Ventricular, atrial, and outflow tract heart progenitors arise from spatially and molecularly distinct regions of the primitive streak

The heart develops from 2 sources of mesoderm progenitors, the first and second heart field (FHF and SHF). Using a single-cell transcriptomic assay combined with genetic lineage tracing and live imaging, we find the FHF and SHF are subdivided into distinct pools of progenitors in gastrulating mouse embryos at earlier stages than previously thought. Each subpopulation has a distinct origin in the primitive streak. The first progenitors to leave the primitive streak contribute to the left ventricle, shortly after right ventricle progenitor emigrate, followed by the outflow tract and atrial progenitors. Moreover, a subset of atrial progenitors are gradually incorporated in posterior locations of the FHF. Although cells allocated to the outflow tract and atrium leave the primitive streak at a similar stage, they arise from different regions. Outflow tract cells originate from distal locations in the primitive streak while atrial progenitors are positioned more proximally. Moreover, single-cell RNA sequencing demonstrates that the primitive streak cells contributing to the ventricles have a distinct molecular signature from those forming the outflow tract and atrium. We conclude that cardiac progenitors are prepatterned within the primitive streak and this prefigures their allocation to distinct anatomical structures of the heart. Together, our data provide a new molecular and spatial map of mammalian cardiac progenitors that will support future studies of heart development, function, and disease

A gene regulatory network balances neural and mesoderm specification during vertebrate trunk development

Transcriptional networks, regulated by extracellular signals, control cell fate decisions and determine the size and composition of developing tissues. One example is the network controlling bipotent neuromesodermal progenitors (NMPs) that fuel embryo elongation by generating spinal cord and trunk mesoderm tissue. Here, we use single-cell transcriptomics to identify the molecular signature of NMPs and reverse engineer the mechanism that regulates their differentiation. Together with genetic perturbations, this reveals a transcriptional network that integrates opposing retinoic acid (RA) and Wnt signals to determine the rate at which cells enter and exit the NMP state. RA, produced by newly generated mesodermal cells, provides feedback that initiates NMP generation and induces neural differentiation, thereby coordinating the production of neural and mesodermal tissue. Together, the data define a regulatory network architecture that balances the generation of different cell types from bipotential progenitors in order to facilitate orderly axis elongation

Narbonne et son territoire. Exploitation, utilisation et rejets des matériaux polluants

International audienc

Automated inference of 4-D cell polarization fields in an agent-based model of early vertebrate embryogenesis

International audienceWe present a theoretical model of animal morphogenesis construed as a self-organized phenomenon emerging from a complex system made of a myriad of individual cell behaviors. It is implemented in an agent-based simulation centered on the mechanic-chemical coupling between cellular and genetic dynamics. The goal is to integrate the collective motion of cells and the dynamics of their gene expression underlying the patterning of morphogenetic fields. Within this larger framework, we examine here cell intercalation, a generic process underlying tissue elongation in vertebrate embryogenesis, in particular the convergence and extension movements shaping the embryonic axes during gastrulation. Cell intercalation is thought to arise from polarized cell movements. In our model, we include monopolar and bipolar protrusive activity of polarized cells to investigate the causal bottom-up link from local cell behavior to global tissue deformation. Conversely, this model also allows reverse inference, e.g., by evolutionary optimization, of the local quantitative features of cell adhesion and polarization from a global 4 D (3 D + time) computational reconstruction of the cell lineage tree, itself based on in toto imaging data of developing zebrafish embryos

