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in category developmental biology

2,702 results found. For more information, click each entry to expand.

101: Establishment In Culture Of Expanded Potential Stem Cells
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Posted to bioRxiv 06 Apr 2017

Establishment In Culture Of Expanded Potential Stem Cells
1,601 downloads developmental biology

Jian Yang, David J. Ryan, Wei Wang, Jason Cheuk-Ho Tsang, Guocheng Lan, Hideki Masaki, Xuefei Gao, Liliana Antunes, Yong Yu, Zhexin Zhu, Juexuan Wang, Aleksandra A. Kolodziejczyk, Lia S Campos, Cui Wang, Fengtang Yang, Zhen Zhong, Beiyuan Fu, Melanie Eckersley-Maslin, Michael Woods, Yosuke Tanaka, Adam C. Wilkinson, James Bussell, Jacqui White, Ramiro Ramirez-Solis, Wolf Reik, Berthold Göttgens, Sarah A. Teichmann, Hiromitsu Nakauchi, Xiangang Zou, Liming Lu, Pentao Liu

Mouse embryonic stem cells are derived from in vitro explantation of blastocyst epiblasts and contribute to both the somatic lineage and germline when returned to the blastocyst but are normally excluded from the trophoblast lineage and primitive endoderm. Here, we report that cultures of expanded potential stem cells (EPSCs) can be established from individual blastomeres, by direct conversion of mouse embryonic stem cells (ESCs) and by genetically reprogramming somatic cells. Remarkably, a single EPSC contributes to the embryo proper and placenta trophoblasts in chimeras. Critically, culturing EPSCs in a trophoblast stem cell (TSC) culture condition permits direct establishment of TSC lines without genetic modification. Molecular analyses including single cell RNA-seq reveal that EPSCs share cardinal pluripotency features with ESCs but have an enriched blastomere transcriptomic signature and a dynamic DNA methylome. These proof-of-concept results open up the possibility of establishing cultures of similar stem cells in other mammalian species.

102: Live imaging of heart tube development in mouse reveals alternating phases of cardiac differentiation and morphogenesis
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Posted to bioRxiv 01 Aug 2017

Live imaging of heart tube development in mouse reveals alternating phases of cardiac differentiation and morphogenesis
1,600 downloads developmental biology

Kenzo Ivanovitch, Susana Temiño, Miguel Torres

During vertebrate heart development two progenitor populations, first and second heart fields (FHF, SHF), sequentially contribute to longitudinal subdivisions of the heart tube (HT), with the FHF contributing the left ventricle and part of the atria, and the SHF the rest of the heart. Here we study the dynamics of cardiac differentiation and morphogenesis by tracking individual cells in live analysis of mouse embryos. We report that during an initial phase, FHF precursors differentiate rapidly to form a cardiac crescent, while limited morphogenesis takes place. In a second phase, no differentiation occurs while extensive morphogenesis, including splanchnic mesoderm sliding over the endoderm, results in HT formation. In a third phase, cardiac precursor differentiation resumes and contributes to SHF-derived regions and the dorsal closure of the HT. These results reveal tissue-level coordination between morphogenesis and differentiation during HT formation and provide a new framework to understand heart development.

103: Reconstruction of cell lineages and behaviors underlying arthropod limb outgrowth with multi-view light-sheet imaging and tracking
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Posted to bioRxiv 28 Feb 2017

Reconstruction of cell lineages and behaviors underlying arthropod limb outgrowth with multi-view light-sheet imaging and tracking
1,595 downloads developmental biology

Carsten Wolff, Jean-Yves Tinevez, Tobias Pietzsch, Evangelia Stamataki, Benjamin Harich, Stephan Preibisch, Spencer Shorte, Philipp J. Keller, Pavel Tomancak, Anastasios Pavlopoulos

