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Rxivist combines preprints from bioRxiv with data from Twitter to help you find the papers being discussed in your field. Currently indexing 94,912 bioRxiv papers from 404,161 authors.

Most downloaded bioRxiv papers, all time

in category developmental biology

2,773 results found. For more information, click each entry to expand.

41: Single-cell transcriptome analysis of human, marmoset and mouse embryos reveals common and divergent features of preimplantation development
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Posted to bioRxiv 07 Aug 2018

Single-cell transcriptome analysis of human, marmoset and mouse embryos reveals common and divergent features of preimplantation development
2,517 downloads developmental biology

Thorsten Edwin Boroviak, Giuliano G. Stirparo, Sabine Dietmann, Irene Hernando-Herraez, Hisham Mohammed, Wolf Reik, Austin Smith, Erika Sasaki, Jennifer Nichols, Paul Bertone

The mouse embryo is the canonical model for mammalian preimplantation development. Recent advances in single-cell profiling allow detailed analysis of embryogenesis in other eutherian species, including human, to distinguish conserved from divergent regulatory programs and signalling pathways in the rodent paradigm. Here, we identify and compare transcriptional features of human, marmoset and mouse embryos by single-cell RNA-seq. Zygotic genome activation correlates with the presence of Polycomb Repressive Complexes in all three species, while ribosome biogenesis emerges as a predominant attribute in primate embryos, supporting prolonged translation of maternally deposited RNAs. We find that transposable element expression signatures are species-, stage- and lineage-specific. The pluripotency network in the primate epiblast lacks certain regulators operative in mouse, but encompasses WNT components and genes associated with trophoblast specification. Sequential activation of GATA6, SOX17 and GATA4 markers of primitive endoderm identity is conserved in primates. Unexpectedly, OTX2 is also associated with primitive endoderm specification in human and nonhuman primate blastocysts. Our cross-species analysis demarcates both conserved and primate-specific features of preimplantation development and underscores the molecular adaptability of early mammalian embryogenesis.

42: A single cell transcriptional roadmap for cardiopharyngeal fate diversification
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Posted to bioRxiv 15 Jun 2017

A single cell transcriptional roadmap for cardiopharyngeal fate diversification
2,515 downloads developmental biology

Wei Wang, Xiang Niu, Tim Stuart, Estelle Jullian, William Mauck, Robert G. Kelly, Rahul Satija, Lionel Christiaen

In vertebrates, multipotent progenitors located in the pharyngeal mesoderm form cardiomyocytes and branchiomeric head muscles, but the dynamic gene expression programs and mechanisms underlying cardiopharyngeal multipotency and heart vs. head muscle fate choices remain elusive. Here, we used single cell genomics in the simple chordate model Ciona, to reconstruct developmental trajectories forming first and second heart lineages, and pharyngeal muscle precursors, and characterize the molecular underpinnings of cardiopharyngeal fate choices. We show that FGF-MAPK signaling maintains multipotency and promotes the pharyngeal muscle fate, whereas signal termination permits the deployment of a pan-cardiac program, shared by the first and second lineages, to define heart identity. In the second heart lineage, a Tbx1/10-Dach pathway actively suppresses the first heart lineage program, conditioning later cell diversity in the beating heart. Finally, cross-species comparisons between Ciona and the mouse evoke the deep evolutionary origins of cardiopharyngeal networks in chordates.

43: Molecular Logic of Cellular Diversification in the Mammalian Cerebral Cortex
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Posted to bioRxiv 02 Jul 2020

Molecular Logic of Cellular Diversification in the Mammalian Cerebral Cortex
2,493 downloads developmental biology

Daniela J. Di Bella, Ehsan Habibi, Sun-Ming Yang, Robert R. Stickels, Juliana Brown, Payman Yadollahpour, Fei Chen, Evan Z. Macosko, Aviv Regev, Paola Arlotta