Jeux d’échelle dans l’urbanisme

Contribuer par le biais des pratiques pédagogiques à renouveler la recherche architecturale fondamentale et conceptuelle constitue un des paris essentiel posé par la réponse « Jeux d’échelles dans l’urbanisme », tout en visant à éclairer les dynamiques actorielles et spatiales propres aux territoires émergents. Initialement adossé à deux unités d’enseignement pédagogique de projet situés dans deux contextes différents (suisse et français), le dispositif a dès lors constitué l’espace pédagogique en moment d’interactions et d’interférences entre trois mondes fonctionnant suivant des logiques spécifiques : professionnel, pédagogique et scientifique. Les objets et terrains retenus auraient pu constituer le principal noyau commun d’échange, de dialogue, de confrontation, de mise en regard respectif et ce faisant évoluer vers un modèle du « layers » : par couche successives et comparatives, les postures respectives seraient ainsi venues s’additionner de manière synchronique ou diachronique. Elles auraient ainsi produit un savoir d’ordre cumulatif se différenciant des savoirs et pratiques propres à chacun de ces mondes respectifs du fait de leur mise en commun par des lieux et temps pédagogique. Étrangement, c’est pourtant une toute autre orientation qu’a prise ce dispositif en se laissant déranger sur le terrain nantais par un objet commun ni aux unes ni aux autres, ni au premier contexte (français) ni au second (suisse) : la figure. La perturbation été considérable d’implications tant au niveau des problématiques initiales que sur l’organisation même du dispositif de recherche. Loin de s’éloigner des lignes programmatiques initialement définies, c’est au contraire une manière plus puissante d’en réarticuler l’ensemble des éléments constitutifs que la figure a pu constituer en jouant le rôle de trame exploratrice, expérimentale, de traceurs révélateurs de jeux d’échelles : tant ceux du petit écart à l’intérieur de configurations locales spécifiques (rapport entre une commune suburbaine, St Herblain, et son agglomération) que du grand écart à tous points de vue qui a pris pour forme l’exploration trans-contextuelle entre deux régimes d’agglomérations différenciés (suisse et français), deux mondes nettement différenciés de production du projet. D’où la structure finale du présent rapport visant dans un premier temps à établir un bilan croisé du dispositif expérimental, puis à s’attacher dans toute sa mesure aux apports et révélations des jeux d’échelles par leurs figures quant aux pratiques urbanistiques spécifiques aux contextes de ville émergente

Ventricular, atrial, and outflow tract heart progenitors arise from spatially and molecularly distinct regions of the primitive streak.

The heart develops from 2 sources of mesoderm progenitors, the first and second heart field (FHF and SHF). Using a single-cell transcriptomic assay combined with genetic lineage tracing and live imaging, we find the FHF and SHF are subdivided into distinct pools of progenitors in gastrulating mouse embryos at earlier stages than previously thought. Each subpopulation has a distinct origin in the primitive streak. The first progenitors to leave the primitive streak contribute to the left ventricle, shortly after right ventricle progenitor emigrate, followed by the outflow tract and atrial progenitors. Moreover, a subset of atrial progenitors are gradually incorporated in posterior locations of the FHF. Although cells allocated to the outflow tract and atrium leave the primitive streak at a similar stage, they arise from different regions. Outflow tract cells originate from distal locations in the primitive streak while atrial progenitors are positioned more proximally. Moreover, single-cell RNA sequencing demonstrates that the primitive streak cells contributing to the ventricles have a distinct molecular signature from those forming the outflow tract and atrium. We conclude that cardiac progenitors are prepatterned within the primitive streak and this prefigures their allocation to distinct anatomical structures of the heart. Together, our data provide a new molecular and spatial map of mammalian cardiac progenitors that will support future studies of heart development, function, and disease

Olig2 and Hes regulatory dynamics during motor neuron differentiation revealed by single cell transcriptomics

<div><p>During tissue development, multipotent progenitors differentiate into specific cell types in characteristic spatial and temporal patterns. We addressed the mechanism linking progenitor identity and differentiation rate in the neural tube, where motor neuron (MN) progenitors differentiate more rapidly than other progenitors. Using single cell transcriptomics, we defined the transcriptional changes associated with the transition of neural progenitors into MNs. Reconstruction of gene expression dynamics from these data indicate a pivotal role for the MN determinant Olig2 just prior to MN differentiation. Olig2 represses expression of the Notch signaling pathway effectors Hes1 and Hes5. Olig2 repression of Hes5 appears to be direct, via a conserved regulatory element within the Hes5 locus that restricts expression from MN progenitors. These findings reveal a tight coupling between the regulatory networks that control patterning and neuronal differentiation and demonstrate how Olig2 acts as the developmental pacemaker coordinating the spatial and temporal pattern of MN generation.</p></div

Olig2 binds to an evolutionarily conserved element near Hes5.