During development coordinated cell behaviors orchestrate tissue and organ morphogenesis to suit the lifestyle of the organism. We have used here the crustacean Parhyale hawaiensis to study the cellular basis of limb development. Transgenic Parhyale embryos with fluorescently labeled nuclei were imaged at high spatiotemporal resolution with multi-view light-sheet fluorescence microscopy over several days of embryogenesis spanning appendage morphogenesis from early specification up to late differentiation stages. Cell tracking with a new tool called Massive Multi-view Tracker (MaMuT) enabled the reconstruction of the complete cell lineage of an outgrowing thoracic limb with single-cell resolution. In silico clonal analyses suggested that the limb primordium becomes subdivided from an early stage first into anterior-posterior and then into dorsal-ventral compartments whose boundaries intersect at the distal tip of the growing limb. Limb bud formation is associated with the spatial modulation of cell proliferation, while limb elongation is also driven by the preferential orientation of division of epidermal cells along the proximal-distal axis of growth. Cellular reconstructions were predictive of the expression patterns of limb development genes including the Decapentaplegic (Dpp) morphogen.

104: Bayesian inference of transcriptional branching identifies regulators of early germ cell development in humans
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Posted to bioRxiv 24 Jul 2017

Bayesian inference of transcriptional branching identifies regulators of early germ cell development in humans
1,593 downloads developmental biology

Christopher A. Penfold, Anastasiya Sybirna, John Reid, Aracely Castillo Venzor, Elena Drousioti, Yun Huang, Murray Grant, Lorenz Wernisch, Zoubin Ghahramani, M. Azim Surani

During embryonic development, cells undertake a series of cell fate decisions to form a complete organism, epitomising a branching process. In some instances, these decisions are reversible, particularly during the onset of disease. Single cell transcriptomics provides a rich resource to explore the temporal progression of bifurcations in gene activity and are therefore useful for elucidating the mechanisms of cell fate decisions, provided that the cells can be suitably ordered over a developmental axis. Most methods for inferring this ordering have been developed for heterogeneous populations of cells collected at single time points, with few approaches specifically designed with structured data in mind, such as single cell time-series data. Recent advances based on Gaussian process latent variable models (GPLVMs) address this by allowing the incorporation of prior information, such as capture time, to yield more accurate ordering of cells. However, such approaches do not allow the ordering of cells over developmental processes with more than one branch. Here we develop a pseudotime approach that allows the ordering of cells over developmental trajectories with arbitrary numbers of branches, in the form of branch-recombinant Gaussian process latent variable models (B-RGPLVM). We use first demonstrate the advantage of our approach compared to existing pseudotime algorithms. Subsequently, we use B-RGPLVMs to infer cell ordering that occurs during early human development as primordial germ cells (PGCs), the precursors of sperm and egg, and somatic cells diverge in the developing embryo. Using our approach, we identify known master regulators of human PGC development, and predict roles for a variety of signalling pathways, as well as transcription factors and epigenetic modifiers. By concentrating on the earliest branched signalling events, we identified an antagonistic role for FGF receptor (FGFR) signalling pathway in the acquisition of competence for human PGC fate. We experimentally validate our predictions using pharmacological blocking of FGFR or its downstream effectors (MEK, PI3K and JAK), and demonstrate enhanced competency for PGC fate in vitro. Thus, B-RGPLVMs represent a powerful and flexible data-driven approach for dissecting the temporal dynamics of cell fate decisions, providing unique insights into the mechanisms of early embryogenesis.

105: Dissecting the dynamics of signaling events in the BMP, WNT, and NODAL cascade during self-organized fate patterning in human gastruloids.
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Posted to bioRxiv 10 Oct 2018

Dissecting the dynamics of signaling events in the BMP, WNT, and NODAL cascade during self-organized fate patterning in human gastruloids.
1,588 downloads developmental biology