The neocortex has an unparalleled diversity of cell types, which are generated during development through a series of temporally orchestrated events that are under tight evolutionary constraint and are critical for proper cortical assembly and function. However, the molecular logic that governs the establishment and organization of cortical cell types remains elusive, largely due to the large number of cell classes undergoing dynamic cell-state transitions over extended developmental timelines. Here, we have generated a comprehensive single-cell RNA-seq and single-cell ATAC-seq atlas of the developing mouse neocortex, sampled every day throughout embryonic corticogenesis. We computationally reconstruct developmental trajectories across the diversity of cortical cell classes, and infer the gene regulatory programs that accompany their lineage bifurcation decisions and their differentiation trajectories. Finally, we demonstrate how this developmental map pinpoints the origin of lineage-specific developmental abnormalities linked to aberrant corticogenesis in mutant animals. The data provides the first global picture of the regulatory mechanisms governing cellular diversification in the neocortex. ### Competing Interest Statement P.A. is a SAB member in System 1 Biosciences and Foresite Labs and is a co-founder of FL60. A.R. is a co-founder of and equity holder in Celsius Therapeutics, equity holder in Immunitas, and a SAB member of ThermoFisher Scientific, Syros Pharmaceuticlas, Asimov, and Neogene Therapeutics.

44: Single cell transcriptomics reveals spatial and temporal dynamics of gene expression in the developing mouse spinal cord
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Posted to bioRxiv 16 Nov 2018

Single cell transcriptomics reveals spatial and temporal dynamics of gene expression in the developing mouse spinal cord
2,441 downloads developmental biology

Julien Delile, Teresa Rayon, Manuela Melchionda, Amelia Edwards, James Briscoe, Andreas Sagner

The coordinated spatial and temporal regulation of gene expression in the vertebrate neural tube determines the identity of neural progenitors and the function and physiology of the neurons they generate. Progress has been made deciphering the gene regulatory programmes responsible for this process, however, the complexity of the tissue has hampered the systematic analysis of the network and the underlying mechanisms. To address this, we used single cell mRNA sequencing to profile cervical and thoracic regions of the developing mouse neural tube between embryonic days (e)9.5-e13.5. We confirmed the data accurately recapitulates neural tube development, allowing us to identify new markers for specific progenitor and neuronal populations. In addition, the analysis highlighted a previously underappreciated temporal component to the mechanisms generating neuronal diversity and revealed common features in the sequence of transcriptional events that lead to the differentiation of specific neuronal subtypes. Together the data offer insight into the mechanisms responsible for neuronal specification and provide a compendium of gene expression for classifying spinal cord cell types that will support future studies of neural tube development, function, and disease.

45: Lineage recording reveals dynamics of cerebral organoid regionalization
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Posted to bioRxiv 20 Jun 2020

Lineage recording reveals dynamics of cerebral organoid regionalization
2,415 downloads developmental biology

Zhisong He, Tobias Gerber, Ashley Maynard, Akanksha Jain, Rebecca Petri, Malgorzata Santel, Kevin Ly, Leila Sidow, Fátima Sanchís-Calleja, Stephan Riesenberg, J. Gray Camp, Barbara Treutlein

Diverse regions develop within cerebral organoids generated from human induced pluripotent stem cells (iPSCs), however it has been a challenge to understand the lineage dynamics associated with brain regionalization. Here we establish an inducible lineage recording system that couples reporter barcodes, inducible CRISPR/Cas9 scarring, and single-cell transcriptomics to analyze lineage relationships during cerebral organoid development. We infer fate-mapped whole organoid phylogenies over a scarring time course, and reconstruct progenitor-neuron lineage trees within microdissected cerebral organoid regions. We observe increased fate restriction over time, and find that iPSC clones used to initiate organoids tend to accumulate in distinct brain regions. We use lineage-coupled spatial transcriptomics to resolve lineage locations as well as confirm clonal enrichment in distinctly patterned brain regions. Using long term 4-D light sheet microscopy to temporally track nuclei in developing cerebral organoids, we link brain region clone enrichment to positions in the neuroectoderm, followed by local proliferation with limited migration during neuroepithelial formation. Our data sheds light on how lineages are established during brain organoid regionalization, and our techniques can be adapted in any iPSC-derived cell culture system to dissect lineage alterations during perturbation or in patient-specific models of disease. ### Competing Interest Statement The authors have declared no competing interest.