<p>(A) Identification of an evolutionarily conserved element containing an E-box in the vicinity of the <i>Hes5</i> genomic locus in chick, mouse, and human (Hes5(e1)). (B) Analysis of Olig2 Chip-Seq data from [<a href="http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.2003127#pbio.2003127.ref063" target="_blank">63</a>] reveals Olig2 binding sites in the vicinity of the <i>Hes1</i> and <i>Hes5</i> genes. The peak corresponding to the Hes5(e1) element is highlighted in red. (C) Electrophoretic mobility shift assays show that both Olig2 and E12 homodimers can individually bind to the Hes5(e1) E-box and do not form any heterodimeric complexes (lanes 1–4). Positions of the different protein complexes are indicated by colored arrows. Binding depends on the E-box, as both proteins fail to bind probes containing an E-box mutation (Hes5(e1ΔE)) (lanes 5–7). Olig2 binding to Hes5(e1) can be abolished by the addition of unlabelled Hes5(e1) probes, but not those containing the E-box mutation (lanes 8–14). (D) Id1 inhibits binding of E12, but not of Olig2 or Ngn2, to the Hes5(e1) element. Olig2, E12, and Ngn2 alone or Ngn2/E12 heterodimers can bind the Hes5(e1) element. Mixing Olig2 or Ngn2 with Id1 does not inhibit their homodimeric binding activities (lanes 2, 5, 8, and 10). In contrast, Id1 strongly inhibits binding of both E12/E12 and Ngn2/E12 complexes (lanes 6 and 10). The addition of E12 without and with Id1 does not affect Olig2 binding efficiency (lanes 2, 4, and 7). ATG, translational initation codon; Chip-Seq, chromatin immunoprecipitation-sequence; E-box, bHLH transcription factor binding site; N2, Ngn2 protein; O2, Olig2 protein.</p

Characterization of MN differentiation from ESCs.

<p>(A) Scheme outlining the differentiation protocol. ESCs are plated in N2B27 + FGF for 2 days before being exposed to N2B27 + FGF/CHIR, resulting in the production of NMPs at day 3. Cells are subsequently exposed to RA and SAG to promote differentiation into ventral NPs and MNs. (B, C) Expression of NP (Pax6, Olig2, Nkx2.2, Sox1) and MN (Isl1/2) markers between day 4 and day 7 in differentiating ESCs. (D) RT-qPCR analysis of <i>Irx3</i>, <i>Pax6</i>, <i>Nkx6</i>.<i>1</i>, <i>Olig2</i>, and <i>Nkx2</i>.<i>2</i> expression from day 3 to day 7 reveals progressive ventralization in response to increasing duration of Shh signaling. Underlying data are provided in <a href="http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.2003127#pbio.2003127.s013" target="_blank">S1 Data</a>. (E) MN induction after day 5, revealed by RT-qPCR analysis of <i>Sox1</i>, <i>Ngn2</i>, <i>Isl1</i>, and <i>Tubb3</i>. Underlying data are provided in <a href="http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.2003127#pbio.2003127.s013" target="_blank">S1 Data</a>. Scale bars = 40 μm. CHIR, Wnt pathway activator CHIR99021; ESC, embryonic stem cell; FGF, fibroblast growth factor 2; MN, motor neuron; NMP, neuromesodermal progenitor; NP, neural progenitor; N2B27, N2 and B27 media supplements; RA, retinoic acid; RT-qPCR, real-time quantitative polymerase chain reaction; SAG, Smoothened/Shh signalling agonist.</p