Sapna Chhabra, Lizhong Liu, Ryan Goh, Aryeh Warmflash

During gastrulation, the pluripotent epiblast is patterned into the three germ layers, which form the embryo proper. This patterning requires a signaling cascade involving the BMP, WNT and NODAL pathways; however, how these pathways regulate one another in space and time to generate cell-fate patterns remains unknown. Using a human gastruloid model, we show that BMP signaling initiates a wave of WNT signaling, which, in turn, initiates a wave of NODAL signaling. While WNT propagation depends on continuous BMP activity, NODAL propagates independently of upstream signals. We further show that the duration of BMP signaling determines the position of mesodermal differentiation while WNT and NODAL synergize to achieve maximal differentiation. The waves of both WNT and NODAL signaling activity extend farther into the colony than mesodermal differentiation. Combining dynamic measurements of signaling activity with mathematical modeling revealed that the formation of signaling waves is inconsistent with WNT and NODAL forming a stable spatial pattern in signaling activities, and the final signaling state is spatially homogeneous. Thus, dynamic eventsin the BMP, WNT, and NODAL signaling cascade, in the absence of a signaling gradient, have the potential to mediate epiblast patterning.

106: In vitro characterization of the human segmentation clock
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Posted to bioRxiv 04 Nov 2018

In vitro characterization of the human segmentation clock
1,583 downloads developmental biology

Margarete Diaz-Cuadros, Daniel E. Wagner, Christoph Budjan, Alexis Hubaud, Jonathan Touboul, Arthur Michaut, Ziad Al Tanoury, Kumiko Yoshioka-Kobayashi, Yusuke Niino, Ryoichiro Kageyama, Atsushi Miyawaki, Olivier Pourquié

The vertebral column is characterized by the periodic arrangement of vertebrae along the anterior-posterior (AP) axis. This segmental or metameric organization is established early in embryogenesis when pairs of embryonic segments called somites are rhythmically produced by the presomitic mesoderm (PSM). The tempo of somite formation is controlled by a molecular oscillator known as the segmentation clock. While this oscillator has been well characterized in model organisms whether a similar oscillator exists in humans remains unknown. We have previously shown that human embryonic stem (ES) cells or induced pluripotent stem (iPS) cells can differentiate in vitro into PSM upon activation of the Wnt signaling pathway combined with BMP inhibition. Here, we show that these human PSM cells exhibit Notch and YAP-dependent oscillations of the cyclic gene HES7 with a 5-hour period. Single cell RNA-sequencing comparison of the differentiating iPS cells with mouse PSM reveals that human PSM cells follow a similar differentiation path and exhibit a remarkably coordinated differentiation sequence. We also demonstrate that FGF signaling controls the phase and period of the oscillator. This contrasts with classical segmentation models such as the Clock and Wavefront where FGF merely implements a signaling threshold specifying where oscillations stop. Overall, our work identifying the human segmentation clock represents an important breakthrough for human developmental biology.

107: Micro computed tomography as an accessible imaging platform for exploring organism development and human disease modeling
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Posted to bioRxiv 13 Aug 2018

Micro computed tomography as an accessible imaging platform for exploring organism development and human disease modeling
1,563 downloads developmental biology

Todd A. Schoborg, Samantha L. Smith, Lauren N. Smith, H. Douglas Morris, Nasser M. Rusan

Understanding how events at the molecular and cellular scales contribute to tissue form and function is key to uncovering mechanisms driving animal development, physiology and disease. Elucidating these mechanisms has been enhanced through the study of model organisms and the use of sophisticated genetic, biochemical and imaging tools. Here we present an optimized method for non-invasive imaging of Drosophila melanogaster at high resolution using micro computed tomography (μ-CT). Our method allows for rapid processing of intact animals at any developmental stage, provides precise quantitative assessment of tissue size and morphology, and permits analysis of inter-organ relationships. We then use the power of μ-CT imaging to model human diseases through the characterization of microcephaly in the fly. Our work demonstrates that μ-CT is a versatile and accessible tool that complements standard imaging techniques, capable of uncovering novel biological mechanisms that have remained undocumented due to limitations of current methods.