46: Interplay of TGFb superfamily members governs optic fissure closure
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Posted to bioRxiv 24 Oct 2014

Interplay of TGFb superfamily members governs optic fissure closure
2,389 downloads developmental biology

Stephan Heermann, Priska Eckert, Juan L Mateo, Eleni Roussa, Belal Rahhal, Aimee Zuniga, Kerstin Krieglstein, Jochim Wittbrodt

The optic fissure is a gap in the developing vertebrate eye and must be closed as development proceeds. A persisting optic fissure is referred to as coloboma, a major cause for blindness in children. Multiple factors have been linked to coloboma formation, however, the actual process of fissure closure is only poorly understood. Based on our findings we propose an important role of TGFb signaling for optic fissure closure. We show active TGFb signaling in the fissure margins, analyzed by a new TGFb signaling reporter zebrafish. We found BMP antagonists regulated by TGFb. These antagonists we also found expressed in the fissure margins. Finally we show a coloboma phenotype in a TGFb KO mouse. Microarray data analysis indicates intense TGFb dependent remodeling of the extracellular matrix (ECM) during optic fissure closure. We propose that TGFb is driving optic fissure closure by ECM remodeling. As previously shown, inhibition of BMP signaling is important for such TGFb dependent ECM remodeling. We show that this is achieved by the regulation of BMP antagonists, expressed in the optic fissure margins.

47: Generation of Aggregates of Mouse ES Cells that Show Symmetry Breaking, Polarisation and Emergent Collective Behaviour in vitro.
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Posted to bioRxiv 15 May 2014

Generation of Aggregates of Mouse ES Cells that Show Symmetry Breaking, Polarisation and Emergent Collective Behaviour in vitro.
2,367 downloads developmental biology

Peter Baillie-Johnson, Susanne C. van den Brink, Tina Balayo, David A Turner, Alfonso Martinez-Arias

Dissociated mouse embryonic stem (ES) cells were cultured to form aggregates in small volumes of basal medium in U-bottomed, non tissue-culture-treated 96-well plates and subsequently maintained in suspension culture. After growth for 48 hours, the aggregates are competent to respond to ubiquitous experimental signals which result in their symmetry-breaking and generation of defined polarised structures by 96 hours. It is envisaged that this system can be applied both to the study of early developmental events and more broadly to the processes of self-organisation and cellular decision-making. It may also provide a suitable niche for the generation of cell types present in the embryo but unobtainable from conventional adherent culture.

48: Zika Fetal Neuropathogenesis: Etiology of a Viral Syndrome
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Posted to bioRxiv 29 Apr 2016

Zika Fetal Neuropathogenesis: Etiology of a Viral Syndrome
2,363 downloads developmental biology

Zachary A. Klase, Svetlana Khakhina, Adriano De Bernardi Schneider, Michael V Callahan, Jill Glasspool-Malone, Robert Malone

The ongoing Zika Virus epidemic in the Americas, and the observed association with both fetal abnormalities (primary microcephaly) and adult autoimmune pathology (Guillain-Barre syndrome) has brought attention to this neglected pathogen. While initial case studies generated significant interest in the Zika virus outbreak, larger prospective epidemiology and basic virology studies examining the mechanisms of Zika viral infection and associated pathophysiology are only now starting to be published. In this review, we analyze Zika fetal neuropathogenesis from a comparative pathology perspective, using the historic metaphor of TORCH viral pathogenesis to provide context. By drawing parallels to other viral infections of the fetus, we identify common themes and mechanisms that may illuminate the observed pathology. The existing data on the susceptibility of various cells to both Zika and other flavivirus infections are summarized. Finally, we highlight relevant aspects of the known molecular mechanisms of flavivirus replication.

