on their target genes making it essential exploring their dynamics in living cells to understand the transcriptional output. Non-invasive and very sensitive fluorescence microscopy methods are making it possible visualizing the dynamics of TFs in living specimens, complementing the information extracted from studies in fixed specimens and bulk assays. In this work, we briefly describe the basis of these microscopy methods and review how they contributed to our knowledge of the function of TFs relevant to embryo development and cell differentiation in a variety of systems ranging from single cells to whole organisms.
Topics: Animals; Cell Differentiation; Embryonic Development; Germ Layers; Humans; Microscopy, Fluorescence; Pluripotent Stem Cells; Transcription Factors; Transcription, Genetic
PubMed: 29753812
DOI: 10.1016/j.mod.2018.05.003 -
Proceedings of the National Academy of... Jun 2021Markers for the endoderm and mesoderm germ layers are commonly expressed together in the early embryo, potentially reflecting cells' ability to explore potential fates...
Markers for the endoderm and mesoderm germ layers are commonly expressed together in the early embryo, potentially reflecting cells' ability to explore potential fates before fully committing. It remains unclear when commitment to a single-germ layer is reached and how it is impacted by external signals. Here, we address this important question in , a convenient model system in which mesodermal and endodermal fates are associated with distinct cellular movements during gastrulation. Systematically applying endoderm-inducing extracellular signal-regulated kinase (ERK) signals to the ventral medial embryo-which normally only receives a mesoderm-inducing cue-reveals a critical time window during which mesodermal cell movements and gene expression are suppressed by proendoderm signaling. We identify the ERK target gene () as the main cause of the ventral furrow suppression and use computational modeling to show that Hkb repression of the mesoderm-associated gene is sufficient to account for a broad range of transcriptional and morphogenetic effects. Our approach, pairing precise signaling perturbations with observation of transcriptional dynamics and cell movements, provides a general framework for dissecting the complexities of combinatorial tissue patterning.
Topics: Animals; DNA-Binding Proteins; Drosophila Proteins; Drosophila melanogaster; Endoderm; Gastrula; Gastrulation; MAP Kinase Signaling System; Mesoderm; Models, Biological
PubMed: 34083443
DOI: 10.1073/pnas.2102691118 -
Journal of Biomedical Science Aug 2019Thrombomodulin (TM), an integral membrane protein, has long been known for its anticoagulant activity. Recent studies showed that TM displays multifaceted activities,...
BACKGROUND
Thrombomodulin (TM), an integral membrane protein, has long been known for its anticoagulant activity. Recent studies showed that TM displays multifaceted activities, including the involvement in cell adhesion and collective cell migration in vitro. However, whether TM contributes similarly to these biological processes in vivo remains elusive.
METHODS
We adapted zebrafish, a prominent animal model for studying molecular/cellular activity, embryonic development, diseases mechanism and drug discovery, to examine how TM functions in modulating cell migration during germ layer formation, a normal and crucial physiological process involving massive cell movement in the very early stages of life. In addition, an in vivo assay was developed to examine the anti-hemostatic activity of TM in zebrafish larva.
RESULTS
We found that zebrafish TM-b, a zebrafish TM-like protein, was expressed mainly in vasculatures and displayed anti-hemostatic activity. Knocking-down TM-b led to malformation of multiple organs, including vessels, heart, blood cells and neural tissues. Delayed epiboly and incoherent movement of yolk syncytial layer were also observed in early TM-b morphants. Whole mount immunostaining revealed the co-localization of TM-b with both actin and microtubules in epibolic blastomeres. Single-cell tracking revealed impeded migration of blastomeres during epiboly in TM-b-deficient embryos.
CONCLUSION
Our results showed that TM-b is crucial to the collective migration of blastomeres during germ layer formation. The structural and functional compatibility and conservation between zebrafish TM-b and mammalian TM support the properness of using zebrafish as an in vivo platform for studying the biological significance and medical use of TM.
Topics: Animals; Blastomeres; Embryo, Nonmammalian; Germ Layers; Morphogenesis; Organogenesis; Thrombomodulin; Zebrafish; Zebrafish Proteins
PubMed: 31451113
DOI: 10.1186/s12929-019-0549-2