108: Transcriptome landscape of the developing olive fruit fly embryo delineated by Oxford Nanopore long-read RNA-Seq
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Posted to bioRxiv 24 Nov 2018

Transcriptome landscape of the developing olive fruit fly embryo delineated by Oxford Nanopore long-read RNA-Seq
1,561 downloads developmental biology

Anthony Bayega, Spyros Oikonomopoulos, Eleftherios Zorbas, Yu Chang Wang, Maria-Eleni Gregoriou, Konstantina T Tsoumani, Kostas D Mathiopoulos, Jiannis Ragoussis

The olive fruit fly or olive fly (Bactrocera oleae) is the most important pest of cultivated olive trees. Like all insects the olive fly undergoes complete metamorphosis. However, the transcription dynamics that occur during early embryonic development have not been explored, while detailed transcriptomic analysis in the absence of a fully annotated genome is challenging. We collected olive fly embryos at hourly intervals for the first 6 hours of development and performed full-length cDNA-Seq using a purpose designed SMARTer cDNA synthesis protocol followed by sequencing on the MinION (Oxford Nanopore Technologies). We generated 31 million total reads across the timepoints (median yield 4.2 million per timepoint). The reads showed 98 % alignment rate to the olive fly genome and 91 % alignment rate to the NBCI predicted B. oleae gene models. Over 50 % of the expressed genes had at least one read covering its entire length validating our full-length RNA-Seq procedure. Expression of 68 % of the predicted B. oleae genes was detected in the first six hours of development. We generated a de novo transcriptome assembly of the olive fly and identified 3553 novel genes and a total of 79,810 transcripts; a fourfold increase in transcriptome diversity compared to the NCBI predicted transcriptome. On a global scale, the first six hours of embryo development were characterized by dramatic transcriptome changes with the total number of transcripts per embryo dropping to half from the first hour to the second hour of embryo development. Clustering of genes based on temporal co-expression followed by gene-set enrichment analysiss of genes expressed in the first six hours of embryo development showed that genes involved in transcription and translation, macro-molecule biosynthesis, and neurodevelopment were highly enriched. These data provide the first insight into the transcriptome landscape of the developing olive fly embryo. The data also reveal transcript signatures of sex development. Overall, full-length sequencing of the cDNA molecules permitted a detailed characterization of the isoform complexity and the transcriptional dynamics of the first embryonic stages of the B. oleae.

109: A high-resolution mRNA expression time course of embryonic development in zebrafish
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Posted to bioRxiv 10 Feb 2017

A high-resolution mRNA expression time course of embryonic development in zebrafish
1,556 downloads developmental biology

Richard J. White, John E Collins, Ian M. Sealy, Neha Wali, Christopher M. Dooley, Zsofia Digby, Derek L. Stemple, Daniel N Murphy, Thibaut Hourlier, Anja Füllgrabe, Matthew P. Davis, Anton J. Enright, Elisabeth M. Busch-Nentwich

We have produced an mRNA expression time course of zebrafish development across 18 time points from 1-cell to 5 days post-fertilisation sampling individual and pools of embryos. Using poly(A) pulldown stranded RNA-seq and a 3′ end transcript counting method we characterise the temporal expression profiles of 23,642 genes. We identify temporal and functional transcript co-variance that associates 5,024 unnamed genes with distinct developmental time points. Specifically, a class of over 100 previously uncharacterised zinc finger domain containing genes, located on the long arm of chromosome 4, is expressed in a sharp peak during zygotic genome activation. The data reveal complex and widespread differential use of exons and previously unidentified 3′ ends across development, new primary microRNA transcripts and temporal divergence of gene paralogues generated in the teleost genome duplication. To make this dataset a useful baseline reference, the data are accessible to browse and download at Expression Atlas and Ensembl.