49: CytoCensus: mapping cell identity and division in tissues and organs using machine learning
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Posted to bioRxiv 14 May 2017

CytoCensus: mapping cell identity and division in tissues and organs using machine learning
2,325 downloads developmental biology

Martin Hailstone, Dominic Waithe, Tamsin J. Samuels, Lu Yang, Ita Costello, Yoav Arava, Elizabeth J. Robertson, Richard M. Parton, Ilan Davis

A major challenge in cell and developmental biology is the automated identification and quantitation of cells in complex multilayered tissues. We developed CytoCensus: an easily deployed implementation of supervised machine learning that extends convenient 2D “point- and-click” user training to 3D detection of cells in challenging datasets with ill-defined cell boundaries. In tests on these datasets, CytoCensus outperforms other freely available image analysis software in accuracy and speed of cell detection. We used CytoCensus to count stem cells and their progeny, and to quantify individual cell divisions from time-lapse movies of explanted Drosophila larval brains, comparing wild-type and mutant phenotypes. We further illustrate the general utility and future potential of CytoCensus by analysing the 3D organisation of multiple cell classes in Zebrafish retinal organoids and cell distributions in mouse embryos. CytoCensus opens the possibility of straightforward and robust automated analysis of developmental phenotypes in complex tissues. Summary Hailstone et al . develop CytoCensus, a “point-and-click” supervised machine-learning image analysis software to quantitatively identify defined cell classes and divisions from large multidimensional data sets of complex tissues. They demonstrate its utility in analysing challenging developmental phenotypes in living explanted Drosophila larval brains, mammalian embryos and zebrafish organoids. They further show, in comparative tests, a significant improvement in performance over existing easy-to-use image analysis software. ![Figure][1]</img> Highlights [1]: pending:yes

50: Interactions between Nodal and Wnt signalling Drive Robust Symmetry Breaking and Axial Organisation in Gastruloids (Embryonic Organoids)
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Posted to bioRxiv 04 May 2016

Interactions between Nodal and Wnt signalling Drive Robust Symmetry Breaking and Axial Organisation in Gastruloids (Embryonic Organoids)
2,318 downloads developmental biology

D.A. Turner, C.R. Glodowski, L. Alonso-Crisostomo, P. Baillie-Johnson, P.C. Hayward, J. Collignon, C. Gustavsen, P. Serup, C. Schröter, A. Martinez Arias

Generation of asymmetry within the early embryo is a critical step in the establishment of the three body axes, providing a reference for the patterning of the organism. To study the establishment of asymmetry and the development of the anteroposterior axis (AP) in culture, we utilised our Gastruloid model system. Gastruloids, highly reproducible embryonic organoids formed from aggregates of mouse embryonic stem cells, display symmetry-breaking, polarised gene expression and axial development, mirroring the processes on a time-scale similar to that of the mouse embyro. Using Gastruloids formed from mouse ESCs containing reporters for Wnt, FGF and Nodal signalling, we were able to quantitatively assess the contribution of these signalling pathways to the establishment of asymmetry through single time-point and live-cell fluorescence microscopy. During the first 24-48h of culture, interactions between the Wnt/β-Catenin and Nodal/TGFβ signalling pathways promote the initial symmetry-breaking event, manifested through polarised Brachyury (T/Bra) expression. Neither BMP nor FGF signalling is required for the establishment of asymmetry, however Wnt signalling is essential for the amplification and stability of the initial patterning event. Additionally, low, endogenous levels of FGF (24-48h) has a role in the amplification of the established pattern at later time-points. Our results confirm that Gastruloids behave like epiblast cells in the embryo, leading us to translate the processes and signalling involved in pattern formation of Gastruloids in culture to the development of the embryo, firmly establishing Gastruloids as a highly reproducible, robust model system for studying cell fate decisions and early pattern formation in culture.

51: Self-organised symmetry breaking in zebrafish reveals feedback from morphogenesis to pattern formation
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Posted to bioRxiv 14 Sep 2019

Self-organised symmetry breaking in zebrafish reveals feedback from morphogenesis to pattern formation
2,307 downloads developmental biology

Vikas Trivedi, Timothy Fulton, Andrea Attardi, Kerim Anlas, Chaitanya Dingare, Alfonso Martinez-Arias, Ben Steventon

A fundamental question in developmental biology is how the early embryo breaks initial symmetry to establish the spatial coordinate system later important for the organisation of the embryonic body plan. In zebrafish, this is thought to depend on the inheritance of maternal mRNAs [[1][1]–[3][2]], cortical rotation to generate a dorsal pole of beta-catenin activity [[4][3]–[8][4]] and the release of Nodal signals from the yolk syncytial layer (YSL) [[9][5]–[12][6]]. Recent work aggregating mouse embryonic stem cells has shown that symmetry breaking can occur in the absence of extra-embryonic tissue [[19][7],[20][8]]. To test whether this is also true in zebrafish, we separated embryonic cells from the yolk and allowed them to develop as aggregates. These aggregates break symmetry autonomously to form elongated structures with an anterior-posterior pattern. Extensive cell mixing shows that any pre-existing asymmetry is lost prior to the breaking morphological symmetry, revealing that the maternal pre-pattern is not strictly required for early embryo patterning. Following early signalling events after isolation of embryonic cells reveals that a pole of Nodal activity precedes and is required for elongation. The blocking of PCP-dependent convergence and extension movements disrupts the establishment of opposing poles of BMP and Wnt/TCF activity and the patterning of anterior-posterior neural tissue. These results lead us to suggest that convergence and extension plays a causal role in the establishment of morphogen gradients and pattern formation during zebrafish gastrulation. [1]: #ref-1 [2]: #ref-3 [3]: #ref-4 [4]: #ref-8 [5]: #ref-9 [6]: #ref-12 [7]: #ref-19 [8]: #ref-20

52: Genome-wide analysis of H3K4me3 and H3K27me3 modifications throughout the mouse urogenital ridge at E11.5.
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Posted to bioRxiv 15 Jun 2018

Genome-wide analysis of H3K4me3 and H3K27me3 modifications throughout the mouse urogenital ridge at E11.5.
2,294 downloads developmental biology

Yisheng Yang, Megan J Wilson

In mammals, the adrenal gland, testis and ovary arise from a common progenitor tissue known as the urogenital ridge (UGR). This small population of cells will adopt a number of different cell fates following sex determination, including forming the precursors of somatic cells (such as Sertoli and granulosa cells) and steroidogenic cells. In addition, this tissues also contains the Wolffian and Müllerian ducts that later form components of the reproductive tracts. A potential mechanism to maintain developmental plasticity of the UGR until gonad formation is through the epigenetic modification of histone proteins. In order to provide a resource for future studies, we used chromatin immunoprecipitation followed by high throughput sequencing (ChIP-seq) for two histone modifications, H3K4me3 and H3K27me3, in the E11.5 mouse UGR. These marks are both known to reflect the active, repressive or a poised chromatin state. We found that enrichment for each histone mark reflected transcriptional activity in precursor cells of the developing gonad. From the analysis of potential enhancer/regulator peak regions for DNA binding motifs, we identified several candidate transcription factors that may contribute to gonadal cell lineage specification. We additionally identified signaling pathway genes that are targeted by both chromatin modifications. Together, these datasets provide a useful resource for investigating gene regulatory networks functioning during UGR development at E11.5.

53: Mouse embryonic stem cells self-organize into trunk-like structures with neural tube and somites
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Posted to bioRxiv 04 Mar 2020

Mouse embryonic stem cells self-organize into trunk-like structures with neural tube and somites
2,255 downloads developmental biology

Jesse V Veenvliet, Adriano Bolondi, Helene Kretzmer, Leah Haut, Manuela Scholze-Wittler, Dennis Schifferl, Frederic Koch, Milena Pustet, Simon Heimann, Rene Buschow, Lars Wittler, Bernd Timmermann, Alexander Meissner, Bernhard G Herrmann

Post-implantation embryogenesis is a highly dynamic process comprising multiple lineage decisions and morphogenetic changes inaccessible to deep analysis in vivo. Mouse embryonic stem cells (mESCs) can form aggregates reflecting the post-occipital embryo (gastruloids), but lacking proper morphogenesis. Here we show that embedding of aggregates derived from mESCs in an extracellular matrix compound results in Trunk-Like-Structures (TLS) with a high level of organization comprising a neural tube and somites. Comparative single-cell RNA-seq analysis demonstrates that TLS execute gene-regulatory programs in an embryo-like order, and generate primordial germ cell like cells (PGCLCs). TLS lacking Tbx6 form ectopic neural tubes, mirroring the embryonic mutant phenotype. ESC-derived trunk-like structures thus constitute a novel powerful in vitro platform for investigating lineage decisions and morphogenetic processes shaping the post-implantation embryo.