110: Evaluation and rational design of guide RNAs for efficient CRISPR/Cas9-mediated mutagenesis in Ciona
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Posted to bioRxiv 28 Feb 2016

Evaluation and rational design of guide RNAs for efficient CRISPR/Cas9-mediated mutagenesis in Ciona
1,549 downloads developmental biology

Shashank Gandhi, Maximilian Haeussler, Florian Razy-Krajka, Lionel Christiaen, Alberto Stolfi

The CRISPR/Cas9 system has emerged as an important tool for various genome engineering applications. A current obstacle to high throughput applications of CRISPR/Cas9 is the imprecise prediction of highly active single guide RNAs (sgRNAs). We previously implemented the CRISPR/Cas9 system to induce tissue-specific mutations in the tunicate Ciona. In the present study, we designed and tested 83 single guide RNA (sgRNA) vectors targeting 23 genes expressed in the cardiopharyngeal progenitors and surrounding tissues of Ciona embryo. Using high-throughput sequencing of mutagenized alleles, we identified guide sequences that correlate with sgRNA mutagenesis activity and used this information for the rational design of all possible sgRNAs targeting the Ciona transcriptome. We also describe a one-step cloning-free protocol for the assembly of sgRNA expression cassettes. These cassettes can be directly electroporated as unpurified PCR products into Ciona embryos for sgRNA expression in vivo, resulting in high frequency of CRISPR/Cas9-mediated mutagenesis in somatic cells of electroporated embryos. We found a strong correlation between the frequency of an Ebf loss-of-function phenotype and the mutagenesis efficacies of individual Ebf-targeting sgRNAs tested using this method. We anticipate that our approach can be scaled up to systematically design and deliver highly efficient sgRNAs for the tissue-specific investigation of gene functions in Ciona.

111: DUX4 regulates oocyte to embryo transition in human
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Posted to bioRxiv 12 Aug 2019

DUX4 regulates oocyte to embryo transition in human
1,542 downloads developmental biology

Sanna Vuoristo, Christel Hydén-Granskog, Masahito Yoshihara, Shruti Bhagat, Lisa Gawriyski, Eeva-Mari Jouhilahti, Anastassius Damdimopoulos, Vipin Ranga, Mahlet Tamirat, Mikko Huhtala, Kosuke Hashimoto, Kaarel Krjutškov, Gaëlle Recher, Sini Ezer, Priit Paluoja, Pauliina Paloviita, Yujiro Takegami, Ai Kanemaru, Karolina Lundin, Tomi Airenne, Timo Otonkoski, Juha S Tapanainen, Hideya Kawaji, Yasuhiro Murakawa, Thomas R. Bürglin, Markku Varjosalo, Mark S Johnson, Timo Tuuri, Shintaro Katayama, Juha Kere

During the human oocyte-to-embryo transition, the fertilized oocyte undergoes final maturation and the embryo genome is gradually activated during the first three cell divisions. How this transition is coordinated in humans is largely unknown. We show that the double homeodomain transcription factor DUX4 contributes to this transition. DUX4 knockdown in human zygotes caused insufficient transcriptome reprogramming as observed three days after fertilization. Induced DUX4 expression in human embryonic stem cells activated transcription of thousands of newly identified bi-directional transcripts, including putative enhancers for embryonic genome activation genes such as LEUTX. DUX4 protein interacted with transcriptional modifiers that are known to couple enhancers and promoters. Taken together, our results reveal that DUX4 is a pioneer regulating oocyte-to-embryo transition in human through activation of intergenic genome, especially enhancers, and hence setting the stage for early human embryo development.

112: A Transcriptional Lineage of the Early C. elegans Embryo
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Posted to bioRxiv 08 Apr 2016

A Transcriptional Lineage of the Early C. elegans Embryo
1,537 downloads developmental biology

Sophia C Tintori, Erin Osborne Nishimura, Patrick Golden, Jason D Lieb, Bob Goldstein

During embryonic development, cells must establish fates, morphologies and behaviors in coordination with one another to form a functional body. A prevalent hypothesis for how this coordination is achieved is that each cell's fate and behavior is determined by a defined mixture of RNAs. Only recently has it become possible to measure the full suite of transcripts in a single cell. Here we quantify the abundance of every mRNA transcript in each cell of the C. elegans embryo up to the 16-cell stage. We describe spatially dynamic expression, quantify cell-specific differential activation of the zygotic genome, and identify critical developmental genes previously unappreciated because of their partial redundancy. We present an interactive data visualization tool that allows broad access to our dataset. This genome-wide single-cell map of mRNA abundance, alongside the well-studied life history and fates of each cell, describes at a cellular resolution the mRNA landscape that guides development.