54: A safer, urea-based in situ hybridization method improves detection of gene expression in diverse animal species
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Posted to bioRxiv 03 May 2017

A safer, urea-based in situ hybridization method improves detection of gene expression in diverse animal species
2,230 downloads developmental biology

Chiara Sinigaglia, Daniel Thiel, Andreas Hejnol, Evelyn Houliston, Lucas Leclère

In situ hybridization is a widely employed technique allowing spatial visualization of gene expression in fixed specimens. It has proven to be essential to our understanding of biological processes, including developmental regulation. In situ protocols are today routine in numerous laboratories, and although details might change, they all include a hybridization step, where specific antisense RNA or DNA probes anneal to the target nucleic acids strand. This step, in general, is carried out at high temperatures and in a denaturing solution, the hybridization buffer, commonly containing 50% (v/v) formamide. An important drawback is that hot formamide poses a significant health risk and so must be handled with great care. We were prompted to test alternative hybridization solutions for in situ detection of gene expression in the medusa of the hydrozoan Clytia hemisphaerica, where traditional protocols caused extensive deterioration of the morphology and texture during hybridization, hindering observation and interpretation of results. Inspired by optimized protocols for Northern and Southern blot analysis, we substituted the 50% formamide with an equal volume of 8 M urea solution in the hybridization buffer. The new protocol yielded better morphologies and consistency of tissues, and also notably improved the resolution of the signal, allowing more precise localization of gene expression, as well as reduced staining at non-specific sites. Given the improved results using a less toxic hybridization solution, we tested the urea protocol on a number of other metazoans: two brachiopod species (Novocrania anomala and Terebratalia transversa) and the worm Priapulus caudatus, obtaining a similar reduction of aspecific probe binding. Overall, substitution of formamide by urea in in situ hybridization offers safer alternative protocols, potentially useful in research, medical and teaching contexts. We encourage other workers to test this approach on their study organisms, and hope that they will also obtain better sample preservation, more precise expression patterns and fewer problems due to aspecific staining, as we report here for Clytia medusae and Novocrania and Terebratalia developing larvae.

55: An engineered CRISPR/Cas9 mouse line for simultaneous readout of lineage histories and gene expression profiles in single cells
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Posted to bioRxiv 17 Oct 2019

An engineered CRISPR/Cas9 mouse line for simultaneous readout of lineage histories and gene expression profiles in single cells
2,213 downloads developmental biology

Sarah Bowling, Duluxan Sritharan, Fernando G. Osorio, Maximilian Nguyen, Priscilla Cheung, Alejo Rodriguez-Fraticelli, Sachin Patel, Yuko Fujiwara, Bin E Li, Stuart H. Orkin, Sahand Hormoz, Fernando D Camargo

Tracing the lineage history of cells is key to answering diverse and fundamental questions in biology. Particularly in the context of stem cell biology, analysis of single cell lineages in their native state has elucidated novel fates and highlighted heterogeneity of function. Coupling of such ancestry information with other molecular readouts represents an important goal in the field. Here, we describe the CARLIN (for CRISPR Array Repair LINeage tracing) mouse line and corresponding analysis tools that can be used to simultaneously interrogate the lineage and transcriptomic information of single cells in vivo . This model exploits CRISPR technology to generate up to 44,000 transcribed barcodes in an inducible fashion at any point during development or adulthood, is compatible with sequential barcoding, and is fully genetically defined. We have used CARLIN to identify intrinsic biases in the activity of fetal liver hematopoietic stem cell (HSC) clones and to uncover a previously unappreciated clonal bottleneck in the response of HSCs to injury. CARLIN also allows the unbiased identification of transcriptional signatures based on in vivo stem cell function without a need for markers or cell sorting.

56: Developmentally regulated Shh expression is robust to TAD perturbations
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Posted to bioRxiv 15 Apr 2019

Developmentally regulated Shh expression is robust to TAD perturbations
2,175 downloads developmental biology

Iain Williamson, Lauren Kane, Paul S Devenney, Eve Anderson, Fiona Kilanowski, Robert E Hill, Wendy A. Bickmore, Laura A Lettice

Topologically Associating Domains (TADs) have been proposed to both guide and constrain enhancer activity. Shh is located within a TAD known to contain all its enhancers. To investigate the importance of chromatin conformation and TAD integrity on developmental gene regulation, we have manipulated the Shh TAD, creating internal deletions, deleting CTCF sites including those at TAD boundaries, as well as larger deletions and inversions of TAD boundaries. Chromosome conformation capture and fluorescence in situ hybridisation assays were used the investigate changes in chromatin conformation that result from these manipulations. Our data suggest that the substantial alteration of TAD structure has no readily detectable effect on Shh expression patterns during development, except where enhancers are deleted, and results in no detectable phenotypes. Only in the case of a larger deletion of one TAD boundary could some ectopic influence of the Shh limb enhancer be detected on a gene, Mnx1 in the neighbouring TAD. Our data suggests that, contrary to expectations, the developmental regulation of Shh expression is remarkably robust to TAD perturbations.

57: Profiling cellular diversity in sponges informs animal cell type and nervous system evolution
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Posted to bioRxiv 05 Sep 2019

Profiling cellular diversity in sponges informs animal cell type and nervous system evolution
2,141 downloads developmental biology

Jacob M. Musser, Klaske J. Schippers, Michael Nickel, Giulia Mizzon, Andrea B Kohn, Constantin Pape, Jörg U. Hammel, Florian Wolf, Cong Liang, Ana Hernández-Plaza, Kaia Achim, Nicole L. Schieber, Warren R. Francis, Sergio Vargas, Svenja Kling, Maike Renkert, Roberto Feuda, Imre Gaspar, Pawel Burkhardt, Peer Bork, Martin Beck, Anna Kreshuk, Gert Wörheide, Jaime Huerta-Cepas, Yannick Schwab, Leonid L. Moroz, Detlev Arendt

The evolutionary origin of metazoan cell types such as neurons, muscles, digestive, and immune cells, remains unsolved. Using whole-body single-cell RNA sequencing in a sponge, an animal without nervous system and musculature, we identify 18 distinct cell types comprising four major families. This includes nitric-oxide sensitive contractile cells, digestive cells active in macropinocytosis, and a family of amoeboid-neuroid cells involved in innate immunity. We uncover presynaptic genes in an amoeboid-neuroid cell type, and postsynaptic genes in digestive choanocytes, suggesting asymmetric and targeted communication. Corroborating this, long neurite-like extensions from neuroid cells directly contact and enwrap choanocyte microvillar collars. Our data indicate a link between neuroid and immune functions in sponges, and suggest that a primordial neuro-immune system cleared intruders and controlled ciliary beating for feeding.

58: Unidirectional fork movement coupled with strand-specific histone incorporation ensures asymmetric histone inheritance
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Posted to bioRxiv 04 Jan 2018

Unidirectional fork movement coupled with strand-specific histone incorporation ensures asymmetric histone inheritance
2,132 downloads developmental biology

Matthew Wooten, Jonathan Snedeker, Zehra Nizami, Xinxing Yang, Rajesh Ranjan, Elizabeth Urban, Jee Min Kim, Joseph Gall, Jie Xiao, Xin Chen