113: Self-organization of a functional human organizer by combined WNT and NODAL signalling
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Posted to bioRxiv 15 Dec 2017

Self-organization of a functional human organizer by combined WNT and NODAL signalling
1,536 downloads developmental biology

I. Martyn, T.Y. Kanno, A. Ruzo, E.D. Siggia, A.H. Brivanlou

In amniotes, the development of the primitive streak (PS) and its accompanying 'organizer' define the first stages of gastrulation. Despite detailed characterization in model organisms, the analogous human structures remain a mystery. We have previously shown that when stimulated with BMP4, micropatterned colonies of human embryonic stem cells (hESCs) self-organize to generate early embryonic germ layers1. Here we show that in the same type of colonies WNT signalling is sufficient to induce a PS, and WNT with ACTIVIN is sufficient to induce an organizer, as characterized by embryo-like sharp boundary formation, epithelial-to-mesenchymal transition (EMT) markers, and expression of the organizer specific transcription factor GSC. Moreover, when grafted into chick embryos, WNT and ACTIVIN treated human cells induce and contribute autonomously to a secondary axis while inducing neural fate in the host. This fulfills the most stringent functional criteria for an organizer, and its discovery represents a major milestone in human embryology.

114: Cell type boundaries organize plant development
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Posted to bioRxiv 11 Apr 2017

Cell type boundaries organize plant development
1,528 downloads developmental biology

Monica Pia Caggiano, Xiulian Yu, Neha Bhatia, André Larsson, Hasthi Ram, Carolyn Ohno, Pia Sappl, Elliot M. Meyerowitz, Henrik Jönsson, Marcus G. Heisler

In plants the dorsoventral boundary of leaves defines an axis of symmetry through the centre of the organ separating the top (dorsal) and bottom (ventral) tissues. Although the positioning of this boundary is critical for leaf morphogenesis, how the boundary is established and how it influences development remains unclear. Using live-imaging and perturbation experiments we show that leaf orientation, morphology and position are pre-patterned by HD-ZIPIII and KAN gene expression in the shoot, leading to a model in which dorsoventral genes coordinate to regulate plant development by localizing auxin response between their expression domains. However we also find that auxin levels feedback on dorsoventral patterning by spatially organizing HD-ZIPIII and KAN expression in the shoot periphery. By demonstrating that the regulation of these genes by auxin also governs their response to wounds, our results also provide a parsimonious explanation for the influence of wounds on leaf dorsoventrality.

115: A simple bioreactor-based method to generate kidney organoids from pluripotent stem cells
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Posted to bioRxiv 20 Dec 2017

A simple bioreactor-based method to generate kidney organoids from pluripotent stem cells
1,520 downloads developmental biology

Aneta Przepiorski, Veronika Sander, Tracy Tran, Jennifer A. Hollywood, Brie Sorrenson, Jen-Hsing Shih, EJ Wolvetang, Andrew P. McMahon, Teresa M Holm, Alan J. Davidson

Kidney organoids generated from human pluripotent stem cells have the potential to revolutionize how kidney development and injury are studied. Current protocols are technically complex and suffer from poor reproducibility and high reagent costs restricting scalability. To overcome these issues, we have established a simple, inexpensive and robust method to grow kidney organoids in bulk from human induced pluripotent stem cells. Our organoids develop tubular structures by day (d) 8 and show optimal tissue morphology at d14. A comparison with fetal human kidney suggests that d14 organoid renal structures most closely resemble capillary loop stage nephrons. We show that deletion of HNF1B, a transcription factor linked to congenital kidney defects, interferes with tubulogenesis, validating our experimental system for studying renal developmental biology. Taken together, our protocol provides a fast, efficient and cost-effective method for generating large quantities of human fetal kidney tissue, enabling the study of normal and aberrant human renal development.