One of the most fundamental questions in developmental biology concerns how cells with identical genomes differentiate into distinct cell types. One important context for understanding cell fate specification is asymmetric cell division, where the two daughter cells establish different cell fates following a single division. Many stem cells undergo asymmetric division to produce both a self-renewing stem cell and a differentiating daughter cell1-5. Here we show that histone H4 is inherited asymmetrically in asymmetrically dividing Drosophila male germline stem cells, similar to H36. In contrast, both H2A and H2B are inherited symmetrically. By combining superresolution microscopy with the chromatin fiber method, we are able to study histone inheritance patterns on newly replicated chromatin fibers. Using this technique, we find asymmetric inheritance patterns for old and new H3, but symmetric inheritance patterns for old and new H2A on replicating sister chromatids. Furthermore, co-localization studies on isolated chromatin fibers and proximity ligation assays on intact nuclei reveal that old H3 are preferentially incorporated by the leading strand while newly synthesized H3 are enriched on the lagging strand. Finally, using a sequential nucleoside analog incorporation assay, we detect a high incidence of unidirectional DNA replication on germline-derived chromatin fibers and DNA fibers. The unidirectional fork movement coupled with the strand preference of histone incorporation could explain how old and new H3 are asymmetrically incorporated by replicating sister chromatids. In summary, our work demonstrates that the intrinsic asymmetries in DNA replication may help construct sister chromatids enriched with distinct populations of histones. Therefore, these results suggest unappreciated roles for DNA replication in asymmetrically dividing cells in multicellular organisms.

59: Molecular mechanism of symmetry breaking in a 3D model of a human epiblast
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Posted to bioRxiv 29 May 2018

Molecular mechanism of symmetry breaking in a 3D model of a human epiblast
2,100 downloads developmental biology

Mijo Simunovic, Jakob J Metzger, Fred Etoc, Anna Yoney, Albert Ruzo, Iain Martyn, Gist Croft, Ali H. Brivanlou, E.D. Siggia

Breaking the anterior-posterior (AP) symmetry in mammals takes place at gastrulation. Much of the signaling network underlying this process has been elucidated in the mouse, however there is no direct molecular evidence of events driving axis formation in humans. Here, we use human embryonic stem cells to generate an in vitro 3D model of a human epiblast whose size, cell polarity, and gene expression are similar to a 10-day human epiblast. A defined dose of bone morphogenetic protein 4 (BMP4) spontaneously breaks axial symmetry, and induces markers of the primitive streak and epithelial to mesenchymal transition. By gene knockouts and live-cell imaging we show that, downstream of BMP4, WNT3 and its inhibitor DKK1 play key roles in this process. Our work demonstrates that a model human epiblast can break axial symmetry despite no asymmetry in the initial signal and in the absence of extraembryonic tissues or maternal cues. Our 3D model opens routes to capturing molecular events underlying axial symmetry breaking phenomena, which have largely been unexplored in model human systems.

60: An interplay between extracellular signalling and the dynamics of the exit from pluripotency drives cell fate decisions in mouse ES cells
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Posted to bioRxiv 18 Nov 2013

An interplay between extracellular signalling and the dynamics of the exit from pluripotency drives cell fate decisions in mouse ES cells
2,058 downloads developmental biology

David A Turner, Jamie Trott, Penelope Hayward, Alfonso Martinez Arias, Alfonso Martinez Arias

Embryonic Stem cells derived from the epiblast tissue of the mammalian blastocyst retain the capability to differentiate into any adult cell type and are able to self-renew indefinitely under appropriate culture conditions. Despite the large amount of knowledge that we have accumulated to date about the regulation and control of self-renewal, efficient directed differentiation into specific tissues remains elusive. In this work, we have analysed in a systematic manner the interaction between the dynamics of loss of pluripotency and Activin/Nodal, BMP4 and Wnt signalling in fate assignment during the early stages of differentiation of mouse ES cells in culture. During the initial period of differentiation, cells exit from pluripotency and enter an Epi-like state. Following this transient stage, and under the influence of Activin/Nodal and BMP signalling, cells face a fate choice between differentiating into neuroectoderm and contributing to Primitive Streak fates. We find that Wnt signalling does not suppress neural development as previously thought and that it aids both fates in a context dependent manner. Our results suggest that as cells exit pluripotency they are endowed with a primary neuroectodermal fate and that the potency to become endomesodermal rises with time. We suggest that this situation translates into a ?race for fates? in which the neuroectodermal fate has an advantage.

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