116: Morphogen dynamics control patterning in a stem cell model of the human embryo
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Posted to bioRxiv 13 Oct 2017

Morphogen dynamics control patterning in a stem cell model of the human embryo
1,517 downloads developmental biology

Idse Heemskerk, Kari Burt, Matthew Miller, Sapna Chhabra, M. Cecilia Guerra, Aryeh Warmflash

During embryonic development, diffusible signaling molecules called morphogens are thought to determine cell fates in a concentration-dependent manner, and protocols for directed stem cell differentiation are based on this picture. However, in the mammalian embryo, morphogen concentrations change rapidly compared to the time for making cell fate decisions. It is unknown how changing ligand levels are interpreted, and whether the precise timecourse of ligand exposure plays a role in cell fate decisions. Nodal and BMP4 are morphogens crucial for gastrulation in vertebrates. Each pathway has distinct receptor complexes that phosphorylate specific signal transducers, known as receptor-Smads, which then complex with the shared cofactor Smad4 to activate target genes. Here we show in human embryonic stem cells (hESCs) that the response to BMP4 signaling indeed is determined by the ligand concentration, but that unexpectedly, the expression of many mesodermal targets of Activin/Nodal depends on rate of concentration increase. In addition, we use live imaging of hESCs with GFP integrated at the endogenous SMAD4 locus to show that a stem cell model for the human embryo generates a wave of Nodal signaling. Cells experience rapidly increasing Nodal specifically in the region of mesendoderm differentiation. We also demonstrate that pulsatile stimulation with Activin induces repeated strong signaling and enhances mesoderm differentiation. Our results break with the paradigm of concentration-dependent differentiation and demonstrate an important role for morphogen dynamics in the cell fate decisions associated with mammalian gastrulation. They suggest a highly dynamic picture of embryonic patterning where some cell fates depend on rapid concentration increase rather than absolute levels, and point to ligand dynamics as a new dimension to optimize protocols for directed stem cell differentiation.

117: Stage-specific transcriptomes and DNA methylomes indicate an early and transient loss of transposon control in Arabidopsis shoot stem cells
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Posted to bioRxiv 29 Sep 2018

Stage-specific transcriptomes and DNA methylomes indicate an early and transient loss of transposon control in Arabidopsis shoot stem cells
1,511 downloads developmental biology

Ruben Gutzat, Klaus Rembart, Thomas Nussbaumer, Rahul Pisupati, Falko Hofmann, Gabriele Bradamante, Nina Daubel, Angelika Gaidora, Nicole Lettner, Mattia Donà, Magnus Nordborg, Michael D. Nodine, Ortrun Mittelsten Scheid

In contrast to animals, postembryonic development in plants is modular, and aerial organs originate from stem cells in the center of the shoot apical meristem (SAM) throughout life. Descendants of SAM stem cells in the subepidermal layer (L2) will give also rise to male and female gametes 1and therefore can be considered primordial germ cells. In these cells, transmission of somatic mutations including virus and TE insertions must be avoided. Despite their essential role for plant development and intergenerational continuity, a comprehensive molecular analysis of SAM plant stem cells has been missing, due to their low number, deep embedding among non-stem cells and difficult isolation. Here we present a comprehensive analysis of stage-specific gene expression and DNA methylation dynamics in Arabidopsis SAM stem cells. This revealed that stem cell expression signatures are mostly defined by development, but we also identified a core set of differentially expressed stemness genes. Surprisingly, vegetative SAM stem cells showed increased expression of transposable elements (TEs) relative to surrounding cells, despite high expression of genes connected to epigenetic silencing. We also find increasing methylation at CHG and a drop in CHH methylation at TEs before stem cells enter the reproductive lineage, indicating an onset of epigenetic reprogramming at an early stage. Transiently elevated TE expression is reminiscent of that in animal primordial germ cells (PGCs) 2 and demonstrates commonality of transposon biology. Our results connect SAM stem cells with germline development and transposon evolution and will allow future experiments to determine the degree of epigenetic heritability between generations.

118: Staged developmental mapping and X chromosome transcriptional dynamics during mouse spermatogenesis
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Posted to bioRxiv 20 Jun 2018

Staged developmental mapping and X chromosome transcriptional dynamics during mouse spermatogenesis
1,511 downloads developmental biology

Christina Ernst, Nils Eling, Celia P Martinez-Jimenez, John C Marioni, Duncan T. Odom

Understanding male fertility requires an in-depth characterisation of spermatogenesis, the developmental process by which male gametes are generated. Spermatogenesis occurs continuously throughout a male's reproductive window and involves a complex sequence of developmental steps, both of which make this process difficult to decipher at the molecular level. To overcome this, we transcriptionally profiled single cells from multiple distinct stages during the first wave of spermatogenesis, where the most mature germ cell type is known. This naturally enriches for spermatogonia and somatic cell types present at very low frequencies in adult testes. Our atlas, available as a shiny app (https://marionilab.cruk.cam.ac.uk/SpermatoShiny), allowed us to reconstruct the three main processes of spermatogenesis: spermatogonial differentiation, meiosis, and spermiogenesis. Additionally, we profiled the chromatin changes associated with meiotic silencing of the X chromosome, revealing a set of genes specifically and strongly repressed by H3K9me3 in the spermatocyte stage, but which escape post-meiotic silencing in spermatids.

119: Systematic Imaging Reveals Features of Localized mRNAs and Their Changing Subcellular Destinations in Development
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Posted to bioRxiv 09 Sep 2014

Systematic Imaging Reveals Features of Localized mRNAs and Their Changing Subcellular Destinations in Development
1,498 downloads developmental biology

Pavel Tomancak

The asymmetric distribution of cytoplasmic components by mRNA localization is critical for eukaryotic cells and affects large numbers of transcripts. How such global subcellular localization of mRNAs is regulated is still unknown. We combined transcriptomics and systematic imaging to determine tissue-specific expression and subcellular localizations of 5862 mRNAs during Drosophila oogenesis. While the transcriptome is stable and alternative splicing and polyadenylation is rare, cytoplasmic localization of mRNAs is widespread. Localized mRNAs have distinct gene features and diverge in expression level, 3'UTR length and sequence conservation. We show that intracellular localization of mRNAs depends on an intact microtubule cytoskeleton and that specifically the posterior enrichment requires the localization of oskar mRNA to the posterior cortex. Using cross-tissue comparison we revealed that the localization landscape differs substantially between epithelial, germline and embryonic cells and the localization status of mRNAs also changes considerably within the oocyte over the course of oogenesis.

120: Transcriptional induction and mechanical propagation of a morphogenetic wave
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Posted to bioRxiv 29 Sep 2018

Transcriptional induction and mechanical propagation of a morphogenetic wave
1,484 downloads developmental biology

Anais Bailles, Claudio Collinet, Jean-Marc Philippe, Pierre-françois Lenne, Edwin Munro, Thomas Lecuit

Tissue morphogenesis emerges from coordinated cell shape changes driven by actomyosin contractions. Patterns of gene expression regionalize and polarize cell behaviours by controlling actomyosin contractility. Yet how mechanical feedbacks affect tissue morphogenesis is unclear. We report two modes of control over Rho1 and MyosinII activation in the Drosophila endoderm. First, Rho1/MyoII are induced in a primordium via localized transcription of the GPCR ligand Fog. Second, a tissue-scale wave of Rho1/MyoII activation and cell invagination progresses anteriorly. The wave does not require sustained gene transcription, and is not governed by regulated Fog delivery. Instead, MyoII inhibition blocked acute Rho1 activation and propagation, revealing a mechanical feedback driven by MyoII. Last, we identify a cycle of 3D cell deformations whereby MyoII activation and invagination in each row of cells drives adhesion to the vitelline membrane, apical spreading, MyoII activation and invagination in the next row. Thus endoderm morphogenesis emerges from local transcriptional initiation and a mechanically driven wave of cell deformation.

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